First on Ground Tests
First on-ground measurements
- Here we present first preliminary results of atmospheric methane and CO2 MAMAP measurements performed on-ground on the Campus of the University of Bremen. The retrieval algorithm is a modified DOAS algorithm, called WFM-DOAS (Buchwitzet al., 2000), also used for retrieval of methane and CO2 columns from SCIAMACHY nadir observations (Buchwitz et al., 2005, 2006). WFM-DOAS is based on fitting a linearized radiative transfer model to the observed spectra. The fit parameters are scaling factors for the retrieved (partial) columns. For the results shown here the fit parameters correspond to the (total) vertical columns of CH4 and CO2.Figures 2 and 3 show typical CH4 and CO2 spectral fits. The measurement viewing geometry roughly corresponds to a nadir view from an aircraft flying at very low altitude.
- The line-of-sight of the spectrometer has been pointed towards a group of trees located on the Campus of the University of Bremen (“Sun-illuminated target”). The integration time (for a single detector readout) of the measurement was 0.148 s. A very good fit of the spectral absorption features of methane and CO2 has been obtained, as shown in figures 2 and 3. Figure 4 shows the results of a time series ofthese measurements. The bottom panel displays the maximum value of the measured signal, varying due to e.g. clouds and aerosols.
- The top panel shows the retrieved normalized CH4 and CO2 columns as a function of time. The columns have been normalized to their profile scaling factor of the first measurement, which is 1.0057 for methane (i.e. the retrieved methane column agrees within 0.57% with the column assumed for the radiative transfer simulations). The second panel shows the ratio of the methane column and the CO2 column which is stable within +/-1%,despite the signal fluctuations due to clouds. Figures 5-7 show similar results as shown in Fig. 2-4 but for zenith sky observations (S/N equivalent to nadir view over low albedo scenes).