It has been commonly observed that soil moisture conditions,
in addition to soil chemical components such as organic matters and free
iron oxides, complicate the interpretation of soil reflection. Based on
the idea that darkening of soils on wetting is attributed to an increase
in the average degree of forward scattering, which is caused by changing
the medium surrounding soil particles from air to water, a theoretical
model was formulated to estimate the effect of soil moisture on soil reflection.
This was done by using the delta-Eddington approximation for multiple scattering,
together with Mie theory for single scattering. The model contains only
one adjustable parameter, a complex refractive index of soil particles,
The complex index of soil particles was identified from the observed spectral
albedos on both dry and wet surfaces o soils. The imaginary refractive
index obtained was highly correlated with the soil chemical properties.
Especially, the correaltions between the imaginary index and the free iron
oxides content were sufficiently higher than between the spectral albedo
and its contents, so that the imaginary index would be of some use in estimating
free iron oxides content. With the advent of high spectral resolution sensors
currently in design for Earth observational remote sensing from space,
this results offers promising advancements in the use of multitemporal
remotely sensed data, that is, the data collected when both dry and wet
for soil studies.