Field measurements (line point program) are limited in spatial extent, challenging valley-wide assessments of vegetation change. Advances have been made in extracting vegetation abundance from satellite-based measures of radiance. Vegetation Indices (VIs) (such as NDVI, EVI, SAVI) and also Spectral Mixture Analysis (SMA) are two different methods to quantify vegetation abundance in comparable units to field measures.
ICWD computes VIs and SMA fractional cover of green vegetation from Landsat TM data as an independent measure of vegetation change in addition to field sampling. The Landsat TM time series extends back to the baseline vegetation inventory providing the ability to monitor vegetation cover across the entire Owens Valley over the salient time period of relevance to the Agreement; the 30-m spatial resolution of Landsat TM imagery is insufficient for species-level resolution but the temporal frequency, spatial extent and infrared band are distinct advantages for vegetation monitoring.
Remote sensing from satellite and aircraft is used increasingly to map and monitor vegetation change by both ICWD and LADWP but no single method has been adopted by the Technical Group for Greenbook compliance monitoring.
Enhanced Vegetation Index (EVI) – The EVI is a common vegetation index that was developed to optimize the vegetation signal through a de-coupling of the canopy background signal and atmosphere influences.
Above – Median EVI computed from Jun 1 to Aug 31 in 1984-1987 compared to median EVI from 2015 Jun 1 to Aug 31. Red color represents declines in EVI while Green represents increases in EVI from baseline to 2015. EVI from Bishop, and Laws area is shown here.
Spectral Mixture Analysis (SMA) – coming soon
Landsat annual timelapse of Owens Valley
Google Earth Engine Annual Timelapse consists of 29 cloud-free mosaics of the planet.
Below – The time lapse of Owens Valley was created using CMU CREATE Lab’s Time Machine library, a technology for creating and viewing zoomable and pannable time lapses over space and time.