Title:
1996-2000 NOAA/USGS/NASA Airborne LiDAR Assessment of Coastal Erosion (ALACE) Project for the US Coastline
Abstract:
This data set includes data collected from 1996-2000 and covers the states of AL,FL,LA,MS,DE,MD,VA,CT,MA,ME,NH,
NJ,NY,RI,NC,SC,GA,CA OR,WA,TX OH,PA.
Laser beach mapping uses a pulsed laser ranging system mounted onboard an aircraft to measure ground
elevation and coastal topography. The laser emits laser beams at high frequency and is directed downward at the
earth's surface through a port opening in the bottom of the aircraft's fuselage. The laser system records the
time difference between emission of the laser beam and the reception of the reflected laser signal in the
aircraft. The aircraft travels over the beach at approximately 60 meters per second while surveying from
the low water line to the landward base of the sand dunes.
Supplemental information:
This data set was collected with a LIDAR
(LIght Detection And Ranging) instrument designed and
developed by the Observational Sciences Branch (OSB) of
NASA at the Wallops Flight Facility in Virginia. The
instrument, originally designed for mapping ice sheets
in Greenland, is called the Airborne Topographic Mapper
or ATM. The ATM II (the latest version), operates with
a Spectra Physics laser transmitter, which provides a
7 nanoseconds long, 250 microjoules pulse at a
frequency-doubled wavelength of 523 nanometers in the
blue-green spectral region. The laser transmitter
can function at pulse rates from 2 to 10 kilohertz
(kHz). The laser system with a separate cooling unit
weighs approximately 45 kilograms (kg) and requires
approximately 15 amperes of power at 115 volts.
The transmitted laser pulse is reflected to the surface
of the earth with the aid of a small folding mirror mounted
on the back of a secondary mirror of a rotating scan
mirror assembly mounted directly in front of the
telescope. The scan mirror, which is rotated at 20
hertz, is comprised of a section of round aluminum
stock, machined to a specific off-nadir angle.
A scan mirror with the off-nadir angle of 15 degrees
was utilized, producing an elliptical scan pattern
with a swath width equal to 50 percent of the
approximately 700-meter aircraft altitude. The reflected
laser pulse is transmitted to a photo-multiplier
assembly that consists of a lens, a narrow bandpass
filter, and a single photomultiplier tube.
Note: The Spatial Reference section of this document
may lack fully FGDC-compliant information regarding
projection parameters (i.e., Central meridian, false
Northing, etc.). The State Plane or UTM Zone will be
supplied, and the corresponding parameters can be found
in Appendix C of:
Snyder, John, 1987, Map Projections, a Working Manual
(U.S. Geological Survey Professional Paper 1395):
Washington, U.S. Government Printing Office.
