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Data Set ID:
ILSIG1B

IceBridge Photon Counting Lidar L1B Unclassified Geolocated Photon Elevations, Version 1

This data set contains geolocated photon elevations captured over Antarctica using the Sigma Space photon counting lidar. 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.

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Geographic Coverage

Parameter(s):
  • Glaciers/Ice Sheets > Glacier Topography/Ice Sheet Topography
Spatial Coverage:
  • N: -53, S: -90, E: 180, W: -180

Spatial Resolution:
  • 10 cm x 10 cm
Temporal Coverage:
  • 29 November 2011 to 23 December 2011
Temporal Resolution: Varies
Data Format(s):
  • HDF
  • XML
Platform(s) BT-67
Sensor(s): Sigma Space Lidar
Version: V1
Data Contributor(s): Donald Blankenship, Scott Kempf, Duncan Young, Laura Lindzey

Data Citation

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. 2015. IceBridge Photon Counting Lidar L1B Unclassified Geolocated Photon Elevations, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/U3E4Q5WWVSP9. [Date Accessed].

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Detailed Data Description

Format

The data files are in HDF5 format. Each data file is paired with an associated XML file. The XML files contain location, platform, and instrument metadata.

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File and Directory Structure

Data are available on the following HTTPS site:

https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/ILSIG1B.001/

Within this directory, folders are organized by date, for example /2011.11.29/ to /2011.12.23/. Folders contain HDF5 (.h5) and XML (.xml) files.

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File Naming Convention

The files are named according to the following convention and as described in Table 1:

ILSIG1B_2011333_ICP4_JKB2e_F09T03a_001.h5

ILSIG1B_2011333_ICP4_JKB2e_F09T03a_001.h5.xml

ILSIG1B_YYYYDOY_PPPP_JKB2h_TTTT_xxx.h5

Where:

Table 1. Naming Convention
Variable Description
ILSIG1B Short name for IceBridge Photon Counting Lidar L1B Unclassified Geolocated Photon Elevations
YYYY Four-digit year of survey
DOY Day of year of survey
PPPP Geographic area (Project)
JKB2h Host platform for timing (System)
TTTT Transect name within Project
xxx Granule within line
.h5 Indicates HDF5 file
.h5.xml Indicates XML metadata file
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File Size

The HDF5 data files range from approximately 139 MB to 207 MB.

The XML data files range from approximately 4 KB to 12 KB.

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Volume

The entire data set is approximately 890 GB.

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Spatial Coverage

The target region for this data is East Antarctica, Greenland, and the Antarctic Peninsula. Please see HDF5 metadata for targets for each granule.

Greenland:
Southernmost Latitude 59° N
Northernmost Latitude: 83° N
Westernmost Longitude: 74° W
Easternmost Longitude: 12° W

Antarctica:
Southernmost Latitude: 90° S
Northernmost Latitude: 53° S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E

Spatial Resolution

10 centimeter spot on the ground at 800 meters (per photon).

Projection and Grid Description

Polar Stereographic at −71 degrees latitude EPSG:3031

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Temporal Coverage

These data were collected as part of ICECAP, NSF, NERC, and Operation IceBridge funded campaigns from 29 November 2011 to 23 December 2011.

Temporal Resolution

ICECAP campaigns were conducted on an annual basis. East Antarctic campaigns for this data set typically extend from November to early January.

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Parameter or Variable

Parameter Description

Parameters in the HDF5 files are organized as photon data, granule georeferencing data, and transect georeferencing data attributes. In addition, top level attributes store metadata describing platform, beam location on scan, and additional campaign information.

Photon data attributes for described in Table 2.

Table 2. Photon Data Attributes
Parameter Description Units
DOY Day Of Year of survey Day
DScontinuous_time_of_day Seconds since 2011-11-29 0:0:0 Seconds
DSdelta_time_start Seconds since 2011-11-29T02:03:54 Seconds
Easting Apparent projected Easting of photon (WGS-84/ITRF08/EPSG:3031) Meters
Elevation Apparent elevation of photon (WGS-84/ITRF08) Meters
Northing Apparent projected northing of photon (WGS-84/ITRF08/EPSG:3031) Meters
X_range_vector Cross track component of detected surface spot with respect to the lidar body; positive is along right wing Meters
YEAR Current year (UTC) (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
cell Numbered counting channel on detector array Count
seconds_of_day Seconds of current day (UTC) (on day of survey) Seconds

Granule and transect georeferencing data attributes are described in Table 3.

