HR: 09:15h
AN: B41E-04    [Abstracts]
TI: Challenges for Characterizing Land Surface Phenology
AU: * Reed, B C
EM: reed@usgs.gov
AF: USGS, Flagstaff Science Center 2255 North Gemini Drive, Flagstaff, AZ 86001 United States
AB: Considerable progress in developing phenology metrics from satellite-based multispectral sensors has been made over the past 25 years. A number of approaches using time-series vegetation index (VI) data collected at a synoptic scale of observation have been used to produce metrics that correspond to different phenological stages of vegetation, such as the start of the growing season, end of growing season, length of growing season, and others. However, there are a number of challenges in this field that must be faced head-on in order to advance the field of land surface phenology, such as 1) addressing non-vegetation related impacts on the satellite signal (e.g., effects of variable soil moisture, plant litter, atmospheric contamination); 2) characterization of evergreen environments; 3) identification and characterization of sparsely vegetated areas with poorly defined seasonality, and 4) identification and characterization of multiple growing seasons. Progress toward meeting these challenges include clarifying the requirements of the phenology user community (decision makers, modeling community, etc.) to produce meaningful satellite estimates, creative time-series processing methods to remove non-vegetative impacts on the signal (such as temporal VI smoothing, cloud screening, and snow/ice masking), and a more thorough understanding of the ecology of the communities that are being characterized. It is clear that the growing season has different meaning for different ecosystems (e.g., croplands, shrublands, and evergreen forests). Perhaps the most important challenges facing remote sensing phenology studies are 1) identifying the surface biophysical characteristics that are being estimated by the various approaches, and 2) scaling ground observations of phenology to the scale observed by the near-daily sensors (250 to 1000m ground resolution). A pilot study comparing satellite phenology estimates to CO2 flux data gathered by the USDA-ARS Agriflux network in the western US grasslands show a strong agreement regarding the timing of the growing season. Further investigations where remote sensing phenology measures are compared to the timing of these and other directly measured fluxes need to be undertaken for improved understanding and validation. Recent progress in forming a National Phenology Network (NPN), which will collect multiple levels of detailed phenology data across the country, promises to support large area scaling efforts by collecting ground observations of indicator species and other naturally occurring plants across the country that can be compared to satellite-scale observations.
DE: 0429 Climate dynamics (1620)
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0476 Plant ecology (1851)
DE: 0480 Remote sensing
SC: Biogeosciences [B]
MN: Fall Meeting 2005