Sources of digital elevation models

 Digital Elevation Models (DEMs) are digital representations of the Earth's surface terrain. They provide detailed information on the elevation and slope of the terrain and are useful for a wide range of applications, including mapping, geology, hydrology, and urban planning.

There are several sources of Digital Elevation Models, which are listed below:

1. Shuttle Radar Topography Mission (SRTM): SRTM is a joint mission between NASA and the National Geospatial-Intelligence Agency (NGA) that was launched in 2000. The mission used a specially equipped radar instrument to collect data on the Earth's surface elevation. The data was then processed to produce a global DEM with a resolution of 90 meters.

2. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER): ASTER is a sensor onboard NASA's Terra satellite that was launched in 1999. The sensor collects data on the Earth's surface elevation, as well as temperature and reflectance. The data is processed to produce a global DEM with a resolution of 30 meters.

3. Global Digital Elevation Model (GDEM): GDEM is a DEM product produced by the Japanese Ministry of Economy, Trade, and Industry (METI) using data collected by the ASTER sensor. The GDEM has a resolution of 30 meters and covers the entire world.

4. Light Detection and Ranging (LiDAR): LiDAR is a remote sensing technology that uses laser pulses to measure the distance between the sensor and the Earth's surface. LiDAR data can be used to produce highly accurate DEMs with resolutions ranging from a few centimeters to several meters.

5. Interferometric Synthetic Aperture Radar (InSAR): InSAR is a radar-based remote sensing technology that uses radar waves to measure changes in the elevation of the Earth's surface. InSAR data can be used to produce DEMs with high accuracy and resolution, particularly in areas with rugged terrain.

6. National Mapping and Resource Information Authority (NAMRIA): NAMRIA is a government agency in the Philippines that produces and maintains the country's topographic maps, including DEMs. The agency uses LiDAR and other remote sensing technologies to produce accurate and high-resolution DEMs.

7. Indian Space Research Organization (ISRO): ISRO is India's space agency, which produces DEMs using data collected by its Cartosat satellites. The Cartosat DEMs have a resolution of up to 2.5 meters and are useful for applications such as urban planning, disaster management, and environmental monitoring.

8. European Space Agency (ESA): ESA produces several DEM products using data collected by its satellite missions, including the Digital Elevation Model over the Antarctic (DEMANT) and the Global Digital Elevation Model (GDEM).

In conclusion, there are several sources of digital elevation models, ranging from satellite missions to ground-based LiDAR surveys. Each source has its strengths and weaknesses, and the choice of source depends on the specific application and requirements of the user.

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