LVIS Level-1B Geolocated Return Energy Waveforms binary files are named according to the following convention and as described in Table 2.

File name example: LVIS_GL2011_MJD55666_LEVEL1B_20110915_A.LGW4

LVIS_LOYYYY_MJDnnnnn_LEVEL1B_YYYYMMDD_a.LGW4

Where:

The LVIS Level-1B LGW2 files are described in Table 3.

Version 1.02 binary data contain 492 bytes per record.

The LVIS Level-1B LGW3 files are described in Table 4.

Version 1.03 binary data contain 584 bytes per record.

The LVIS Level-1B LGW4 files are described in Table 5.

Version 1.04 binary data contain 1368 bytes per record.

Below are example output records from the different input formats. For version 1.02 data, the LVIS C reader generates one ASCII text output record for every input record. The output record generated from the first 492-byte binary record in the v1.02 file LVIS_PIG_2009_MJD55124_VECT_20100929.lgw2, is:

For versions 1.03 and 1.04 data, the LVIS C reader creates two output records for every one input record. The first output record contains all data parameters except the received waveform, and the second output record contains the received waveform. The difference between the 1.03 and 1.04 formats is in the number of samples in the transmitted and received waveforms. Below are the two output records generated from the first 1368-byte binary record in the v1.04 file LVIS_ANT2009_MJD55129_LEVEL1B_20120118_D.LGW4. The first output record is:
The second output record is:

Note that the output file size is very large. For the above example, the binary input file is 1.9 gigabytes and the ASCII text output file is 4.75 gigabytes.

Data are available via FTP.

NSIDC provides an LVIS C reader that reads a binary data file from the Operation IceBridge LVIS instrument and prints the records to standard output. Version 1.04 of the LVIS C reader should be used to read the older LGW2 and LGW3 binary data files and the newer LGW4 binary data files. Note that the ASCII text results create very large output files.

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 binary format 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 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.
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.

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.

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.

Blair, J. B., D. L. Rabine., and M. A. Hofton. 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: 115-122.

Hofton, M. A., J. B. Blair, J. B. Minster., J. R. Ridgway, N. P. Williams, J. L Bufton, and D. L. Rabine. 2000. An Airborne Scanning Laser Altimetry Survey of Long Valley, California, International Journal of Remote Sensing, 21(12): 2413-2437.

Hofton, M. A., J. B. Blair, S. B. Luthcke, and D. L. Rabine. 2008. Assessing the Performance of 20-25 m Footprint Waveform Lidar Data Collected in ICESat Data Corridors in Greenland, Geophysical Research Letters, 35: L24501, doi:10.1029/2008GL035774.

• LVIS Web site at NASA Goddard Space Flight Center (http://lvis.gsfc.nasa.gov).
• IceBridge Data Web site at NSIDC (http://nsidc.org/data/icebridge/index.html).
• IceBridge Web site at NASA (http://www.nasa.gov/mission_pages/icebridge/index.html).
• ICESat/GLAS Web site at NASA Wallops Flight Facility (http://glas.wff.nasa.gov/).
• ICESat/GLAS Web site at NSIDC (http://nsidc.org/daac/projects/lidar/glas.html).