| Record 1 of 42 | |
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| Author(s): | Haggerty JA; Curry JA; Liu GS |
| Title: | Potential for estimating cloud liquid water path over sea ice from airborne passive microwave measurements |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2002, Vol 107, Iss D1-D2, art. no. 4007 |
| Abstract: | [1] In this paper we investigate the feasibility of determining cloud liquid water path from passive microwave measurements over sea ice. Simulations using a 32-stream plane-parallel microwave radiative transfer model indicate a consistent increase in brightness temperature attributable to cloud liquid water for conditions observed in the Arctic during the Surface Heat Budget of the Arctic (SHEBA) experiment. Uncertainties in brightness temperature simulations due to variations in surface emissivity, surface temperature, cloud temperature, and atmospheric water vapor are investigated. Surface emissivity variations are found to cause the largest uncertainties in top-of-atmosphere brightness temperature over the range of liquid water paths examined. An algorithm previously developed for estimating liquid water path over oceans from SSM/I data is adapted for retrievals over sea ice. The algorithm is applied to brightness temperature measurements from airborne microwave radiometers. Mean retrieved liquid water path (LWP) is compared to in situ measurements from airborne cloud microphysical probes. The correlation coefficient for the two data sets is found to be 0.989 with an RMS error of 14 g m(-2), although the retrieved LWP values show a high degree of variability. Accuracy is highest when LWP values are 100 g m(-2) and above. Poorest accuracies are obtained for small LWP (<50 g m(-2)) where errors in the specification of surface emissivity have a large effect. These case studies provide evidence that liquid water clouds over sea ice produce detectable changes in microwave brightness temperature and suggest that interpretation of sea ice properties using certain microwave frequencies may be affected by the presence of liquid water clouds. |
| Source item page count: | 13 |
| Publication Date: | JAN |
| IDS No.: | 609EC |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 2 of 42 | |
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| Author(s): | Atlas D; Ulbrich CW; Marks FD |
| Title: | Potential for estimating cloud liquid water path over sea ice from airborne passive microwave measurements - Reply |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2002, Vol 107, Iss D1-D2, art. no. 4006 |
| Source item page count: | 2 |
| Publication Date: | JAN |
| IDS No.: | 609EC |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 3 of 42 | |
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| Author(s): | Zabolotskikh EV; Timofeev YM; Uspenskii AB; Mitnik LM; Bobylev LP; Jochannessen OM; Cherny IV |
| Title: | Errors of microwave satellite measurements of sea surface wind speed, atmospheric water vapor, and cloud liquid water |
| Source: | IZVESTIYA ATMOSPHERIC AND OCEANIC PHYSICS 2002, Vol 38, Iss 5, pp 592-596 |
| Abstract: | Errors of sea surface wind speed V, total atmospheric water vapor Q, and total cloud liquid water W retrieved from the data measured with the MTVZA radiometer launched onboard the Russian Meteor-3M (no. 1) satellite on December 10, 2001 are estimated using numerical simulations. It is shown that the proposed procedures (the neural network algorithms and physical criteria for data sampling) ensure that potential errors in V, Q, and W meet the current WMO requirements for both light and heavy clouds. A comparison of the retrieval errors simulated for the MTVZA radiometer and the SSM/I onboard radiometer of the DMSP satellite in the same conditions proves that the MTVZA radiometer ensures V and W retrieval with errors not exceeding those characteristic of the SSM/I radiometer. |
| Source item page count: | 5 |
| Publication Date: | SEP-OCT |
| IDS No.: | 606XA |
| 29-char source abbrev: | IZV ATMOS OCEAN PHYS |
| Record 4 of 42 | |
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| Author(s): | Westwater ER; Han Y; Shupe MD; Matrosov SY |
| Title: | Analysis of integrated cloud liquid and precipitable water vapor retrievals from microwave radiometers during the Surface Heat Budget of the Arctic Ocean project |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2001, Vol 106, Iss D23, pp 32019-32030 |
| Abstract: | We investigated a variety of factors that influence the determination of precipitable water vapor (V) and integrated cloud liquid (L) by dual-channel microwave radiometers (MWRs). These factors include radiometric calibration; dry, water vapor, and liquid absorption coefficients; and physical versus statistical retrieval methods. We then applied the analysis to the MWR that was operated by the Atmospheric Radiation Measurement Program (ARM) during the Surface Heat Budget of the Arctic Ocean project. In the work reported here, MWR data taken from April 1 to July 31, 1998, were analyzed. Data acquired in situ did not always agree with the original MWR liquid retrievals, with MWR estimates at times being too large by perhaps a factor of 2. These differences led us to examine in detail several of the assumptions that go into V and L retrievals. The radiometer was carefully examined and found to be well calibrated with a 0.3 K RMS error. The predicted accuracy in the L retrievals, for this 0.3 K RMS radiometric error and a statistical retrieval, was 25 g m(-2) RMS. This accuracy improves to 10%, if we use the improved knowledge of cloud temperature, as can be obtained using radiosondes and cloud radar/lidar measurements. We also studied the degree to which different clear air and cloud liquid models have an effect on V and L retrievals. The most significant changes from the original ARM retrievals were due to the dry opacity and the cloud liquid dielectric model. Although nothing was found in the original ARM data that was grossly incorrect, application of these models reduced the original ARM retrievals by roughly 20 to 30%. The change of clear-air absorption model from the original to a more recent one has little impact on V retrievals except when V is <0.5 cm. |
| Source item page count: | 12 |
| Publication Date: | DEC 16 |
| IDS No.: | 515DA |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 5 of 42 | |
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| Author(s): | Migliorini S; Nativi S |
| Title: | PIn-Part I: An operational nonlinear physical inversion algorithm for precipitable and cloud liquid water estimate in nonraining conditions over sea |
| Source: | IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 2001, Vol 39, Iss 12, pp 2566-2574 |
| Abstract: | An operational nonlinear physical inversion (PIn) algorithm for precipitable and cloud liquid water estimate is described. It is suited for a generic conical scanning satellite microwave radiometer acquisition over sea in nonraining conditions. The algorithm does not need any calibration phase and is independent of the availability of in situ data, being consistent in different geographical and climatological situations.
Adopted formulation is addressed to provide observational data to help in validating water vapor and cloud fields produced by a numerical weather prediction model. Furthermore, such a technique can be utilized for the purpose of global reanalysis, improving estimates of primary fields of the hydrological cycle. A sensitivity study of the forward model and a comparison between output brightness temperatures and those from a robust numerical code are also reported: achieved discrepancies result acceptable with respect to instrumental constrains and computation time. |
| Source item page count: | 9 |
| Publication Date: | DEC |
| IDS No.: | 511ZK |
| 29-char source abbrev: | IEEE TRANS GEOSCI REMOT SEN |
| Record 6 of 42 | |
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| Author(s): | Mallet C; Moreau E; Casagrande L; Klapisz C |
| Title: | Determination of integrated cloud liquid water path and total precipitable water from SSM/I data using a neural network algorithm |
| Source: | INTERNATIONAL JOURNAL OF REMOTE SENSING 2002, Vol 23, Iss 4, pp 661-674 |
| Abstract: | A new algorithm is developed whereby the cloud Liquid Water Path (LWP) and the Total Precipitable Water (TPW) may be determined from SSM/I microwave radiometric data. An artificial Neural Network (NN) with a five-neuron single hidden layer with five neurons yields the best results.
