| Record 1 of 6 | |
|---|---|
| Author(s): | Fahnestock MA; Abdalati W; Shuman CA |
| Title: | Long melt seasons on ice shelves of the Antarctic Peninsula: an analysis using satellite-based microwave emission measurements |
| Source: | ANNALS OF GLACIOLOGY, VOL 34, 2002 2002, Vol 34, pp 127-133 |
| Abstract: | We have examined the record of melt-season duration on the Antarctic Peninsula using two techniques for detecting the presence of a melt signal in microwave-emission time series covering the period 1978-2000. We have obtained similar estimates of melt-season length using the cross-polarized gradient ratio (XPGR) technique and calibrations previously applied in Greenland and a technique which detects the jump In emission caused by melt without using a sensor- and frequency-dependent threshold value. The close correspondence between results from the two techniques on peninsula ice shelves suggests that the XPGR analysis can be used over the length of the time series. The results show that the long melt seasons of 1992/93 and several later years were exceptional occurrences on the northern parts of the Larsen Ice Shelf These melt seasons were followed by disintegration events, supporting a possible cause-and-effect relationship. |
| Source item page count: | 7 |
| Book series title: | ANNALS OF GLACIOLOGY |
| IDS No.: | BU99C |
| 29-char source abbrev: | ANN GLACIOL |
| Record 2 of 6 | |
|---|---|
| Author(s): | Haggerty JA; Curry JA |
| Title: | Variability of sea ice emissivity estimated from airborne passive microwave measurements during FIRE SHEBA |
| Source: | JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2001, Vol 106, Iss D14, pp 15265-15277 |
| Abstract: | Passive microwave radiometers with frequencies ranging from 37 GHz to 220 GHz were flown over the Surface Heat Budget of the Arctic (SHEBA) experimental site in May and July 1998. These measurements were motivated by the possibility of determining cloud liquid water path, ice water path, and precipitation over sea ice from these frequencies. The comprehensive cloud data set collected in this experiment offers a unique opportunity for improving and adapting passive microwave retrieval methods for application to arctic clouds. However, retrieval of cloud properties from a downward looking radiometer requires an estimate of the surface emissivity and its spectral, spatial, and temporal variation. In this study, brightness temperature measurements are used to calculate sea ice emissivity at each frequency using ancillary aircraft data to characterize the atmosphere and obtain surface temperature. Surface emissivities on clear sky days during the FIRE Arctic Cloud Experiment (FIRE ACE) aircraft campaign have been calculated and compared with previous estimates cited in the literature. Average emissivity at nadir for snow-covered sea ice in the experimental region during late May is estimated as 0.89 at 37 GHz, 0.74 at 89 GHz, 0.72 at 90 GHz, 0.73 at 150 GHz, and 0.84 at 220 GHz. In early July the average nadir emissivity for melting sea ice is 0.86 for 37 GHz and 0.84 for 90 GHz. Estimates of emissivity at 50 degrees off nadir are compared with previous satellite and ground-based measurements of dual polarized emissivities at 37 GHz and 90 GHz. Significant variability exists in published emissivity values due to variations in dielectric and physical properties of snow and ice, but our results fall within previously observed ranges. Uncertainties in the emissivity calculations are estimated, and the accuracy required for use of surface emissivity estimates in cloud retrieval methods is discussed. |
| Source item page count: | 13 |
| Publication Date: | JUL 27 |
| IDS No.: | 456YE |
| 29-char source abbrev: | J GEOPHYS RES-ATMOS |
| Record 3 of 6 | |
|---|---|
| Author(s): | Schmidt K; Wauer J |
| Title: | Application of the dense medium radiative transfer theory for calculating microwave emissivities of different sea ice types |
| Source: | INTERNATIONAL JOURNAL OF REMOTE SENSING 1999, Vol 20, Iss 15-16, pp 3165-3182 |
| Abstract: | The dense medium radiative transfer theory (DMRT) was used to calculate microwave emissivities of different undeformed sea ice types in the Arctic and Antarctic. The computed results were compared with measurements. More often taken for describing snow, we show that the DMRT can be applied to both sea ice and snow cover. While doing so the choice of appropriate parameters needed in the DMRT is discussed. As a result a multi-layered, uniform model for a variety of sea ice types including snow cover is obtained. |
| Source item page count: | 18 |
| Publication Date: | OCT 15 |
| IDS No.: | 239LC |
| 29-char source abbrev: | INT J REMOTE SENS |
| Record 4 of 6 | |
|---|---|
| Author(s): | Hewison TJ; English SJ |
| Title: | Airborne retrievals of snow and ice surface emissivity at millimeter wavelengths |
| Source: | IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 1999, Vol 37, Iss 4, pp 1871-1879 |
