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IceBridge ATM L1B Elevation and Return Strength, Version 2
This data set contains spot elevation measurements of Arctic and Antarctic sea ice, and Greenland, Antarctic Peninsula, and West Antarctic region ice surface acquired using the NASA Airborne Topographic Mapper (ATM) instrumentation. The data were collected as part of Operation IceBridge funded aircraft survey campaigns.
Version 2 data are in HDF5 format beginning with the 2013 Arctic campaign.
Version 1 data are in Qfit binary format for 2012 and earlier campaigns.
- Qfit data files for all previous campaigns are to be replaced with HDF5 files.
- The V02 data set title (longname) changes from "IceBridge ATM L1B Qfit Elevation and Return Strength" to "IceBridge ATM L1B Elevation and Return Strength".
|Platform(s)||C-130, DC-8, HU-25A, HU-25C, P-3B, WP-3D Orion|
|Data Contributor(s):||Michael Studinger|
|Metadata XML:||View Metadata Record|
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.Studinger, M. S. 2013, updated 2016. IceBridge ATM L1B Elevation and Return Strength, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/19SIM5TXKPGT. [Date Accessed].
Detailed Data Description
The 2013 data are in HDF5 format. The fundamental form of the ATM topography data is a sequence of laser footprint locations acquired in a swath along the aircraft flight track.
The root group in the HDF5 file contains individual parameters for the latitude, longitude and elevation of the laser footprint. The root group also contains two subgroups as described in Table 3. Each data file is paired with an associated XML file. The XML files contain location, platform, and instrument metadata.
For details on the Qfit data, see the Version 1 documentation.
Note: For sub-sampled ATM data, see the IceBridge ATM L2 Icessn Elevation, Slope, and Roughness data set.
The ATM data are organized in chronological order. Data from a single aircraft flight is broken into a sequence of files, each of which contains about a million laser measurements (about 5.5 minutes duration at 3 kHz laser pulse rate). The name of each file in the sequence contains the starting date and time for that file.
Data are available on the HTTPS site in the
https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/ILATM1B.002/ directory. Within this directory, the folders are organized by date, for example
Data fles are named according to the following conventions and as described in Table 1:
||File name prefix indicating ATM L1B data|
||Four-digit year of survey|
||Two-digit month of survey|
||Two-digit day of survey|
||Two-digit hours, beginning of file time|
||Two-digit minutes, beginning of file time|
||Two-digit seconds, beginning of file time|
||Airborne Topographic Mapper instrument identification, e.g. atm4c or ATM4B or ATM5A|
||Identifier of transceiver used, affecting off-nadir scan angle:
T2 = 15-degree
T3 = 23-degree
T4 = 30-degree
||indicates output file: e.g. h5, or h5.xml|
XML metadata file names use the above convention, with a .xml extension.
HDF5 elevation measurement files range from approximately 60 KB to 27 MB.
XML files range from approximately 3 KB 31 KB.
The HDF files are approximately 134 GB.
The XML files are approximately 60 MB.
Spatial coverage for the IceBridge ATM campaigns includes the Arctic, Greenland, Antarctica, and surrounding ocean areas. In effect, this represents the coverage noted below.
Arctic / Greenland:
Southernmost Latitude 60° N
Northernmost Latitude: 90° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Southernmost Latitude: 90° S
Northernmost Latitude: 53° S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
The ATM surface elevation measurements have been acquired from a conically scanning LIDAR system. Coupled with the motion of the aircraft in flight, the resulting array of laser spot measurements is a tight spiral of elevation points. The surface elevation measurements generally consist of a pattern of overlapping roughly elliptical patterns on the surveyed surface, forming a swath of measurements along the path of the aircraft. Resolution varies with the altitude flown and the scanner configuration for the LIDAR. At a typical altitude of 500 m above ground level, a laser pulse rate of 5 kHz, and a scan width of 22.5 degrees off-nadir, the average point density is one laser shot per 10 m2 within the swath.
Projection and Grid Description
Data are given in geographic latitude and longitude coordinates. Data coordinates are referenced to the WGS84 ellipsoid. Reference frame is prescribed by the International Terrestrial Reference Frame (ITRF) convention in use at the time of the surveys. For more on the reference frame, see the ITRF specification Web site.
These data were collected as part of Operation IceBridge funded campaigns from 31 March 2009 to 19 May 2016.
