Data Set ID:
ILVIS2

IceBridge LVIS L2 Geolocated Surface Elevation Product, Version 2

This data set contains surface elevation measurements from NASA's Land, Vegetation, and Ice Sensor (LVIS) over parts of Greenland. The data were collected as part of NASA Operation IceBridge funded campaigns.

This is the most recent version of these data.

Version Summary:

The data for 2009 through 2015 are stored in Version 1 of this data set.

Version 2 of this data set contains more parameters than Version 1. In addition, some parameters were renamed or removed. Essentially, Version 2 comprises the following changes:

  • LVIS_LFID is now called LFID.
  • LONGITUDE_LOW, LATITUDE_LOW, and ELEVATION_LOW were renamed to GLON, GLAT, and ZG.
  • LONGITUDE_HIGH, LATITUDE_HIGH, and ELEVATION_HIGH were renamed to HLON, HLAT, and ZH.
  • LONGITUDE_CENTROID, LATITUDE_CENTROID, and ELEVATION_CENTROID were removed.
  • TLON, TLAT, and ZT were added.
  • RH10 through RH100 were added.
  • AZIMUTH, INCIDENTANGLE, RANGE, and COMPLEXITY were added.
  • CHANNEL_ZT, CHANNEL_ZG, and CHANNEL_RH were added.

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):
  • ASCII Text
Spatial Coverage:
N: 90, 
S: 60, 
E: 180, 
W: -180
Platform(s):AIRCRAFT, B-200, C-130, DC-8, G-V, HU-25C, P-3B, RQ-4
Spatial Resolution:
  • Varies x Varies
Sensor(s):ALTIMETERS, LASERS, LVIS
Temporal Coverage:
  • 25 August 2017 to 20 September 2017
Version(s):V2
Temporal ResolutionVariesMetadata XML:View Metadata Record
Data Contributor(s):J. Blair, Michelle Hofton

Geographic Coverage

Other Access Options

Other Access Options

Close

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. 2019. IceBridge LVIS L2 Geolocated Surface Elevation Product, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/E9E9QSRNLYTK. [Date Accessed].
Created: 
7 March 2019
Last modified: 
28 August 2019

Data Description

The data in this Level-2 product were collected as part of Operation IceBridge campaigns by the NASA Land, Vegetation, and Ice Sensor (LVIS). The corresponding Level-1B data set, IceBridge LVIS L1B Geolocated Return Energy Waveforms, contains the spatially geolocated laser return waveforms. The LVIS Level-2 data products are derived from these waveforms and provide measurements for a variety of scientific applications. See the Related Data Collections section for links to other LVIS data sets.

Parameters

This data set includes mean elevation and other height measurements. All the parameters contained in the data files are described in Table 1.

Note: The LVIS facility is working toward establishing a standard set of data parameters that are applicable to a range of fields. Thus, not all parameters contained in the Level-2 files are currently relevant to every field of research. Additionally, some parameter names were changed; see the Version History section for more information.

