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This data set contains radar echograms taken over Greenland and Antarctica using the Center for Remote Sensing of Ice Sheets (CReSIS) Accumulation Radar instrument. The data were collected as part of Operation IceBridge funded campaigns.
Data Set ID:
IRACC1B
IceBridge Accumulation Radar L1B Geolocated Radar Echo Strength Profiles, Version 2
This is the most recent version of these data.
Version Summary:
Version 2 data are in netCDF format beginning with the 2013 Arctic campaign.
Version 1 data are in MATLAB and binary format for 2012 and earlier campaigns.
- Beginning with the 2013 Arctic campaign, the data file format is netCDF.
- Data files for all previous campaigns are to be replaced with netCDF files.
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
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Geographic Coverage |
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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. IceBridge Portal: Tool to visualize, search, and download IceBridge data. Earthdata Search: This application allows you to search, visualize, and access data across thousands of Earth science data sets. Additional customization services are available for select data sets, including subsetting, reformatting, and reprojection. |
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.
Paden, J., J. Li, C. Leuschen, F. Rodriguez-Morales, and R. Hale. 2014, updated 2018. IceBridge Accumulation Radar L1B Geolocated Radar Echo Strength Profiles, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/0ZY1XYHNIQNY. [Date Accessed].Collapse All / Open All
Detailed Data Description
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.
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.
Format
The data files are in netCDF format. The echogram and flight path image files are JPEG files.
Each data file is paired with an associated XML file, which contains additional metadata.
The Echogram.jpg files contain depth echograms. The echograms are useful for tracking internal layers and shallow ice thickness.
The Map.jpg files show campaign flight locations and flight lines.
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 0-60 m or 0-80 m for land ice, and 0-4 m for sea ice.
Currently, IceBridge Accumulation Radar L1B Geolocated Radar Echo Strength Profiles (IRACC1B) data for 2009 through 2012 are in MATLAB and binary format stored separately as IRACC1B Version 1. In the near future, data from all campaigns prior to Spring 2013 will be replaced with netCDF data and added to Version 2. For details on the IRACC1B Version 1 data, see the Version 1 documentation.
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File Naming Convention
Data Files
Data files are named according to the following conventions and as described in Table 1.
Example:IRACC1B_20130321_01_123.nc
IRACC1B_YYYYMMDD_xx_xxx.NNN
| Variable | Description |
|---|---|
| IRACC1B | Short name for IceBridge Accumulation Radar L1B Geolocated Radar Echo Strength Profiles |
| YYYY | Four-digit year of survey |
| MM | Two-digit month of survey |
| DD | Two-digit day of survey |
| xx | Segment number |
| xxx | Frame number |
| NNN | Indicates file type. For example: netCDF (.nc), or XML (.xml) |
JPEG Files
JPEG files are named according to the following convention and as described in Table 2:
Example:IRACC1B_20130321_01_123_Echogram.jpg
IRACC1B_YYYYMMDD_xx_xxx_aaa.NNN
| Variable | Description |
|---|---|
| IRACC1B | Short name for IceBridge Accumulation Radar L1B Geolocated Radar Echo Strength Profiles |
| YYYY | Four-digit year of survey |
| MM | Two-digit month of survey |
| DD | Two-digit day of survey |
| xx | Segment number |
| xxx | Frame number |
| aaa | Image type. Examples: Echogram, Map |
| NNN | Indicates file type. For example: JPEG (.jpg) |
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File Size
The netCDF files range from approximately 8 MB to 39 MB. The total netCDF file volume is approximately 258 GB.
The JPEG files range from approximately 58 KB to 260 KB. The total JPEG file volume is approximately 3 GB.
The entire data set volume is approximately 261 GB.
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Spatial Coverage
Spatial coverage for the IceBridge accumulation radar campaigns includes Greenland and Antarctica and surrounding ocean areas.
Arctic / Greenland:
Southernmost Latitude 60° N
Northernmost Latitude: 90° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Antarctica:
Southernmost Latitude: 90° S
Northernmost Latitude: 53° S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Spatial Resolution
Spatial Resolution varies dependent on along-track, cross-track, and aircraft height characteristics.
