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Poster Session 3
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Earth Surface Geophysical Parameters Determination From ATSR Data
Tests and Results
The date and time of the ATSR data were 2nd August 1995 and 11:00 GMT. The area is located in the middle of UK. In this area there are land and sea surfaces. The algorithms have been used to calculate reflectances and albedo from dual view ATSR visible band data. Figure 1 (a) shows the Earth's surface albedo. Figure 1 (b) gives Earth Surface temperature (LST and SST) in °K. Figures (c) and (d) show the land surface emissivity for 11 mm and 12 mm channels respectively. Cloudy areas (white plot) were not calculated.
The 1995 is the hottest year since first global temperature recording in 1860 from the Meterological Office, UK. The sunny and exceptionally hot weather which began at the end of July lasted through the first three days of August with the temperature exceeding 33°C (306 degK) daily at several places. August 1995 was, averaged over the whole United Kingdom, probably the hottest and sunniest on record, and one of the driest (Eden 1995). In Fig. 1(a), we can see that the temperatures in most areas are around 30°C. Some areas in Midland are higher than 36°C. The surface temperature determined from satellite data is the instantaneous effective surface temperature. The temperature from weather forecasting is the air temperature at 1 m height. The black plots are cloudy areas. From Fig. 1 (b) and (c), we can see that the emissivity is not very close to unity. The values of the emissivity is around 0.97 - 0.99 for the 11 mm channel and 0.96 - 0.98 for the 12 mm channel. This agrees with the result of Taylor (1979) that the surface in agricultural areas behaves almost like a black body ( e = 0.97). It will be noticed that the emissivity for the 11 mm channel is greater than for the 12 mm channel.
Conclusions
An accurate determination of the surface properties is therefore essential to obtain the various terms of the energy budget: the reflected solar flux - knowledge of the emissivity and the temperature; the upward longwave flux - knowledge of the emissivity and the surface temperature; the heat and water fluxes are the turbulent sensible and latent heat fluxes, both depending on the surface temperature (Xue et al. 1998, 2000a, b).
The paper demonstrated that ATSR-2 data can be used to determine the Earth's surface Albedo, temperature and emissivity. The approaches are simple methods to remove the atmospheric effects from visible and thermal band data. For a non-Lambertian surface, the bidirectional properties of the ground surface should be taken into account. The narrow-band reflectances are combined into a measure of surface albedo by use of a weighted averaged scheme.
Acknowledgement
The author thanks Professor D. T. Llewellyn-Jones and the RAL, Oxford, for supplying the ATSR data.
References
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(a)
(b)
(a)
(b)
Figure 1 Geophysical parameters derived from ATSR data in UK and surrounding
area. The date and time of the ATSR data were 2nd August 1995 and 11:00
GMT. The unit for Land Surface Temperature (LST) and Sea Surface
Temperature (SST) is °K.
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