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The b-factor as a function of frequency and canopy type at H-polarization

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2 Author(s)
Van de Griend, A.A. ; Dept. of Hydrology & Geo-Environ. Sci., Vrije Univ. Amsterdam, Netherlands ; Wigneron, J.-P.

For anticipated synergistic approaches of the L-band radiometer on the Soil Moisture and Ocean Salinity (SMOS) mission with higher frequency microwave radiometers such as the Advanced Microwave Scanning Radiometer (AMSR) (C-band), a reanalysis has been performed on the frequency dependence of the linear relationship between vegetation optical depth (τo) and vegetation water content (W), given by τo=b·W. Insight into the frequency dependence of the b-factor is important for the retrieval of surface moisture from dual- or multifrequency microwave brightness temperature observations from space over vegetation-covered regions using model inversion techniques. The b-values presented in the literature are based on different methods and approaches. Therefore, a direct comparison is not straightforward and requires a critical analysis. This paper confirms that when a large frequency domain is considered, the b-factor is inversely proportional to the power of the wavelength b=c/(λ)x, which is in line with theoretical considerations. It was found that different canopy types could be separated into different groups, each with a different combination of values for log(c) and x, which characterize the linearized relationship log(b)=log(c)-x·log(λ). A comparison of ratios bC/bL (with C and L denoting C- and L-band, respectively) also resulted in basically the same groups.

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Geoscience and Remote Sensing, IEEE Transactions on  (Volume:42 ,  Issue: 4 )