modis是可以免费获取的数据，具有多种数据产品，但是因为是光学数据，会受到云的干扰，因为检测modis数据的云是一项十分重要的工作(Modis is can free access to the data, have a variety of data products, but because is optical data, the moderating effect of cloud, because the detection of the modis data cloud is a very important work)