Spatiotemporal Monitoring of Urban Vegetation

Monitoring spatiotemporal changes in urban agglomorations will become increasingly important as the number and proportion of urban residents continue to increase. Intra-urban variations in vegetation abundance influence environmental conditions and energy fluxes by selective reflection and absorbtion of solar radiation, by modulation of evapotranspiration and by sequestration of pollutants. The spatiotemporal distribution of vegetation may be effectively monitored with multispectral satellite observations. This study examines spatiotemporal analysis of urban vegetation using a linear spectral mixing model to estimate vegetation abundance from Landsat TM data. The inherent dimensionality of TM imagery of the New York City area suggests that urban reflectance measurements may be described by linear mixing between high albedo, low albedo and vegetative endmembers. Quantitative validation using vegetation abundance measurements from high resolution aerial photography shows agreement to within fractional abundances of 0.1 for vegetation fractions greater than 0.2. A spatiotemporal analysis of vegetation fraction in the New York metro area in 1996 shows intra-urban gradients of several tens of percent and pronounced spatial variations in phenology.