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 sampling frequency for the Airborne Topographic Mapper is 3 or 5 kHz.
The ATM L1B Elevation and Return Strength data set includes glacier, ice sheet, and sea ice elevation measurements, and relative transmitted and return reflectance.
The ATM times are rounded to 0.001 seconds. The ATM instrument operates at a sampling rate 3 or of 5 kHz. When rounding to 0.001 seconds, three or five points will appear with the same time stamp.
Parameters contained in HDF5 ATM data files are described in Table 2.
|/(root)||latitude||Laser spot latitude||Degrees|
|longitude||Laser spot longitude||Degrees|
|elevation||Laser spot elevation above ellipsoid||Meters|
|/instrument_parameters/||azimuth||Scanner azimuth angle||Degrees|
|gps_pdop||GPS dilution of precision (PDOP)||Dimensionless|
|rcv_sigstr||Received (reflected) signal strength||dimensionless relative values (or data numbers, DN)|
|xmt_sigstr||Transmitted (start pulse) signal strength||dimensionless relative values (or data numbers, DN)|
|pulse_width||Laser received pulse width at half height, number of digitizer samples at 0.5 nanosecond per sample||Count|
|rel_time||Relative time measured from start of file||Seconds|
|time_hhmmss||GPS time packed, example: 153320.100 = 15 hours 33 minutes 20 seconds 100 milliseconds.||Seconds|
|/ancillary_data/||reference_frame||ITRF designation of reference frame||Text name|
|Min_latitude||Minimum value of latitude for this file||Degrees|
|Min_longitude||Minimum value of longitude for this file||
Maximum value of latitude for this file
Maximum value of longitude for this file
|Header_text||Raw data (in human readable form) containing comments or processing history of the parameter data.||None|
|Header_binary||Raw data (in binary form) containing comments or processing history of the parameter data.||None|
Sample Data Record
Below is an ASCII format excerpt of the
ILATM1B_20091030_212220.atm4cT3.qi data file converted from the binary. The 12 fields in each record correspond to the columns described in Table 2.
Software and Tools
The following external links provide access to software for reading and viewing HDF5 data files. Please be sure to review instructions on installing and running the programs.
HDFView: Visual tool for browsing and editing HDF4 and HDF5 files.
Panoply netCDF, HDF and GRIB Data Viewer: Cross-platform application. Plots geo-gridded arrays from netCDF, HDF and GRIB datasets.
For additional tools, see the HDF-EOS Tools and Information Center.
Data Acquisition and Processing
A laser altimeter measures range from the instrument to a target by measuring the elapsed time between emission of a laser pulse and detection of laser energy reflected by the target surface. Range to the target is calculated as half the elapsed emission/return time multiplied by the speed of light. Target range is converted to geographic position by integration with platform GPS and attitude or Inertial Measurement Unit (IMU) information.
The ATM instrument package includes suites of LIDAR, GPS and attitude measurement subsystems. The instrument package is installed onboard the aircraft platform and calibrated during ground testing procedures. Installation mounting offsets, the distances between GPS and attitude sensors and the ATM LIDARs, are measured using surveying equipment. One or more ground survey targets, usually aircraft parking ramps, are selected and surveyed on the ground using differential GPS techniques. Prior to missions, one or more GPS ground stations are established by acquiring low rate GPS data over long time spans. Approximately one hour prior to missions both the GPS ground station and aircraft systems begin data acquisition. During the aircraft flight, the ATM instrument suite acquires LIDAR, GPS and attitude sensor data over selected targets, including several passes at differing altitudes over the selected ground survey calibration sites. The aircraft and ground systems continue to acquire data one hour post-mission. Instrument parameters estimated from the surveys of calibration sites are used for post-flight calculation of laser footprint locations. These parameters are later refined using inter-comparison and analysis of ATM data where flight lines cross or overlap.
Each ATM surface elevation measurement corresponds to one laser pulse. The measurements have not been re-sampled. The transmitted laser pulse and the received backscatter pulse from the ground surface are photodetected and captured by a waveform digitizer. Post-flight processing of the waveforms yields the time of flight between transmitted and received signals. This time of flight value is converted to a distance compensated for speed of light through atmosphere. The scan azimuth of the LIDAR scanner mirror together with the aircraft attitude determine the pointing angle of the LIDAR. GPS aircraft position, pointing angle of the LIDAR, and range measured by the LIDAR are used to compute position of laser footprint on the ground.
