Airborne Laser Polarization Sensor (ALPS) Experiment During the Forest Ecosystem Dynamics - Multisensor Airborne Campaign

Forest Ecosystem Dynamics Multisensor Airborne Campaign (FED MAC):
Airborne Laser Polarization Experiment

The Biospheric Sciences Branch (formerly Earth Resources Branch)
within the Laboratory for Terrestrial Physics at NASA's Goddard Space
Flight Center and associated University investigators are involved in
a research program entitled Forest Ecosystem Dynamics (FED) which is
fundamentally concerned with vegetation change of forest ecosystems at
local to regional spatial scales (100 to 10,000 meters) and temporal
scales ranging from monthly to decadal periods (10 to 100 years). The
nature and extent of the impacts of these changes, as well as the
feedbacks to global climate, may be addressed through modeling the
interactions of the vegetation, soil, and energy components of the
boreal ecosystem.

A new remote sensing instrument, the Airborne Laser Polarization
Sensor (ALPS), mounted on a helicopter, was used to make multispectral
radiometric and polarization measurements of the Earth's surface using
a polarized laser light source. The ALPS system consists of a pulsed,
polarized laser source, an optical receiver package, a video camera and
recorder, and data acquisition and analysis hardware and software. The
choice of laser wavelengths is limited to frequencies from the
ultraviolet to the near-infrared by the photo-cathode response of the
selected photo multiplier tube (PMT) detectors. Twelve PMTs were used
corresponding to the 12 channels of data: Channels 1,2,3,4,9 & 10 have
1090 nm bandpass filters. The reminder are for 532 nm. Channels 9 and
11 have no polarization filters.

For each wavelength, polarization filters are mounted in front of each
PMT at angles relative to the transmitted polarization. A pulsed (7 ns)
Nd:YAG laser is employed. It operates in the infrared at 1060 nm and
the visible at 532 nm. The 532 nm green wavelength can be seen near
the center of the TV screen as it hits the surface in most cases. This
is used for ground truth correlation. The spot is about 20 cm in
diameter from 100 meters altitude.

In these data for ALPS Experiment for the FED MAC 90, the file
tabulation refers to data files taken on September 9 and 11. A
standard VHS video tape is available (the master tapes are recorded at
the SP speed on Super-VHS). The first half of this tape is from a
camera coaxial with the laser transmission. Time on the tape
correspond to file times while oral comments on the tape supplement
the general comments. The second half of the tape consists primarily
of site descriptive narration on the ground and some pictures of the
helicopter setup.

The FED Home Page is at: "https://forest.gsfc.nasa.gov/".