J. Qiu et al., INVERTING OPTICAL REFLECTANCE TO ESTIMATE SURFACE-PROPERTIES OF VEGETATION CANOPIES, International journal of remote sensing, 19(4), 1998, pp. 641-656
An inversion method using a simple bidirectional reflectance model and
data on optical reflectances remotely-sensed from satellites has been
improved to derive surface properties such as the leaf area index (LA
I). Such properties are important in deriving the resistance of the ve
getative canopy to uptake of gaseous trace chemicals from the atmosphe
re and in the study of radiation transfer processes. We found that a m
ulti-pass retrieval technique can greatly improve a model's ability to
retrieve surface properties. Because the sensitivity of the model inv
ersion to initial values is an important issue that depends on (1) the
partial derivative of reflectance with respect to each parameters to
be retrieved (partial derivative R/partial derivative x) and (2) the d
egree of independence among model parameters, we investigated the issu
e with synthetic data constructed by a bidirectional reflectance model
. The results revealed that, although the surface optical properties a
re mostly independent of each other, their initial values did have som
e effect on the retrieved value of the LAI, with the worse case caused
by leaf angle distribution index, n, at close-to-nadir solar and view
zenith angles of the reflectance data. At near-nadir angles, n and LA
I were strongly correlated, and their retrieval was not unique. When a
pplied to satellite remote sensing data obtained with the advanced ver
y-high-resolution radiometer (AVHRR), the model-retrieved seasonal var
iation of surface properties agreed reasonably well with independent g
round measurements made in the First International Satellite Land-Surf
ace Climatology Project (ISLSCP) Field Experiment (FIFE) campaign. App
lication to Landsat data to retrieve spatial variation was less succes
sful, largely because of the close-to-nadir solar and view zenith angl
es in the data.