PARENT SESSION
Oral Session #71: Remote Sensing and GIS.
Presiding: J.D. Allan
Wednesday, August 7. 1:00 PM to 4:45 PM. Palo Verde Room, Radisson.

Multi-scale comparison of vegetation productivity observations with MODIS derived net photosynthesis estimates .

Reeves, Matthew^*,1, Running, Steven¹, ¹ University of Montana, Missoula, MT

ABSTRACT- Validation of remotely sensed estimates of vegetation productivity is problematic due to the disparate spatial scales at which both ground truth and remote sensing data are typically collected. This situation begs the question, how can we compare observed vegetation dynamics at traditional scales of ground measurement to regional remotely sensed estimates of similar metrics? Here we present methodology and results from a comparison of seventeen scenes of 2001, eight-day composite Moderate Resolution Imaging Spectroradiometer (MODIS) derived estimates of net photosynthesis with spatially scaled field observations of northern mixed grass prairie biomass. Biomass observations were made during the 2001 growing season at more than 2,200 plots, across four time periods, each five days in length, in the Little Missouri National Grasslands in western North Dakota. Interpolation between sampling points across the entire region was achieved by modeling observed productivity as a function of biophysical and meteorological data and Normalized Difference Vegetation Index (NDVI) computed from Landsat Enhanced Thematic Mapper (ETM+) spectral reflectance. This procedure permitted analysis of spatial relations between field observations and remote sensing data first at 30-meter resolution, which were subsequently aggregated to 1-kilometer resolution. Modeled vegetation productivity spawned from fine resolution ground data was compared with 2001 growing season MODIS derived estimates of net photosynthesis at 1-kilometer resolution. The MODIS derived net photosynthesis estimates emulate trajectory and magnitude of observed grassland vegetation through space and time. The results of the study provide a framework for linking small-scale field observations to regional remote sensing measures of vegetation productivity and provide insight to the reliability of the MODIS net photosynthesis product for evaluating grassland vegetation dynamics.

KEY WORDS: modis, ecological scale, vegetation productivity , grassland