Introduction
When we perform remote sensing image analysis, we may need to query the year of the image data. In many cases, in addition to the information given by the data set, in gee, sometimes the available time range of the data often needs to be checked by ourselves. , because the time range is only one year in some areas, or it is possible that all data are analyzed according to different years of the image collection, but the entire data set is only 1 year, so here we use a simple for loop to traverse the monitoring to achieve the Analysis of years in which data are available.
What we need to pay attention to here is that we have time conversion here, because most of the states in the data set are attribute marked according to the millisecond type, so here we need to convert the standardized data. The format function is used here, and the final result is the standardized result time of year, month and day, which is convenient for us to view images in the specified time range.
data set
The Copernicus DEM is a digital surface model (DSM) that represents the Earth's surface, including buildings, infrastructure, and vegetation. This DEM is derived from an edited DSM called WorldDEM&trade, which is the flattening of water bodies and the consistent flow of rivers. In addition, coastlines, special features such as airports, and incredible terrain structures have been edited.
The WorldDEM product is based on radar satellite data acquired during the TanDEM-X mission, which is funded by a public-private partnership between the German government and Airbus Defense and Space, represented by the German Aerospace Center (DLR). More details can be found in the dataset documentation.
Earth Engine assets have been obtained from DGED files.
Note: See the code example for the recommended method of calculating slope. Unlike most DEMs in Earth Engine, this is a collection of images that cannot be tessellated into one asset due to the different resolutions of the source files, so the slope calculation requires reprojection.