On Friday, 23 January 2015 from 8:00 a.m. to 5:00 p.m. (USA Mountain Time), we will be performing scheduled maintenance, which may cause temporary disruptions to our Web site, applications, and FTP. We apologize for any inconvenience this may cause you.
This data set contains internal layer measurements taken over Greenland using the Center for Remote Sensing of Ice Sheets (CReSIS) Accumulation Radar instrument. The data were collected as part of Operation IceBridge funded campaigns.
Operation IceBridge products may include test flight data that are not useful for research and scientific analysis. Test flights usually occur at the beginning of campaigns. Users should read flight reports for the flights that collected any of the data they intend to use. Check IceBridge campaign Flight Reports for dates and information about test flights.
We kindly request that you cite the use of this data set in a publication using the following citation. For more information, see our Use and Copyright Web page.
Leuschen, Carl. 2011, updated 2012. IceBridge Accumulation Radar L1B Geolocated Radar Echo Strength Profiles, Version 1, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://nsidc.org/data/iracc1b.html.
NASA P-3B aircraft
CReSIS Accumulation Radar
Varies dependent on along-track, cross-track, and aircraft height characteristics.
06 May 2010 to 07 May 2012
Binary, MATLAB, JPEG, PNG, KML, and Applanix output files.
See the Version History section of this document for previous version information.
Carl Leuschen, Austin Arnett, John Paden, Ben Panzer, Kevin Player
2335 Irving Hill Road
University of Kansas
Lawrence, Kansas 66045
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
form: Contact NSIDC User Services
Data and data products from CReSIS were generated with support from NSF grant ANT-0424589 and NASA grant NNX10AT68G.
CReSIS faculty, staff, and students designed, developed, operated, and processed data from the radar systems.
The data set includes measurements for echograms, time, latitude, longitude, elevation, and surface, as well as flight path charts and echograms images. The background images in the flight path files are Landsat-7 natural color imagery in polar stereographic format where 70 degrees true scale latitude and -45 degrees longitude is center for Greenland/Canada, and -71 degrees true scale latitude and 0 degrees longitude is center for Antarctica.
Note: Currently IRACC1B data for 2009 through 2012 are in MATLAB and binary format stored separately as IRACC1B V01. Beginning with the 2013 Arctic campaign, all data are provided in netCDF format. In the near future, data from all campaigns prior to Spring 2013 will be replaced with netCDF data and added to V02. For details on the Version 02 data, see the V02 documentation.
Binary files contain a vector stream of record data. Each record includes seven header values and a Fast Fourier Transform (FFT) window of snow radar data. The FFT window has dimensions N-number of range bins.
Digital image files are JPEG and PNG files. The y-axis in the JPEG files shows depth relative to a range around the surface. The surface is in the center of the y-axis and the y-axis is set to a fixed range, usually from 0 meters to 60 or 80 meters for the land ice, and 0 meters to 4 meters for sea ice.
MATLAB files are binary files produced and readable by the proprietary Matlab software or other tools such as the Octave high-level language.
KML files are flight line browse images for each segment. There is an entry for the location of the first record for each data frame.
The most convenient way to browse the imagery quickly is through the JPEG files. The quickest way to plot the data set is to look at the KML browse files for the entire season.
The files are organized on the FTP site, ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE_FTP/, as described in Figure 1.
Figure 1. Directory Structure
The data are divided into segments. A segment is a contiguous dataset where the radar settings do not change. A day is divided into segments if the radar settings were changed, hard drives were switched, or other operational constraints required that the radar recording be turned off and on. All data from a particular segment are stored in a directory with the following nomenclature YYYYMMDD_SS where YYYY is the year, MM is the month, DD is the day, and SS is the segment. Segments are always sorted in the order in which the data was collected.
The binary files are named according to the following convention and as described in Table 1:
Binary file name example: accum.20100507A.1.1_50.dat
|accum||Accumulation radar file|
|M||Multiple flights were flown some days, first flight of the day is A, second flight B, and so on.|
|N||Indicates subsection during data processing||n_nn||Indicates raw file numbers combined during data processing, for example 1_50, 51_100.|
|.dat||Indicates a binary data file|
The MATLAB files are named according to the following convention and as described in Table 2:
|Data||Indicates data file|
|.mat||Indicates a MATLAB file|
For each data frame, there is a flight path file (0map) and an echogram file (1echo). The file naming conventions are shown below and as described in Table 3.
|HHmmss||GPS time stamp for the first range line in the image where HH is 00-23 hours, mm is 00-59 minutes, and ss is 00-59 seconds.|
|0maps||Flight path file|
|.jpg or .png||Indicates JPEG or PNG image file|
|Browse_Data||Indicates browse data file|
|SS||Day segment||.kml||Indicates KML file|
|GPS||Indicates GPS file|
|MMM||Month||YYYY||Four-digit year||.mat||Indicates MATLAB file|
|BD960||Trimble BD960 GNSS receiver|
|.out||Indicates Applanix output file|
The binary files range from approximately 61 MB to 203 MB.
