Close

Service Interruption

IceBridge LVIS L1B Geolocated Return Energy Waveforms

This data set contains laser altimetry return energy waveform measurements taken from NASA's Land, Vegetation, and Ice Sensor (LVIS) over areas including Greenland and Antarctica. The data were collected as part of Operation IceBridge funded campaigns.

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.

Table of Contents

  1. Contacts and Acknowledgments
  2. Detailed Data Description
  3. Data Access and Tools
  4. Data Acquisition and Processing
  5. References and Related Publications
  6. Document Information

Citing These Data

The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.

Blair, Bryan, and Michelle Hofton. 2011, updated 2012. IceBridge LVIS L1B Geolocated Return Energy Waveforms, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://nsidc.org/data/ilvis1b.html.

Overview

Platform

NASA DC-8
NASA P-3B
NASA HU-25C Falcon Jet
NSF/NCAR G-V
NASA LARC King Air B-200

Sensor

Land, Vegetation, and Ice Sensor (LVIS)

Spatial Coverage

Greenland, Antarctica

Spatial Resolution

Nominally 20 meters

Temporal Coverage

Periodic, ongoing, from 14 April 2009 to the present.

Temporal Resolution

Seasonal

Parameters

Geolocated return energy waveforms
Most files also include the transmitted energy waveform.

Data Format

Big-endian binary

Metadata Access

View Metadata Record

Data Access

FTP

1. Contacts and Acknowledgments

Investigator(s) Name and Title

Bryan Blair
Laser Remote Sensing Laboratory, Code 694
NASA Goddard Space Flight Center
Greenbelt, MD 20771

Michelle Hofton
Department of Geography
2181 LeFrak Hall
University of Maryland
College Park, MD 20742

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

Acknowledgements

This work was supported by NASA Grant Number NNX11AH69G, LVIS: A Topographic Mapping Capability for IceBridge.

2. Detailed Data Description

Format

The LVIS Level-1B Geolocated Return Energy Waveforms data files are in big-endian binary format. Most files are in format version 1.04 (.LGW4 files). Some older files are in format version 1.02 (.lgw2 files) or 1.03 (.lgw3 files).

File and Directory Structure

Data files are organized on the FTP site, ftp://n4ftl01u.ecs.nasa.gov/SAN2/ICEBRIDGE_FTP/, as described in Figure 1.

directory structure

Figure 1. Directory Structure

File Naming Convention

LVIS Level-1B Geolocated Return Energy Waveforms binary files are named according to the following convention and as described in Table 2.

File name example: LVIS_GL2011_MJD55666_LEVEL1B_20110915_A.LGW4

LVIS_LOYYYY_MJDnnnnn_LEVEL1B_YYYYMMDD_a.LGW4

Where:

Table 2. Binary File Naming Convention
Variable Description
LVIS Instrument: Land, Vegetation, and Ice Sensor
LOYYYY Campaign identifier. LO = location, where GL = Greenland and ANT = Antarctica. YYYY= four-digit year of campaign.
MJDnnnnn Modified Julian Date of data collection = nnnnn
LEVEL1B Data processing Level-1B
YYYY Four-digit data release year
MM Two-digit data release month
DD Two-digit data release day
A Alphabetical indicator of sub-files (A, B, C, ... S). Data files larger than 2 GB are divided into sub-files according to system requirements.
.lgw2, .lgw3, or .LGW4 Indicates LVIS Geolocated Waveform file version.
lgw2 = version 1.02. lgw3 = version 1.03. LGW4 = version 1.04.
Described in Tables 3, 4 and 5.

File Size

Data files range from approximately 37 MB to 1.9 GB.

Volume

Data volume for the full data set is approximately 797 GB.

Spatial Coverage

Spatial coverage for the IceBridge LVIS 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

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

Spatial Resolution

Spatial resolution is nominally 20 meters, but varies with aircraft altitude. Laser spot size is a function of beam divergence and altitude. Nominal spot spacing is a function of scan rate and pulse repetition rate.

Projection and Grid Description

International Terrestrial Reference Frame (ITRF 2000), WGS-84 Ellipsoid.

Temporal Coverage

These data were collected as part of Operation IceBridge funded campaigns from 14 April 2009 to the present.

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.

Parameter or Variable

The LVIS Level-1B files include geolocated return energy waveforms. The three versions of the binary file structure are described in Tables 3, 4, and 5. Note that two of the three format versions include the transmitted waveform as well. The LVIS C reader is provided to read any of these binary files and produce ASCII text output.

