Relationship between AVHRR NDVI Time Series and Single Point Vegetation Measurements from an Automated Climate Station Network in the Swiss Alps

摘要

An important contribution to climate impact studies can be made by comparing remote sensing and ground based phenology. Here, Start of Season (SOS) dates from three AVHRR NDVI products (Fourier smoothed, Savitzky-Golay filtered, and Best Index Slope Extraction (BISE)) were compared with single point ultrasonic vegetation height measurements at 13 alpine grassland sites between 2001 and 2005. SOS from all three NDVI products were significantly correlated with the ground based melt-out and start of growth dates. As expected, NDVI SOS products best represented ground based melt-out dates, with average differences ranging from 1.35 days (Fourier product) to 7.93 days (Savitzky-Golay product). The BISE algorithm displayed the best correlation (r=0.58). Remaining differences result from complex topography and high land cover variability within the direct surroundings of the measuring site. Overall, the ground based data appeared to be a valuable tool helping to understand and interpret remote sensing NDVI data.