Data Set ID: 
HMA_DEM8m_MOS

High Mountain Asia 8-meter DEM Mosaics Derived from Optical Imagery, Version 1

This data set contains 8-meter Digital Elevation Model (DEM) mosaics of high mountain Asia glacier and snow regions generated from very-high-resolution (VHR) commercial satellite imagery.

This is the most recent version of these data.

Version Summary: 

Initial release

STANDARD Level of Service

Data: Data integrity and usability verified

Documentation: Key metadata and user guide available

User Support: Assistance with data access and usage; guidance on use of data in tools

See All Level of Service Details

Parameter(s):
  • TOPOGRAPHY > TERRAIN ELEVATION > DIGITAL ELEVATION/TERRAIN MODEL (DEM)
Data Format(s):
  • GeoTIFF
  • PNG
Spatial Coverage:
N: 46, 
S: 26, 
E: 103, 
W: 67
Platform(s):GEOEYE-1, QUICKBIRD-2, WORLDVIEW-1, WORLDVIEW-2, WORLDVIEW-3
Spatial Resolution:
  • 8 m x 8 m
Sensor(s):CAMERAS, QUICKBIRD/BHRC-60
Temporal Coverage:
  • 28 January 2002 to 24 November 2016
Version(s):V1
Temporal ResolutionVariesMetadata XML:View Metadata Record
Data Contributor(s):David Shean

Geographic Coverage

Other Access Options

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As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Shean, D. 2017. High Mountain Asia 8-meter DEM Mosaics Derived from Optical Imagery, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/KXOVQ9L172S2. [Date Accessed].

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Detailed Data Description

The DEM mosaics provided in this data set were generated from very-high-resolution (VHR) along- and cross-track stereoscopic imagery from DigitalGlobe satellites.

To generate DEM mosaic tiles, over 4000 DEM strips were merged with a weighted-average mosaicking routine that reduced errors and removed seams.

Mosaic tiles are 100 km by 100 km with 12500 x 12500 pixels at 8 m.

DEM mosaic over Everest region of Nepal
Figure 1. Sample Data Record
Sample of DEM mosaic over the Everest region of Nepal. Produced by D. Shean for the NASA High Mountain Asia project.

Parameter

This data set reports elevation in meters above the WGS84 ellipsoid. The mosaics are derived from all available DEMs, regardless of date or sensor. The values represent a weighted average of all valid elevations at each pixel. Weights are assigned to penalize isolated pixels or “islands,” so that values from more spatially continuous DEMs have higher weights. The fill value for pixels containing no data is -9999. 

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Format

Mosaics are provided as tiled, LZW-compressed* GeoTIFFs (.tif) with elevations stored as single precision, floating point numbers (Float32).

Shaded relief browse images in PNG (.png) format accompany each mosaic file. These images were created using a standard azimuth setting of 315 degrees and an elevation of 45 degrees.

An associated Extensible Markup Language (XML) metadata file is also provided for each data file.

*Refers to lossless Lempel–Ziv–Welch (LZW) compression.

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File and Directory Structure

Data are available via HTTPS at: 

https://n5eil01u.ecs.nsidc.org/HMA/HMA_DEM8m_MOS.001/

Within this main directory, files are organized by the processing date: 2002.01.28 (in YYYY.MM.DD format).

Note: The subdirectory name (i.e. 2002.01.28) conforms to NASA archiving requirements, but in this case does not reflect the temporal resolution/timestamps of the data. These blended mosaics were created using DEMs from several years, and therefore do not have a single timestamp.

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File Naming Convention

File names vary slightly as shown in the following examples. Variables used in the file names are defined in Table 1. 

Example File Names

  • HMA_DEM8m_MOS_20170716_tile-043.tif
  • HMA_DEM8m_MOS_20170716_tile-043_hs_05pct.png

Naming Conventions

  • HMA_DEM8m_MOS_[YYYYMMDD]_tile-NNN.tif
  • HMA_DEM8m_MOS_[YYYYMMDD]_tile-NNN_hs_05pct.png
Table 1. File Name Variables and Definitions
Variable Definitions
HMA_DEM8m_MOS Data set ID [abbreviation for High Mountain Asia (HMA) DEM 8 m Mosaic]
YYYYMMDD Mosaic generation date (4-digit year, 2-digit month, 2-digit day)
tile-NNN 3-digit tile number
hs_05pct Shaded relief/hillshade (hs) 5 percent size browse image
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File Size

File sizes vary significantly depending on the file type. Individual DEM tiles range from approximately .4 MB to 406 MB and browse images range from approximately 1 KB to 46 KB.

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Spatial Coverage

Northernmost Latitude: 46° N
Southernmost Latitude: 26° N
Easternmost Longitude: 103° E
Westernmost Longitude: 67° E

Coverage extends to portions of the following eleven countries:
Afghanistan
Bhutan
China
India
Kazakhstan
Kyrgyzstan
Myanmar
Nepal
Pakistan
Tajikistan
Uzbekistan

Figure 2 shows the spatial coverage of the mosaic and the number of DEM strips at each location.

