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’. Longterm
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. Multitemporal
MODIS NDVI and NPP provided recent regional patterns and trend of vegetation activity and
productivity.
Keywords: Drought, AVIRIS, hyperspectral, MODIS, NDVI, NPP, greenness