Table 1. ASCII Text File Parameters

Parameter

Description

Units

LFID LVIS file identification. The format is XXYYYYYZZZ, where XX identifies instrument version, YYYYY is the Modified Julian Date of the flight departure day, and ZZZ represents the file number. N/A
SHOTNUMBER LVIS shot number assigned during collection. Together with LFID, it provides a unique identifier to every LVIS laser shot. N/A
TIME UTC decimal seconds of the day Seconds
GLON Longitude of the lowest detected mode within the waveform Degrees East
GLAT Latitude of the lowest detected mode within the waveform Degrees North
ZG Mean elevation of the lowest detected mode within the waveform Meters
HLON Longitude of the center of the highest detected mode within the waveform Degrees East
HLAT Latitude of the center of the highest detected mode within the waveform Degrees North
ZH Mean elevation of the highest detected mode within the waveform Meters
TLON Longitude of the highest detected signal Degrees East
TLAT Latitude of the highest detected signal Degrees North
ZT Elevation of the highest detected signal Meters
RH10 Height (relative to ZG) at which 10% of the waveform energy occurs Meters
RH15 Height (relative to ZG) at which 15% of the waveform energy occurs Meters
RH20 Height (relative to ZG) at which 20% of the waveform energy occurs Meters
RH25 Height (relative to ZG) at which 25% of the waveform energy occurs Meters
RH30 Height (relative to ZG) at which 30% of the waveform energy occurs Meters
RH35 Height (relative to ZG) at which 35% of the waveform energy occurs Meters
RH40 Height (relative to ZG) at which 40% of the waveform energy occurs Meters
RH45 Height (relative to ZG) at which 45% of the waveform energy occurs Meters
RH50 Height (relative to ZG) at which 50% of the waveform energy occurs Meters
RH55 Height (relative to ZG) at which 55% of the waveform energy occurs Meters
RH60 Height (relative to ZG) at which 60% of the waveform energy occurs Meters
RH65 Height (relative to ZG) at which 65% of the waveform energy occurs Meters
RH70 Height (relative to ZG) at which 70% of the waveform energy occurs Meters
RH75 Height (relative to ZG) at which 75% of the waveform energy occurs Meters
RH80 Height (relative to ZG) at which 80% of the waveform energy occurs Meters
RH85 Height (relative to ZG) at which 85% of the waveform energy occurs Meters
RH90 Height (relative to ZG) at which 90% of the waveform energy occurs Meters
RH95 Height (relative to ZG) at which 95% of the waveform energy occurs Meters
RH96 Height (relative to ZG) at which 96% of the waveform energy occurs Meters
RH97 Height (relative to ZG) at which 97% of the waveform energy occurs Meters
RH98 Height (relative to ZG) at which 98% of the waveform energy occurs Meters
RH99 Height (relative to ZG) at which 99% of the waveform energy occurs Meters
RH100 Height (relative to ZG) at which 100% of the waveform energy occurs Meters
AZIMUTH Azimuth angle of laser beam Degrees
INCIDENTANGLE Off-nadir incident angle of laser beam Degrees
RANGE Distance along laser path from the instrument to the ground Meters
COMPLEXITY Complexity metric for the return waveform N/A
CHANNEL_ZT Flag indicating LVIS channel waveform contained in the matching Level-1B file N/A
CHANNEL_ZG Flag indicating LVIS channel used to locate ZG N/A
CHANNEL_RH Flag indicating LVIS channel used to calculate RH metrics N/A

File Information

Format

The data files are in ASCII text format. Each data file is paired with an associated XML file, which contain additional metadata.

File Contents

Figure 1 shows the first five records from the ASCII data file ILVIS2_GL2017_0825_R1805_052154.TXT.

Figure 1. A sample of records from the ILVIS2_GL2017_0825_R1805_052154.TXT data file. The column headings and values are wrapped to fit into the figure.

Naming Convention

Example file names:

ILVIS2_GL2017_0825_R1805_052154.TXT
ILVIS2_GL2017_0825_R1805_052154.TXT.xml

The data files are named according to the following convention and as described in Table 2:

ILVIS2_LOYYYY_MMDD_RYYMM_nnnnnn.xxx

Table 2. File Naming Convention
Variable Description
ILVIS2 Short name for IceBridge LVIS L2 Geolocated Surface Elevation Product
LOYYYY Campaign identifier. LO = location, where GL = Greenland. YYYY= four-digit year of campaign
MMDD Two-digit month, two-digit day of campaign
RYYMM Date (YY year / MM month) of data release
nnnnnn Number of seconds since UTC midnight of the day on which the data collection started
.xxx

Indicates file type:

  • ASCII data file (.TXT)
  • XML metadata file (.TXT.xml)

File Size

The total data file volume is approximately 241 GB.

Spatial Information

Coverage

Spatial coverage for this data set includes areas of the Arctic and Greenland, as noted below:

Arctic / Greenland:
Southernmost Latitude: 60° N
Northernmost Latitude: 90° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E

Resolution

Spatial resolution for the LVIS-Facility instrument is nominally 8 m, 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.

Geolocation

The following table provides the geolocation details for this data set.

Table 3. Geolocation Details
Geographic coordinate system WGS 84
Projected coordinate system WGS 84 / NSIDC Sea Ice Polar Stereographic North
Longitude of true origin -45° E
Latitude of true origin 70° N
Scale factor at longitude of true origin 1
Datum WGS 84
Ellipsoid/spheroid WGS 84
Units meters
False easting 0
False northing 0
EPSG code 3413
PROJ4 string +proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs
Reference https://epsg.io/3413

Temporal Information

Coverage

25 August 2017 to 20 September 2017

Resolution

IceBridge campaigns are conducted on an annually repeating basis. Arctic, Greenland, and Alaska campaigns are typically conducted in March, April, and May; Antarctic campaigns are typically conducted in October and November.

Data Acquisition and Processing

Background

A laser altimeter is an instrument that measures the 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 for the signal 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. The mean noise level provides the threshold relative to which all signal processing is referenced. 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 is also typically returned from multilevel vegetation land cover such as a forest.

Figure 2. Sample Level-1B product waveforms, from which the Level-2 products are derived.

