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Data Set ID:
ABLVIS1B

ABoVE LVIS L1B Geolocated Return Energy Waveforms, Version 1

This data set contains laser altimetry return energy waveform measurements over Alaska and Western Canada taken from the NASA Land, Vegetation, and Ice Sensor (LVIS). The data were collected as part of NASA's Terrestrial Ecology Program campaign, the Arctic-Boreal Vulnerability Experiment (ABoVE).

This is the most recent version of these data.

Version Summary:

New data set.

Parameter(s):
  • INFRARED WAVELENGTHS > SENSOR COUNTS
Data Format(s):
  • HDF5
Spatial Coverage:
N: 72, 
S: 48, 
E: -104, 
W: -158
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:
  • 29 June 2017 to 17 July 2017
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. 2018. ABoVE 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/UMRAWS57QAFU. [Date Accessed].

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Detailed Data Description

The data in this Level-1B product were collected by the NASA Land, Vegetation, and Ice Sensor (LVIS) as part of the Arctic-Boreal Vulnerability Experiment (ABoVE). ABoVE is a NASA Terrestrial Ecology Program field campaign conducted in Alaska and Western Canada. The ABoVE data are used to study environmental change and its implications for social-ecological systems. The data files of this Level-1B product contain geolocated laser waveform data for each laser footprint. The data are also distributed in the Level-2 format, through the ABoVE LVIS Level-2 Geolocated Surface Elevation Product data set. The Level-2 data files contain canopy top and ground elevations, as well as relative heights derived from the Level-1B data. Other related LVIS data sets include Level-0, Level-1B, and Level-2 products collected as part of the Operation IceBridge campaigns. See the Related Data Collections section for links to these data sets.

Format

The data files are in HDF5 format (.h5). Each data file is paired with an associated XML file (.xml), which contains additional metadata.

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File Naming Convention

The data files are named according to the following conventions and as described in Table 1:

Example File Names

LVIS1B_ABoVE2017_0629_R1803_056233.h5
LVIS1B_ABoVE2017_0629_R1803_056233.h5.xml

File Naming Convention

LVIS1B_ABoVEYYYY_MMDD_RYYMM_nnnnnn.NN

Table 1. File Naming Convention
Variable Description
LVIS1B Short name for LVIS L1B Geolocated Return Energy Waveforms
ABoVEYYYY Campaign identifier. ABoVE = acronym for Arctic-Boreal Vulnerability Experiment; 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
NN Indicates file type: .h5 (HDF5 file) or .h5.xml (XML metadata file)
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File Size

The total HDF5 file volume is approximately 967 GB and the total XML file volume is approximately 0.005 GB.

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Spatial Coverage

Spatial coverage for the ABoVE LVIS campaigns includes Alaska and Western Canada, as noted by the coverage below.

Alaska / Canada:
Southernmost Latitude: 48° N
Northernmost Latitude: 72° N
Westernmost Longitude: 158° W
Easternmost Longitude: 104° W

Spatial Resolution

The spatial resolution is on average 20 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.

Projection and Grid Description

International Terrestrial Reference Frame (ITRF 2008), WGS-84 Ellipsoid.

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Temporal Coverage

29 June 2017 to 17 July 2017

Temporal Resolution

The ABoVE Alaska and Canada campaigns were conducted on 13 days between 29 June and 17 July 2017. Table 2 lists all the flight dates and locations for those days. For more detailed information, visit the NASA ABoVE campaign website.

Table 2. Flight Dates and Locations
Date Location
29 Jun 2017 Saskatoon to Yellowknife
29 Jun 2017 Slave Lake
30 Jun 2017 Yellowknife to Inuvik
30 Jun 2017 Inuvik to Yellowknife
01 Jul 2017 Daring Lake
02 Jul 2017 W and SW Slave Lake
03 Jul 2017 Yellowknife to Whitehorse
03 Jul 2017 Whitehorse to Fairbanks
06 Jul 2017 Kluane
07 Jul 2017 Healy
09 Jul 2017 Fairbanks to Barrow
14 Jul 2017 Fairbanks to Deadhorse via Toolik Lake
14 Jul 2017 Deadhorse to Fairbanks via Fort Yukon
15 Jul 2017 Fort Yukon
16 Jul 2017 Fairbanks to Ketchikan
16 Jul 2017 Ketchikan to Glasgow
17 Jul 2017 Boreal Ecosystem Research and Monitoring Sites (BERMS) Flight
18 Jul 2017 Glasgow to Toledo
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Parameter or Variable

The data files include geolocated return energy waveforms, transmitted waveforms, and ancillary data.

Parameter Description

Parameters contained in the HDF5 files are described in Table 3.

Table 3. HDF5 File Parameters

Group

Parameter

Description

Units

/(root) 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
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
TIME UTC decimal seconds of the day Seconds
LON0 Longitude of the highest sample of the return waveform Degrees East
LAT0 Latitude of the highest sample of the return waveform Degrees North
Z0 Elevation of the highest sample of the waveform with respect to the reference ellipsoid Meters
LON1215 Longitude of the lowest sample of the return waveform Degrees East
LAT1215 Latitude of the lowest sample of the return waveform Degrees North
Z1215 Elevation of the lowest sample of the waveform with respect to the reference ellipsoid Meters
SIGMEAN Signal mean noise level, calculated in-flight Counts
TXWAVE Transmitted waveform, 256 bins long, 12 bits at 1GHz Counts
RXWAVE Return waveform, 1216 bins long, 12 bits at 1GHz Counts
/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 North
Maximum Longitude Maximum value of longitude to be found in this file

Degrees East

Minimum Latitude

Minimum value of latitude to be found in this file

Degrees North

Minimum Longitude

Minimum value of longitude to be found in this file

Degrees East

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).
N/A

Sample Data Record

Figure 1 shows an illustration of range and lat1215 values from a sample of the LVIS1B_ABoVE2017_0629_R1803_056233.h5 data file as displayed in the HDFView tool.

Figure 1. Sample values for the parameters RANGE (left) and LAT1215 (right), visualized using the HDFView software.
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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.

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Data Acquisition and Processing

As described on the NASA LVIS website, 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 reflection to return yields the range to the target.

Figure 2 shows two example return waveforms. A simple waveform (left) occurs when the surface is relatively smooth within the laser footprint, which generates a laser return waveform that consists of a single mode. The detection threshold is computed relative to the mean noise level and is used to detect the return signals that are geolocated for Level-2 data products. Multilayered surfaces, such as forests, vegetated landcover, ice crevasses, or rocky terrain, produce complex waveforms (right) containing more than one mode. Different modes represent the various surfaces within the footprint, such as the canopy top, the ground, the crevasse bottom, or the top of the broken ice surface, and are distributed according to their relative elevations within the footprint.

Figure 2. 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 product 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, 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. See the NASA LVIS website for more information.

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Derivation Techniques and Algorithms

This data set is generated from the raw instrument data as described below. 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.

  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 because temperature and pressure affect 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.
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Sensor or Instrument Description

As described on the NASA LVIS website, 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 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 m to 25 m 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 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 through funding from Hank Margolis (NASA - SMD - ESD Terrestrial Ecology).

Document Information

Document Creation Date

May 2018

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