Table 3. Granule and Transect Georeferencing Data Attributes
Parameter Description Units
DOY Day Of Year of survey Day
DScontinuous_time_of_day Seconds since 2011-11-29 0:0:0 Seconds
DSdelta_time_start Seconds since 2011-11-29T02:03:54 Seconds
EW_acceleration East-West acceleration of the aircraft Milligal
NS_acceleration North-South acceleration of the aircraft Milligal
YEAR Current year (UTC) (Year of survey) Year
aircraft_elevation Elevation of center of gravity GNSS antenna, as determined by real time kalman filter (WGS-84/ITRF08) Meters
heading_angle Rotation around aircraft Z axis (with respect to true north, clockwise is positive) Degrees
latitude Latitude of laser altimeter spot (WGS-84/ITRF08) Degrees North
longitude Longitude of laser altimeter spot (WGS-84/ITRF08) Degrees East
pitch_angle Rotation around aircraft Y axis (with respect to local geodetic vertical, nose up is positive, zero is aircraft level) Degrees
position_error The geometric sum of the expected horizontal and vertical position errors derived by taking the square root of the corresponding Kalman filter variances Degrees
roll_angle Rotation around aircraft X axis (with respect to local geodetic vertical, right wing up is positive, zero is wings level) Meters
seconds_of_day Seconds of current day Seconds (UTC)
vertical_acceleration Vertical acceleration of the aircraft Milligal

Sample Data Record

Below are Elevation values from a sample of the ILSIG1B_2011333_ICP4_JKB2e_F09T03a_001.h5 data file as displayed in the HDFView tool.

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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.

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Data Acquisition and Processing

Theory of Measurements

The concept of a Photon Counting Lidar (PCL) is described in Degnan, 2002. While the fundamental principles are similar to that of a traditional laser ranging system, a PCL relies on very fast pulse rates and statistical integration to allow detection of lower energy returns, which results in substantial reduction in power, mass, and optical structure requirements. The scanning PCL system (Degnan et al., 2007) from which the PCL was derived was originally developed as an outer-planets exploration test bed, then adapted for deployment on unmanned airborne vehicles.

The ability to field a light weight instrument with multiple lidar beams was a fundamental driver of the decision to use a photon counting system (the Advanced Topographic Laser Altimeter System, ATLAS) on ICESat-2 (Yu, 2010). The PCL system differs from NASA's Multiple Altimeter Beam Experimental Lidar or MABEL (Brunt et al., 2010), in that the PCL is typically flown at much lower heights (800 meters versus 20,000 m), has more cells (up to 100 versus 16), and actively scans versus having fixed discrete beams.

Unlike the complementary IceBridge Photon Counting Lidar L1B Subset Geolocated Photon Elevations (ILSNP1B) data set, the IceBridge Photon Counting Lidar L1B Unclassified Geolocated Photon Elevations (ILSIG1B) data set is not spatially filtered.

Refer to Figure 1 for locations of geolocated PCL surface recoveries in the Indo-Pacific sector of East Antarctica. Background is bed elevations showing major subglacial basins (Fretwell et al, 2013).

Figure 1: Locations of geolocated PCL surface recoveries in the Indo-Pacific sector of East Antarctica.
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Data Acquisition Methods

The ICECAP geophysical system was installed on the aircraft at the McMurdo seasonal sea ice runway at the start of each field season. Installation is followed by a calibration flight involving multiple crossovers over flat ice. On typical data-collection flights, the aircraft is flown 600 m to 1000 m above the ground, at a ground speed of 90 m sec-1.

A range gate is applied to limit incoming photons on the PCL. This is adjusted to match the aircraft's height above ice, and was typically 1000 m tall, centered at a distance of 1000 m. Approximately 100 GB of range data are acquired per six hour flight.

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Derivation Techniques and Algorithms

After the trajectory is obtained, for each time step the position and orientation in Earth Centered Earth Fixed space is found, and matrix translations are performed for the sensor lever arm and range vector, following Vaughn et al. (1996) and Koks (2006). The data are then transformed back to the WGS-84 ellipsoidal reference frame.