Parameter Description

The LVIS Level-1B LGW2 files are described in Table 3.

Table 3. Version 1.02 Parameter Description (LGW2 files)
Parameter Bytes Type Description Units
LVIS_LFID 4 Unsigned long integer LVIS file identification, including date and time of collection and file number. The third through seventh values in first field represent the Modified Julian Date of data collection. n/a
SHOTNUMBER 4 Unsigned long integer Laser shot assigned during collection n/a
TIME 8 Double UTC decimal seconds of the day Seconds
LON_0 8 Double Longitude of the highest sample in the waveform Degrees east
LAT_0 8 Double Latitude of the highest sample in the waveform Degrees north
Z_0 4 Float Elevation of the highest sample in the waveform Meters
LON_431 8 Double Longitude of the lowest sample in the waveform Degrees east
LAT_431 8 Double Latitude of the lowest sample in the waveform Degrees north
Z_431 4 Float Elevation of the lowest sample in the waveform Meters
SIGMEAN 4 Float Signal mean noise level Counts
WAVE 432 Byte array Return waveform (432 samples, 1 byte per sample) Counts

Version 1.02 binary data contain 492 bytes per record.

The LVIS Level-1B LGW3 files are described in Table 4.

Table 4. Version 1.03 Parameter Description (LGW3 files)
Parameter Bytes Type Description Units
LVIS_LFID 4 Unsigned long integer LVIS file identification, including date and time of collection and file number. The third through seventh values in first field represent the Modified Julian Date of data collection. n/a
SHOTNUMBER 4 Unsigned long integer Laser shot assigned during collection n/a
AZIMUTH 4 Float Azimuth angle of laser beam Degrees
INCIDENTANGLE 4 Float Off-nadir angle of laser beam Degrees
RANGE 4 Float Along-laser-beam distance from the instrument to the ground Meters
TIME 8 Double UTC decimal seconds of the day Seconds
LON_0 8 Double Longitude of the highest sample in the waveform Degrees east
LAT_0 8 Double Latitude of the highest sample in the waveform Degrees north
Z_0 4 Float Elevation of the highest sample in the waveform Meters
LON_527 8 Double Longitude of the lowest sample in the waveform Degrees east
LAT_527 8 Double Latitude of the lowest sample in the waveform Degrees north
Z_527 4 Float Elevation of the lowest sample in the waveform Meters
SIGMEAN 4 Float Signal mean noise level Counts
TXWAVE 80 Byte array Transmitted waveform (80 samples, 1 byte per sample) Counts
RXWAVE 432 Byte array Received waveform (432 samples, 1 byte per sample) Counts

Version 1.03 binary data contain 584 bytes per record.

The LVIS Level-1B LGW4 files are described in Table 5.

Table 5. Version 1.04 Parameter Description (LGW4 files)
Parameter Bytes Type Description Units
LVIS_LFID 4 Unsigned long integer LVIS file identification, including date and time of collection and file number. The third through seventh values in first field represent the Modified Julian Date of data collection. n/a
SHOTNUMBER 4 Unsigned long integer Laser shot assigned during collection n/a
AZIMUTH 4 Float Azimuth angle of laser beam Degrees
INCIDENTANGLE 4 Float Off-nadir angle of laser beam Degrees
RANGE 4 Float Along-laser-beam distance from the instrument to the ground Meters
TIME 8 Double UTC decimal seconds of the day Seconds
LON_0 8 Double Longitude of the highest sample in the waveform Degrees east
LAT_0 8 Double Latitude of the highest sample in the waveform Degrees north
Z_0 4 Float Elevation of the highest sample in the waveform Meters
LON_527 8 Double Longitude of the lowest sample in the waveform Degrees east
LAT_527 8 Double Latitude of the lowest sample in the waveform Degrees north
Z_527 4 Float Elevation of the lowest sample in the waveform Meters
SIGMEAN 4 Float Signal mean noise level Counts
TXWAVE 2 x 120 Unsigned integer array Transmitted waveform (120 samples, 2 bytes per sample) Counts
RXWAVE 2 x 528 Unsigned integer array Received waveform (528 samples, 2 bytes per sample) Counts

Version 1.04 binary data contain 1368 bytes per record.

