W. Gao et Bm. Lesht, MODEL INVERSION OF SATELLITE-MEASURED REFLECTANCES FOR OBTAINING SURFACE BIOPHYSICAL AND BIDIRECTIONAL REFLECTANCE CHARACTERISTICS OF GRASSLAND, Remote sensing of environment, 59(3), 1997, pp. 461-471
An inversion method that can be used to derive information about bioph
ysical and radiative conditions of a grassland surface from remotely s
ensed surface spectral reflectances is described. A previously develop
ed simple surface bidirectional reflectance model was expanded for use
in this inversion process. In the inversion process, a multidimension
al optimization scheme is used to obtain a set of model parameters tha
t minimizes the difference between modeled and observed reflectances.
The effect of the slumber of data points used in the inversion on the
accuracy of the model inversion was investigated with ground based hem
ispheric scan measurements of surface spectral reflectances over a tal
lgrass prairie in Kansas. The result shows that the total inversion er
ror consists of minimum or systematic error and ambiguity error The fo
rmer result from uncertainties in the accuracies of the model and meas
urements, whereas the latter is caused by the ambiguity of the model i
nversion when a limited number of data points are used The systematic
error is independent of the number of data points, whereas the ambigui
ty error decreases sharply with increasing data points when the num be
r of data points is small (fewer than about seven). An inversion metho
d with appropriate data grouping applied to the reflectance data from
the Advanced Very High Resolution Radiometer is shown to improve estim
ates of surface parameters over the grassland site. Relative differenc
es between measured surface bidirectional reflectances and those calcu
lated with the derived surface parameters range from 6% to 15% (12.9%
for band 1 [0.65-0.67 mu m] 6.9% for band 2 [0.81-0.84 mu m] and 7.6%
for band 3 [1.62-1.69 mu m]). (C)Elsevier Science Inc., 1997.