Microwave vegetation indexes for detecting biomass and water conditions of agricultural crops

Abstract Experimental and theoretical investigations have shown that microwave emission from canopies depends on crop type and physical conditions. However, since the sensitivity of the brightness temperature to vegetation parameters is rather low, accurate observations and suitable models are necessary to extract geophysical parameters from radiometer data. The most significant results, obtained over the past years on the basis of measurements carried out with passive microwave sensors at 10 GHz and 36 GHz, are summarized in this paper. The relations between the microwave vegetation indexes and plant biophysical parameters are discussed, using a simple slab model that considers vegetation as a uniform absorbing and scattering medium upon the soil surface. It is shown that simultaneous observations at 10 GHz and 36 GHz, in V and H polarizations, especially if combined with thermal infrared measurements, are useful in separating different crops and in identifying moisture conditions of the surfaces. The difference (δTN), between the normalized temperatures at 36 GHz and 10 GHz, and the polarization index (PI) at 10 GHz are functions of biomass and can be related to the leaf area index of some crops.