Abstract
Vegetation has been effectively monitored using remote sensing time-series vegetation index (VI) data for several decades. Drought monitoring has been a common application with algorithms tuned to capturing anomalous temporal and spatial vegetation patterns. Drought stress models, such as the Vegetation Drought Response Index (VegDRI), often use VIs like the Normalized Difference Vegetation Index (NDVI). The EROS expedited Moderate Resolution Imaging Spectroradiometer (eMODIS)-based, 7-day NDVI composites are integral to the VegDRI. As MODIS satellite platforms (Terra and Aqua) approach mission end, the Visible Infrared Imaging Radiometer Suite (VIIRS) presents an alternate NDVI source, with daily collection, similar band passes, and moderate spatial resolution. This study provides a statistical comparison between EROS expedited VIIRS (eVIIRS) 375-m and eMODIS 250-m and tests the suitability of replacing MODIS NDVI with VIIRS NDVI for drought monitoring and vegetation anomaly detection. For continuity with MODIS NDVI, we calculated a geometric mean regression adjustment algorithm using 375-m resolution for an eMODIS-like NDVI (eVIIRS’) eVIIRS’ = 0.9887 × eVIIRS − 0.0398. The resulting statistical comparisons (eVIIRS’ vs. eMODIS NDVI) showed correlations consistently greater than 0.84 throughout the three years studied. The eVIIRS’ VegDRI results characterized similar drought patterns and hotspots to the eMODIS-based VegDRI, with near zero bias.
Highlights
Four composites of expedited VIIRS (eVIIRS) Normalized Difference Vegetation Index (NDVI) data over the conterminous United States (CONUS) for mid-summer were transformed and analyzed using the new geometric mean regression (GMR) developed from 2016–2018 data
The process evaluated if previous years could predict, or transform, a subsequent year and how robust the function was to transform eVIIRS NDVI to expedited Moderate Resolution Imaging Spectroradiometer (eMODIS)-like NDVI values
After evaluating eVIIRS’ 1-km results, the eVIIRS’ NDVI 1-km inputs for four weeks of CONUS Vegetation Drought Response Index (VegDRI) products were tested from July 20 through August 9, 2020
Summary
Drought conditions can range from moderate to exceptional and with varying duration, requiring continuous, operational monitoring. The longer a drought lasts and the more exceptional its effects on vegetation and water resources, the more a drought can alter services for humans and modify natural systems. Drought effects include the degradation of habitat for wildlife and water quality, reduced access to water resources [1], and increases in disturbances like fire events [2]. Drought can affect agriculture, water supplies, energy production, and many other aspects of society [3]. Drought monitoring is critical for researchers, land managers, and decision makers to identify regions where drought mitigation and planning are necessary.
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