NASA

National Aeronautics and Space Administration

Wallops Flight Facility

Airborne Topographic Mapper > Data Products

Data Products

The best way to find and use ATM data is through the  NSIDC IceBridge portal.

A test ILATMW1B file was created to assist in software testing of the reading and reconstruction of the waveforms in our file format.  The /waveforms/twv/wvfm/amplitude values were modified in a sample file, such that record:1 gate:1 contains all 11’s; record:1 gate:2 contains all 12’s; record:2 gate:1 contains all 21’s; etc.  The file only contains 20 records, since the amplitude field doesn’t accept any values larger than 255 and we wanted to keep the values unique.  The gate lengths (/waveforms/twv/gate/wvfm_length) were not changed, so the gates have various lengths.  Here is the sample of a qfit file for any software testing ->  HDF5 Qfit file

Below are direct links to data housed at NSIDC

Altimetry Products
QFIT (narrow & wide)
ICESSN
dh/dt
Waveforms
Ancillary Data Products
KT-19 Pyrometer Thermal Imaging (FLIR)
Camera/Optical Spectrometer
GPS trajectories

The primary data product from the ATM laser altimeter is “QFIT”.  A QFIT file is a collection of geolocated laser shots tagged with time and elevation.  ICESSN is a sub-sampled version of QFIT which separates the data in platelets making it smaller and easier to analyze.  An example of QFIT vs ICESSN is in the image below

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QFIT (top) vs ICESSN (bottom)

More recently, the ATM group has begun releasing waveform data to complement the standard altimetry products. These waveform data are of particular use when the surface within a single laser footprint is not uniform. Conditions such as pressure ridging on sea ice, or melt ponds that produce surface and bottom returns are examples where a single elevation measurement is inadequate and the waveform data is necessary to accurate interpret the return signal.

Example of surface conditions that would cause multiple waveform peaks to be observed.

Example of complex return waveforms (blue) over a sea-ice pressure ridge. The transmit waveform is shown in dashed gray and scaled to the maximum amplitude of the return pulse to show the deviation of the return pulse. The vertical dashed line in both panels marks the location of the centroid. Multiple separate return pulses can be identified in (a), but the overlapping pulses in (b) result in the centroid estimate being shifted, indicating that the centroid estimates from complex return pulses need to be interpreted properly.