Monitoring Seasonal Dynamics of Arid Land Vegetation Using AVIRIS Data

Seasonal changes in the density of photosynthetically active vegetation have been observed in derivative-based green vegetation index (DGVI) values derived from AVIRIS reflectance spectra of arid land shrub and saltgrass communities adjacent to Mono Lake, California. The study was conducted using AVIRIS datasets acquired in late August and early October of 1992. 2DZ_DGVI (second-order DGVI-derived in reference to zero baseline) showed a strong linear relationship (r2>0.93 for August and October) with green leaf area index (LAI) values of ten bitterbrush (Purshia tridentata) sample stands. After accounting for background errors introduced to the calculation of 1DL_DGVI (first-order DGVI-derived in reference to local rock-soil baseline), a modified 1DL_DGVI (1DL_MDGVI) exhibited a high linear correlation (r2> 0.92 for both seasons) with green LAI values of the bitterbrush stands. 2DZ_DGVI was applied to the two AVIRIS scenes acquired for the two periods to quantify and compare green vegetation cover. Areas covered by saltgrass (Distichlis spicata var. stricta) showed the largest change in 2DZ_DGVI from August to October. Shrubs, including bitterbrush and big sagebrush (Artemisia tridentata), changed less during the same period. The lowest seasonal change in 2DZ_DGVI occurred in barren areas and locations covered by Jeffrey pine (Pinus jeffreyi). The DGVI concept has potential for monitoring ecosystems in arid and semiarid lands where the influence of exposed rock–soil backgrounds reduces the effectiveness of broadband red-vs.-NIR vegetation indices.