The NN algorithm for TPW and LWP is compared with log-linear regression algorithms developed on the same database. The results obtained on the simulated dataset are nearly twice as good with this new algorithm. In particular, this NN seems to be able to give a better fit for large values of LWP. Furthermore, in the case of TPW, a validation and comparison with conventional algorithms is presented, which is based on SSM/I measurements and collocated radiosonde observations (RAOBs). The main conclusion is that the NN algorithm is more regular than most of the other algorithms. Through this particular study, we try to elaborate a general methodology. The conclusions concern the variability of the database used to develop and test retrieval algorithms and the relevant parameters to characterize the performance of an algorithm. |
| Source item page count: | 14 |
| Publication Date: | FEB |
| IDS No.: | 508UW |
| 29-char source abbrev: | INT J REMOTE SENS |
| Record 7 of 42 | |
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| Author(s): | Liu GS; Curry JA; Haggerty JA; Fu YF |
| Title: | Retrieval and characterization of cloud liquid water path using airborne passive microwave data during INDOEX |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2001, Vol 106, Iss D22, pp 28719-28730 |
| Abstract: | During the 1999 intensive observation period of the Indian Ocean Experiment (INDOEX), the Airborne Imaging Microwave Radiometer (AIMR) was deployed on the National Center for Atmospheric Research (NCAR) C-130 aircraft to measure upwelling microwave radiation that can be used to retrieve cloud liquid water path (LWP). In this study, we present a LWP retrieval algorithm that is optimized for tropical atmospheric conditions, typical of conditions observed in INDOEX. Radiative transfer modeling and error analysis are conducted for the four AIMR channels, to guide selection of AIMR. channels used for the LWP retrievals. Results show that the horizontal polarization channels outperform vertical 2 polarization channels at both 37 and 90 GHz. Additionally, for LWP less than similar to 300 g m(-2) the best results are expected from the 90 GHz horizontal polarization channel, while the 37 GHz horizontal polarization channel performs better for higher LWPs. On the basis of these findings we formulated the LWP retrieval algorithm from the combination of the retrievals of 37 and 90 GHz horizontal polarization channels. Results of several indirect validations show that in nearly clear condition the LWP retrievals have essentially no bias and a random error of about 28 g m(-2) The image of the retrieved LWP compares well with observations by a 0.64 mum visible channel, and the magnitude of the retrieved LWP for large convective cells is comparable to the estimation based on in situ measurements. It is also shown that the retrieved LWPs for convective cells are smaller than those estimated by assuming adiabatic process while the two have a similar trend in the LWP versus cloud top temperature diagram. By analyzing all available AIMR observations, it is found that the mean LWP for cloudy pixels measured during the INDOEX experiment is about 50 g m(-2). A significant north-south gradient of the mean LWP is found in INDOEX domain during this period, with the mean LWP in the region south of 5 degreesS being twice as high as that in the region north of 5 degreesN, The LWP frequency distribution shows that clouds with larger LWPs occur more often in the southern region than in the northern region. |
| Source item page count: | 12 |
| Publication Date: | NOV 27 |
| IDS No.: | 495TE |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 8 of 42 | |
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| Author(s): | Lohnert U; Crewell S; Simmer C; Macke A |
| Title: | Profiling cloud liquid water by combining active and passive microwave measurements with cloud model statistics |
| Source: | JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2001, Vol 18, Iss 8, pp 1354-1366 |
| Abstract: | A method for combining ground-based passive microwave radiometer retrievals of integrated liquid water (LWP), radar reflectivity profiles (Z), and statistics of a cloud model is proposed for deriving cloud liquid water profiles (LWC). A dynamic cloud model is used to determine Z-LWC relations and their errors as functions of height above cloud base. The cloud model is also used to develop an LWP algorithm based on simulations of brightness temperatures of a 20-30-GHz radiometer. For the retrieval of LWC, the radar determined Z profile, the passive microwave retrieved LWP, and a model climatology are combined by an inverse error covariance weighting method. Model studies indicate that LWC retrievals with this method result in rms errors that are about 10%-20% smaller in comparison to a conventional LWC algorithm, which constrains the LWC profile exactly to the measured LWP. According to the new algorithm, errors in the range of 30%-60% are to be anticipated when profiling LWC. The algorithm is applied to a time series measurement of a stratocumulus layer at GKSS in Geesthacht, Germany. The GKSS 95-GHz cloud radar, a 20-30-GHz microwave radiometer, and a laser ceilometer were collocated within a 5-m radius and operated continuously during the measurement period. The laser ceilometer was used to confirm the presence of drizzle-sized drops. |
| Source item page count: | 13 |
| IDS No.: | 464WJ |
| 29-char source abbrev: | J ATMOS OCEAN TECHNOL |
| Record 9 of 42 | |
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| Author(s): | Aires F; Prigent C; Rossow WB; Rothstein M |
| Title: | A new neural network approach including first guess for retrieval of atmospheric water vapor, cloud liquid water path, surface temperature, and emissivities over land from satellite microwave observations |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2001, Vol 106, Iss D14, pp 14887-14907 |
| Abstract: | The analysis of microwave observations over land to determine atmospheric and surface parameters is still limited due to the complexity of the inverse problem. Neural network techniques have already proved successful as the basis of efficient retrieval methods for nonlinear cases; however, first guess estimates, which are used in variational assimilation methods to avoid problems of solution nonuniqueness or other forms of solution irregularity, have up to now not been used with neural network methods. In this study, a neural network approach is developed that uses a first guess. Conceptual bridges are established between the neural network and variational assimilation methods. The new neural method retrieves the surface skin temperature, the integrated water vapor content, the cloud liquid water path and the microwave surface emissivities between 19 and 85 GHz over land from Special Sensor Microwave Imager observations. The retrieval, in parallel, of all these quantities improves the results for consistancy reasons. A database to train the neural network is calculated with a radiative transfer model and a global collection of coincident surface and atmospheric parameters extracted from the National Center for Environmental Prediction reanalysis, from the International Satellite Cloud Climatology Project data, and from microwave emissivity atlases previously calculated. The results of the neural network inversion axe very encouraging. The theoretical RMS error of the surface temperature retrieval over the globe is 1.3 K in clear-sky conditions and 1.6 K in cloudy scenes. Water vapor is retrieved with a theoretical RMS error of 3.8 kg m(-2) in clear conditions and 4.9 kg m(-2) in cloudy situations. The theoretical RMS error in cloud liquid water path is 0.08 kg m(-2). The surface emissivities are retrieved with an accuracy of better than 0.008 in clear conditions and 0.010 in cloudy conditions. Microwave land surface temperature retrieval presents a very attractive complement to the infrared estimates in cloudy areas: time record of land surface temperature will be produced. |
| Source item page count: | 21 |
| Publication Date: | JUL 27 |
| IDS No.: | 456YE |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 10 of 42 | |
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| Author(s): | Liljegren JC; Clothiaux EE; Mace GG; Kato S; Dong XQ |
| Title: | A new retrieval for cloud liquid water path using a ground-based microwave radiometer and measurements of cloud temperature |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2001, Vol 106, Iss D13, pp 14485-14500 |
| Abstract: | A new method to retrieve cloud liquid water path using 23.8 and 31.4 GHz microwave radiometer brightness temperature measurements is developed. This method does not depend on climatological estimates of either the mean radiating temperature of the atmosphere T-mr or the mean cloud liquid water temperature T-cloud Rather, T-mr is estimated from surface temperature and relative humidity measurements, while Tcloud is estimated using millimeter-wave cloud radar data, together with atmospheric temperature profiles obtained from either radiosonde or rapid update cycle (RUC) model output. Simulations demonstrate that the new retrieval method significantly reduces the biases in the liquid water path estimates that are apparent in a site-specific retrieval based on monthly stratified, local climatology. An analysis of the liquid water path estimates produced by the two retrievals over four case study days illustrates trends and retrieval performances consistent with the model simulations. |