Projection and Grid Description
Referenced to WGS-84 Ellipsoid.
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Temporal Coverage
21 March 2013 to 25 November 2017.
Temporal Resolution
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.
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Parameter or Variable
The Accumulation Radar L1B Geolocated Radar Echo Strength Profiles data set contains elevation and surface measurements.
Parameter Description
The Accumulation Radar netCDF files contain fields as described in Table 3.
| Parameter | Description | Units |
|---|---|---|
| Heading | Platform heading attitude. Zero is north, positive to east. Dimension is time. | Degrees |
| Pitch | Platform pitch attitude. Zero is level flight, positive is up. Dimension is time. | Degrees |
| Roll | Platform roll attitude. Zero is level flight, positive is right wing tip down. Dimension is time. | Degrees |
| Surface | Estimated two way propagation time to the surface from the collection platform. This uses the same frame of reference as the fasttime variable. This information is sometimes used during truncation to determine the range bins that can be truncated. Dimension is time. | Seconds |
| alt | WGS-84 geodetic elevation coordinate of the measurement's phase center. Dimension is time. | Meters |
| amplitude | Power detected radar echogram data matrix. The first dimension is fasttime and time is the second dimension. Power is relative to the current range line only. Each range line may contain a different bias and so power comparisons between range lines may not be possible. | Relative power (log scale) |
| fasttime | Fast time. Zero time is the time at which the transmit waveform begins to radiate from the transmit antenna. | Microseconds |
| lat | WGS-84 geodetic latitude coordinate where data were collected, potentially modified by motion compensation. Always referenced to North. Represents the location of the origin of the trajectory data which is generally not the radar's phase center, but some other point on the aircraft, for example the GPS antenna or the INS. | Degrees |
| lon | WGS-84 geodetic longitude coordinate where data were collected, potentially modified by motion compensation. Always referenced to East. Represents the location of the origin of the trajectory data which is generally not the radar's phase center, but some other point on the aircraft, for example the GPS antenna or the INS. | Degrees |
| time | UTC time of day. This is also known as the slow time dimension. The parameter "units" attribute contains a string of the form "seconds since YYYY-MM-DD 00:00:00" which indicates the day related top this time parameter. This pertains to data sets that wrap over a UTC day boundary which will cause this parameter to be outside the range [0,86400]. | Seconds |
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Software and Tools
See the NetCDF Resources at NSIDC page for tools to work with netCDF files.
CReSIS netCDF files are compatible with HDF5 libraries, and can be read by HDF readers such as HDFView. If the netCDF file reader you are using does not read the data, see http://www.unidata.ucar.edu/software/netcdf/ and http://nsidc.org/data/netcdf/tools.html for information on updating the reader.
CReSIS MATLAB readers are available for loading, plotting, and elevation compensation for CReSIS Level-1B radar products. These tools are provided by the Principal Investigator as-is as a service to the user community in the hope that they will be useful. Please note that support for these tools is limited. Bug reports, comments, and suggestions for improvement are welcome; please send to nsidc@nsidc.org.
JPEG files may be opened using any image viewing program that recognizes the JPEG file format.
XML files can be read with browsers such as Firefox and Internet Explorer.
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Data Acquisition and Processing
Data Acquisition Methods
The radar architecture before the 2012 Greenland P-3 aircraft campaign 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 radar architecture from 2012 Greenland P-3 aircraft campaign and later uses a single wideband chirp. The digital acquisition system was replaced to enable this. The chirp is 600 to 900 MHz and is directly sampled using a 1 GigaSample-Per-Second (GSPS) Analog to Digital Converter (ADC).
The accumulation radar is only installed on the P-3 aircraft using an antenna installed in the bomb bay.
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Derivation Techniques and Algorithms
Flat Surface Range Resolution
For a flat surface the range resolution is expressed by Equation 1.
(Equation 1)
Where:
| Variable | Description |
|---|---|
| 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 5.
| Index of Refraction | Range Resolution (m) | Medium |
|---|---|---|
| 1 | 0.75 | Air |
| 1.3 | 0.58 | Snow |
| sqrt(3.51) | 0.42 | Solid Ice |
Footprint
The antenna installed in the bomb bay of the P-3 aircraft 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.
