Research needs toward this goal are extensive and
include the calibration and validation of vegetation
and soil moisture retrieval methodologies
corresponding to current (SMOS, AMSR-E) and
future (SMAP) soil moisture missions as well as a
better theoretical understanding of microwave
radiative transfer particularly in dense vegetation.
Some of these issues are being investigated using
ground based L-band radiometry to understand the
vegetation effect through temporal monitoring of
brightness temperature for complete growth cycle of
wheat, corn, and soybean [98].