I want to ground-truth value (other than the DGPS survey) for the accuracy assessment of the digital elevation model for Indian region imagery. I want to compare the generated DEM elevation value with the ground truth value.
Hi Litech
For your purpose, you've 2 options:
1- use field sampling survey to obtain groung control point. This method require a lot of time and money depending on the area and the spatial resolution needed.
2- use georeferenced topographic map at the corresponding spatial résolution and some sampling point for accuracy assessment with the DEM generated
Good luck
Where is the extent of your area of interest? Whether you are dealing with mountains or a mangrove forest is going to inform the answer.
That's helpful, but is still a large area. To start, there have been some major airborne Lidar surveys of the area, and frequently ground control points are established for those surveys and provided as an auxiliary to the point cloud or processed products. In our area, the USGS, the State of Washington, King County and City of Renton all have vertical and horizontal benchmarks continually updated and the positions publicly published - apparently such is not the case in India ( https://surveyofindia.gov.in/ ). Other ad-hoc sources of control data ( especially vertical ) are airports and airstrips, cell tower sites, seismic stations, stream flow gauges, automated weather stations are some I've used to spot check a DEM. Due to the current border situation, even these might be under restriction in that area. The precision and accuracy of each set will of course vary, but with due consideration of the limitations they can be leveraged together, as sometimes they may share come common points. A handy way to compile a list of those candidate spot feature where one might find secondary sources, like mountains from mountaineering records, etc. is use the NGA's gazetteer: https://geonames.nga.mil/namesgaz/ - the elevation services require US-DoD credentials ( https://earth-info.nga.mil/GandG/update/index.php?dir=elevation&action=elevation#tab_elev-srv ). NASA also has some laser altimetery data, but that generally really sucks in mountain areas.
https://surveyofindia.gov.in/pages/national-gcp-library looks unpopulated at first glance, but the pdf at the top indicates 87 GCPs in Uttarakhand as of 2014. Finding the right person (as opposed to an online source) in the Survey of India may well enable access to much more benchmark data.
Ground truthing points could be collected from many sources that have higher accuracy the the DEMs such as field survey, topographic maps or even aerial photos.
Best wishes
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