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IceBridge LVIS L1B Geolocated Return Energy Waveforms, Version 2
The IceBridge LVIS L1B Geolocated Return Energy Waveforms (ILVIS1B) data set contains Greenland and Antarctica laser altimetry return energy waveform measurements taken from the NASA Land, Vegetation, and Ice Sensor (LVIS). The data were collected as part of Operation IceBridge funded campaigns.
- Version 2 data are HDF5 format beginning with the 2013 Arctic campaign.
- Version 1 data are binary format for 2012 and earlier campaigns.
|Platform(s)||AIRCRAFT, B-200, DC-8, G-V, HU-25C, P-3B, RQ-4|
|Sensor(s):||ALTIMETERS, LASERS, LVIS|
|Data Contributor(s):||J. Blair, Michelle Hofton|
|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.Blair, J. B. and M. Hofton. 2014, updated 2016. IceBridge LVIS L1B Geolocated Return Energy Waveforms, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/RDT1MZVS0VG9. [Date Accessed].
Detailed Data Description
The Version 2 LVIS Level-1B Geolocated Return Energy Waveforms data files are in HDF5 format.
Note: Currently ILVIS1B data for 2009 through 2012 are in binary format stored separately as ILVIS1B Version 1. Beginning with the 2013 Arctic campaign, all data are provided in HDF5 format. In the near future, data from all campaigns prior to 2013 will be replaced with HDF5 data and added to Version 2. For details on the Version 1 data, see the V1 documentation.
The Version 2 files are organized on the FTP site,
ftp://n5eil01u.ecs.nsidc.org/SAN2/ICEBRIDGE/ILVIS1B.002/, organized in folders by date, such as
2014 ARISE campaign data are included in dates from 02 September 2014 through 02 October 2014, that is, folder names 2014.09.06 through 2014.10.02.
LVIS Version 2 Level-1B Geolocated Return Energy Waveforms data fles are named according to the following conventions and as described in Table 1:
||Short name for IceBridge LVIS L1B Geolocated Return Energy Waveforms data|
||Campaign identifier. LO = location, where GL = Greenland and AQ = Antarctica. YYYY= four-digit year of campaign|
||Two digit month, two-digit day of campaign|
||Date (YY year/ MM month) of the data release|
||Number of seconds since UTC midnight of the day the data collection started|
||Indicates file type: .h5 (HDF5), or .xml|
HDF5 data files range from approximately 61 MB to 913 MB.
XML files range from approximately 10 KB to 159 KB.
Data volume for the Version 2 data is approximately 248 GB.
Spatial coverage for the IceBridge LVIS campaigns includes the Arctic, Greenland, Antarctica, and surrounding ocean areas. In effect, this represents the coverage noted below. Current coverage for the Version 2 data is Greenland.
Arctic / Greenland:
Southernmost Latitude: 60° N
Northernmost Latitude: 90° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Southernmost Latitude: 90°S
Northernmost Latitude: 53°S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
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.
These data were collected from 30 October 2013 to the present as part of Operation IceBridge funded campaigns.
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.
The LVIS Level-1B files include geolocated return energy waveforms, transmitted waveform, and ancillary data.
The LVIS Level-1B HDF5 files are described in Table 2.
|/(root)||AZIMUTH||Azimuth angle of laser beam||Degrees|
|INCIDENTANGLE||Off-nadir incident angle of laser beam||Degrees|
|LAT0||Latitude of the highest sample of the return waveform (degrees north)||Degrees|
|LAT527||Latitude of the lowest sample of the return waveform (degrees north)||Degrees|
|LFID||LVIS file identification. Together with SHOTNUMBER these are a unique identifier for every LVIS laser shot. Format is XXYYYYYZZZ where XX identifies instrument version, YYYYY is the Modified Julian Date of the flight departure day, ZZZ represents file number.||n/a|
|LON0||Longitude of the highest sample of the return waveform (degrees east)||Degrees|
|LON527||Longitude of the lowest sample of the return waveform (degrees east)||Degrees|
|RANGE||Distance along laser path from the instrument to the ground||Meters|
|RXWAVE||Returned waveform (528 samples long)||Counts|
|SHOTNUMBER||Laser shot number assigned during collection. Together with LFID provides a unique identifier to every LVIS laser shot.||n/a|
|SIGMEAN||Signal mean noise level, calculated in-flight||Counts|
|TIME||UTC decimal seconds of the day||Seconds|
|TXWAVE||Transmitted waveform (120 samples long)||Counts|
|Z0||Elevation of the highest sample of the waveform with respect to the reference ellipsoid||Meters|
|Z527||Elevation of the lowest sample of the waveform with respect to the reference ellipsoid||Meters|
|/ancillary_data/||HDF5 Version||HDF5 version number based on IDL version||Number|
|Maximum Latitude||Maximum value of latitude to be found in this file||Degrees|
|Maximum Longitude||Maximum value of longitude to be found in this file||
Manimum value of latitude to be found in this file
Minimum value of longitude to be found in this file
|ancillary_text||Ancillary information relevant to data collection and processing||n/a|
|reference_frame||Reference frame for LVIS data products, derived from
reference frame for global navigation satellite system (GNSS) orbits.
Using International Terrestrial Reference Frame (ITRF 2008).
Sample Data Record
Below is an illustration of RXWAVE, LAT0, and LAT527 values from a sample of the
ILVIS1B_GL2013_1114_R1405_063767.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.
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 datasets.
For additional tools, see the HDF-EOS Tools and Information Center.
Also available: an IDL program that reads the LVIS Level-1B data into an IDL structure: read_ilvis1b.pro.
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.
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.
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).
The following processing steps are performed by the data provider to produce the Level-1B data.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
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 2.0 of the ILVIS1B data: beginning with the 2013 Arctic campaign, all data are provided in HDF5 format. In the near future, data from all campaigns prior to 2013 will be replaced with HDF5 data.
For details on the Version 1 data, see the V1 documentation.
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.
References and Related Publications
Contacts and Acknowledgments
Laser Remote Sensing Laboratory, Code 694
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Department of Geography
2181 LeFrak Hall
University of Maryland
College Park, MD 20742
This work was supported by NASA Grant Number NNX11AH69G, LVIS: A Topographic Mapping Capability for IceBridge.
Document Creation Date
11 August 2014
Document Revision Date
14 March 2016
27 June 2016