Sample Data Record

Below are example output records from the different input formats. For version 1.02 data, the LVIS C reader generates one ASCII text output record for every input record. The output record generated from the first 492-byte binary record in the v1.02 file LVIS_PIG_2009_MJD55124_VECT_20100929.lgw2, is:

For versions 1.03 and 1.04 data, the LVIS C reader creates two output records for every one input record. The first output record contains all data parameters except the received waveform, and the second output record contains the received waveform. The difference between the 1.03 and 1.04 formats is in the number of samples in the transmitted and received waveforms. Below are the two output records generated from the first 1368-byte binary record in the v1.04 file LVIS_ANT2009_MJD55129_LEVEL1B_20120118_D.LGW4. The first output record is:
The second output record is:

Note that the output file size is very large. For the above example, the binary input file is 1.9 gigabytes and the ASCII text output file is 4.75 gigabytes.

3. Data Access and Tools

Data Access

Data are available via FTP.

Software and Tools

NSIDC provides an LVIS C reader that reads a binary data file from the Operation IceBridge LVIS instrument and prints the records to standard output. Version 1.04 of the LVIS C reader should be used to read the older LGW2 and LGW3 binary data files and the newer LGW4 binary data files. Note that the ASCII text results create very large output files.

4. Data Acquisition and Processing

As described on the NASA LVIS Web site, a laser altimeter is an instrument that measures range from the instrument to a target object or surface. The device sends a laser beam toward the target, and measures the time it takes for the signal to reflect back from the surface. Knowing the precise round-trip time it takes for the reflection to return yields the range to the target.

Figure 1 shows two examples of return energy waveforms. A simple waveform occurs where the ice surface is relatively smooth within the footprint of the laser pulse (approximately 20 meters in diameter). Mean noise level, provided with the Level-1B data product, provides the threshold relative to which the centroid and all modes are later computed for the Level-2 data product. A complex waveform might be returned from a rougher ice surface and could contain more than one mode, originating from different reflecting surfaces within the laser footprint such as crevasse sides and bottom, open water, large snowdrifts, and other steep or multiple slopes. A complex waveform would be more typically returned from multilevel vegetation landcover such as a forest.

Figure 1. Sample Level-1B product waveforms illustrating some possible distributions of reflected light.

Data Acquisition Methods

LVIS employs a signal digitizer, disciplined with a very precise oscillator, to measure both the transmitted and reflected laser pulse energies versus time. These digitized and captured photon histories are known as waveforms. For the outgoing pulse, it represents the profile of the individual laser shot, and for the return pulse it records the interaction of that transmitted pulse with the target surface.

Processing of these waveforms yields many products, but the primary is range from the instrument to the Earth's surface and the distribution of reflecting surfaces within the area of the laser footprint. For vegetated terrain these surfaces are tree canopies, branches, other forms of vegetation, and open ground. For cryospheric data these surfaces are snow, ice, crevasses, snowdrifts, sea ice possibly interspersed with open ocean, exposed rock, and water.

LVIS uses a waveform-based measurement technique to collect data instead of just timing detected returns of the laser pulse. The return signal is sampled rapidly, and stored completely for each laser shot. Retaining all waveform information allows post processing of the data to extract many different products. With the entire vertical extent of surface features recorded, metrics can be extracted about the sampled area. An advantage of saving all of the waveform data is that new techniques can be applied to these data long after collection to extract even more information. See the NASA LVIS Web site.

Derivation Techniques and Algorithms

The LVIS Level-1B Geolocated Return Energy Waveforms Product is generated from the raw instrument data as described under Processing Steps. More details can be found in (Hofton et al. 2000).

Processing Steps

The following processing steps are performed by the data provider to produce the binary format Level-1B data.