| Abstract: | Passive microwave radiometers (24-157 GHz) have been down over Baltic sea ice and snow sites in April 1995 and on March 15, 1997. Data from these instruments are analyzed with reference to ground measurements of snow and ice conditions, and emissivity spectra are presented for 12 classifications of surface type. A simple model based on dielectric permittivity can accurately represent the microwave spectra of sea ice, but cannot be extended to the behavior of dry snow above 100 GHz without the addition of an extra term to represent volume scattering. The parameterization presented is intended to provide a background for temperature and humidity retrievals from satellite sounders, but the results will be of interest to the snow and ice remote-sensing communities. |
| Source item page count: | 9 |
| Publication Date: | JUL |
| IDS No.: | 217VP |
| 29-char source abbrev: | IEEE TRANS GEOSCI REMOT SEN |
| Record 5 of 6 | |
|---|---|
| Author(s): | Abdalati W; Steffen K |
| Title: | Accumulation and hoar effects on microwave emission in the Greenland ice-sheet dry-snow zones |
| Source: | JOURNAL OF GLACIOLOGY 1998, Vol 44, Iss 148, pp 523-531 |
| Abstract: | The relationships between accumulation and microwave emissivity in the dry-snow regions of the Greenland ice sheet are studied with special focus on hear formation. With the use of a discrete-ordinate radiative-transfer model, the relative contributions of hear and accumulation to microwave emission are examined. The results show that the link between microwave emission and accumulation rates in the dry-snow area of the Greenland ice sheet is significant; however, the emissivity is also dependent on the extent of boar development. As a result, accumulation estimates based on passive microwave observations in the low-accumulation dry-snow areas will require successful parameterization of hear formation. Furthermore, the increasing Tb trends that were observed during the 1980s, which have been hypothesized to be related to accumulation changes, may be strongly related to variations in hoar development. Other possible explanations for these observed trends, such as slight surface melt or atmospheric conditions, are also discussed. |
| Source item page count: | 9 |
| IDS No.: | 170JW |
| 29-char source abbrev: | J GLACIOLOGY |
| Record 6 of 6 | |
|---|---|
| Author(s): | Barber DG; Fung AK; Grenfell TC; Nghiem SV; Onstott RG; Lytle VI; Perovich DK; Gow AJ |
| Title: | The role of snow on microwave emission and scattering over first-year sea ice |
| Source: | IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 1998, Vol 36, Iss 5, pp 1750-1763 |
| Abstract: | The primary objective of this paper is to investigate the geophysical and thermodynamic effects of snow on sea ice in defining the electromagnetic (EM) interaction within the microwave portion of the spectrum. We combine observational evidence of both the physical and thermodynamic characteristics of snow with direct measurements of scattering and emission at a variety of frequencies. We explain our observational results using various "state-of-the-art" forward scattering and emission models.
Results show that geophysical characteristics of snow effect emission above about 37 GHz and above 5 GHz for active microwave scattering. We understand these effects to be driven by grain size and its contribution to volume scattering in both passive and active interactions within the volume. With snow cover, the Brewster angle effect is not significant and there is a gradual rise in emission from 10 to 37 GHz, We find emissivity to be dominated by direct emission from saline ice through the snow layer. Hence, the influence of grain size is small but the trend is clearly a drop in total emission as the grain size increases. We find that the role of the volume fraction of snow on emission and scattering is a complex relationship between the number density of scatterers relative to the coherence of this scattering ensemble. At low volume fractions, we find that independent scattering dominates, resulting in an increase in albedo and the extinction coefficient of the snow with frequency. The thermodynamic effects of snow on microwave scattering and emission are driven by the role that thermal diffusivity and conductivity play in the definition of brine volumes at the ice surface and within the snow volume, Prior to the presence of water in liquid phase within the snow volume, we find that the indirect effects are dominated by an impedance matching process across the snow-ice interface. We find that the complex permittivity at the snow-ice interface is considerably higher than over the bare ice surface. Our results showed that only a small change occurs between the cold and warm cases at lower frequencies, but as expected, the change in emissivity is larger at higher frequencies. Once water in liquid phase appears within the snow cover, we find that both emission and scattering are directly affected by the high complex permittivity of this volume fraction within the snow layer. |
| Source item page count: | 14 |
| Publication Date: | SEP |
| Part number: | 2 |
| IDS No.: | 121ZQ |
| 29-char source abbrev: | IEEE TRANS GEOSCI REMOT SEN |