Assessment of harm degree of Crofton weeds invasion in southwest China with NDVI

The MOD13Q1 product from 2001 to 2007 has been utilized to generate NDVI background data of Yunnan-Guizhou plateau, then the vector composed of annually continuous NDVI values of each pixel was compared with the average value vector of pure pixels covering Crofton weeds and the similarity between each pair of vectors was calculated using SAM algorithm. Based on that, a normalized index to assess the harm degree of Crofton weeds was defined, which was named HCWI (Harm of Crofton Weeds Index). To evaluate the effectively of HCWI, its calculated results at some field investigation points were verified with the field investigation records of Crofton weeds. The results have proved the reliability of HCWI in the assessment of growth density and involving harm degree of Crofton weeds.