| Source item page count: | 16 |
| Publication Date: | JUL 16 |
| IDS No.: | 453EQ |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 11 of 42 | |
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| Author(s): | Lin B; Minnis P; Fan A; Curry JA; Gerber H |
| Title: | Comparison of cloud liquid water paths derived from in situ and microwave radiometer data taken during the SHEBA/FIREACE |
| Source: | GEOPHYSICAL RESEARCH LETTERS 2001, Vol 28, Iss 6, pp 975-978 |
| Abstract: | Mean cloud liquid water path LWP derived from microwave measurements using the standard ARM retrieval technique is nearly twice as large as coincident in situ aircraft data taken over the SHEBA ice camp in the Arctic during FIRE ACE. Using an algorithm adopted from satellite remote sensing that more completely accounts for the temperature dependence of water absorption and atmospheric gas absorption results in a 25 to 4.5 % reduction in LWP values relative to the standard ARM estimates. If possible precipitation cases are excluded, the mean results from the new technique differ by only 3% from the in situ data. Greater differences for heavier clouds may result from in situ probe uncertainties. This algorithm should provide accurate LWP retrievals for a variety of cloud conditions from the tropics to the highly supercooled Arctic clouds. |
| Source item page count: | 4 |
| Publication Date: | MAR 15 |
| IDS No.: | 411JD |
| 29-char source abbrev: | GEOPHYS RES LETT |
| Record 12 of 42 | |
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| Author(s): | Grody N; Zhao J; Ferraro R; Weng FH; Boers R |
| Title: | Determination of precipitable water and cloud liquid water over oceans from the NOAA 15 advanced microwave sounding unit |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2001, Vol 106, Iss D3, pp 2943-2953 |
| Abstract: | The advanced microwave sounding unit (AMSU) was finally launched in May 1998 aboard the NOAA 15 satellite. Algorithms are provided for retrieving the total precipitable water (TPW) and cloud liquid water (CLW) over oceans using the AMSU measurements at 23.8 and 31.4 GHz. Extensive comparisons are made between the AMSU retrievals of CLW and TPW and those obtained using other satellite instruments (Special Sensor Microwave Imager (SSM/I) and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI)) and ground-based radiometers. The AMSU TPW is also compared against radiosonde data, where all of the results are in good agreement with rms differences less than 3 mm and biases less than 1 mm over the range between 5 and 60 mm. The CLW comparisons show greater variability, although the time series of the AMSU and ground-based sensors follow each other and cover the same dynamic range of 0-0.5 mm. The AMSU CLW also compares well with the other satellite measurements, although a bias exists between AMSU and TMI when the CLW exceeds 0.5 mm. |
| Source item page count: | 11 |
| Publication Date: | FEB 16 |
| IDS No.: | 401TW |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 13 of 42 | |
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| Author(s): | Czekala H; Crewell S; Simmer C; Thiele A |
| Title: | Discrimination of cloud and rain liquid water path by groundbased polarized microwave radiometry |
| Source: | GEOPHYSICAL RESEARCH LETTERS 2001, Vol 28, Iss 2, pp 267-270 |
| Abstract: | We propose a new approach for groundbased remote sensing of liquid water path (LWP) in the presence of precipitating clouds. Dual polarized groundbased microwave radiometers are capable of detecting the unique scattering signature of nonspherical precipitation sized particles. This polarization signal is only produced by the precipitation particles for which the brightness temperature emission has a different sensitivity to LWP than the smaller cloud drops. By using the information that is contained in the polarization difference of the downwelling brightness temperature the cloud and rain liquid water fractions can be estimated independently. Future retrieval algorithms based on our proposed approach will enable the detection of small precipitation fractions in thick clouds and also allow for estimates of cloud and rain LWP in raining conditions. |
| Source item page count: | 4 |
| Publication Date: | JAN 15 |
| IDS No.: | 392MN |
| 29-char source abbrev: | GEOPHYS RES LETT |
| Record 14 of 42 | |
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| Author(s): | Miao JG; Johnsen KP; Kern S; Heygster G; Kunzi K |
| Title: | Signature of clouds over Antarctic sea ice detected by the special sensor microwave/imager |
| Source: | IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 2000, Vol 38, Iss 5, pp 2333-2344 |
| Abstract: | A method to detect the cloud signature (mainly the cloud liquid water) over the sea ice-covered Weddell Sea in the Austral summer season is presented. By using the polarization differences at the two high frequency channels (i.e., 37 and 85 GHz) of the special sensor microwave/imager (SSM/I), a new quantity called R-factor is defined. Using the R-factor, the atmospheric signal can be easily separated from the surface signal and, more importantly, the surface signal and its variation can be strongly suppressed, especially in regions with low ice concentrations. In regions with high ice concentrations, other sea ice parameters like snow cover play an important role as indicated by simulations using in situ measured sea ice emissivities and observed by the SSM/I, Under the assumption that the sea ice parameters remain sufficiently stable within a short period (e.g., ten days), a method is proposed to determine the background term from SSM/I measurements, allowing the detection of the cloud signature. A comparison with a known SSM/I cloud liquid water algorithm over the open ocean shows a high degree of correlation (0.958) among the cloud signatures detected by the two algorithms. On January 2 and 3, 1996, a low pressure system moved into the sea ice-covered Weddell Sea. Its cloud signature detected using the R-factor method compares well with coincident observations from both visible and infrared sensors. |
| Source item page count: | 12 |
| Publication Date: | SEP |
| Part number: | 1 |
| IDS No.: | 357PP |
| 29-char source abbrev: | IEEE TRANS GEOSCI REMOT SEN |
| Record 15 of 42 | |
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| Author(s): | Snider JB |
| Title: | Long-term observations of cloud liquid, water vapor, and cloud-base temperature in the North Atlantic Ocean |
| Source: | JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2000, Vol 17, Iss 7, pp 928-939 |
| Abstract: | Measurements of precipitable water vapor, cloud liquid, and cloud-base temperature made at Porto Santo Island, Madeira Archipelago, are presented. The observations were made continuously over a 1-yr period from July 1992 to June 1993. Instrumentation consisted of a 20- and 31-GHz ground-based microwave radiometer for measurement of water vapor and cloud liquid, and a 10.7-mu m infrared radiometer for measurement of cloud-base temperature, A statistical summary of the data is presented for clear and cloudy conditions, considered both separately and combined. The mean and variance of precipitable water vapor are smaller during clear than during cloudy periods. Values of water vapor during the winter are 26% smaller than during summer months. The mean decorrelation time of precipitable water vapor is generally found to be less than 12 h. |
| Source item page count: | 12 |
| Publication Date: | JUL |
| IDS No.: | 336RC |
| 29-char source abbrev: | J ATMOS OCEAN TECHNOL |
| Record 16 of 42 | |
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| Author(s): | Frisch AS; Martner BE; Djalalova I; Poellot MR |
| Title: | Comparison of radar/radiometer retrievals of stratus cloud liquid-water content profiles with in situ measurements by aircraft |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2000, Vol 105, Iss D12, pp 15361-15364 |
| Abstract: | In situ sampling of cloud droplets by aircraft in Oklahoma in 1997 is used to evaluate a ground-based remote sensing technique for retrieving profiles of cloud liquid-water content. The technique uses vertically pointing measurements from a high-sensitivity millimeter-wavelength radar and a collocated dual-frequency microwave radiometer to obtain height-resolved estimates of the liquid content of stratiform clouds. Comparisons with the aircraft measurements are made for 16 overpasses through thin cloud layers within a 1.5-km radius of the remote sensor site. Over a range of liquid-water contents from 0.04 to 0.57 g m(-3) the mean difference between the aircraft and the radar/radiometer values was 0.02 g m(-3), and the maximum difference was 0.09 g m(-3). Although the number of comparisons is limited, these results suggest that the ground-based estimates may be sufficiently accurate for many scientific purposes. |
| Source item page count: | 4 |
| Publication Date: | JUN 27 |
| IDS No.: | 328HP |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 17 of 42 | |
|---|---|
| Author(s): | Bobak JP; Ruf CS |
