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We investigate anisotropy in 1.4-GHz brightness induced by a field corn vegetation canopy. We find that both polarizations of brightness are isotropic in azimuth during most of the growing season. When the canopy is senescent, the brightness is a strong function of row direction. On the other hand, the 1.4-GHz brightness is anisotropic in elevation: an isotropic zero-order radiative transfer model could not reproduce the observed change in brightness with incidence angle. Significant scatter darkening was found. The consequence of unanticipated scatter darkening would be a wet bias in soil moisture retrievals through a combination of underestimation of soil brightness (at H-pol) and underestimation of vegetation biomass (at V-pol). A new zero-order parameterization was formulated by allowing the volume scattering coefficient to be a function of incidence angle and polarization. The small magnitude of the scattering coefficients allows the zero-order model to retain its limited physical significance.

An L-band total power receiver for use in a synthetic thinned array radiometer (STAR) is described. The total power architecture of a radiometer receiver requires special considerations to control gain fluctuations due to small temperature drifts. The STAR application requires consistent passband and stable phase between receivers. The design presented incorporates direct detection to eliminate distributed local oscillators for phase stability, distributed ceramic interference reject filters for passband consistency and temperature compensating attenuators for gain stability. The receiver is packaged in a unique "winged-hex" shape to enable close packaging with the STAR antennas and to facilitate thermal management. The resulting low cost, compact receiver is made from COTS components.