  1. The differential kinematic GPS data are post-processed to generate the airplane trajectory. The trajectory is merged with the laser data to produce the latitude, longitude, and altitude of the airplane for each laser shot.
  2. An atmospheric correction is applied to each laser measurement. This adjustment is necessary due to effects of temperature and pressure on the speed of light through the atmosphere. It is computed using a model, and data extrapolated from the nearest meteorological station.
  3. Laser pulse timing errors, due to the internal system response time and further affected by the amplitude of the return, are determined by calibration experiments. These are performed at the beginning and end of each flight. Each range measurement is corrected accordingly.
  4. The attitude (roll, pitch, and yaw) of the airplane is recorded by the Inertial Navigation System (INS), and is interpolated for the time of each laser shot to know the precise pointing.
  5. Several instrument biases are determined next. Timing biases are due to the delay between the actual observation of aircraft attitude and the recording of those data in the computer following the calculations. Laser mounting biases come from slight angular differences between the orientations of the three axes of the INS and those of the airplane. The timing and angle biases are determined after flying the airplane through controlled roll and pitch maneuvers over a known, preferably flat, surface.
  6. The offset between the GPS antenna and the laser scan mirror must be known in order to relate the airplane trajectory and the range measurement. The offset vector is found by performing a static GPS survey between several system components inside and outside the grounded airplane.
  7. The laser range measurement is transformed from a local reference system within the airplane to a global reference frame and ellipsoid. This creates the geolocated data product.

Version History

On November 20 2012, the 2011 Antarctica LVIS Level 1B data were replaced with V01.1. The LVIS transmit laser waveform is improved in the 2011 Antarctica data.

Sensor or Instrument Description

As described on the NASA LVIS Web site the Land, Vegetation, and Ice Sensor (LVIS) is an airborne LIDAR scanning laser altimeter used by NASA for collecting surface topography and vegetation coverage data. LVIS uses a signal digitizer with oscillator to measure transmitted and reflected laser pulse energies versus time capturing photon histories as waveforms. The laser beam and telescope field of view scan a raster pattern along the surface perpendicular to aircraft heading as the aircraft travels over a target area. LVIS has a scan angle of approximately 12 degrees, and can cover 2 km swaths from an altitude of 10 km. Typical collection size is 10 to 25 meter spots. In addition to waveform data, GPS satellite data is recorded at ground tie locations and on the airborne platform to precisely reference aircraft position. An Inertial Measurement Unit (IMU) is attached directly to the LVIS instrument and provides information required for coordinate determination.

5. References and Related Publications

Blair, J. B., D. L. Rabine., and M. A. Hofton. 1999. The Laser Vegetation Imaging Sensor: A Medium-Altitude, Digitisation-Only, Airborne Laser Altimeter for Mapping Vegetation and Topography, ISPRS Journal of Photogrammetry and Remote Sensing, 54: 115-122.

Hofton, M. A., J. B. Blair, J. B. Minster., J. R. Ridgway, N. P. Williams, J. L Bufton, and D. L. Rabine. 2000. An Airborne Scanning Laser Altimetry Survey of Long Valley, California, International Journal of Remote Sensing, 21(12): 2413-2437.

Hofton, M. A., J. B. Blair, S. B. Luthcke, and D. L. Rabine. 2008. Assessing the Performance of 20-25 m Footprint Waveform Lidar Data Collected in ICESat Data Corridors in Greenland, Geophysical Research Letters, 35: L24501, doi:10.1029/2008GL035774.

Related Data Collections

Related Web Sites

  • LVIS Web site at NASA Goddard Space Flight Center (http://lvis.gsfc.nasa.gov).
  • IceBridge Data Web site at NSIDC (http://nsidc.org/data/icebridge/index.html).
  • IceBridge Web site at NASA (http://www.nasa.gov/mission_pages/icebridge/index.html).
  • ICESat/GLAS Web site at NASA Wallops Flight Facility (http://glas.wff.nasa.gov/).
  • ICESat/GLAS Web site at NSIDC (http://nsidc.org/daac/projects/lidar/glas.html).

6. Document Information

Acronyms and Abbreviations

The acronyms used in this document are listed in Table 6.

Table 6. Acronyms and Abbreviations
Acronym Description
ASCII American Standard Code for Information Interchange
CIRES Cooperative Institute for Research in Environmental Science
ECS NASA Earth Observing System Data and Information System (EOSDIS) Core System
FTP File Transfer Protocol
GPS Global Positioning System
IMU Inertial Measurement Unit
INS Inertial Navigation System
ITRF International Terrestrial Reference Frame
Level-1B Level 1B processing
Level-2 Level 2 processing
LFID LVIS File ID
LIDAR LIght Detection And Ranging
LVIS Land, Vegetation, and Ice Sensor
NASA National Aeronautics and Space Administration
NSIDC National Snow and Ice Data Center
URL Uniform Resource Locator
WGS 84 World Geodetic System 1984

Document Creation Date

09 July 2012

Document Revision Date

Document URL

http://nsidc.org/data/docs/daac/icebridge/ilvis1b/index.html