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Data Set ID: 
LVISC2

LVIS Classic L2 Geolocated Surface Elevation and Canopy Height Product, Version 1

This data set contains Level-2 geolocated surface elevation and canopy height measurements collected by the NASA Land, Vegetation, and Ice Sensor (LVIS), an airborne lidar scanning laser altimeter. The data were collected either as part of NASA’s Terrestrial Ecology Program campaign, the Arctic-Boreal Vulnerability Experiment (ABoVE), or of the Global Ecosystem Dynamics Investigation (GEDI) mission.

This is the most 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):
  • ASCII Text
Spatial Coverage:
N: 72, 
S: 9, 
E: -81, 
W: -168
Platform(s):G-V
Spatial Resolution:
  • Varies x Varies
Sensor(s):LVIS
Temporal Coverage:
  • 21 May 2019 to 8 August 2019
Version(s):V1
Temporal ResolutionVariesMetadata XML:View Metadata Record
Data Contributor(s):J. Blair, Michelle Hofton

Geographic Coverage

Other Access Options

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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. 2020. LVIS Classic L2 Geolocated Surface Elevation and Canopy Height Product, 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/W569D47GCOUX. [Date Accessed].
Created: 
9 March 2020
Last modified: 
21 May 2020

Data Description

This Level-2 data set contains measurements taken by NASA's Land, Vegetation, and Ice Sensor (LVIS) in support of the NASA Arctic-Boreal Vulnerability Experiment (ABoVE) and the NASA Global Ecosystem Dynamics Investigation (GEDI). ABoVE is a NASA Terrestrial Ecology Program conducted in Alaska and Western Canada. The ABoVE data are used to study environmental change and its implications for social-ecological systems. GEDI was launched to the International Space Station (ISS) in December 2018 to measure forest canopy height, structure, and surface elevation to improve characterization of important carbon and water cycle processes, biodiversity, and habitats. These flights provide data for ABoVE science investigations, as well as calibration and validation of GEDI mission in the United States, Canada, and Central America.

Two LVIS instruments were co-mounted and operated during flights, with data products referred to as LVISC (from the LVIS-Classic instrument) and LVISF (from the LVIS-Facility instrument). This data set contains measurements taken by the LVIS-Classic instrument, whereas the corresponding Level-2 LVISF data set, LVIS Facility L2 Geolocated Surface Elevation and Canopy Height Product, contains data from the co-mounted LVIS-Facility instrument. These two LVIS instruments differ in the laser footprint size and spacing on the ground. The Level-1B versions of these data sets, LVIS Classic L1B Geolocated Return Energy Waveforms and LVIS Facility L1B Geolocated Return Energy Waveforms, contain geolocated return energy waveforms used to create the Level-2 data sets.

This data set is also closely related to the ABoVE LVIS L2 Geolocated Surface Elevation Product data set, which provides ABoVE data, and the AfriSAR LVIS L2 Geolocated Surface Elevation Product data set, which provides GEDI calibration and validation data.

Parameters

All of the parameters contained in the data files are described in Table 1.

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
SENSITIVITY(*) Sensitivity metric for the return waveform N/A
CHANNEL_ZT Flag indicating LVIS channel waveform contained in the 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

Note:
(*) This parameter was newly added. The rest of the parameters are the same as in the AfriSAR LVIS L2 Geolocated Surface Elevation Product data set.

File Information

Format

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

Naming Convention

Example file names:

LVISC2_ABoVE2019_0715_R2002_086485.TXT
LVISC2_ABoVE2019_0715_R2002_086485.TXT.xml


LVISC2_GEDI2019_0521_R2002_073401.TXT
LVISC2_GEDI2019_0521_R2002_073401.TXT.xml

Files are named according to the following convention, which is described in Table 2:

LVISC2_CAMPYYYY_MMDD_RYYMM_nnnnnn.ext

Table 2. File Naming Convention
Variable Description
LVISC2 Data set ID
CAMPYYYY Campaign identifier: ABoVE = Arctic-Boreal Vulnerability Experiment; GEDI = Global Ecosystem Dynamics Investigation; YYYY= four-digit year of campaign
MMDD Two-digit month, two-digit day of start of data collection
RYYMM Date (YY year / MM month) of the data release
nnnnnn Number of seconds since UTC midnight of the day the data collection started
ext Indicates file type: .TXT (ASCII text data file) or .TXT.xml (XML metadata file)

Spatial Information

Coverage

Spatial coverage for this data set currently includes parts of Alaska, Western Canada, the continental United States, and central America, as noted by the spatial extents below:

Southernmost latitude: 9° N
Northernmost latitude: 72° N
Westernmost longitude: 168° W
Easternmost longitude: 81° W

Resolution

The nominal spatial resolution of the LVISC data sets is 20 m, but varies slightly with aircraft altitude and speed. Laser spot size is a function of beam divergence and altitude. Nominal spot spacing is a function of scan rate, pulse repetition rate, and airplane ground speed. The instrument resolution and footprint size are comparable to those in the AfriSAR LVIS L2 Geolocated Surface Elevation Product data set, but are lower than in the ABoVE LVIS L2 Geolocated Surface Elevation Product and the LVIS Facility L2 Geolocated Surface Elevation and Canopy Height Product data sets.

