Observing Land Surface Phenologies: Back to the Future with the Planetary Macroscope

Among the first studies conducted using data from sensors onboard the first Earth Resource Technology Satellite (ERTS-1, later renamed Landsat-1) were investigations into tracking the seasonal progression of vegetation at the continental scale. Although these remote sensing pioneers demonstrated that observations from Landsat could indeed track the “green wave”, various logistical constraints inhibited widespread development of land surface phenology until the advent of synoptic time series from Advanced Very High Resolution Radiometers (AVHRR) onboard NOAA's operational the Polar Orbiting Environmental Satellites (POES) nearly a decade later. Trading higher temporal resolution for lower spatial resolution, AVHRR time series enabled the use of maximum value compositing of the Normalized Difference Vegetation Index (NDVI) to defeat cloud cover and reveal the land surface. The Moderate Resolution Imaging Spectrometer (MODIS) on the NASA Terra and Aqua satellites launched in 1999 and 2002, respectively, ushered in a productive era for land surface phenology with multiple high quality products freely available. The opening of the USGS Landsat archive in 2008 to free online access marked a watershed event in terrestrial remote sensing. The mining of the archive is now well underway, but of particular note are the NASA Web Enabled Landsat Data (WELD) projects that are lowering the technical bar to access high quality time series of historic Landsat data. I will survey the current state-of-the-art in land surface phenology with particular emphasis on exploiting WELD for high spatial resolution land surface phenology in croplands and in urbanized areas.