INTERPRETATION OF VEGETATION INDEXES DERIVED FROM MULTITEMPORAL SPOT IMAGES

A temporal sequence of 15 SPOT HRV images and low altitude aircraft reflectance data were obtained over soil and cotton fields at the Maricopa Agricultural Center, Arizona from April to October 1989. The SPOT data included different view angles (- 28-degrees - + 24-degrees) while the aircraft data were obtained with a nadir-viewing radiometer equipped with SPOT filters. View angle/direction, atmosphere, and soil influences on individual band and vegetation indices were observed in the SPOT data. The relative magnitude among the three influences was dependent on surface conditions, varied with canopy growth, and was different for red and near-infrared (NIR) reflectances and vegetation indices (VIs). View angle. effects were most pronounced in red and NIR reflectance data and were secondary with the use of VIs. View angle variations, and to some extent soil variations, influenced VI responses from partial canopies while relative atmospheric influences became most dominant at higher densities of vegetation. The results suggest that the current compositing routine for temporal vegetation index imagery may not be entirely adequate.