ON THE USE OF PASSIVE MICROWAVES AT 37 GHZ IN REMOTE-SENSING OF VEGETATION

Recently, a number of studies have investigated the use of the 37 GHz channels of the Nimbus-7 Scanning Multichannel Microwave Radiometer (S MMR) for vegetation monitoring and for studying synergisms between the SMMR and the NOAA Advanced Very High Resolution Radiometer (AVHRR). T he approaches are promising but raise a number of issues concerning in terpretation of the results, specifically on the relative effects of v egetation and other surface and atmospheric characteristics on the obs erved signal. This article analyses the 37 GHz Microwave Polarization Difference Temperature (MPDT) in terms of its sensitivity to surface a nd atmospheric parameters. For this, a radiative transfer model is use d which indicates some limitations of the MPDT index and suggests the importance of accounting for atmospheric effects in the data analysis. An alternative approach to the MPDT, including lower SMMR frequencies than 37 GHz, is discussed.