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IceBridge Merged Photon Counting Lidar/Profiler L4 Surface Slope and Elevations, Version 1
This data set contains geolocated surface elevation measurements captured over Antarctica using the Sigma Space Mapping Photon Counting Lidar and Riegl Laser Altimeter. The data were collected by scientists working on the International Collaborative Exploration of the Cryosphere through Airborne Profiling (ICECAP) project, which was funded by the National Science Foundation (NSF), the Antarctic Climate and Ecosystems Collaborative Research Center, and the Natural Environment Research Council (NERC) with additional support from NASA Operation IceBridge.
|Temporal Resolution:||12 month|
|Sensor(s):||Sigma Space Lidar|
|Data Contributor(s):||Donald Blankenship, Scott Kempf, Duncan Young, Laura Lindzey|
|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.Blankenship, D. D., S. D. Kempf, D. A. Young, and L. E. Lindzey. 2014. IceBridge Merged Photon Counting Lidar/Profiler L4 Surface Slope and Elevations, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/STLZLZ7ZI7Z4. [Date Accessed].
Detailed Data Description
This data set consists of airborne photon counting lidar and laser altimetry observations. The following are the goals of this product:
- to provide an estimate of surface elevation along the aircraft ground track
- to provide estimates of local surface slopes
- to parameterize the quality of the Photon Counting Lidar data set.
Data files contain attributes for Elevation and Slope, and Photon Altimetry. Top level properties and attributes include file level metadata as well as campaign details.
The data files are Hierarchical Data Format (HDF5). Each data file is paired with an associated XML file. The XML files contain location, platform, and instrument metadata.
Data files are organized in folders by date in the https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/ILSNP4.001/ directory, for example /2012.12.04/.
The HDF5 files are named according to the following convention and as described in Table 1:
File name examples:
||Short name for IceBridge Merged Photon Counting Lidar/Profiler L4 Surface Slope and Elevations|
||Four-digit year of survey|
||Day of year of survey|
||Geographic area (Project)|
||Host platform for timing (System)|
||Transect name within Project|
||Granule within line|
||Indicates HDF5 file (.h5), or XML file (.xml)|
The data files range from approximately 218 KB to 11 MB.
The XML files range from approximately 10 KB to 41 KB.
The entire data set is approximately 540 MB.
The target region for this data is East Antarctica and the Antarctic Peninsula. Please see the metadata in the top level of each HDF5 data file for targets for each granule.
Southernmost Latitude: 90° S
Northernmost Latitude: 53° S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
10 meter spot on the ground at 800 meters.
Projection and Grid Description
Polar Stereographic true at −71 degrees latitude EPSG:3031
These data were collected from 25 November 2010 to the present as part of the ICECAP, ICEGRAV, NSF, NERC, and Operation IceBridge funded campaigns.
ICECAP campaigns were conducted on an annual basis. East Antarctic campaigns for this data set typically extend from November to early January.
Parameters are organized in the HDF5 files as Elevation and Slope attributes, and Photon Altimetry attributes. File level HDF5 attributes store metadata describing targets, collection parameters and details of funding and logistical support.
Elevation and Slope attributes are described in Table 2.
|DOY||Day Of Year of survey||Day|
|DScontinuous_time_of_day||Seconds since 2012-12-04 0:0:0||Seconds|
|DSdelta_time_start||Seconds since 2012-12-04T00:12:03||Seconds|
|YEAR||Year of survey||Year|
|latitude||Latitude of laser altimeter spot (WGS-84/ITRF08)||Degrees North|
|longitude||Longitude of laser altimeter spot (WGS-84/ITRF08)||Degrees East|
|mean_swath_surface_elevation||Mean nadir surface elevation of plane through all beams of the photon counting lidar swath (WGS-84/ITRF08)||Meters|
|point_surface_elevation||Surface elevation of laser altimeter spot (WGS-84/ITRF08)||Meters|
|point_swath_divergence_angle||Angular difference between normals of the swath best fit plane and the along track laser altimeter||Degrees|
|seconds_of_day||Seconds of day of survey||Seconds (UTC)|
|x_gradient||Gradient in x direction with respect to polar stereographic −71 projection (EPSG:3031)||dimensionless|
|y_gradient||Gradient in y direction with respect to polar stereographic −71 projection (EPSG:3031)||dimensionless|
Photon Altimetry includes information for BEAM0 through BEAM5. The exact location of the beams varies with scan pattern, but beam 0 and 1 are located along track, beam 2 and 3 are located at the edge of the scan pattern, and beams 4 and 5 are halfway between the edge and the flight track. Beam 0 was not used on data collected with a linear scan pattern. Please see granule metadata for specific details of beam layout and scan pattern used.