| Title: | Improvements and complications involved with adding an 85-GHz channel to cloud liquid water radiometers |
| Source: | IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 2000, Vol 38, Iss 1, pp 214-225 |
| Abstract: | The improvement in cloud-liquid estimates by a microwave radiometer with the addition of measurements at 85 GHz is quantified. Atmospheric emission is simulated from radiosonde data at frequencies commonly used by ground-based water-vapor radiometers (22.235 and 31.65 GHz) and also at 85.5 GHz, Retrieval algorithms are developed from opacities based on full Mie extinction by cloud droplets and under an assumption that ice effects are not significant for downwelling emission. The algorithms use either three frequencies or only the lower two. The inclusion of 85-GHz information significantly improves liquid-water path estimates at all levels of integrated liquid water. The Rayleigh approximation is shown to be valid for most cloudy conditions. Uncertainty in the calculated opacities due to varying cloud droplet-size distributions and liquid-water content profiles is quantified. The accuracy of a retrieval algorithm trained by Rayleigh approximation opacities and including the additional uncertainty is shown to provide estimates with error levels similar to those from the algorithm trained with full Mie opacities. |
| Source item page count: | 12 |
| Publication Date: | JAN |
| Part number: | 1 |
| IDS No.: | 283XF |
| 29-char source abbrev: | IEEE TRANS GEOSCI REMOT SEN |
| Record 18 of 42 | |
|---|---|
| Author(s): | Greenwald TJ; Christopher SA; Chou J; Liljegren JC |
| Title: | Intercomparison of cloud liquid water path derived from the GOES 9 imager and ground based microwave radiometers for continental stratocumulus |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1999, Vol 104, Iss D8, pp 9251-9260 |
| Abstract: | Solar reflectance measurements (0.6 and 3.9 mu m) from 15-min Geostationary Operational Environmental Satellite (GOES) 9 imager data were used to estimate cloud liquid water path (LWP) for an extensive stratocumulus system over Oklahoma on May 2, 1996. The objective was to determine the consistency between these satellite estimates and retrievals from high temporal resolution (20 s) surface microwave radiometer (SMWR) measurements. The SMWRs were located at the Atmospheric Radiation Measurement (ARM) program cloud and radiation test bed (CART) sites at Morris and Purcell in Oklahoma. Results show that while the comparisons are in favorable agreement at both sites in the morning and early afternoon (root-mean-square difference of 17 g m(-2) and correlation of 0.94), large cloud LWP maxima in the midafternoon as measured by the SMWR at the Morris site are not captured by the satellite retrievals. On the basis of indirect evidence (in situ microphysical measurements were unavailable), it is hypothesized that the discrepancies may be the result of the formation of light drizzle in the middle to lower portions of the cloud, unseen at visible and near-infrared wavelengths from space but easily sensed by microwave radiometry. These results demonstrate that extra care must be taken in future efforts to validate satellite derived cloud properties on a routine basis using SMWR data. Additional information about the cloud microphysical properties may also be required to help properly interpret the comparisons, particularly in the later stages of development of stratocumulus. |
| Source item page count: | 10 |
| Publication Date: | APR 27 |
| IDS No.: | 189UY |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 19 of 42 | |
|---|---|
| Author(s): | Greenwald TJ; Combs CL; Jones AS; Randel DL; Vonder Haar TH |
| Title: | Error estimates of spaceborne passive microwave retrievals of cloud liquid water over land |
| Source: | IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 1999, Vol 37, Iss 2, pp 796-804 |
| Abstract: | Cloud liquid water path (LWP) retrievals from the Special Sensor Microwave/Imager (SSM/I) and surface microwave radiometers are compared over land to assess the errors in selected satellite methods, These techniques require surface emissivity composites created from SSM/I and infrared (IR) data. Two different physical methods are tested: a single-channel (SC) approach (either 85.5-GHz channel); and a normalized polarization difference (NPD) approach (37 or 85.5 GHz). Comparisons were made at four sites in Oklahoma and Kansas over an 11-month period.
The 85.5-GHz NPD method was the most accurate and robust under most conditions. An error analysis shows that the method's random errors are dominated by uncertainties in the surface emissivity and instrument noise. Since the SC method is more prone to systematic errors (such as surface emissivity errors caused by rain events), it initially compared poorly to the ground observations. After filtering for rain events, the comparisons improved. Overall, the root mean square (rms) errors ranged from 0.12 to 0.14 kg m(-2), suggesting these methods can provide, at best, three categories of cloud LWP, It is anticipated that the techniques and strategies developed in this study, and prior related studies, to analyze passive microwave data will be requisite for maximizing the information content of future instruments. |
| Source item page count: | 9 |
| Publication Date: | MAR |
| Part number: | 1 |
| IDS No.: | 177VJ |
| 29-char source abbrev: | IEEE TRANS GEOSCI REMOT SEN |
| Record 20 of 42 | |
|---|---|
| Author(s): | Solheim F; Godwin JR |
| Title: | Passive ground-based remote sensing of atmospheric temperature, water vapor, and cloud liquid water profiles by a frequency synthesized microwave radiometer |
| Source: | METEOROLOGISCHE ZEITSCHRIFT 1998, Vol 7, Iss 6, pp 370-376 |
| Abstract: | An advanced microwave radiometer for profiling atmospheric parameters is described in this paper. The method accomplishing profiling is described. The innovations of the radiometer system, including utilization of a stable frequency synthesizer and the calibration system are described. The performance of several mathematical retrieval methods and representative profiles are presented, as well as several comparisons with radiosondes. |
| Source item page count: | 7 |
| IDS No.: | 164QL |
| 29-char source abbrev: | METEOROL Z |
| Record 21 of 42 | |
|---|---|
| Author(s): | Lipton AE; Griffin MK; Ling AG |
| Title: | Microwave transfer model differences in remote sensing of cloud liquid water at low temperatures |
| Source: | IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 1999, Vol 37, Iss 1, pp 620-623 |
| Abstract: | Results from two popular models for the complex permittivity of liquid water were? compared, as applied to radiative transfer computations in the 5-250-GHz range. Substantial differences were found in situations with cloud temperatures below 0 degrees C, Simulations of cloud liquid water retrievals from satellite and ground-based instruments demonstrated that uncertainties in the models at low temperatures can lead to large retrieval errors. |
| Source item page count: | 4 |
| Publication Date: | JAN |
| Part number: | 2 |
| IDS No.: | 158NY |
| 29-char source abbrev: | IEEE TRANS GEOSCI REMOT SEN |
| Record 22 of 42 | |
|---|---|
| Author(s): | Frisch AS; Feingold G; Fairall CW; Uttal T; Snider JB |
| Title: | On cloud radar and microwave radiometer measurements of stratus cloud liquid water profiles |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1998, Vol 103, Iss D18, pp 23195-23197 |
| Abstract: | We show a method for determining stratus cloud liquid water profiles using a microwave radiometer and cloud radar. This method is independent of the radar calibration and the cloud-droplet size distribution provided that the sixth moment of the size distribution can be related to the square of the third moment. We have calculated these moments with a wide variety of in situ measurements and show that this is a reasonable assumption. Examples of droplet distributions that meet this requirement are the lognormal and gamma distributions. |
| Source item page count: | 3 |
| Publication Date: | SEP 27 |
| IDS No.: | 126PT |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 23 of 42 | |
|---|---|
| Author(s): | Jung T; Ruprecht E; Wagner F |
| Title: | Determination of cloud liquid water path over the oceans from Special Sensor Microwave/Imager (SSM/I) data using neural networks |
| Source: | JOURNAL OF APPLIED METEOROLOGY 1998, Vol 37, Iss 8, pp 832-844 |
| Abstract: | A neural network (NN) has been developed in order to retrieve the cloud liquid water path (LWP) over the oceans from Special Sensor Microwave/Imager (SSM/I) data. The retrieval with NNs depends crucially on the SSM/I channels used as input and the number of hidden neurons-that is, the NN architecture. Three different combinations of the seven SSM/I channels have been tested. For all three methods an NN with five hidden neurons yields the best results. The NN-based LWP algorithms for SSM/I observations are intercompared with a standard regression algorithm. The calibration and validation of the retrieval algorithms are based on 2060 radiosonde observations over the global ocean. For each radiosonde profile the LWP is parameterized and the brightness temperatures (Tb's) are simulated using a radiative transfer model.
