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This data set, part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program, consists of 6-day and 12-day 50 m resolution image mosaics of the Greenland coastline and ice sheet periphery. The mosaics are derived from C-band Synthetic Aperture Radar (C-SAR) acquired by the Copernicus Sentinel-1A and -1B imaging satellites starting in January 2015.
See Greenland Ice Mapping Project (GIMP) for related data.
This is the most recent version of these data.
The changes for Version 2 include:
COMPREHENSIVE Level of Service
Data: Data integrity and usability verified; data customization services available for select data
Documentation: Key metadata and comprehensive user guide available
User Support: Assistance with data access and usage; guidance on use of data in tools and data customization services
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Geographic Coverage |
Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login.
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.
Joughin, I. 2017, updated 2019. MEaSUREs Greenland Image Mosaics from Sentinel-1A and -1B, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/GPVL3SACPBW4. [Date Accessed].As a condition of using these data, we request that you acknowledge the author(s) of this data set by referencing the following peer-reviewed publication.
Joughin, I., B. Smith, I. Howat, T. Moon, and T. Scambos. 2016. A SAR record of early 21st century change in Greenland, Journal of Glaciology. 62. 62-71. https://doi.org/10.1017/jog.2016.10
Each mosaic product spans either a 12-day period (prior to 28 September 2016) or a 6-day period (starting on 28 September 2016). Each mosaic is available in Geographic Tagged Image File Format (GeoTIFF) as a set of four tiles geographically divided into North, Northeast, Northwest, and South regions posted at 50 m, which is approximately equivalent to the image resolution after multi-look averaging. In addition, the following ancillary files are available:
.vrt files, which allow the 50 m GeoTIFF files to be opened as a single file in geographical information system (GIS) programs..vrt.ovr) that contain image pyramids to facilitate rapid viewing of the 50 m mosaics..jpg and .jpg.aux.xml) that provide some geolocation information.Data are available via HTTPS in the following directory:
https://daacdata.apps.nsidc.org/pub/DATASETS/nsidc0723_MEASURES_image_mosaics_v02/
This directory contains folders named by year-month-day (YYYY-MM-DD), where the date corresponds to the first date of the mosaic epoch, and two video files in .mov format: upernavik_v02.1.mov and greenland_v02.1.mov.
This section explains the file naming conventions with examples of each file type. Tables 1 through 3 describe the variables for each naming convention. Beginning with the November 2017 update, the file names changed to S1_[start_date]_[end_date]_v02.2.[ext], with both S1A and S1B data used in each file. As of February 2018, all file names use this convention.
Naming Convention: S1_[start_date]_[end_date]_v02.2.[ext]
Example File Names:
S1_2015-01-01_2015-01-12_v02.2.dbfS1_2015-01-01_2015-01-12_v02.2.prjS1_2015-01-01_2015-01-12_v02.2.shpS1_2015-01-01_2015-01-12_v02.2.shxTable 1 describes the variables used in the shapefile naming convention.
| Variable | Description |
|---|---|
S1 |
Sentinel-1 satellites A and B |
start_date |
Date of first image used in the mosaic period (YYYY-MM-DD) |
end_date |
Date of last image used in the mosaic period (YYYY-MM-DD) |
v02.2 |
Version number |
.ext |
File extension. The shapefile format consists of four files:
|
Naming Convention: S1_[start_date]_[end_date]_mosaic_v02.2.[ext]
Example File Names:
S1_2015-01-01_2015-01-12_mosaic_v02.2.jpgS1_2015-01-01_2015-01-12_mosaic_v02.2.vrtS1_2015-01-01_2015-01-12_mosaic_v02.2.vrt.ovrS1_2015-01-01_2015-01-12_mosaic_v02.2.jpg.aux.xmlTable 2 describes the variables used in the browse file naming convention.
| Variable | Description |
|---|---|
S1 |
Sentinel-1 satellites A and B |
start_date |
Date of first image used in the mosaic period (YYYY-MM-DD) |
end_date |
Date of last image used in the mosaic period (YYYY-MM-DD) |
mosaic |
Denotes that the file is a multiyear mosaic file |
v02.2 |
Version number |
.ext |
File extensions:
|
Naming Convention: S1_[start_date]_[end_date]_[region]_v02.2.tif
Example File Names:
S1_2015-01-01_2015-01-12_south_v02.2.tifS1_2015-01-01_2015-01-12_northwest_v02.2.tifS1_2015-01-01_2015-01-12_northeast_v02.2.tifS1_2015-01-01_2015-01-12_north_v02.2.tifTable 3 describes the variables used in the GeoTIFF file naming convention.
| Variable | Description |
|---|---|
S1 |
Sentinel-1 satellites A and B |
start_date |
Date of first image used in the mosaic period (YYYY-MM-DD) |
end_date |
Date of last image used in the mosaic period (YYYY-MM-DD) |
region |
Regions of Greenland: north, northeast, northwest, or south |
v02.2 |
Version number |
File sizes vary by file type:
.tif) files range from 16 MB to 195.4 MB..jpg) range from 83 KB to 365 KB..jpg.aux.xml) files range from 1 KB to 2 KB each..vrt) files are 3 KB each..vrt.ovr) files are approximately 503 MB each.The total data volume of this data set is approximately 147 GB.
The study area lies within the following bounding box:
The spatial resolution is 50 m x 50 m.
