Estimating soil moisture in a boreal old jack pine forest

Polarimetric L- and P-band AIRSAR data, corresponding model simulations, and classification algorithms have shown that in a boreal old jack pine (OJP) stand, the principal scattering mechanism responsible for radar backscatter is the double-bounce mechanism between the tree trunks and the ground. The data to be used were taken during six flights from April to September 1994 as part of the BOREAS project. The dielectric constants, or equivalently moisture contents, of the trunks and soil, can change rapidly during this period. To estimate these dynamic unknowns, parametric models of observed radar backscatter for the double-bounce mechanism are developed by using a series of simulations of a numerical forest scattering model. The resulting simulated data are used to derive polynomial fits of backscattering cross section as a function of the ground and trunk dielectric constants. Empirical and field data are used to relate the real and imaginary parts of the dielectric constants, and hence formulate the parametric model in terms of two unknowns only. Three data channels, P-HH, P-VV, and L-HH are used to solve of the two unknowns. A nonlinear optimization procedure is used to estimate the dielectric constants, and hence, in particular, soil moisture. Point ground measurements are used to verify the results of the estimation algorithm.