Geolocation

International Terrestrial Reference Frame 2008 (ITRF08), WGS-84 ellipsoid

Temporal Information

Coverage

21 May 2019 to 08 August 2019

Resolution

Varies

Instrumentation

NASA's LVIS is an imaging lidar sensor suite for precise and accurate large-area surface mapping and characterization. LVIS uses airborne lidar scanning laser altimeters to collect topography and vegetation coverage data over land, ocean, and ice surfaces, along with downward-looking, high-resolution camera imagery. The LVIS instruments differ in laser footprint size and spacing on the ground but generate near-identical data products.

Laser altimeters send a laser beam toward a target object and measure the time it takes for the signal to reflect back from the surface. Knowing the precise round-trip time for the reflection to return allows the distance, or range, to the target to be calculated. Range is combined with the pointing and positioning of the laser at the time of each laser shot to determine the location of each laser footprint on the ground relative to a reference ellipsoid (e.g.: Hofton et al., 2000). LVIS employs a signal digitizer with a very precise oscillator to measure both the transmitted and reflected laser pulse energies versus time. These digitized and captured histories are known as waveforms (i.e., the transmitted and return waveforms). The outgoing signal represents the profile of the individual laser pulse versus time; the return pulse comprises the interaction of that transmitted pulse with the target surface versus time.

As the aircraft travels over a target area, the laser beam and the telescope field-of-view scan a pattern along the surface perpendicular to the aircraft heading. LVIS instruments have a scan angle of approximately 12° (+-6° around nadir), allowing them to cover 2 km swaths from an altitude of 10 km. The typical diameter of the laser footprint on the ground is 10 m to 25 m, depending on the aircraft altitude, as well as laser repetition rate and divergence. Laser positioning at the time of each laser shot is provided by GPS satellite data. Laser pointing information is provided by an Inertial Measurement Unit (IMU) attached directly to the LVIS instrument.

Data Acquisition and Processing

Background

Figure 1 shows two examples of return waveforms: a simple waveform (left) and a complex waveform (right). The simple waveform occurs when the surface is relatively smooth within the laser footprint, thus generating 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. Complex waveforms containing more than one mode are produced when the laser beam hits multilayered surfaces, such as forests, vegetated land cover, ice crevasses, or rocky terrain. Different modes represent the various surfaces within the footprint, such as the canopy top, the ground, the crevasse bottom, or the top of broken ice surface, and are distributed according to their relative elevations within the footprint.

Figure 1. Sample Level-1B product waveforms illustrating possible distributions of reflected light.

Acquisition

The primary Level-1B data product is the geolocated laser return waveforms, representing the vertical distribution of reflecting surfaces within the area of the laser footprint over the sampled terrain. For vegetated terrain these surfaces include tree canopies, branches, other forms of vegetation, and open ground. For cryospheric areas these surfaces comprise 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 many different products to be extracted during data post-processing, such as the data presented in the Level-2 data 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 additional information. See the LVIS website at NASA Goddard Space Flight Center for more information.

Processing Steps

This data set is derived from the Level-1B data set, LVIS Classic L1B Geolocated Return Energy Waveforms. The following processing steps are performed by the data provider to produce the Level-2 data:

  1. A background, or threshold, return energy level is determined from the Level-1B waveform data. This threshold forms the datum to which the subsequent measurements are referenced.
  2. The centroid of the waveform above the threshold is computed. The centroid represents the mean location and elevation of all reflecting surfaces within the laser footprint.
  3. All modes in the waveform are identified, followed by a selection of the highest and lowest modes for output. These modes correspond to the mean elevation of the highest and lowest reflecting surfaces, respectively, within the laser footprint.

For more details see Hofton et al. (2000).

Quality, Errors, and Limitations

Obvious lower quality data, such as data collected in areas with clouds and cloud-obscured returns, were removed; however, spurious returns may still be present. Data collected in aircraft turns have been removed from this data set. It is recommended that users review the waveforms for their specific areas of study to verify ground return and canopy top identification. It is possible that some anomalies are still present in the data.

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 supported by the LVIS team that reads the LVIS Level-2 data into an IDL structure.

Related Data Sets

LVIS Classic L1B Geolocated Return Energy Waveforms
LVIS Facility L1B Geolocated Return Energy Waveforms
LVIS Facility L2 Geolocated Surface Elevation and Canopy Height Product
ABoVE LVIS L1B Geolocated Return Energy Waveforms
ABoVE LVIS L2 Geolocated Surface Elevation Product
AfriSAR LVIS L1B Geolocated Return Energy Waveforms
AfriSAR LVIS L2 Geolocated Surface Elevation Product

Related Websites

LVIS website at NSIDC
LVIS website at NASA Goddard Space Flight Center
ABoVE website at NASA
GEDI website

Contacts

Bryan Blair
Laser Remote Sensing Laboratory, Code 61A
NASA Goddard Space Flight Center
Greenbelt, MD 20771

Michelle Hofton
Department of Geographical Sciences
University of Maryland
College Park, MD 20742

Acknowledgments

This work was supported through funding from NASA. GEDI flights were supported by the GEDI mission. ABoVE flights were supported by Hank Margolis (NASA - SMD - ESD Terrestrial Ecology).

References

Hofton, M. A., Blair, J. B., Minster, J.-B., Ridgway, J. R., Williams, N. P., Bufton, J. L., & Rabine, D. L. (2000). An airborne scanning laser altimetry survey of Long Valley, California. International Journal of Remote Sensing, 21(12), 2413–2437. https://doi.org/10.1080/01431160050030547

No technical references available for this data set.

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