Trajectory and Attitude Data
Aircraft position is determined by Global Navigation Satellite System (GNSS) systems that incorporate NAVSTAR Global Positioning System (GPS) and, for later campaigns, the Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS). Carrier phase measurements are logged by an antenna and receiver on the aircraft. In post-flight processing, these measurements are combined with similar measurements from static ground stations to produce a kinematic differential solution of the aircraft trajecotry at 0.5 second intervals, and more recently at 0.1 second intervals.
Aircraft attitude is logged from a commercial Intertial Navigation System (INS), also known as an Inertial Measurement Unit (IMU).
The following processing steps are performed by the data provider.
- Preliminary processing of ATM LIDAR data through the cvalid program, applying calibration factors to convert time of flight to range, scan pointing angles, and interpolate attitude to each LIDAR measurement.
- Processing of GPS data into aircraft trajectory files using double-differenced dual-frequency carrier phase-tracking.
- Determination of all biases and offsets: heading, pitch, roll, ATM-GPS [x,y,z] offset, scanner angles, range bias.
- Processing of the LIDAR and GPS data with all biases and offsets through the qfit program, resulting in output files containing a surface elevation (ellipsoid height) and a geographic location in latitude and east longitude, with ancillary parameters noted in Table 4.
Version 2.0 of the ILATM1B data. Beginning with the 2013 Arctic campaign, all data are provided in HDF5 format. In the near future, qfit data from all campaigns prior to Spring 2013 will be replaced with HDF5 data.
12 and 13 April 2010:
During collection of IceBridge ATM Greenland data on 12 and 13 April 2010, hydraulic oil progressively leaked from the forward landing gear on the DC8 aircraft. The oil was blown back along the bottom of the fuselage and across the nadir window through which the ATM was transmitting and receiving the laser signal. The ATM signal was attenuated, and data in part of the scan is missing as a result. The problem developed during the flight and worsened through time. The ATM still acquired more than half of the shots throughout the scan. The net effect of this problem is to decrease the number of shot returns logged, the same as if the laser power was reduced. To the user this will appear as a reduced point density on the ground. This issue will not affect the accuracy of the data. In the Antarctic 2010 campaign, fuel leakage degraded the signal in a similar fashion.
The April 28, 2012 flight traversed the notoriously turbulent regions of Greenland's southeast glaciers. During the flight, two planned glaciers were skipped due to concern about expected severe turbulence. The survey data spans roughly 11:15 to 18:20 UTC. On the approach to Ikerssuaq glacier at 16:56:19.5 (GPST=60994.5 secs), both the ATM T3 and T4 instruments quit recording data within 0.1 second of each other. T3 resumed at 16:57:05.3 whereas T4 did not resume for the rest of that day's flight. Following this event, the flight followed the Ikerssuaq flow line, then traversed straight west across the icesheet back to the Kangerlussuaq airport. The data gap spans 46 seconds, from the fjord up to about 500 m elevation on the Ikerssuaq glacier. The T4 data quit during the creation of the file
20120428_165532.ATM4BT4.F1.qi. The T4 data is being supplemented by the these narrow swath files of T3 data from the latter part of the survey:
The above files can be found with the IceBridge Narrow Swath ATM L1B Qfit Elevation and Return Strength 2012 Greenland data. For details on the ATM 4BT3 and 4BT4 instruments, see the Sensor Or Instrument Description section, and the IceBridge Narrow Swath ATM L1B Qfit Elevation and Return Strength data set documentation.
No data for 14 April 2015:
On 14 April 2015, the ATM wide-scan instrument suffered a failure in the scanning mechanism and did not collect data for that mission.
Fall 2015 Campaign
For the Fall 2015 ATM data, some ATM elevations are adjusted slightly (~10 cm) to compensate for a systematic anomaly related to the ATM scanner azimuth. The overall mean elevation is not changed, but some elevations around the scan are adjusted upward or downward as a function of scanner azimuth. For further details on the adjustment method, see Yi et al. 2015.