(Equation 2)
Where:
| Variable | Description |
|---|---|
| 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.
(Equation 3)
Where:
| Variable | Description |
|---|---|
| D | Diameter |
| 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.
(Equation 4)
Where:
| Variable | Description |
|---|---|
| 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 |
| B | Bandwidth |
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.
Trajectory and Attitude Data
The trajectory data used for this data release are from a basic GPS receiver. Lever arm and attitude compensation has not been applied to the data.
Processing Steps
Before 2012 Greenland, the steps for the stepped-frequency radar system are:
- Conversion from quantization to voltage at the 50 ohm antenna.
- Removal of DC-bias.
- Channel compensation between each of the 16 subbands. This includes amplitude mismatches only.
- Pulse compression with time domain window which matches transmitted time domain window and an additional frequency domain window.
- Sixteen subbands are combined into a single band.
- The quick look output is generated using presumming or unfocused SAR processing for a total of 160 coherent averages which includes hardware and software averages.
- A 1 range-bin by 10 along-track-range-line boxcar filter is applied to the power detected data and then decimated in along-track by 5.
- The quick look output is used to find the ice surface location (fully automated).
From 2012 Greenland and onward, the processing steps for the directly sampled radar system are:
- Conversion from quantization to voltage at the 50 ohm antenna.
- Removal of DC-bias.
- The data are pulse compressed with a frequency domain window to reduce pulse compression side lobes.
- The quick look output is generated using presumming or unfocused SAR processing for a total of 1280 coherent averages which includes hardware and software averages. As only a single subband needs to be captured, this is equivalent to 80 presums with the old system.
- A 1 range-bin by 5 along-track-range-line boxcar filter is applied to the power detected data and then decimated in along-track by 5.
- The quick look output is used to find the ice surface location (fully automated).
Version History
IRACC1B Version 1: Currently IRACC1B data for 2009 through 2012 are in MATLAB and binary format stored separately as IRACC1B V1. In the near future, data from all campaigns prior to Spring 2013 will be replaced with netCDF data and added to Version 2. For details on the Version 1 data, see the Version 1 documentation.
IRACC1B Version 2: Beginning with the 2013 Arctic campaign, data are provided in netCDF format.
IRACC1B Version 2.1: On 16 September 2014, Version 2 data were replaced by Version 2.1. A time stamp error was discovered in the 2013 Arctic campaign data. The latest leap second (July 1, 2012) was not accounted for in the GPS times for these campaigns. This error has been corrected in Version 2.1.
Error Sources
GPS Time Error:
The CReSIS accumulation, snow, MCoRDS, and kuband 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 ku-band radars which have independent GPS receivers. Comparisons to geographic features and between ocean surface radar return and GPS elevation are also made to ensure GPS synchronization. GPS time corrections are given in the vector worksheet of the parameter spreadsheet.
A time stamp error was discovered in the 2013 Arctic campaign data. The latest leap second (July 1, 2012) was not accounted for in the GPS times for these campaigns.
The error affects Version 2 of the Level 1B CReSIS data sets. Accumulation Radar data are affected for the time period: March 2013 - 2014. In the near future, the NSIDC DAAC will publish updated data files with a correction to the 'Time' field.
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Sensor or Instrument Description
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, the Accumulation radar 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.
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References and Related Publications
Contacts and Acknowledgments
Center for Remote Sensing of Ice Sheets (CReSIS)
Nichols Hall, The University of Kansas
2335 Irving Hill Road
Lawrence, Kansas 66045
data@cresis.ku.edu
Acknowledgments:
The radar systems and software were developed with funding from a variety of sources including NASA (NNX16AH54G), NSF (ACI-1443054), and the State of Kansas. The Operation IceBridge data were collected as part of the NASA Operation IceBridge project. The processing requires GPS and attitude data that are made available by various groups including the Airborne Topographic Mapper team, the Digital Mapping System team, and the Sanders Geophysics company. We also acknowledge all the personnel involved in supporting the field operations.
Document Information
DOCUMENT CREATION DATE
26 June 2014
DOCUMENT REVISION DATE
04 October 2018
No technical references available for this data set.
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