Photon Altimetry beam attributes are described in Table 3.
|DOY||Day Of Year of survey||Day|
|DScontinuous_time_of_day||Time since midnight of the first day of acquisition.||Seconds|
|DSdelta_time_start||Time since the start of the transect||Seconds|
|X_range_vector||Cross track component of detected surface spot with respect to the lidar body; positive is along right wing||Meters|
|YEAR||Year of survey||Year|
|Y_range_vector||Along track component of detected surface spot with respect to the lidar body; positive is toward nose||Meters|
|Z_range_vector||Along track component of detected surface spot with respect to the lidar body; positive is down||Meters|
|course_noise_rate||Number of photons in current beam in a 5 meter window 20 meters above surface over 0.25 second interval||Counts|
|latitude||Latitude of detected surface spot (WGS-84/ITRF08)||Degrees North|
|leading_quartile_range||Range between detected surface and the 25th percentile photon above the surface, from a total population from a 15 meter window around the surface||Meters|
|longitude||Longitude of detected surface spot (WGS-84/ITRF08)||Degrees East|
|peak_event_count_course||Number of photons in current beam in a 5 meter window around the surface counted over 0.25 second period||Counts|
|peak_event_count_fine||Number of photons in current beam in a 1 centimeter window around the surface counted over 0.25 second period||Counts|
|point_surface_elevation||Surface elevation of detected surface spot (WGS-84/ITRF08)||Meters|
|seconds_of_day||Seconds of day of survey||Seconds UTC|
Sample Data Record
point_surface_elevation values from a sample of the
ILSNP4_2012339_SCT_JKB2h_Y46b_000.h5 data file as displayed in the HDFView tool.
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. Version 1.8.5 of the HDF5 libraries was used.
HDFView: Visual tool for browsing and editing HDF4 and HDF5 files.
h5dump: Free standard UNIX command line tool to extract HDF5 content.
h5py: Free python module for interacting with HDF5 data. Depends on the SciPy/NumPy suite of Python Modules.
Matlab: The h5read command in recent versions of Mathworks Matlab can also access HDF5 variables.
For additional tools, see the HDF-EOS Tools and Information Center.
Data Acquisition and Processing
Data were acquired from an aircraft flown between 500 and 1500 meters above the ice sheet surface. A laser altimeter and a scanning photon counting lidar system collected range data, while IMU and GPS instruments were used to collect trajectory information.
Input products are:
- IceBridge GPS/IMU L1B Primary Position and Attitude Solution (IPUTG1B) trajectory data set
- IceBridge Sigma Space Photon Counting Lidar L1B Time-Tagged Nadir Photon Ranges (ILSNP1B) subset of the photon counting lidar data ranges
- IceBridge Riegl Laser Altimeter L2 Geolocated Surface Elevation Triplets (ILUTP2) geolocated surface elevation data from the Riegl laser profiler.
Please review descriptions of these data products for geolocation, initial filtering, and calibration methods.
In order to determine the surface location, the ranges are extracted from the beam's subset photon cloud. For each beam, a coarse histogram is built along the Z_range_vector of the lidar coordinate system with 5 meter bin resolution. The peak bin is selected as the coarse z distance.
In order to determine a more precise location, we return the median z distance of the photons in the maximum coarse bin and the two adjacent bins.
Using the known angles for this beam and the computed distance to the surface in the z direction, we calculate x distance and y distance in the lidar reference frame. We then rotate and translate the lidar range vector using the reported aircraft orientation using the estimated pointing biases and measured lever arm between the IPUTG1B coordinate system and the lidar.
This vector is then added to the aircraft trajectory to obtain the surface location in the WGS-84 reference frame. Statistics on the shape of the surface return peak and background noise character were also reported.
Trajectory and Attitude Data
Please see each granule's HDF5 attributes, and the IPUTG1B dataset for details of trajectory collection.
As absolute ranges for the lidar may have a bias due to uncertainties in the high resolution timing oscillator, the lidar data are integrated with simultaneously acquired laser profiler data.
The local surface slope was determined by fitting a plane to a 400 meter wide segment of the lidar surface elevation data, which was integrated with the laser altimetry ILSNP1B product, and provided the final surface elevation.
On 25 April, 2014, the the ILSNP4 HDF5 data replaced the ASCII data in the previous ILSNP2 data set. The data are newly processed as a Level-4 product. ILSNP4 includes a composite profiler-lidar product for altimetry and cross track slope. Vector rotations now occur in Earth Centered Earth Fixed space.
The lidar coarse clock used to calculate ranges has a temperature and acquisition card dependent uncertainty of 0.1 percent, which translates to a scaling error in range of ∼80 cm. For this reason, we use the ILUTP2 data to calibrate results in the Elevation and Slope part of the ILSNP4 dataset.
GPS relative errors are estimated by Waypoint to be typically 6 cm where a convergent combined GPS-IMU solution is produced, with orientation errors of 50 μrad.
For 2010-2011 data, GPS errors were higher (typically 10 cm) as the GPS data was not constrained by IMU data.
A simple, static 1-D atmospheric model is used to estimate delays due to propagation through air.
Instrumentation is comprised of the following components
Sigma Space Mapping Photon Counting Lidar system
- Lidar scan pattern: circular
- Lidar scan rate: 18 hertz
- Lidar shot rate: 20 kilohertz
- Lidar wavelength: 532 nanometers
As described on the University of Texas Institute for Geophysics Web site, the scanning photon counting lidar images the surface below the aircraft with one hundred laser beamlets which are mechanically scanned in a swath either side of the flight path. A one hundred channel photon counting receiver captures return photons and records time of flight and time tag data allowing a three dimensional reconstruction of the surface flown over. The system can make 2.2 million measurements per second. At the typical survey elevation of 800 meters above the ice sheet, the swath width is about 400 meters.
Reigl LD90-3800HiP-LR Distance Meter
Novatel SPAN OEM-4 GPS; iMAR FSAS IMU
References and Related Publications
Contacts and Acknowledgments
Donald D. Blankenship, Duncan A. Young, Laura E. Lindzey, and Scott D. Kempf
University of Texas at Austin
Institute for Geophysics
Austin, TX, 78759-8500
ICECAP/Operation Ice Bridge. See each granule HDF5 metadata for specific grants and logistical support.
Document Creation Date
24 April 2014