Using airborne and satellite data for multitemporal studies of land degradation

Remote sensing data collected from orbital satellites can provide global coverage at regular intervals at moderate to high spatial resolutions in broad spectral bands. Airborne instruments, such as the Jet Propulsion Laboratory Airborne Visible/Near-Infrared Imaging Spectrometer (AVIRIS), can provide high spatial resolution in narrow spectral bands. High spectral resolution information is potentially useful for identifying and mapping such things as mineralogy and plant communities. However, airborne systems cannot easily provide periodic coverage nor can they provide global coverage of any sort. The logical outgrowth of this problem is to use airborne and satellite data synergistically. In this study, data from the AVIRIS airborne instrument, the Landsat MultiSpectral Scanner (MSS), and the ex-Soviet RESOURCE satellite have been combined into a co-registered temporal dataset covering the period from 1972 to 1991. The data cover the Manix Basin Area of the Mojave Desert, which is located NE of Barstow, California. This area has been cultivated with center-pivot irrigation systems. Beginning in 1973, a series of fields has been abandoned producing a sequence of abandoned fields at different stages of evolution. The remote sensing data shows that the vegetation cover on recently abandoned fields typically exceeds that in the surrounding desert for a few years. This is followed by a rapid decline in vegetation cover leading to the abandoned fields becoming more barren than the adjoining desert. The effects of wind erosion on vegetation cover can be easily seen in the temporal data The time series of data allows quantitative measurements of the area covered by active sand. On-site investigations have confirmed the relative barrenness of old abandoned fields and the relatively high vegetation cover on recently abandoned fields. Regions that have been identified in the remote sensing data as areas undergoing sand mobilization show evidence of wind erosion when observed on the ground. This study shows that the abandonment of irrigated fields in arid regions leads to land degradation which may not be evident from a single on-site or remote sensing observation