The MATLAB files are approximately 3 MB to 8 MB.
The JPEG files are approximately 78 KB to 161 KB.
The PNG files are approximately 372 KB to 693 KB.
The KML files are approximately 3 KB to 216 KB.
The GPS Applanix .mat output files are approximately 139 MB to 235 MB.
The GPS Applanix .out output files are approximately 485 MB to 820 MB.
The entire data set is approximately 150 GB.
Spatial coverage for the IceBridge accumulation radar campaigns include Greenland and surrounding ocean areas.
Arctic / Greenland:
Southernmost Latitude: 60° N
Northernmost Latitude: 90° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Spatial Resolution varies dependent on along-track, cross-track, and aircraft height characteristics.
Referenced to WGS-84 Ellipsoid.
These data were collected as part of Operation IceBridge funded campaigns from 06 May 2010 to 07 May 2012.
IceBridge campaigns are conducted on an annual repeating basis. Arctic and Greenland campaigns are conducted during March, April, and May, and Antarctic campaigns are conducted during October and November.
The Accumulation Radar L1B Geolocated Radar Echo Strength Profiles data set contains elevation and surface measurements.
The Accumulation Radar MATLAB files contain fields as described in Table 7.
|Data||Radar echogram data||Relative linear power|
|Time||Fast time (zero time is the beginning of the transmit event calibrated to within one range resolution cell).||Seconds|
|Depth||Range axis assuming a vacuum (Depth = Time * c/2)||Meters|
|GPS_Time||GPS time when data were collected.||Seconds since January 1, 1970|
|Latitude||Latitude where data were collected (potentially modified by motion compensation).||Degrees|
|Longitude||Longitude where data were collected (potentially modified by motion compensation).||Degrees|
|Elevation||Elevation where data were collected (potentially modified by motion compensation).||Meters referenced to WGS-84 ellipsoid|
|Surface||Estimated two way propagation time to the surface from the collection platform. Uses the same frame of reference as the Time variable. Used to automatically adjust the y-limits of the output PNG files.||Seconds|
|*param*||Radar and processing settings||n/a|
Data are available via FTP.
MATLAB files may be opened using the NSIDC MATLAB reader, or the Octave high-level language.
JPEG files may be opened using any image viewing program that recognizes the JPEG file format.
KML files are read by GIS software packages and earth browsers such as Google Earth or Google Maps.
The radar architecture is a combined stepped-chirped system. The complete bandwidth from 565 MHz to 885 MHz is divided into 16 overlapping subbands 550-600, 570-620,...850-900. Data is recorded on each subband. In post processing, the subbands are combined into a single frequency band. The accumulation radar is only installed on the P-3 aircraft using an antenna installed in the bomb bay.
The MATLAB code below shows how to compensate for elevation so the echogram data mimics constant elevation flight at the maximum elevation in each data frame.
Figure 1 illustrates an echogram without elevation compensation and with elevation compensation.
Figure 1. Elevation Compensation Echogram
For a flat surface the range resolution is expressed by Equation 1.
|kt||kt = 1.6 due to the application of a Hanning time-domain window to reduce the range sidelobes of the chirped transmit waveform.|
|c||Speed of light in a vacuum|
|B||Bandwidth, nominally 320 MHz (565 to 885 MHz range)|
|n||Index of refraction for the medium|
Range resolution for several indices of refraction are given in Table 9.
|Index of Refraction||Range Resolution (m)||Medium|
The antenna installed in the bomb bay of the P-3 is a two by four element antenna array where each element is an elliptical dipole and the array is aligned so that there are two elements in the along-track direction and four elements in the cross-track direction. The dipoles are aligned with the fuselage so that the E-plane is along-track. The element spacing is 26 cm in cross-track and 37 cm in along-track. The approximate beamwidths are 21 degrees in along-track and 18 degrees in cross-track. The footprint is a function of range as shown in Equation 2.
|H||Height above ground level. For H = 500 m, the footprint is 185 m in along-track and 158 m in cross-track.|
|β||Beamwidth in radians|
For a smooth target, for example internal layers, the primary response is from the first Fresnel zone which is considerably smaller than the antenna footprint. The first Fresnel zone is a circle with diameter given in Equation 3.
|H||Height above ground. For H = 500 m, the diameter is 20 m.|
|λc||Wavelength. λc = 0.4 m is the wavelength at the center frequency.|
For a rough surface with no appreciable layover, the cross-track resolution will be constrained by the pulse-limited footprint, which is approximately as shown in Equation 4.
|H||height above the air/ice interface. For H = 500 m, the cross-track resolution is 54.8 m.|
|c||speed of light in a vacuum|
|kt||kt = 1.6 due to the application of a hanning time-domain window to reduce the range sidelobes of the chirped transmit waveform|
In the along-track dimension, data are coherently averaged 160 times which includes both hardware and software averaging, and decimated by this same amount so that the along-track spacing between records with a platform speed of 140 m/s is 7.2 m. A 1 range-bin by 10 along-track-range-line boxcar filter is applied to the power detected data and then decimated in the along-track by 5 so the data product has an along-track resolution of 35.8 m.