Spatial coverage over HMA-wide 8m DEM mosaic
Figure 2. Spatial Coverage Map
Spatial coverage map showing the HMA-wide 8 m DEM mosaic (A) and the number of DEM strips available at each location (B). Areas with higher DEM counts offer improved mosaic accuracy with fewer voids. The overlapping DEM strips can be used for elevation change analysis; refer to the Data Sources section for individual AT and CT DEMs. 

To view the coverage of a particular DEM, refer to the Knowledge Base FAQ: What is the spatial extent of individual HMA DEMs?

Note: Initial archive request and processing was limited to images that intersected one or more of the Randolph Glacier Inventory (RGI) glacier polygons. Future releases will include expanded HMA coverage.

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Spatial Resolution

The DEM mosaics have 8 m posting (output grid pixel size).

Projection and Grid

The DEM mosaics are provided in a custom Albers Equal-Area projection with standard parallels at 25° N and 47° N, and central longitude of 85° E. Projected coordinates are meters, with the origin at 85° E, 36° N. Elevations are in meters above the WGS84 ellipsoid. Refer to Table 2 for more details.

Table 2. Projection and Grid Details
Projection Albers Equal-Area Conical (custom
Grid Spacing 8 m
Latitudes of True Scale (Standard Parallels) 25°, 47° N
Central Longitude (Meridian) 85° E
Central Latitude 36° N
Datum WGS84
Ellipsoid WGS84
Units Meters
EPSG Code None (custom projection parameters
PROJ4 String +proj=aea +lat_1=25 +lat_2=47 +lat_0=36 +lon_0=85 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
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Temporal Coverage

The optical images used for the mosaics were obtained between 2008 and 2017, with the majority of coverage from 2013 to 2016. For HMA stereo:

  • The WorldView-1 (WV-1) record began in late 2008.  
  • The WorldView-2 (WV-2) record began in mid 2010.
  • The WorldView-3 (WV-3) record began in late 2014.
  • The GeoEye-1 (GE-1) record began in late 2009.
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Temporal Resolution

The blended mosaics are created using DEMs from several years, and therefore do not have a single timestamp. Future releases will offer several mosaicked products, including timestamped mosaics with most recent DEMs on top and mosaics with earliest DEMs on top.

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Software and Tools

GeoTIFF files with embedded geospatial metadata can be accessed using GIS software such as QGIS and ArcGIS, or command-line tools such as the GDAL (Geospatial Data Abstraction Library) utilities and API.

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Data Acquisition and Processing

Sensors

For detailed information on the various satellites and sensors used to produce the source imagery for this data set, refer to the DigitalGlobe, Inc. Web site. Satellite and sensor details are also provided in Shean et al. (2016).

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Data Sources

The DEM mosaics were generated from along-track and cross-track DEM strips from the following sources:

 
See Shean et al. (2016) for details of the full processing workflow. For information regarding ASP, refer to the official documentation (PDF, 21 MB).

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Deviation Techniques and Algorithms

All individual DEM strips were generated using the NASA Ames Stereo Pipeline (ASP) and methodology described in Shean et al. The data were processed using the NASA High-Performance Computing (HPC) resources, primarily the NASA Pleiades Supercomputer at the NASA Ames Research Center.

Processing Steps

The tiled mosaics were generated using the dem_mosaic_validtiles.py utility in the gmbtools repository (https://github.com/dshean/gmbtools). This wrapper runs parallel instances of the ASP dem_mosaic utility for each tile in the output mosaic, with all available along-track and cross-track DEMs.

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Error Sources

In general, the mosaicked products have reduced errors and fewer data voids than the individual DEM strips, especially where several overlapping DEMs are available for the same location. The investigators elected to preserve only "valid" DEM pixels, and did not perform any additional interpolation or filling to remove voids.  Future releases will include void-filled products.

Information regarding error sources is provided in the following user guides:

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Quality Assessment

As noted above, quality checks and corrections were performed throughout the processing steps. Refer to Shean et al. (2016) for details.
 

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References and Related Publications

Contacts and Acknowledgments

David Shean
University of Washington
Polar Science Center, Applied Physics Laboratory
Department of Civil and Environmental Engineering
Seattle, Washington 98195 USA
http://psc.apl.uw.edu/people/post-docs/david-shean/http://psc.apl.uw.edu/people/post-docs/david-shean/

Technical Contact
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
e-mail: nsidc@nsidc.org

Acknowledgments: 

These data were generated through funding from the NASA Cryosphere program and the NASA HiMAT project (NNX16AQ88G). Support for the Polar Geospatial Center was provided by the National Science Foundation (ANT-1043681). Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center.

Document Information

Document Creation Date

December 2017

Document Revision Date

N/A

No technical references available for this data set.

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FAQ

What is the spatial extent of individual HMA DEMs?
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