The best LWP algorithm (all SSM/I channels except T85V) shows a theoretical error of 0.009 kg m(-2) for LWPs up to 2.8 kg m(-2) and theoretical "clear-sky noise" (0.002 kg m(-2)), which has been reduced relative to the regression algorithm (0.031 kg m(-2)). Additionally, this new algorithm avoids the estimate of negative LWPs. An indirect validation and intercomparison is presented that is based upon SSM/I measurements (F-IO) under clear-sky conditions, classified with independent IR-Meteosat data. The NN-based algorithms outperform the regression algorithm. The best LWP algorithm shows a clear-sky standard deviation of 0.006 kg m(-2), a bias of 0.001 kg m(-2), nonnegative LWPs, and no correlation with total precipitable water. The estimated accuracy for SSM/I observations and two of the proposed new LWP algorithms is 0.023 kg m(-2) for LWP less than or equal to 0.5 kg m(-2). |
| Source item page count: | 13 |
| Publication Date: | AUG |
| IDS No.: | 106EK |
| 29-char source abbrev: | J APPL METEOROL |
| Record 24 of 42 | |
|---|---|
| Author(s): | Combs CL; Greenwald TJ; Jones AS; Randel DL; Vonder Haar TH |
| Title: | Satellite detection of cloud liquid water over land using polarization differences at 85.5 GHz (vol 25, pg 75, 1998) |
| Source: | GEOPHYSICAL RESEARCH LETTERS 1998, Vol 25, Iss 9, pp 1325-1325 |
| Source item page count: | 1 |
| Publication Date: | MAY 1 |
| IDS No.: | ZL261 |
| 29-char source abbrev: | GEOPHYS RES LETT |
| Record 25 of 42 | |
|---|---|
| Author(s): | Solheim F; Godwin JR; Westwater ER; Han Y; Keihm SJ; Marsh K; Ware R |
| Title: | Radiometric profiling of temperature, water vapor and cloud liquid water using various inversion methods |
| Source: | RADIO SCIENCE 1998, Vol 33, Iss 2, pp 393-404 |
| Abstract: | We have developed a tunable temperature profiler based on a highly stable synthesizer that can observe at multiple frequencies on the shoulder of the 60-GHz atmospheric oxygen feature. We are developing a similar radiometer to obtain the vertical distribution of water vapor by making observations on the pressure-broadened water vapor line from 22 to 29 GHz. Information on cloud liquid water profiles is also contained in these two wave bands. Various mathematical retrieval methods for temperature, water vapor, and cloud liquid water profiles were tested based on these radiometer designs. These include neural networking, Newtonian iteration of statistically retrieved profiles, and Bayesian "most probable" retrievals. On the basis of realistic radiometer errors and performance, very good retrieval capability is demonstrated. The performance of the various retrieval methods are presented and compared. Examples of profile retrievals are also presented. Data were not binned into seasons to reduce computer time; better retrieval results for all methods would be expected with binning. |
| Source item page count: | 12 |
| Publication Date: | MAR-APR |
| IDS No.: | ZE395 |
| 29-char source abbrev: | RADIO SCI |
| Record 26 of 42 | |
|---|---|
| Author(s): | Snider JB; Hazen DA |
| Title: | Surface-based radiometric observations of water vapor and cloud liquid in the temperate zone and in the tropics |
| Source: | RADIO SCIENCE 1998, Vol 33, Iss 2, pp 421-432 |
| Abstract: | Observations of water vapor and cloud liquid made with surface-based microwave radiometers operating near 20, 23, 31, and 90 GHz are described. Measurements were made at several continental locations in the United States, an island and ship in the northern Atlantic Ocean, and an island and ship in the tropical western Pacific Ocean. The instrumentation and statistical inversion technique employed to retrieve vapor and liquid values from radiometric brightnesses are reviewed. Various aspects of the water vapor and cloud liquid data are compared as a function of geographic location. The diurnal and seasonal variability of water vapor, cloud liquid, cloud fraction, and infrared sky brightness temperature observed during a 1-year period at an island in the North Atlantic Ocean are also presented. |
| Source item page count: | 12 |
| Publication Date: | MAR-APR |
| IDS No.: | ZE395 |
| 29-char source abbrev: | RADIO SCI |
| Record 27 of 42 | |
|---|---|
| Author(s): | Gerard E; Eymard L |
| Title: | Remote sensing of integrated cloud liquid water: Development of algorithms and quality control |
| Source: | RADIO SCIENCE 1998, Vol 33, Iss 2, pp 433-447 |
| Abstract: | Algorithms are developed to infer integrated cloud liquid water path (LWP) over the oceans from spaceborne and ground-based passive microwave measurements. These algorithms are built from simulated observations, which are calculated with a radiative transfer model applied to a set of about 10,000 atmospheric profiles obtained from the European Centre for Medium-Range Weather Forecasts forecast model. In this model the liquid water content is computed from a prognostic cloud scheme. A multilinear regression is applied to functions of simulated brightness temperatures (log linear form) and LWP to derive the algorithm coefficients. The retrieval accuracy based on the regression analysis including instrumental noise is 0.0257 and 0.0345 kg m(-2) for the DMSP special sensor microwave imager (SSM/I) and the ERS1 along-track scanning radiometer/microwave (ATSR/M), respectively, and 0.0308 kg m(-2) for the ground-based radiometer. It is shown that the log linear form is adequate to transform the nonlinear problem into a quasi-linear problem for LWP below 0.8 kg m(-2). The coherence of the global approach is verified through the validation of total perceptible water (TPW) algorithms developed in a way similar to LWP algorithms. The LWP retrievals from the algorithm for the ground-based radiometer are in good agreement with retrievals from airborne measurements performed in the vicinity of the radiometer. A coherence test is performed for ATSR/M, benefiting from the coincident infrared images obtained from an infrared radiometer (ATSR/IR) aboard the same platform to select clear-air areas. Regardless of the slight mean bias of the inferred LWP due to inaccurate calibration, there is no anomalous dependency upon latitude, i.e., upon high water vapor contents in the tropics and strong winds in the high latitudes. The results of the algorithm for SSM/I are compared with a Meteosat cloud classification. When the classification detects the ocean surface, the algorithm systematically retrieves contents close to zero. The retrievals for other classes (i.e., low stratiform clouds, medium clouds) are consistent with the Meteosat data; retrievals in the presence of low stratiform clouds appear more realistic than values provided by some already published algorithms. It is also shown that up to 0.8 kg m(-2) the log linear regression approach has a quality of the same order as a variational method, which requires much more computation time. |
| Source item page count: | 15 |
| Publication Date: | MAR-APR |
| IDS No.: | ZE395 |
| 29-char source abbrev: | RADIO SCI |
| Record 28 of 42 | |
|---|---|
| Author(s): | Guissard A |
| Title: | The retrieval of atmospheric water vapor and cloud liquid water over the oceans from a simple radiative transfer model: Application to SSM/I data |
| Source: | IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 1998, Vol 36, Iss 1, pp 328-332 |
| Abstract: | A radiative transfer model is described for the evaluation of the brightness temperatures measured by microwave radiometers above the oceans, For observations at an incidence angle around 50 degrees C from the local vertical, a crude approximation of this model is providing the basis for a wind-independent inversion algorithm For the retrieval of atmospheric integrated water vapor and cloud liquid water, The algorithm is applied to special sensor microwave imager (SSM/I) data, and the results compared with estimates from the ECMWF climatological model and from the algorithms specifically developed for SSM/I. A short discussion on the accuracy of the algorithm is also provided. |
| Source item page count: | 5 |
| Publication Date: | JAN |
| IDS No.: | YT522 |
| 29-char source abbrev: | IEEE TRANS GEOSCI REMOT SEN |
| Record 29 of 42 | |
|---|---|
| Author(s): | Combs CL; Greenwald TJ; Jones AS; Randel DL; Haar THV |
| Title: | Satellite detection of cloud liquid water over land using polarization differences at 85.5 GHz |
| Source: | GEOPHYSICAL RESEARCH LETTERS 1998, Vol 25, Iss 1, pp 75-78 |