The trajectory data used for this data release was from a basic GPS receiver. Lever arm and attitude compensation has not been applied to the data.
The following processing steps are performed by the data provider.
IRACC1B Version 1: Currently Version 1 IRACC1B data for 2009 through 2012 are in MATLAB and binary format. In the near future, data from all V1 campaigns will be replaced with netCDF data and added to Version 2. For details on the V2 data, see the V2 documentation.
The CReSIS ku-band, accumulation, and snow data acquisition systems have a known issue with radar data synchronization with GPS time. When the radar system is initially turned on, the radar system acquires Universal Time Coordinated (UTC) time from the GPS National Marine Electronics Association (NMEA) string. If this is done too soon after the GPS receiver has been turned on, the NMEA string sometimes returns GPS time rather than UTC time. GPS time is 15 seconds ahead of UTC time during this field season. The corrections for the whole day must include the offset -15 second correction. GPS corrections have been applied to all of the data using a comparison between the accumulation, snow, and kuband radars which have independent GPS receivers. A comparison to geographic features and between ocean surface radar return and GPS elevation is also made to ensure GPS synchronization. GPS time corrections are given in the vector worksheet of the parameter spreadsheet.
As described on the CReSIS Sensors Development Radar Web site, fine depth resolution profiling of the top 100 m of the ice column is achieved with the Accumulation Radar designed to map variations in the snow accumulation rate. When operated from aircraft, it operates from 600 to 900 MHz providing 28 cm depth resolution in ice and when operated on the ground (500 MHz to 2 GHz) a 5.6-cm depth resolution in ice is achieved. This fine depth resolution enables extensive spatial mapping of the annual accumulation layers.
Lewis, C. 2010. Airborne UHF Radar for Fine Resolution Mapping of Near Surface Accumulation Layers in Greenland and West Antarctica, Department of Electrical Engineering and Computer Science: Master's Thesis, University of Kansas.
Lewis, C., A. Patel, H. Owen, F. Rodriguez-Morales, C. Leuschen, S. A. Seguin, J. Ledford, K. Player, and S. Gogineni. 2009. A Radar Suite for Ice Sheet Accumulation Measurements and Near-Surface Internal Layer Mapping, Geoscience and Remote Sensing Symposium, IEEE International, IGARSS 2009, pp.V-441 - V-444, doi: 10.1109/IGARSS.2009.5417635.
Rodriguez-Morales, F., P. Gogineni, C. Leuschen, C. T. Allen, C. Lewis, A. Patel, L. Shi, W. Blake, B. Panzer, K. Byers, R. Crowe, L. Smith, and C. Gifford. 2010. Development of a Multi-Frequency Airborne Radar Instrumentation Package for Ice Sheet Mapping and Imaging, Proc. 2010 IEEE Int. Microwave Symp., Anaheim, CA, May 2010, 157-160.
CReSIS Sensors Development Radar Web site (https://cms.cresis.ku.edu/research/sensors-development/radar).
CReSIS Website (https://www.cresis.ku.edu/).
IceBridge Data Web site at NSIDC (http://nsidc.org/data/icebridge/index.html).
IceBridge Web site at NASA (http://www.nasa.gov/mission_pages/icebridge/index.html).
ICESat/GLAS Web site at NASA Wallops Flight Facility (http://glas.wff.nasa.gov/).
ICESat/GLAS Web site at NSIDC (http://nsidc.org/daac/projects/lidar/glas.html).
The acronyms used in this document are listed in Table 13.
|CIRES||Cooperative Institute for Research in Environmental Science|
|CReSIS||Center for Remote Sensing of Ice Sheets|
|CSV||Comma Separated Values|
|DC-8||Douglas DC-8 aircraft|
|FFT||Fast Fourier Transform|
|FTP||File Transfer Protocol|
|GPS||Global Positioning System|
|JPEG||Joint Photographic Experts Group|
|KML||Keyhole Markup Language|
|L1B||Processing Level 1B|
|MATLAB||MATrix LABoratory numerical computing file|
|NASA||National Aeronautics and Space Administration|
|NMEA||National Marine Electronics Association|
|NSF||National Science Foundation|
|NSIDC||National Snow and Ice Data Center|
|P-3||Lockheed P-3B Orion aircraft|
|PNG||Portable Network Graphics|
|URL||Uniform Resource Locator|
|UTC||Universal Time Code|
|WFF||Wallops Flight Facility|
|WGS-84||World Geodetic System 1984|
15 August 2014