A Digital Elevation Model or a DEM is a 3 dimensional representation of elevation of a terrain. DEM’s are usually in raster file format. Each cell in the raster image represents the elevation of a specific area in the terrain. DEM can be used for various purposes such as hydrological modelling, terrain visualization and analysis, contour generation, design of engineering & infrastructure developments etc. Some of the most commonly used freely available DEMs are ASTER GDEM AND SRTM DEM. These data sets can be downloaded from a number of websites. Most of the DEMs are generally available in 1° x 1° tile size and each tile storage size is to the order of several megabytes of data. In order to process the DEM, the user has to download an entire tile even though the Area of Interest of the user is much small.
To avoid the tremendous data download, Google Inc, provides some basic analysis on the data stored in a map server using a web application interface. The user need not download the entire data set for processing. The user can limit the downloading size to his AOI. The Google Earth Engine also provides access to other types of earth observation datasets such as weather data, climate data etc.
The step for downloading SRTM DEM using Google Earth Engine Explorer is given below.
- You need to create a Google Earth Engine account which you can be created from here . After setting up your account Sign Up with your credentials to Google Earth Engine Explorer.
2. Zoom in to your area of interest by using the search bar or scrolling your mouse wheel.
3. Search for “NASA SRTM Digital Elevation 30m” in the search bar.
4. Your search result will be added to both the main window and the Table of Content on the left side of the screen. Also a pop up will appear on the screen. Here you can change options to get a better visualization of your area of interest.
5. You can change the default visualization by increasing Stretch, changing Gamma to Palette option and by adding and removing colors using the + and – button.
6. Finally click on download layer option .
7. Click on View port button to choose either polygon or rectangle to select your area of interest
8. Choose an appropriate file format. Also if necessary you can change the projection. Also Change the resolution to 30 m.
9. Click on download button to download your data.
10 .Unzip your data and open it in your favourite GIS software for further analysis.