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This data set contains laser altimetry energy waveform measurements taken by NASA's Land, Vegetation, and Ice Sensor - Global Hawk (LVIS-GH) over areas including Greenland and Antarctica. The data were collected as part of NASA Operation IceBridge funded campaigns.
Data Set ID:
ILVGH1B
IceBridge LVIS-GH L1B Geolocated Return Energy Waveforms, Version 1
This is the most recent version of these data.
Version Summary:
Initial release
Overview
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Citing These Data
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. 2015. IceBridge LVIS-GH 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/D7ZJT02NGCC1. [Date Accessed].Documentation
Detailed Data Description
Format
The LVIS-GH Level-1B Geolocated Return Energy Waveforms 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 Naming Convention
LVIS-GH Level-1B Geolocated Return Energy Waveforms data files are named according to the following conventions and as described in Table 1:
ILVGH1B_GL2013_1030_R1405_058062.h5
ILVGH1B_GL2013_1030_R1405_058062.h5.xml
ILVGH1B_LOYYYY_MMDD_RYYMM_TTTTTT.xxx
Where:
| Variable | Description |
|---|---|
ILVGH1B |
Short name for IceBridge LVIS-GH 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 (MM), two-digit Day (DD) of campaign |
RYYMM |
Release year (YY) and month (MM) |
TTTTTT |
Number of seconds since UTC midnight of the day the data collection started |
xxx |
Indicates LVIS-GH Geolocated Waveform file type: HDF5 (.h5), or XML (.xml) |
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File Size
HDF5 data files range from approximately 100 MB to 1 GB.
XML files range from approximately 10 KB to 58 KB.
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Volume
Data volume for the full data set is approximately 315 GB.
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Spatial Coverage
Spatial coverage for the IceBridge LVIS-GH campaigns include 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 15 meters, but varies with aircraft altitude. Laser footprint size is a function of beam divergence and altitude. Footprint spacing is a function of laser pulse repetition rate, the instrument field of view, and measurement requirements.
Projection and Grid Description
International Terrestrial Reference Frame (ITRF 2000), WGS-84 Ellipsoid.
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Temporal Coverage
These data were collected from 30 October 2013 to 14 November 2013 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, May, September, October, and November. Antarctic campaigns are conducted during October and November.
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Parameter or Variable
The LVIS-GH Level-1B files include geolocated return energy waveforms.
Parameter Description
The LVIS-GH Level-1B HDF5 files are described in Table 2.
|
Group |
Parameter |
Bytes |
Type |
Description |
Units |
|---|---|---|---|---|---|
| /(root) | LVIS_LFID | 4 | Unsigned long integer | LVIS-GH 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. Together with LVIS_LFID provides a unique identifier to every LVIS-GH laser shot | 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 | Doublet | 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, calculated in-flight | Counts | |
| TXWAVE | 120 | Unsigned integer array | Transmitted waveform (120 samples) | Counts | |
| RXWAVE | 528 | Unsigned integer array | Received waveform (528 samples) | Counts | |
| /ancillary_data/ | HDF5 Version | Text | HDF version number | n/a | |
| Maximum Latitude | Text | Maximum value of latitude for this file | Degrees | ||
| Maximum Longitude | Text | Maximum value of longitude for this file | Degrees | ||
| Minimum Latitude | Text | Minimum value of latitude for this file | Degrees | ||
| Minimum Longitude | Text | Minimum value of longitude for this file | Degrees | ||
| Ancillary text | Text | Information about data set including platform, date collected, etc. | n/a | ||
| Reference_frame | Text | Information about reference frame used for this file | n/a |
Sample Data Record
Below is a graphed illustration of RANGE values in data file ILVGH1B_GL2013_1112_R1405_068936.h5.
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Data Access 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.
HDFView: Visual tool for browsing and editing HDF4 and HDF5 files.
Panoply netCDF, HDF and GRIB Data Viewer: Cross-platform application. Plots geo-gridded arrays from netCDF, HDF, and GRIB data sets.
For additional tools, see the HDF-EOS Tools and Information Center.
Also available: an IDL program that reads the LVIS-GH Level-1B data into an IDL structure: read_ilvis1b.pro.
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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. The laser returned waveform, digitally-recorded by the sensor, provides a record of the vertical interaction of the laser pulse with the reflecting surfaces in the footprint. Information extracted from the return waveform allows the precise location of the reflecting surfaces to be derived. Knowing the precise round-trip time it takes for the reflection to return yields the range to the target.
Figure 2 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. Mean noise level, provided with the Level-1B data product, provides the threshold relative to which the elevation products are later computed for the Level-2 data. 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.
Data Acquisition Methods
LVIS-GH employs three digitizers, disciplined with a single, 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-GH 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-GH Level-1B Geolocated Return Energy Waveforms Product is generated from the raw instrument data as described in the Processing Steps section. 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 Level-1B data.
- The GPS data are post-processed to generate the airplane trajectory. Precise Point Positioning (PPP) techniques are used. The trajectory is merged with the laser data to produce the latitude, longitude, and altitude of the airplane for each laser shot.
- 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.
- 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.
- Measurement model parameters are determined from airplane maneuvers performed during pre- and post-mission calibration flights and during science flights. Parameters include timing, rotational and translational offsets, for example, angular differences between the Inertial Measurement Unit (IMU) and laser pointing reference frames. The measurement model parameters are determined after flying the airplane through controlled maneuvers over a known, preferably flat, surface.
- The laser range measurement, laser pointing, and laser positioning information are combined using the measurement model parameters to calculate the location of two reference points in each laser return waveform (referred to as bin 0 and bin 528) relative to a global reference frame. This creates the geolocated Level-1B data product. Further details can be found in Hofton et al. 2000.
Version History
Beginning with the 2013 Arctic campaign, all Level-1B data are provided in HDF5 format.
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Sensor or Instrument Description
The Land, Vegetation, and Ice Sensor-Global Hawk (LVIS-GH) is an airborne LIDAR scanning laser altimeter developed by NASA for use in the Global Hawk Unmanned Aerial Vehicle (UAV) and available for install in other aircraft. This instrument is used primarily for collecting surface topography and 3D structure information. LVIS-GH uses a three digitizer system with a single 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-GH has scan angles of approximately 12 degrees, and can cover a 4 km swath from an altitude of 20 km. The nominal footprint size is 15 meters in diameter from an altitude of 20 km. In addition to waveform data, GPS satellite data is recorded at fixed ground locations and on the airborne platform to precisely reference aircraft position. An IMU is attached directly to the LVIS-GH instrument and provides information required for coordinate determination.
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References and Related Publications
Contacts and Acknowledgments
Contributor(s) / Investigator(s):
Bryan Blair
Laser Remote Sensing Laboratory, Code 694
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Michelle Hofton
Department of Geographical Sciences
2181 LeFrak Hall
University of Maryland
College Park, MD 20742
Acknowledgments:
This work was supported by NASA Headquarters. Development of the Global Hawk sensor was supported by American Recovery and Reinvestment Act (ARRA) funds and the NASA Earth Science Technology Office (ESTO).
Document Information
Document Creation Date
01 April 2015