GeoTIFFs are provided in a WGS 84 polar stereographic grid with a standard latitude of 70° N and rotation angle of -45° (sometimes specified as a longitude of 45° W). With this convention, the y-axis extends south from the North Pole along the 45° W meridian (EPSG:3413).
The 50 m mosaics are provided as a set of 4 tiles, divided and named by geographic region: north, northeast, northwest, and south.
Start date: 01 January 2015 (ongoing)
This data set undergoes periodic updates as new Sentinel data are collected and processed.
The temporal resolution for data acquired prior to 28 September 2016 is 12 days. The temporal resolution for data acquired after 28 September 2016 is 6 days.
The mosaics provided in this data set consist of uncalibrated C-SAR radar backscatter.
In SAR applications, backscatter is the ratio between the power of a radar pulse transmitted to the target and the power scattered back towards the antenna.
GeoTIFF files can be viewed with a variety of Geographic Information System (GIS) software packages including:
For details about the shapefile format, see the ESRI Shapefile Technical Description (PDF, 124 KB). The VRT format is discussed in detail on the GDAL Virtual Format Tutorial web page. The ArcGIS Resource Center's Raster Pyramids and OVR Pyramid Files help pages provide more information about raster data set downsampling.
The interactions between radar signals and the ground depend upon many factors, such as the density and dielectric properties of surface materials, vegetation cover, surface roughness at the scale of the signal's wavelength, topographic variations, and the instrument's look angle and signal polarization. The image resolution is particularly affected by signal strength, chirp pulse length and bandwidth, return signal integration time, and the time between pulse transmissions.
For a detailed discussion of SAR theory, see SAR Theory/Interpreting Images (PDF, 82.4 KB). For general information about the mathematical derivations and theories behind SAR processing algorithms, see Scientific SAR User's Guide (PDF, 296 KB).
Copernicus Sentinel-1A and -1B satellite imagery was acquired by the European Space Agency and archived and distributed through the Alaska Satellite Facility.
From 01 January 2015 to 15 September 2016, data were acquired from the Sentinel-1A platform only. Beginning 28 September 2016, data were acquired from both Sentinel-1A and Sentinel-1B platforms.
The Alaska Satellite Facility provided all source data as Level-1 burst Single-Look Complex (SLC) data, including digitized voltage values, instrument calibration constants, satellite timing, attitude, and position information. The SLC burst data were processed to full multi-burst SLC scenes using the GAMMA Modular SAR Processor (MSP) package.
The data have been mapped to grey scale values in the range of 0 - 255 (bytes) using a nonlinear stretch to allow visual discrimination of topographical features within the images. As a result, the pixel values for each year are not directly comparable; however, if no change has occurred, they should be relatively consistent from scene to scene.
The mosaics are produced from four descending and two ascending tracks. In some cases, the image tracks overlapped, but at any given pixel, only one image was used. If the overlapping images were ascending (Tracks 74 and 90) and descending (Tracks 26, 112, 141, 170), the descending image was used (see the shapefile attribute field to determine track direction). If two parallel images overlapped, the top polygon in the shapefile should correspond to the image that was included in the mosaic. In some locations, it is possible that one mosaic will have ascending geometry and another descending geometry because of missed acquisitions (i.e., a consistent geometry is used whenever sufficient data are acquired). In such areas, mountains and other topography features will appear to be illuminated from opposite sides. If the images are flickered between, the different viewing geometries can give the impression of large shifts, even though the data are generally well registered. For regions with like-viewing geometry, the co-registration is far better than the 50-m posting, except in cases where the topography is extreme.
.tif) was still generated. The JPEG file (.jpg) that accompanies each four-tile mosaic provides a quicklook view of expected data output when all four tiles are combined.With the exception of extreme terrain regions, geometric accuracy is better than a single 50 m pixel (Joughin et al., 2016).
The data were terrain-corrected with MEaSUREs Greenland Ice Mapping Project (GIMP) Digital Elevation Model, Version 1. Due to this correction, some slight differences in registration relative to MEaSUREs Greenland Ice Sheet Mosaics from SAR Data, Version 1, mosaics exist.
For more information on the SAR satellites Sentinel-1A and -1B, please see the European Space Agency's Copernicus Sentinel-1 web page.
| Version | Description | Effective Date |
|---|---|---|
| V2.2 | Updated the .tif file names within the .vrt files to match the actual .tif files. The .gif files changed were changed to .mov files. |
September 2019 |
| V2.1 | An additional track (Sentinel-1, track 83) is included to improve coverage in the southern part of the ice sheet. This will change the geometry for a small region in the southwest from ascending to predominantly descending from May 2017 forward when track 83 is available. May 2017 v2.0 and June 2017 v2.0 files were replaced. July 2017 data were added. | September 2017 |
| V2 |
|
July 2017 |
| V1 | Initial release | June 2017 |
Dr. Ian Joughin
University of Washington
Applied Physics Laboratory
1013 NE 40th Street
Box 355640
Seattle, Washington 98105
USA
These mosaics were generated through a grant from the NASA MEaSUREs program. Contains modified Copernicus Sentinel data (2015-2018), acquired by the European Space Agency, distributed through the Alaska Satellite Facility, and processed by I. Joughin.
The WMO Polar Space Task Group is acknowledged for its role in coordinating the routine Copernicus Sentinel-1 Greenland acquisition plans.
June 2017
September 2019
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