Environmental science, engineering & technology GPP Google Earth Engine Hangzhou History of engineering & technology MODIS Mongolian oak NDPI NDVI Northeast China Qilian Mountains Qinghai-Tibetan Plateau Technology: general issues Three-River Headwaters region arctic autumn phenology carbon cycle carbon exchange climate change climate changes climatic limitation contribution crop sowing date data suitability development stage different drivers digital camera driving factors enhanced vegetation index evapotranspiration