TEMPORAL VARIATIONS OF THE MICROWAVE POLARIZATION DIFFERENCE INDEX AND ITS RELATIONSHIP TO THE NORMALIZED DIFFERENCE VEGETATION INDEX IN A DENSELY CROPPED AREA

The Microwave Polarization Difference Index (MPDI) for densely cropped areas contains information about the moisture and vegetation status o f the ground surface. The surface parameters affecting MPDI and the re lationship of MPDI to the Normalized Difference Vegetation Index (NDVI ) vary seasonally To better understand this seasonal variation, MPDI d erived from the Special Sensor Microwave/Imager and NDVI derived from the Advanced Very High Resolution Radiometer were geo-registered and c ompared with ground data and with each other. Analysis of MPDI time se ries showed that moisture effects dominated at the beginning of the gr owing season, vegetation effects dominated during the period of peak c anopy cover and both effects were present at other times. MPDI was fou nd to have an inverse, non-linear relationship with NDVI. MPDI varied more during the early part of the season, and NDVI varied more during the latter part of the season. Results were basically consistent with recent questions raised about the MPDI-vegetation relationship. The sy nergism between MPDI and NDVI is important for soil moisture and veget ation studies.