The ATM is an airborne LIDAR instrument used by NASA for observing the Earth's topography for several scientific applications, foremost of which is the measurement of changing Arctic and Antarctic icecaps, glaciers, and sea ice. The ATM instrument is a scanning airborne laser that measures surface elevation of the ground by timing laser pulses transmitted from the aircraft, reflected from the ground and returning to the aircraft. This laser pulse time-of-flight information is used to derive surface elevation measurements by combining measurement of the scan pointing angle, precise GPS trajectories and aircraft attitude information. The ATM measures topography as a sequence of points conically scanned in a swath along the aircraft flight track at rates up to 5000 measurements per second.
The ATM instruments are developed and maintained at NASA's Wallops Flight Facility (WFF) in Virginia, USA. During Operation IceBridge, the ATM has been installed aboard the NASA P3-B aircraft based at WFF, or the NASA DC8 aircraft based at NASA's Dryden Flight Research Center in Palmdale, California. During previous campaigns, the ATM has flown aboard other P-3 aircraft, several de Havilland Twin Otters (DHC-6), and a C-130. The ATM has been used for surveys flown in Greenland nearly every year since 1993. Other uses have included verification of satellite radar and laser altimeters, and measurement of sea-surface elevation and ocean wave characteristics. See also Pre-IceBridge ATM L2 Icessn Elevation, Slope, and Roughness. The ATM often flies in conjunction with a variety of other instruments and has been participating in NASA's Operation IceBridge since 2009.
The ATM project normally installs and operates two lidars on the aircraft platform. From 2009 to 2010, data were provided to NSIDC only from the ATM 4BT2 that collects wide scan lidar data. In 2011, a new ATM transceiver scanner assembly designated as ATM 4BT4 replaced the ATM 4BT2. The second lidar system on the aircraft, designated ATM 4CT3, was operated prior to 2011 as a backup to the ATM 4BT2 lidar instrument, or was modified to test alternate lidar system improvements. In 2011, ATM 4CT3 swath width was reduced. Data from the 4CT3, provided for sea ice missions only, are found in the IceBridge Narrow Swath ATM L1B Qfit Elevation and Return Strength data set.
Table 3 provides information on ATM transceivers used during IceBridge missions and the resultant filename designations.
|Year||Campaign||Wide ATM System*
(xx) = Full Scan Angle (degrees)
|Narrow ATM System*
(x) = Full Scan Angle (degrees)
|2010||Greenland (DC-8)||4CT3 (44)||n/a|
|2010||Greenland (P-3)||4BT2 (30)||n/a|
|2011||Greenland||4BT4 (30)||4CT3 (5)**|
|2011||Antarctica||4BT2 (30)||4CT3 (5)**|
|2012||Greenland||4BT4 (30)||4CT3 (5)**|
|2012||Antarctica||4BT4 (30)||4CT3 (5)**|
|2013||Greenland||4BT4 (30)||4CT3 (5)**|
|2014||Arctic||4BT4 (30)||4CT3/5AT3 (5)**|
|2014||Antarctic||5BT4 (30)||5AT3 (5)**|
|2015||Arctic||5AT3 (30)||5BT5 (5)|
|2015||Fall Arctic||5BT5 (5) ***||
* The ATM system designation is noted in the filename for each data file.
** Data are provided for sea ice missions only.
*** Transceiver is mounted with short axis across swath, ergo swath width is "full scan angle" divided by 1.4
2015 Arctic: narrow swath data was distributed for all missions due to mechanical problems & repair of wide scanner
2015 Fall Arctic: narrow angle scanner flown at high altitude, distributed as wide swath data.
2016 Summer Arctic- Barrow: narrow angle scanner flown at low altitude. Distribution forthcoming.
2016 Autumn Arctic-Greenland: narrow angle scanner flown at high altitude. Distribution forthcoming.
Note: Continuous Airborne Mapping By Optical Translator (CAMBOT) images and .cam files containing aircraft position and attitude data corresponding to the ATM data can be found in the IceBridge CAMBOT L1B Geolocated Images data set.
References and Related Publications
Contacts and Acknowledgments
Cryospheric Sciences Laboratory
NASA Goddard Space Flight Center
Greenbelt, Maryland USA
The ATM project team would like to acknowledge the dedicated flight crews, whose efforts allowed the safe and efficient collection of this data over some of the most isolated and extreme regions on this planet.
Document Creation Date
10 January 2011
Document Revision Date
06 April 2011
07 March 2011
14 July 2011
22 August 2012
08 May 2013
22 November 2013
09 June 2014
14 January 2015
06 July 2015
08 February 2016
08 June 2016
20 December 2016