An Empirical Relationship of Bare Soil Microwave Emissions Between Vertical and Horizontal Polarization at 10.65 GHz

National High Technology Research and Development Program of China 2012AA12A304；National Natural Science Foundation of China 41101332 41231170；Open Research Fund of the Key Laboratory of Digital Earth Science, Center for Earth Observation and Digital Earth, Chinese Academy of Sciences 2012LDE002<p class="FR_field"> Land surface <span class="hitHilite">microwave</span> emission is mainly a function <span class="hitHilite">of</span> <span class="hitHilite">soil</span> moisture and surface roughness. However, the <span class="hitHilite">relationship</span> between vertical and horizontal polarization land surface emissivities is not fully understood. This study attempts to develop a parameterized <span class="hitHilite">relationship</span> to relate the emissivities at different polarizations for <span class="hitHilite">bare</span> surfaces. A <span class="hitHilite">microwave</span> emission database is simulated for <span class="hitHilite">bare</span> surfaces with a wide range <span class="hitHilite">of</span> surface roughness and dielectric properties using the Dobson model and the Advanced Integral Equation Model (AIEM) at 10.65 GHz under the configuration <span class="hitHilite">of</span> the Advanced <span class="hitHilite">Microwave</span> Scanning Radiometer-Earth Observing System (AMSR-E). By analyzing the factors that influence <span class="hitHilite">microwave</span> emission, parameterized relationships between vertical and horizontal polarization emissivities are established. With the proposed relationships, the effects <span class="hitHilite">of</span> <span class="hitHilite">soil</span> moisture and surface roughness on the <span class="hitHilite">soil</span> <span class="hitHilite">microwave</span> emission signal can be separated. Simulated results using the proposed relationships are compared with those <span class="hitHilite">of</span> the AIEM. These results show that the proposed relationships are accurate, with absolute root mean square errors (RMSEs) <span class="hitHilite">of</span> 0.0025, and they can be used as a reliable boundary condition to retrieve other surface geophysical parameters. Combining this <span class="hitHilite">relationship</span> with the calculated <span class="hitHilite">soil</span> moisture, the RMSE <span class="hitHilite">of</span> the estimated <span class="hitHilite">soil</span> moisture is 0.44% using simulated data. As <span class="hitHilite">an</span> example, observations <span class="hitHilite">of</span> AMSR-E are used to estimate the variation in <span class="hitHilite">soil</span> moisture in Saharan Africa in 2004. By comparing with independent <span class="hitHilite">soil</span> moisture data, the result shows that the proposed <span class="hitHilite">relationship</span> is promising for retrieving surface geophysical parameters from <span class="hitHilite">microwave</span> observations.