| Abstract: | A physical retrieval method is described that detects cloud liquid water path (LWP) over land using polarization difference measurements from the Special Sensor Microwave Imager (SSM/I). The brightness temperature difference at 85.5 GHz is divided by the surface emissivity polarization difference to define a normalized polarization difference (NPD). The SSM/I NPD observations are compared to coincident observations of liquid water path fi om upward looking ground-based microwave radiometers in Oklahoma and Kansas for November and December of 1994. The comparisons reveal a moderate correlation and nonlinear relationship (which is expected from theory) between the 85.5 GHz NPD and liquid water path. The NPD method is anticipated to be valid over a broad region of the U.S., excluding the southern Mississippi Valley where the surface emissivity polarization differences are negligible. The observational results indicate that the NPD method holds promise for future routine satellite detection and retrieval of cloud LWP over land. |
| Source item page count: | 4 |
| Publication Date: | JAN 1 |
| IDS No.: | YQ302 |
| 29-char source abbrev: | GEOPHYS RES LETT |
| Record 30 of 42 | |
|---|---|
| Author(s): | Boers R |
| Title: | Simultaneous retrievals of cloud optical depth and droplet concentration from solar irradiance and microwave liquid water path |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1997, Vol 102, Iss D25, pp 29881-29891 |
| Abstract: | A 20-month time series of continuous observations of microwave radiation and solar irradiance was used to estimate the cloud optical depth and droplet number concentration at the Cape Grim Baseline Air Pollution Station, Tasmania, (40 degrees 41'S, 144 degrees 41'E). The data were selected by wind directions. When the air was from "baseline" origin, i.e., it had travelled over long oceanic distances and was mostly devoid of anthropogenic influences, the retrieved droplet concentration and optical depth were lower than when the air was from "nonbaseline" i.e., continental origin. Therefore the observed variation in cloud microphysical properties reflects the difference between the natural background conditions over the Southern Ocean and continental conditions with elevated droplet counts. Under baseline conditions the retrieved cloud optical depth exhibits a weak but perceptible seasonal cycle that has been previously observed from satellite data with a minimum in the austral winter, and a maximum in the austral summer. The results demonstrate that routine retrievals of cloud microphysical properties are possible using only a pyranometer sind a microwave liquid water radiometer. |
| Source item page count: | 11 |
| Publication Date: | DEC 27 |
| IDS No.: | YP443 |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 31 of 42 | |
|---|---|
| Author(s): | Perfilev YP; Trokhimovskii YG |
| Title: | Retrieval of atmospheric water vapor and cloud liquid water using a dual-frequency radiometer |
| Source: | IZVESTIYA AKADEMII NAUK FIZIKA ATMOSFERY I OKEANA 1997, Vol 33, Iss 5, pp 687-691 |
| Abstract: | Atmospheric water vapor and cloud liquid water estimates obtained with two ground-based microwave radiometers of K- and Ka-bands (at wavelengths of 1.5 and 0.8 cm) are given. Two different procedures for determining water vapor content are compared. The effect of various cloud types on the accuracy of water vapor retrieval from differential dual-frequency measurements is investigated. |
| Source item page count: | 5 |
| Publication Date: | SEP-OCT |
| IDS No.: | YE996 |
| 29-char source abbrev: | IZV AKAD NAUK FIZ ATMOS OKEAN |
| Record 32 of 42 | |
|---|---|
| Author(s): | Greenwald TJ; Christopher SA; Chou J |
| Title: | Cloud liquid water path comparisons from passive microwave and solar reflectance satellite measurements: Assessment of sub-field-of-view cloud effects in microwave retrievals |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1997, Vol 102, Iss D16, pp 19585-19596 |
| Abstract: | Satellite observations of the cloud liquid water path (LWP) are compared from special sensor microwave imager (SSM/I) measurements and GOES 8 imager solar reflectance (SR) measurements to ascertain the impact of sub-field-of-view (FOV) cloud effects on SSM/I 37 GHz retrievals. The SR retrievals also incorporate estimates of the cloud droplet effective radius derived from the GOES 8 3.9-mu m channel. The comparisons consist of simultaneous collocated and full-resolution measurements and are limited to nonprecipitating marine stratocumulus in the eastern Pacific for two days in October 1995. The retrievals from these independent methods are consistent for overcast SSM/I FOVs, with RMS differences as low as 0.030 kg m(-2), although biases exist for clouds with more open spatial structure, where the RMS differences increase to 0.039 kg m(-2). For broken cloudiness within the SSM/I FOV the average beam-filling error (BFE) in the microwave retrievals is found to be about 22% (average cloud amount of 73%). This systematic error is comparable with the average random errors in the microwave retrievals. However, even larger BFEs can be expected for individual FOVs and for regions with less cloudiness. By scaling the microwave retrievals by the cloud amount within the FOV, the systematic BFE can be significantly reduced but with increased RMS differences of 0.046-0.058 kg m(-2) when compared to the SR retrievals. The beam-filling effects reported here are significant and are expected to impact directly upon studies that use instantaneous SSM/I measurements of cloud LWP, such as cloud classification studies and validation studies involving surface-based or in situ data. |
| Source item page count: | 12 |
| Publication Date: | AUG 27 |
| IDS No.: | XT934 |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 33 of 42 | |
|---|---|
| Author(s): | Weng FZ; Grody NC; Ferraro R; Basist A; Forsyth D |
| Title: | Cloud liquid water climatology from the special sensor microwave/imager |
| Source: | JOURNAL OF CLIMATE 1997, Vol 10, Iss 5, pp 1086-1098 |
| Abstract: | A Special Sensor Microwave/Imager (SSM/I) algorithm is developed to measure both cloud liquid water path (LWP) and cloud frequency (CF) over the oceans. For climate analysis, the LWP and CF parameters are computed on pentad and monthly timescales. Comparisons are made between cloud frequencies obtained from microwave and visible/infrared measurements. It is shown that the SSM/I CF correlates with International Satellite Cloud Climatology Program low- and middle-level cloudiness. Interannual variations of monthly LWP are found to be strongly correlated with Fl Nino and La Nina events. In general, positive LWP anomalies are associated with positive SST anomalies. However, positive LWP anomalies may also occur in regions of negative SST anomalies. This is probably due to an increase in warm top rain clouds, produced from low-level convergence. When pentads of outgoing longwave radiation data are compared to the LWP, they both show the detailed structure for atmospheric intraseasonal oscillations at 30-60-day periods. However, there are some interesting differences. Finally, as an important application, the monthly LWP is compared with simulations from a general circulation model. While the simulation captures the locations of observed maxima and minima, there is a large discrepancy between the model and measurement for the Northern Hemisphere in summer. |
| Source item page count: | 13 |
| Publication Date: | MAY |
| IDS No.: | XB773 |
| 29-char source abbrev: | J CLIMATE |
| Record 34 of 42 | |
|---|---|
| Author(s): | Greenwald TJ; Combs CL; Jones AS; Randel DL; VonderHaar TH |
| Title: | Further developments in estimating cloud liquid water over land using microwave and infrared satellite measurements |
| Source: | JOURNAL OF APPLIED METEOROLOGY 1997, Vol 36, Iss 4, pp 389-405 |
| Abstract: | Refinements and improvements of an earlier technique to retrieve the cloud liquid water path (LWP) of nonprecipitating clouds over land surfaces using Special Sensor Microwave/Imager (SSM/I) 85.5-GHz measurements are presented. These techniques require estimates of the microwave surface emissivity, which are derived in clear-sky regions from SSM/I measurements and window infrared measurements from the Visible and Infrared Spin Scan Radiometer on GOES-7. A comparison of forward model calculations with SSM/I measurements in clear regions demonstrates that over a 7-day period the surface emissivities are stable.
