Complementarity of ERS-1 wind scatterometer and GVI data for regional vegetation monitoring

The ERS-1 wind scatterometer provides measurements of the radar backscattering coefficient σ° along different azimuthal directions, from which parameters can be retrieved. However, the low spatial resolution (about 50 km.), its high temporal repetitivity (the same point can be seen every 4 days with an incidence angle ranging from 18° to 59°), and above all a frequency (5.3 GHz, VV polarisation) sensitive to land surface parameters such as vegetation cover and soil surface moisture content make this instrument well suited for terrestrial vegetation studies. At present, two years of fully calibrated data acquired by the ERS-1 scatterometer over the whole land surfaces offer a unique opportunity to assess the contribution of low resolution active microwave systems to global monitoring of terrestrial surfaces. On the other hand, several studies with NOAA/AVHRR GVI data (available since 1981) have shown how these data can be related to vegetation phenology and vegetation dynamics. Their rather coarse spatial resolution (about 10 km. At the equator) justifies the comparison with scatterometer data. In this paper, multitemporal profiles of both data sets acquired over representative vegetation types throughout the world for a 2-year period are shown. The complementarity of these two sources of satellite data are then examined. Results show that ERS-1 scatterometer data are sensitive to different land parameters according to their incidence angle. In particular, a good correlation between GVI data and scatterometer data acquired around 45° of incidence angle is observed