Change detection of gravel mining on riverbeds from the multi-temporal and high-spatial-resolution formosat-2 imagery

Gravel mining from river channels is conducted in many countries around the world, yet ground-based monitoring of these activities requires considerable manpower and is not very effective. Therefore, innovative and effective approaches to monitoring gravel mining are urgently required. Deployed as a high spatial resolution sensor in a daily revisit orbit, Formosat-2 has proved to be an ideal satellite for site surveillance. Using one known event of gravel mining in the Tseng-Wen River, Taiwan, between March 2004 and March 2005, we analysed nine Formosat-2 images taken during this period to summarize three characteristics of gravel mining in the images. Based on these characteristics, a standard procedure for processing Formosat-2 imagery to detect gravel mining is proposed. This procedure is validated against ground truthing collected by an unmanned helicopter flying at low altitude. The evolution of this gravel-mining event in the Tseng-Wen River is described by processing all historical Formosat-2 imagery using the proposed procedure. This standard procedure has been successfully incorporated into the Formosat-2 automatic image processing system and has been used to monitor gravel mining on a daily-basis.