To overcome limitations in the single-channel retrieval method under certain situations, a new method is developed that uses a normalized polarization difference (NPD) of the brightness temperatures. This method has the advantages of providing estimates of the LWP for low clouds and being extremely insensitive to the surface skin temperature. Radiative transfer simulations also show that the polarization difference at 37 GHz may be useful for retrievals in high water vapor environments and for large cloud LWP. An intercomparison of the different retrieval methods over Platteville, Colorado, reveals large discrepancies for certain cases, but the NPD method is found to agree best with coincident ground-based microwave radiometer measurements of cloud LWP. This success is primarily due to the larger than average surface polarization differences near the Platteville site. While the NPD method shows promise in distinguishing between low, moderate, and high values of cloud LWP, a comprehensive validation effort is required to further evaluate its accuracy and limitations. |
| Source item page count: | 17 |
| Publication Date: | APR |
| IDS No.: | WV594 |
| 29-char source abbrev: | J APPL METEOROL |
| Record 35 of 42 | |
|---|---|
| Author(s): | Phalippou L |
| Title: | Variational retrieval of humidity profile, wind speed and cloud liquid-water path with the SSM/I: Potential for numerical weather prediction |
| Source: | QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 1996, Vol 122, Iss 530, pp 327-355 |
| Abstract: | Several regression algorithms have been proposed to retrieve geophysical parameters from the Special Sensor Microwave/Imager (SSM/I) radiances. Their performances are generally limited by a simplified handling of nonlinearities and/or by the poor quality of the a priori information. In this paper, a variational method is proposed for retrieving the atmospheric humidity profile, the wind speed and the cloud liquid-water path from SSM/I observations over ocean. This method is based on nonlinear optimal estimation theory. The first guess is derived from a European Centre for Medium-Range Weather Forecasts forecast, and the forecast-error covariance is used as a constraint. The geophysical variable space is mapped into the radiance space through a radiative-transfer model which permits an accurate representation of nonlinearities. This method has been applied to several orbits and the results for one of them are presented and discussed. It is argued that the variational approach is a simple optimal way of extracting information from SSM/I radiances, exploiting the high quality a priori information available from a numerical weather-prediction model. The retrieved humidity profiles are found to compare well with the total precipitable water estimated from a regression algorithm, while avoiding local bias in very dry and very wet conditions. It is also shown that the potential wind speed-cloud ambiguity is removed through the use of a high-quality wind speed first guess. |
| Source item page count: | 29 |
| Publication Date: | JAN |
| Part number: | B |
| IDS No.: | UA808 |
| 29-char source abbrev: | QUART J ROY METEOROL SOC |
| Record 36 of 42 | |
|---|---|
| Author(s): | Sauvageot H |
| Title: | Retrieval of vertical profiles of liquid water and ice content in mixed clouds from Doppler radar and microwave radiometer measurements |
| Source: | JOURNAL OF APPLIED METEOROLOGY 1996, Vol 35, Iss 1, pp 14-23 |
| Abstract: | A new method to retrieve vertical profiles of liquid water content M(w)(z), ice water content M(i)(z), and ice particle size distribution N-i(D, z) (where D is the ice particle size and z the vertical coordinate) in mixed nonprecipitating clouds using the observations of a zenith-viewing Doppler radar and of a microwave radiometer is proposed. In this method, the profile of the vertical air velocity deduced from Doppler radar measurements is used to describe the rate of production by the updrafts of water vapor in excess of saturation with respect to ice. Using a Z(i)-M(i) power-law relation with an unknown linear parameter (let alpha(i) be this parameter) and initially assuming that Z(w) is negligible with respect to Z(i) (where Z(w) and Z(i) are the radar reflectivity factors of liquid water and ice particles, respectively), the measured radar reflectivity factor profile Z(m)(approximate to Z(i)) is inverted to estimate N-i(D, z). From N-i(D, z) the profile of the rate of water vapor that can be consumed by pure deposition on ice particles is calculated. The difference between the rate of production of the excess water vapor and the rate of deposited water vapor is an expression of the rate of liquid water generation at each level. By writing that the integral of the liquid water along the profile has to be equal to the total liquid water deduced from the microwave radiometer measurement, an estimation of the cui parameter is obtained. From alpha(i), an estimation of the profiles M(w)(z), M(i)(z), Z(w)(z), Z(i)(z) (=Z(m) - Z(w)), and N-i(D, z) is calculated. If Z(w) is effectively negligible with respect to Z(i), the computation of the retrieved profiles is ended. If not, Z(i)(z) is corrected and a new estimation of the profiles is computed. The results of the numerical simulation of the algorithm are presented. |
| Source item page count: | 10 |
| Publication Date: | JAN |
| IDS No.: | TQ567 |
| 29-char source abbrev: | J APPL METEOROL |
| Record 37 of 42 | |
|---|---|
| Author(s): | Han Q; Rossow W; Welch R; White A; Chou J |
| Title: | Validation of satellite retrievals of cloud microphysics and liquid water path using observations from FIRE |
| Source: | JOURNAL OF THE ATMOSPHERIC SCIENCES 1995, Vol 52, Iss 23, pp 4183-4195 |
| Abstract: | Cloud effective radii (r(e)) and cloud liquid water path (LWP) are derived from ISCCP spatially sampled satellite data and validated with ground-based pyranometer and microwave radiometer measurements taken on San Nicolas Island during the 1987 FIRE IFO. Values of r(e) derived from the ISCCP data are also compared to values retrieved by a hybrid method that uses the combination of LWP derived from microwave measurement and optical thickness derived from GOES data. The results show that there is significant variability in cloud properties over a 100 km x 80 km area and that the values at San Nicolas Island are not necessarily representative of the surrounding cloud field. On the other hand, even though there were large spatial variations in optical depth, the r(e) values remained relatively constant (with sigma less than or equal to 2-3 mu m in most cases) in the marine stratocumulus. Furthermore, values of r(e) derived from the upper portion of the cloud generally are representative of the entire stratiform cloud. When LWP values are less than 100 g m(-2), then LWP values derived from ISCCP data agree well with those values estimated from ground-based microwave measurements. In most cases LWP differences were less than 20 g m(-2). However, when LWP values become large (e.g., greater than or equal to 200 g m(-2)), then relative differences may be as large as 50%-100%. There are two reasons for this discrepancy in the large LWP clouds: 1) larger vertical inhomogeneities in precipitating clouds and 2) sampling errors on days of high spatial variability of cloud optical thicknesses. Variations of r(e) in stratiform clouds may indicate drizzle: clouds with droplet sizes larger than 15 mu m appear to be associated with drizzling, while those less than 10 mu m are indicative of nonprecipitating clouds. Differences in r(e) values between the GOES and ISCCP datasets are found to be 0.16 +/- 0.98 mu m. |
| Source item page count: | 13 |
| Publication Date: | DEC 1 |
| IDS No.: | TL538 |
| 29-char source abbrev: | J ATMOS SCI |
| Record 38 of 42 | |
|---|---|
| Author(s): | ENGLISH SJ |
| Title: | AIRBORNE RADIOMETRIC OBSERVATIONS OF CLOUD LIQUID-WATER EMISSION AT 89 AND 157 GHZ - APPLICATION TO RETRIEVAL OF LIQUID-WATER PATH |
| Source: | QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 1995, Vol 121, Iss 527, pp 1501-1524 |
| Abstract: | Measurements of the microwave brightness temperature of stratocumulus cloud at 89 and 157 GHz using the Microwave Airborne Radiometer Scanning System on the UK Meteorological Research Flight's C-130 aircraft have been analysed. Comparisons of observed and calculated brightness temperature using models available in the literature have given good agreement for sea-surface emission and atmospheric attenuation in clear and cloudy skies. A nonlinear retrieval scheme has been applied to the observations to retrieve cloud liquid-water paths for comparison with the in situ measurements. Validation of the retrieved liquid-water paths to within 50 g m(-2) has been achieved. Ambiguities between cloud retrievals and water vapour and surface parameters are discussed. The observed differences between the retrieval and the in situ measurement are not found to correlate strongly with cloud temperature, but a higher than expected correlation is found with the drop-size distribution. It is demonstrated that the scheme is applicable to satellite soundings of cloud, and that a similar level of accuracy should be achieved. |
