Data Set ID:

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.

This is the most recent version of these data.

Version Summary:

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".

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

See All Level of Service Details

Data Format(s):
  • HDF5
Spatial Coverage:
N: 90, 
N: -53, 
S: 60, 
S: -90, 
E: 180, 
E: 180, 
W: -180
W: -180
Platform(s):C-130, DC-8, G-V, HU-25A, HU-25C, P-3B, WP-3D ORION
Spatial Resolution:
  • Varies x Varies
Temporal Coverage:
  • 20 March 2013 to 20 November 2019
(updated 2020)
Temporal ResolutionVariesMetadata XML:View Metadata Record
Data Contributor(s):Michael Studinger

Geographic Coverage

Other Access Options

Other Access Options


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. 2013, updated 2020. 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: [Date Accessed].

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Detailed Data Description


The data are provided in HDF5 format (.h5). 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 2. Each data file is paired with an associated XML file (.xml), which contains additional metadata.

Note: For sub-sampled ATM data, see the IceBridge ATM L2 Icessn Elevation, Slope, and Roughness data set.

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File Naming Convention

Example file names:


Files are named according to the following convention, which is described in Table 1:

Table 1. File Naming Convention
Variable Description
ILATM1B Data set ID
YYYYMMDD Year, month, and day of survey
HHMMSS Hours, minutes, and seconds (beginning of file time)
ATMNX Airborne Topographic Mapper instrument identification; e.g., atm4c, ATM4B, or ATM5A
Tn Identifier of transceiver used, affecting off-nadir scan angle: 
  • T2 = 15-degree
  • T3 = 23-degree
  • T4 = 30-degree
.xxx Indicates file type:
  • .h5 = HDF5 data file
  • .h5.xml = XML metadata file

Note: 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 roughly one 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.

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Spatial Coverage

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

Spatial Resolution

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° 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 website.

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Temporal Coverage

20 March 2013 to 20 November 2019

Temporal Resolution

IceBridge campaigns are conducted on an annually repeating basis. Arctic and Greenland campaigns are typically conducted during March, April, and May. Antarctic campaigns are typically conducted during October and November. Flights for the Alaska campaign were conducted from 13 to 21 July 2016.

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Parameter or Variable

This 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 of 3 or 5 kHz. When rounding to 0.001 seconds, three or five points will appear with the same time stamp.

HDF5 File Parameter Description

Parameters contained in the data files are described in Table 2.

Table 2. HDF Group and Contents Description





/(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
pitch Pitch angle Degrees
roll Roll angle Degrees
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.

sample data record

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Software and Tools

The data files can be opened by software that supports the HDF5 and/or netCDF format, such as HDFView and Panoply.

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Data Acquisition and Processing

Theory of Measurements

A laser altimeter measures the range from the instrument to a target by measuring the elapsed time between the emission of a laser pulse and the 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.

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Data Acquisition Methods

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 the 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 for 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.

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Derivation Techniques and Algorithms

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).

Processing Steps

The following processing steps are performed by the data provider.

  1. 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.
  2. Processing of GPS data into aircraft trajectory files using double-differenced dual-frequency carrier phase-tracking.
  3. Determination of all biases and offsets: heading, pitch, roll, ATM-GPS [x,y,z] offset, scanner angles, range bias.
  4. 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 History

  • Version 1: The data for 2009 through 2012 are stored in qfit format as ILATM1B Version 1.
  • Version 2: Beginning with the 2013 Arctic campaign, all data are provided in HDF5 format.
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Quality, Errors, and Limitations

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 flight on 28 April 2012 traversed the notoriously turbulent regions over 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. After this event, the flight followed the Ikerssuaq flow line, then traversed directly 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 are 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 ILNSA1B 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).

Fall 2016 Campaign:
On 07 November 2016, the ATM wide-scan lidar (ATM6aT6) suffered a laser system failure and did not collect any usable ILATM1B data for that flight. However, the ATM narrow-scan lidar (ATM5bT5) operated normally. Generally, data from the narrow-scan instrument are only provided for sea ice flights, where the smaller off-nadir angle is beneficial for lead detection. In this case however, ILNSA1B data were made available for the flight on 07 November 2016 as a substitute for the missing ILATM1B data.

Fall 2018 and Spring 2019 Campaigns (10/10/2018 to 05/16/2019):
As compared to most other Operation IceBridge ATM laser altimetry data sets, this particular data set has certain limitations in accuracy that result from a recently identified problem related to the application of the solid Earth tide correction in the data processing stage. This error can cause long-wavelength errors in elevations that are less than decimeter in magnitude and which vary in both space and time. The error wavelength is typically hundreds of kilometers, so it should not significantly affect most analyses of this data set, but it can be smaller because it depends on the number and position of base stations used for the trajectory solution and on other factors including moon phase. The error only affects the 2018 DC-8 Antarctic and 2019 P-3 Arctic Spring ATM data sets published at NSIDC DAAC. Resolution of this error is in progress, and a future version of this data set will eliminate it. The user should consider the elevation issue in any scientific interpretation or other use of the data set. Users are requested to report their findings about data quality to NSIDC User Services, to be forwarded to the ATM team, for information and comment before publication or reporting elsewhere.

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Sensor or Instrument Description

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 the Pre-IceBridge ATM L2 Icessn Elevation, Slope, and Roughness data set. 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 the NSIDC DAAC 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. More information on the ATM transceivers used during IceBridge missions and the associated filename designations can be found under Technical References in the List of ATM Transceivers Used During IceBridge Missions.

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Contacts and Acknowledgments

Michael Studinger
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 Information


February 2017


August 2020

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