Pointing biases are determined using an iterative minimization of crossover errors during the creation of the IceBridge Merged Photon Counting Lidar/Profiler L4 Surface Slope and Elevations (ILSNP4) data set. See Table 4.

Table 4. Pointing Biases
Season Date Roll Bias Pitch Bias Crossings Error (cm) Target
ICP3 December 18, 2010 0.325° (−0.2 25°) −4.525° (−0.525°) 107 (1976) 10.7 (37) Law Dome
ICP4 December 23, 2011 0.370° (0.150°) −4.200° (0.075°) 62 (443) 6.0 (16.9) McMurdo Ice Shelf
ICP5 November 13, 2012 0.475° (0.175°) −3.450° (0.025°) 96 (968) 12.5 (23.4) Ross Ice Shelf

Trajectory and Attitude Data

Please see each granule's HDF5 attributes, and the IPUTG1B data set for details of trajectory collection.

Error Sources

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 2010-11 data, GPS errors were higher (typically 10 cm) as the GPS data was not constrained by IMU data.

We used a simple, static 1-D atmospheric model to estimate delays due to propagation through air.

Ranges for the lidar may have a bias due to uncertainties in the high resolution timing oscillator. However, for the 2011-12 data set, we confirmed that offsets between simultaneously acquired IceBridge Riegl Laser Altimeter L2 Geolocated Surface Elevation Triplets (ILUTP2) data and this data were minimal.

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Sensor or Instrument Description

In the Photon Counting Lidar (PCL) system a 532 nm laser beam, pulsed at ~19 kHz, is split into a 10 x 10 grid of beamlets and projected through a Risley prism beam steering unit, with time of the outgoing pulse recorded as the pulse start. The angular spread of the beamlets is 0.12° along each side of the grid yielding an illuminated grid on the ground of about 1-2 meters for every shot.

For the 2010-11 season, two prisms were used to generate a 45 degrees linear scan pattern, with a maximum deflection from nadir of 14.9 degrees. During the 2011 and 2012 seasons only one prism was used, which resulted in a reduced circular scan pattern with 7.3 degrees deflection from nadir. The beam steering unit is synchronized to the laser, such that one cycle of the beam steering unit corresponds to 1024 shots after the system has spun up after starting; thus the system scans underlying terrain at 18.5 Hz. Return photons are received through the same optics and directed to a 10 x 10 cell anode microchannel plate photomultiplier. Timing of the returns is split 50/50 between two independent Field-Programmable Gate Arrays (FPGAs).

Each cell has a coarse, 16 bit approximately 295 Hz clock (range resolution ~0.5 meters) and a fine 8 bit ~12.5 GHz clock (range resolution ~1.2 cm), calibrated per shot that allows ~0.1 nsec precision for detection times (stops). The differences between the starts and stops is the time of flight, which multiplied by an appropriate velocity of light provides the apparent range to the photon source. The coarse clock rate can drift due to temperature and hardware issues by up to 0.01 percent, limiting absolute accuracy to 80 cm without registration to the LAS.

The 0.7 nsec pulse width limits the precision of start times, yielding a minimum range precision per-photon of ~10.5 cm. Systematic biases between individual cells are estimated to be symmetrically distributed with a root mean squared (RMS) deviation of 15 cm. Higher precision requires stacking numerous individual shots.

Time stamps are generated with every shot, every prism rotation, and on reception of a 1 Hz GPS generated pulse from timing calibration. The timing data from each FPGA is recorded directly to independent hard drives, typically at 4-5 MB sec-1. In post-processing, these time stamps allow each photon's time-of-flight to be converted into an X, Y, and Z location relative to the sensor.

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References and Related Publications

Contacts and Acknowledgments

Donald D. Blankenship, Duncan A. Young, Laura E. Lindzey, Scott D. Kempf
University of Texas at Austin
Institute for Geophysics
Austin, TX, 78759-8500

Acknowledgments: 

ICECAP/Operation Ice Bridge. See each granule HDF5 metadata for specific grants and logistical support.

Document Information

Document Creation Date

10 June 2015

No technical references available for this data set.
No FAQs or How Tos available for this data set.

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