| Source item page count: | 24 |
| Publication Date: | OCT |
| Part number: | A |
| IDS No.: | TA293 |
| 29-char source abbrev: | QUART J ROY METEOROL SOC |
| Record 39 of 42 | |
|---|---|
| Author(s): | WENG FZ; GRODY NC |
| Title: | RETRIEVAL OF CLOUD LIQUID WATER USING THE SPECIAL SENSOR MICROWAVE IMAGER (SSM/I) |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1994, Vol 99, Iss D12, pp 25535-25551 |
| Abstract: | The special sensor microwave imager (SSM/I) is a microwave radiometer having dual-polarized channels at 19.35, 37, and 85.5 GHz and a vertically polarized channel at 22.235 GHz. The measurements at these frequencies are used to retrieve the liquid water path in precipitating and nonprecipitating clouds over oceans. Three separate algorithms, each accurate for different ranges of liquid water, are combined to measure a large dynamic range of cloud liquid water path up to 3.0 mm. The major improvements of our present algorithm over many other previous studies are (1) the algorithm detects the liquid water in optically thin stratus and low-level clouds very well; (2) the algorithm measures the liquid water in highly convective clouds; (3) the algorithm can be applied to any climate regime because some of the coefficients (a(1) and a(2)) are derived using a comprehensive training SSM/I data set obtained from various clear sky conditions; and (4) the liquid water derived using the present algorithm agree with that derived using the ground-based microwave radiometer measurements very well. Global distributions of the cloud liquid water over oceans for August 1993 and January 1994 are derived using the SSM/I data from DMSP F10 and F11 satellites. Our analyses show that the cloud liquid water exhibits a strong diurnal variation over many regions. In particular, the variation over the tropical western Pacific and northwestern Pacific is largest and is attributed to the diurnal variation of raining clouds. The variation over the west coasts of major continents is also very large and is associated with nonraining stratus clouds. |
| Source item page count: | 17 |
| Publication Date: | DEC 20 |
| IDS No.: | PY229 |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 40 of 42 | |
|---|---|
| Author(s): | KARSTENS U; SIMMER C; RUPRECHT E |
| Title: | REMOTE-SENSING OF CLOUD LIQUID WATER |
| Source: | METEOROLOGY AND ATMOSPHERIC PHYSICS 1994, Vol 54, Iss 1-4, pp 157-171 |
| Abstract: | A method is presented to infer cloud liquid water path (LWP in kg/m2) over the ocean from passive microwave measurements of SSM/I. The algorithm to retrieve LWP is based on simulated satellite observations. They are calculated with a radiative transfer model applied to about 3000 radiosonde ascents over the Atlantic Ocean. Since radiosonde observations do not contain direct information about cloud water and ice, these parameters are parameterized based on relative humidity and temperature using modified adiabatic liquid water density profiles. A multiple linear regression is applied water density profiles. A multiple linear regression is applied to the simulated radiances and the calculated LWP to derive the algorithm. The retrieval accuracy based on the regression analysis including instrumental noise is 0.03 kg/m2. Validation of the LWP-algorithm was pursued through a comparison with measurements of a ground-based 33 GHz-microwave radiometer on board of R.V. ''Poseidon'' during the International Cirrus Experiment 1989 at the North Sea (ICE'89). The LWP values agree within the range of uncertainty caused by the different sampling characteristics of the observing systems. The retrieval accuracy for clear-sky cases determined using colocated METEOSAT data over the North Sea is 0.037 kg/m2 and confirms the accuracy estimated from regression analysis for the low liquid water cases.
The algorithm was used to derive maps of monthly mean LWP over the Atlantic Ocean. As an example the Octobers of the 5 years 1987-1991 were selected to demonstrate the interannual variability of LWP. The results were compared with the cloud water content produced by the climate model ECHAM-T2 from the Max-Planck-Institut Hamburg. Observations during ICE'89 were used to check the accuracy of the applied radiative transfer model. Brightness temperatures were calculated from radiosonde ascents launched during the overpass of DMSP-F8 in cloud-free situations. The channel-dependent differences range from about - 2 to 3 K. The possibility to identify different cloud types using microwave and infrared observations was examined. The main conclusion is that simultaneous microwave and infrared measurements enable the separation of dense cirrus and cirrus with underlying water clouds. A classification of clouds with respect to their top heights and LWP was carried out using a combination of SSM/I derived LWP and simultaneously recorded Meteosat IR-data during ICE'89. |
| Source item page count: | 15 |
| IDS No.: | PN896 |
| 29-char source abbrev: | METEOROL ATMOS PHYS |
| Record 41 of 42 | |
|---|---|
| Author(s): | LIN B; ROSSOW WB |
| Title: | OBSERVATIONS OF CLOUD LIQUID WATER PATH OVER OCEANS - OPTICAL AND MICROWAVE REMOTE-SENSING METHODS |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 1994, Vol 99, Iss D10, pp 20907-20927 |
| Abstract: | Published estimates of cloud liquid water path (LWP) from satellite-measured microwave radiation show little agreement, even about the relative magnitudes of LWP in the tropics and midlatitudes. To understand these differences and to obtain a more reliable estimate, optical and microwave LWP retrieval methods are compared using the International Satellite Cloud Climatology Project (ISCCP) and special sensor microwave/imager (SSM/I) data. Errors in microwave LWP retrieval associated with uncertainties in surface, atmosphere, and cloud properties are assessed. Sea surface temperature may not produce great LWP errors, if accurate contemporaneous measurements are used in the retrieval. An uncertainty of estimated near-surface wind speed as high as 2 m/s produces uncertainty in LWP of about 5 mg/cm(2). Cloud liquid water temperature has only a small effect on LWP retrievals (rms errors < 2 mg/cm(2)), if errors in the temperature are < 5 degrees C; however, such errors can produce spurious variations of LWP with latitude and season. Errors in atmospheric column water vapor (CWV) are strongly coupled with errors in LWP (for some retrieval methods) causing errors as large as 30 mg/cm(2) Because microwave radiation is much less sensitive to clouds with small LWP (less than 7 mg/cm(2)) than visible wavelength radiation, the microwave results are very sensitive to the process used to separate clear and cloudy conditions. Different cloud detection sensitivities in different microwave retrieval methods bias estimated LWP values. Comparing ISCCP and SSM/I LWPs, we find that the two estimated values are consistent in global, zonal, and regional means for warm, nonprecipitating clouds, which have average LWP values of about 5 mg/cm(2) and occur much more frequently than precipitating clouds. Ice water path (IWP) can be roughly estimated from the differences between ISCCP total water path and SSM/I LWP for cold, nonprecipitating clouds. IWP in the winter hemisphere is about 3 times the LWP but only half the LWP in the summer hemisphere. Precipitating clouds contribute significantly to monthly, zonal mean LWP values determined from microwave, especially in the intertropical convergence zone (ITCZ), because they have almost 10 times the liquid water (cloud plus precipitation) of nonprecipitating clouds on average. There are significant differences among microwave LWP estimates associated with the treatment of precipitating clouds. |
| Source item page count: | 21 |
| Publication Date: | OCT 20 |
| IDS No.: | PN309 |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 42 of 42 | |
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| Author(s): | KADYGROV EN; KOLDAEV AV; KHAIKIN MN |
| Title: | SOME RESULTS OF CLOUD LIQUID WATER MEASUREMENTS BY MICROWAVE RADIOMETERS |
| Source: | IZVESTIYA AKADEMII NAUK FIZIKA ATMOSFERY I OKEANA 1994, Vol 30, Iss 2, pp 230-232 |
| Abstract: | The results of cloud liquid water measurements by means of the ground-based 2.7 mm and 8.0 mm microwave radiometers am described. The observations were carried out in September 1992 during the Zvenigorod experiment. Lidar and radar observations of cloud parameters were also available during the measurements. The total amount of cloud liquid water was obtained for different types of clouds. |
| Source item page count: | 3 |
| Publication Date: | MAR-APR |
| IDS No.: | NJ567 |
| 29-char source abbrev: | IZV AKAD NAUK FIZ ATMOS OKEAN |