Impact of errors in the atmospheric correction

The proposed approach to estimate foliage and soil temperatures requires the determination of Bottom-Of-Atmosphere (BOA) spectral directional radiance. Uncertainty in the knowledge of the atmospheric state affects the accuracy of the retrieved radiance. On the other hand there is a simple relation between the impact of atmospheric state at two view angles, when the atmospheric state is known. We have analyzed the impact of uncertainty on the atmospheric state by comparing the frequency distribution of [TBo(^,0) -as obtained past the data screening procedure described above in three different cases:

a) Atmospheric transmittance and path radiance calculated (MODTRAN) with actual radio-soundings;

b) Same as A, but atmospheric profile modified to give a 20% increase in the column water content;

The frequency distributions of [TBo(A.,0) - TBO(^,53)] for cases A, B and C are given in Fig. 5.

The range of the TBo difference [nadir minus forward] is limited by the data screening bounds described above. The data screening does not modify significantly the distributions for the 11 (¿m case while it has a clear impact on the 12 pini case, where it cuts out part of the lower tail. On the other hand, the impact of errors in the atmospheric correction, appears limited, since the distributions are similar in the three cases. We note that the distributions relate to all valid (i.e. past the screening) observations used to retrieve soil and vegetation temperatures.

Tb011{nadir)-Tb011(forward) (°C) Tb012(nadir) • Tb0(forward) (°C)

Figure 5. Frequency distribution of the difference in BOA brightness temperature in the nadir and forward view direction: A: 11 |im and B: 12p.m

Tb011{nadir)-Tb011(forward) (°C) Tb012(nadir) • Tb0(forward) (°C)

Figure 5. Frequency distribution of the difference in BOA brightness temperature in the nadir and forward view direction: A: 11 |im and B: 12p.m

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