Data Set ID: 
ILVIS1B

IceBridge LVIS L1B Geolocated Return Energy Waveforms, Version 1

This data set contains return energy waveform data over Greenland and Antarctica, measured by the NASA Land, Vegetation, and Ice Sensor (LVIS), an airborne lidar scanning laser altimeter. The data were collected as part of Operation IceBridge funded campaigns.

There is a more recent version of these data.

Version Summary: 

Initial release

STANDARD Level of Service

Data: Data integrity and usability verified

Documentation: Key metadata and user guide available

User Support: Assistance with data access and usage; guidance on use of data in tools

See All Level of Service Details

Parameter(s):
  • TOPOGRAPHY > TERRAIN ELEVATION
Data Format(s):
  • Binary
Spatial Coverage:
N: 90, 
N: -53, 
S: 60, 
S: -90, 
E: 180, 
E: 180, 
W: -180
W: -180
Platform(s):AIRCRAFT, B-200, DC-8, G-V, HU-25C, P-3B, RQ-4
Spatial Resolution:
  • Varies x Varies
Sensor(s):ALTIMETERS, LASERS, LVIS
Temporal Coverage:
  • 14 April 2009 to 10 May 2012
(updated 2014)
Version(s):V1
Temporal ResolutionVariesMetadata XML:View Metadata Record
Data Contributor(s):J. Blair, Michelle Hofton

Geographic Coverage

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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.

Blair, J. B. and M. Hofton. 2011, updated 2014. IceBridge LVIS L1B Geolocated Return Energy Waveforms, 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/E50N2D14492H. [Date Accessed].

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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.

Detailed Data Description

Format

The LVIS Level-1B Geolocated Return Energy Waveforms data files are in big-endian binary format.

Version 2 ILVIS1B data: beginning with the 2013 Arctic campaign, all data are provided in HDF5 format. In the near future, all Version 1 data will be replaced with HDF5 data. For more on Version 2 ILVIS1B data see the Version 2 documentation.

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File and Directory Structure

Data files are available via HTTPS, https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/ILVIS1B.001/ in folders organized by date, for example /2012.05.10/. Each data file is paired with an associated XML file. The XML files contain location, platform, and instrument metadata.

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File Naming Convention

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

File name example:

ILVIS1B_GL2012_0505_R1210_063682.LGW4

ILVIS1B_GL2012_0505_R1210_063682.LGW4.xml

ILVIS1B_LOYYYY_MMDD_RYYMM_nnnnnn.xxx

Where:

Table 1. Binary File Naming Convention
Variable Description
ILVIS1B Short name for IceBridge LVIS L1B Geolocated Return Energy Waveforms data
LOYYYY Campaign identifier. LO = location, where GL = Greenland and AQ = Antarctica. YYYY= four-digit year of campaign.
MMDD Two digit month, two-digit day of campaign
RYYMM Date (YY year/ MM month) of the data release
nnnnnn Number of seconds since UTC midnight of the day the data collection started
.xxx Indicates file type: binary (.LGW4) or XML (.xml)
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File Size

Binary data files range from approximately 17 MB to 913 MB.

XML files range from approximately 9 KB to 88 KB.

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Volume

Data volume for the full data set is approximately 834 GB.

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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.

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Temporal Coverage

ILVIS1B Version 1 data were collected periodically from 14 April 2009 to 10 May 2012 as part of Operation IceBridge funded campaigns.

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.

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Parameter or Variable

The Version 1 LVIS Level-1B files include geolocated return energy waveforms. The LVIS Level-1B LGW4 files are described in Table 2.

Parameter Description

Table 2. LGW4 File Parameter Description
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

LGW4 binary data contain 1368 bytes per record.

Sample Data Record

Below are sample output records generated from 25 October 2009 data using the LVIS C reader. The 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. 
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.

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Software and Tools

Get Data

Version 1 binary data for 2012 and earlier campaigns are available via HTTPS.

IceBridge Portal: Tool to visualize, search, and download IceBridge data.

Version 2 HDF5 data beginning with the 2013 Arctic campaign are available via HTTPS.

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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. Note that the ASCII text results create very large output files.

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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.Caption

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.

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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.

Version 2 ILVIS1B data: beginning with the 2013 Arctic campaign, all data are provided in HDF5 format. In the near future, all Version 1 data will be replaced with HDF5 data. For more on Version 2 ILVIS1B data see the Version 2 documentation.

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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.

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References and Related Publications

Contacts and Acknowledgments

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

Acknowledgments: 

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

Document Information

Document Creation Date

09 July 2012

No technical references available for this data set.

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