Assessing land cover performance in North piedmont of Yinshan Mountain using time-series NDVI data

North piedmont of Yinshan mountain is a typical ecological fragile zone and an important eco-shelter in north China. It is very important to study impact of global change in this area in order to monitor and analyze dynamics of vegetation cover. This paper illustrates the application of a local variance technique to assess vegetation cover change in Yinshan Mountain using integrated growing season NDVI measurements. The paper calculated seasonal integrated normalized difference vegetation index (NDVI) for each of 8 years using a time-series of 1-km data from SPOT Vegetation (1998-2005) sensors. Based on the data, we can construct the smoothed NDVI time-series to locate the onset and end of the growing season of vegetation. Then we can calculate the integrated NDVI (iNDVI) as the area under the NDVI curve from the start of season to the end of season. The paper uses a local variance method to detect local spatial anomalies of iNDVI for study area. We summarized the number of years that a given pixel was identified as an anomaly. The resulting anomaly maps were analyzed using Landsat ETM+ imagery and extensive ground knowledge to assess the results. The local variance analysis is a reliable method for assessing vegetation cover change from human pressures or increased land productivity from natural resource management practices. The result provides a good support for analyzing relation between vegetation change and climatic factors.