Comparing near-earth and satellite remote sensing based phenophase estimates: an analysis using multiple webcams and MODIS
In recent years several studies have used digital cameras and webcams to monitor green leaf phenology. Such "near-surface" remote sensing has been shown to be a cost effective means of accurately capturing phenology. Specifically, it allows for accurate tracking of intra- and inter-annual phenological dynamics at high temporal frequency and over broad spatial scales compared to visual observations or tower-based fAPAR and broadband NDVI measurements. Near surface remote sensing measurements therefore show promise for bridging the gap between traditional in-situ measurements of phenology and satellite remote sensing data. For this work, we examined the relationship between phenophase estimates derived from satellite remote sensing (MODIS) and near-earth remote sensing derived from webcams for a select set of sites with high-quality webcam data. A logistic model was used to characterize phenophases for both the webcam and MODIS data. We documented model fit accuracy, phenophase estimates, and model biases for both data sources. Our results show that different vegetation indices (VI's) derived from MODIS produce significantly different phenophase estimates compared to corresponding estimates derived from webcam data. Different VI's showed markedly different radiometric properties, and as a result, influenced phenophase estimates. The study shows that phenophase estimates are not only highly dependent on the algorithm used but also depend on the VI used by the phenology retrieval algorithm. These results highlight the need for a better understanding of how near-earth and satellite remote data relate to eco-physiological and canopy changes during different parts of the growing season.
Fall Meeting, American Geophysical Union (AGU)
American Geophysical Union Publications
Hufkens, K., Richardson, A., Migliavacca, M., Frolking, S., Braswell, B., Milliman, T. and Friedl, M. Comparing near-earth and satellite remote sensing based phenophase estimates: an analysis using multiple webcams and MODIS, Abstract B52C-03 presented at 2010 Fall Meeting, AGU, San Francisco, Calif., 13-17 Dec.