An empirical analysis of emitting depth from controlled ground-based passive microwave observations

In a recent experiment in Huntsville, Alabama in, 1998 involving ground-based L (1.4 GHz), S (2.6 GHz), and C (6.34 GHz) band passive microwave sensors, special attention was given to near surface sampling in an attempt to shed additional light on characterizing emitting depth. Using a forward radiative transfer model with detailed near surface gravimetric observations, 50% of the total energy observed at L band emitting depth was found to be emitted from a depth of 3.5-5.0 cm. Likewise, 50% of the total energy observed at C band was emitted from a depth of 0.8-1.4 cm, depending on moisture and temperature conditions. As such, these results imposes certain sampling constraints on validation activities planned for 2002-2004 in conjunction with the Advanced Microwave Scanning Radiometer to be deployed from Aqua by mid 2002.