Acquisition

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; however, the primary products are the elevations of the Earth's surface and the distribution of reflecting surfaces within the laser footprint area. For vegetated terrain, these surfaces include tree canopies, branches, other forms of vegetation, and open ground. For cryospheric data, these surfaces are snow, ice, crevasses, snowdrifts, and 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. For more information, see the NASA LVIS website.

Processing

This data set is derived from the LVIS Level-1B Geolocated Return Laser Waveform product. The following processing steps are performed by the data provider to produce the Level-2 data in ASCII text format.

  1. Proceeding from the Level-1B waveform, a background or threshold return energy level is first determined. This threshold forms the datum to which the subsequent measurements are referenced.
  2. All modes in the waveform are identified, followed by selection of the highest and lowest modes for output. These correspond to the mean elevation of the highest and lowest reflecting surfaces, respectively, within the laser footprint.
  3. Several other elevation and relative height products are derived and output, including the elevation of the highest detected surface and the heights of energy levels above the lowest mode. These provide additional information on the 3D surface structure within the laser footprint.

Quality, Errors, and Limitations

The data have received limited quality assurance checking. Obvious low-quality data were removed, such as clouds and cloud-obscured returns. Currently, there are no known errors or limitations in this data set.

Instrumentation

LVIS is an airborne lidar scanning laser altimeter used by NASA to collect surface topography and vegetation coverage data. LVIS uses a signal digitizer with oscillator to measure transmitted and reflected laser pulse energies versus time and capture photon histories as waveforms. The laser beam and telescope field of view scan a raster pattern along the surface perpendicular to the aircraft heading as the aircraft travels over a target area. LVIS has a scan angle of approximately 12°, and can cover 2 km swaths from an altitude of 10 km. A typical collection size is 10 m to 25 m spots. In addition to waveform data, GPS satellite data are recorded at ground tie locations and on the airborne platform to precisely reference the aircraft position. An IMU is attached directly to the LVIS instrument and provides information required for coordinate determination.

Software and Tools

The data files can be opened by any software that reads ASCII text files.

Also available: read_ilvis2.pro, an IDL program that reads the LVIS Level-2 data into an IDL structure.

A tutorial on accessing and understanding LVIS data can be found at: https://lvis.gsfc.nasa.gov/Home/GabonWorkshop.html

Version History

The data for 2009 through 2015 are stored in Version 1 of this data set.

Version 2 of this data set contains more parameters than Version 1. In addition, some parameters were renamed or removed. Essentially, Version 2 comprises the following changes:

  • LVIS_LFID is now called LFID.
  • LONGITUDE_LOW, LATITUDE_LOW, and ELEVATION_LOW were renamed to GLON, GLAT, and ZG.
  • LONGITUDE_HIGH, LATITUDE_HIGH, and ELEVATION_HIGH were renamed to HLON, HLAT, and ZH.
  • LONGITUDE_CENTROID, LATITUDE_CENTROID, and ELEVATION_CENTROID were removed.
  • TLON, TLAT, and ZT were added.
  • RH10 through RH100 were added.
  • AZIMUTH, INCIDENTANGLE, RANGE, and COMPLEXITY were added.
  • CHANNEL_ZT, CHANNEL_ZG, and CHANNEL_RH were added.

Related Data Sets

Related Websites

Contacts and Acknowledgments

Bryan Blair
Geodesy and Geophysics Laboratory, Code 61A
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

The NASA LVIS Facility is funded by NASA Headquarters.

References

Blair, J. B., Rabine, D. L., & Hofton, M. A. (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(2–3), 115–122. https://doi.org/10.1016/s0924-2716(99)00002-7

Hofton, M. A., Blair, J. B., Luthcke, S. B., & Rabine, D. L. (2008). Assessing the performance of 20–25 m footprint waveform lidar data collected in ICESat data corridors in Greenland. Geophysical Research Letters, 35(24). https://doi.org/10.1029/2008gl035774

No technical references available for this data set.

How To

Programmatically access data using spatial and temporal filters
This article provides a step-by-step getting started guide to utilizing an Application Programming Interface, or API, for programmatic access to data from the NSIDC Distributed Active Archive Center (DAAC) based on spatial and temporal filters. Programmatic access is provided via an HTTPS URL... read more
ICESat, IceBridge, and ICESat-2: A primer on data access across the three missions
This guide will provide an overview of the altimetry measurements and data sets across the missions, as well as a guide for accessing the data through NASA Earthdata Search and programmatically using an Application Programming Interface (API). Overview  The NASA ICESat, Operation IceBridge,... read more