262 
Table 6. Pearson correlation coefficient (r) matrix for 
AVHRR surface parameters and antecedent precipitation 
for Tambacounda. 
1) Pvis 
2) Pnir 
3) Palb 
4) NDVI 
5) Tsuj- 
6) Pp’t (2 -wks) 
7) Pp’t (4 wfas) 
12 3 
1 
.25 1 
.83 .64 1 
-.80 .29 -.37 
.32 -.57 -.11 
-.67 .10 -.25 
-.65 -.02 -.27 
4 5 
1 
-.67 1 
.85 -.49 
.79 -.44 
6 7 
1 
.97 1 
Table 7. Pearson correlation coefficient matrix for 
AVHRR surface parameters and antecedent precipitation 
for Podor. 
antecedent precipitation events or green leaf 
vegetation changes. The bright soil/substrate 
contributed to a high albedo for the dry related 
scenes, whereas the high internal leaf 
reflectance in green vegetation canopies in the 
near-IR contributed to high solar albedo for the 
wet scenes. Furthermore, the relationship 
between solar albedo and ground temperature was 
poor, indicating the solar albedo has little 
control of the ground temperature. NDVI and the 
derived visible reflectance were more sensitive 
to green vegetation changes than were near-IR 
changes as indicated through comparisons with 
antecedent precipitation. 
5.0 ACKN0WLGCK3EMENTS 
1 2 3 4 5 6 7 
1) Pvis 1 
2) Pnir •38 1 
3) Palb .79 1 
4) NDVI -.82 -.02 -.62 1 
5) W -15 -.41 -.07 -.49 1 
6) Pp’t (2 wks) -.56 -.02 -.41 .72 -.53 1 
7) Pp’t (4 wks) -.64 -.14 -.52 .75 -.52 .88 1 
We thank G. Asrar and R. Murphy of NASA 
Headquarters for supporting this research under 
RT0P 677-21-24. R. Irish, ST Systems Corporation 
provided support for image rectification and 
registration and R. Kennard, ST Systems 
Corporation, provided image processing 
assistance. 
Several problems affecting the derivation of 
surface biophysical parameters were examined. 
Correction for post-launch radiometric 
calibration and atmospheric correction in a 
multiple scattering atmosphere were indicated to 
substantially affect the derived surface 
reflectance. To correct for atmospheric effects 
when deriving a surface spectral reflectance, 
surface horizontal visibility (to estimate an 
aerosol optical depth), and surface dew point 
temperature (to estimate a water vapor optical 
depth) were used in an atmospheric radiative 
transfer model. The range of Sun zenith angles 
for the study minimi zed much of anisotropic 
variation affecting the derived surface 
reflectances. The AVHRR narrow band visible and 
near-IR derived reflectances were used to 
estimate a solar albedo. In the transformation 
procedure a middle-IR reflectance was estimated 
by multiplying the visible reflectance by 1.5. 
The relationship between visible and middle-IR 
reflectance for a vegetative surface is frem a 
related absorption of solar radiation by plant 
pigments in the visible and by leaf water in the 
middle-IR, coupled with leaf internal scattering, 
likely form from refractive index 
discontinuities. The near-IR radiation 
interaction in a leaf is typically either 
transmitted or reflected with little to no 
absorption. In the conversion model, the 
spectral composition of the solar irradiance 
(ultraviolet, visible, near-IR, and middle-IR) 
was indicated to be insensitive to clear sky 
atmospheric optical depth changes, thereby 
improving on the estimation of a solar albedo. 
NDVI estimates frem the visible and near-IR 
ground reflectance were used to adjust the split- 
window derived sea surface temperature to a land 
surface temperature. 
The estimated biophysical parameters were 
obtained for 17 dates for two sites in Senegalese 
area of the western sub-Saharan. The dates 
covered spectral data frem the years 1981-1985, 
representing both dry and wet periods. Satellite 
derived parameters were compared to surface 
meteorological data of precipitation, air 
temperature and atmospheric moisture. Solar 
albedo estimates did not change markedly with 
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