Monitoring Recent Vegetation Greenness Trend Impacted from Past Drought Events in Northern Arizona with AVIRIS and MODIS

Abstract

Northern Arizona has experienced a severe drought with significant impacts on various ecosystems. There have been extensive mortality and bark beetle insect population in conjunction with the multi-year drought. We evaluated remotely-sensed drought indicator with Airborne Visible Infra-Red Imaging Spectrometer (AVIRIS) hyperspectral data flown across the C. Hart Merriam Transect in northern Arizona and MODIS multispectral sensor. Drought impacts on vegetation were analyzed across a series of ecosystems from pinyon-juniper woodland, ponderosa pine forest and mixed conifer forest. Spectral signatures from AVIRIS provided opportunities to assess canopy chemistry within the drought suffered ecosystems.

We utilized chlorophyll-based index relationships as surrogates for canopy water status and health conditions. We found tree mortality sites exhibited high non-photosynthetic vegetation (NPV) and soil signals accompanied with low ‘greenness’.  Long-term time-series from MODIS NDVI and NPP was used to monitor recent vegetation activity across ecosystems. Large drought impacted areas have not been recovered to most vegetation greenness in 2001. Our results showed that ecosystem health and drought impact response can be characterized by spectral band absorption. Multi-temporal MODIS NDVI and NPP provided recent regional patterns and trend of vegetation activity and productivity.

Keywords: Drought, AVIRIS, hyperspectral, MODIS, NDVI, NPP, greenness