Performance evaluation of single and multichannel microwave radiometers for soil moisture retrieval

The performance of single-channel, two-channel, and six-channel microwave r adiometers is evaluated for the retrieval of soil moisture using parameteri zed numerical simulations. Commonly used frequencies of 1.4 GHz, 2.7 GHz, a nd 6.6 GHz at vertical and/or horizontal linear polarizations are considere d. The best single-channel retrieval uses 1.4 GHz at vertical polarization (1.4 V). This channel is least sensitive to variable surface roughness and vegetation canopy, but all single-channel sensors, including 1.4 V, are deg raded without some level of a priori information about these masking variab les. The sensitivity to surface roughness is reduced significantly at 2.7 G Hz and 6.6 GHz by increasing the angle of incidence beyond 25 degrees. The best two-channel case uses 1.4 V and 2.7 H to simultaneously retrieve both soil moisture and surface roughness. This improves the soil moisture retrie val and eliminates the need for a priori information about surface roughnes s. The sensitivity to variations in vegetation canopy is also acceptably sm all. Simultaneous use of all six channels to retrieve soil moisture, surfac e roughness, and vegetation canopy provides only marginal improvement over the best two-channel performance. The small amount of additional informatio n contained in the other four channels is largely masked by typical levels of measurement noise. (C) Elsevier Science Inc., 2001.