New Global DEM released from METI and NASA

The Ministry of Economy, Trade, and Industry (METI) of Japan and the United States National Aeronautics and Space Administration (NASA) at 29th of June jointly released Version 1 of the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) Global Digital Elevation Model (GDEM).

Some information about the ASTER instrument:

• Building Agency: METI of Japan
• Carrier Spacecraft: USA NASA’s Terra
• Launch date: December 1999
• Stereoscopic capability: Along-track (no need to pass multiple times over the same area to collect stereo image data)
• Bands available for DEM generation: VNIR (near infrared spectral band)
• DEM base-to-height ratio: 0.6
• Spatial resolution: 15m in the horizontal plane
• Single ASTER VNIR scene size: About 60 km-by-60 km ground area (4,100 samples by 4,200 lines)

Some information about the ASTER GDEM:

• Land surface coverage: between 83°N and 83°S
• Grid cell size: 1 arc-second (30 m)
• Tiles Format: GeoTIFF
• Number of tiles: 22,600
• Single tile size: 1°-by-1°
• Coordinate System Type: Geographic (Lat/Long coordinates)
• Earth Model: WGS84/EGM96 geoid
• Collection Date: 2000-2009
• Vertical accuracy estimate: 20 meters (at 95 % confidence)
• Horizontal accuracy estimate: 30 meters (at 95 % confidence)
• Area of missing data: Areas with constant cloud coverage

This mission is remarkable because it involved the automated processing of the entire 1.5-million-scene ASTER archive, it took approximately one year to complete production of the beta version of the ASTER GDEM using a fully automated approach.

The process included:

1. Stereo-correlation to produce 1,264,118 individual scene-based ASTER DEMs
2. Cloud masking to remove cloudy pixels
3. Stacking all cloud-screened DEMs
4. Removing residual bad values and outliers
5. Averaging selected data to create final pixel values
6. Correcting residual anomalies
7. Partitioning the data into 1°-by-1° tiles.

Previously, the most complete Global DEM publicly available was the SRTM (Shuttle Radar Topography Mission), it has an 80% land coverage (between 60°N and 57°S). The ASTER GDEM expands coverage to 99%; also the SRTM data has a grid cell size of 3 arc-seconds (90 m) outside of the USA borders, despite being captured at 1 arc-second, it was later averaged before being publicly released.

I hope that NASA would release the full resolution 1 arc-second data of the SRTM DEM globally to augment the ASTER GDEM data and allow for a unified DEM which benefits from the ability of the Radar to collect data in the places constantly covered by clouds.

I currently don't know the shoreline data used to outline the DEM data, but I hope they release it as well or use a publicly available one, such as the NGA Prototype Global Shoreline (PGS) data.

A good technical page about the new ASTER GDEM can be found here.

METI and NASA marks version 1 of the ASTER GDEM as “experimental” or “research grade”, but the size and accuracy of the data makes such an initial release a very good step toward a highly enhanced and accurate Global DEM very near.

Download sources:

Earth Remote Sensing Data Analysis Center (ERSDAC) of Japan

NASA’s Land Processes Distributed Active Archive Center (LP DAAC)

I will post shortly about my experience with the download of the new GDEM and its estimated size and usage characteristics.

Sources and News Coverage:

NASA’s Land Processes Distributed Active Archive Center

The Map Room, Astronomy Magazine, Universe Today, BBC News