2002 NASA/USGS Airborne LiDAR Assessment of Coastal Erosion (ALACE) Project for California, Oregon, and Washington Coastlines

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.

Original contact information:

Contact Org: NOAA Office for Coastal Management

Phone: 843-740-1202

Email: coastal.info@noaa.gov

This data was collected as part of an effort by the USGS and NASA to map beach topography and assess beach change for the states of California,

Oregon and Washington.

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This data set was collected with the NASA Airborne Topographic Lidar 3 (ATM3) LIDAR (LIght Detection and Ranging) instrument which was designed

and developed by the NASA Observational Science Branch (OSB Code 972) Goddard Space Flight Center, Wallops Island VA. The ATM3 measures the time

of flight of a narrow pulse (5 nanoseconds) of green laser light (532 nm) from the aircraft to the ground and back to the aircraft. The laser is

pulsed at 5000 Hz and the pulses are reflected from a 22 degree off-nadir scanning mirror rotating at 20 Hz which directs the laser light and the

telescope view in an elliptical scan pattern under the aircraft. The telescope collects the reflected laser light which passes through a narrow

bandpass filter (to reject background light) and is detected by a photomultiplier tube detector. The ATM3 time of flight measurements are

calibrated and combined with GPS data (to provide position) and aircraft inertial gyro data (to provide the aircraft attitude when each laser

measurement was recorded) resulting in a calculated latitude, longitude, and elevation for each laser spot in the 250 laser shot elliptical scan

under the aircraft. The scan pattern (at 22 degrees off nadir) covers a width of ~560 meters from a nominal aircraft altitude of 700 meters.

Depending on aircraft ground speed, several consecutive scans may overlap along the aircraft flight track. Normally parallel flight tracks will

be flown with ~20% overlap to cover areas wider than a single ATM3 scan width. The resultant data set is normally resampled and binned to create

a digital elevation model of the desired area. 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.

This data was collected for the purposes of research. Any conclusions drawn from analysis of this information are not the responsibility of NOAA,

the Office for Coastal Management or its partners.

This data can be obtained on-line at the following URL: https://coast.noaa.gov/dataviewer. The data set is dynamically generated

based on user-specified parameters.

;

None

This data was collected for the purposes of research. Any conclusions drawn from analysis of this information are not the responsibility of NASA,

USGS, or NOAA. This data is likely to contain returns from the water surface and vegetation. No processing has been done to remove returns from

water or vegetation. Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data

may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its

limitations.

See Vertical_Positional_Accuracy_Report. Processing steps (datum conversion, projection, grid interpolation, etc.) introduce additional error

factors which have not been tested at the time of this publication.

The ATM LIDAR elevation points are estimated to be horizontally accurate to +/- 0.8 meters at an aircraft altitude of 700 meters.

The accuracy of this data set has not been validated against ground truth measurements. An internal consistency check of the data was conducted.

The process compared elevation points determined to be over beaches and non-vegetated areas from overlapping flights. The elevation of points

within a meter of each other were compared. The average RSME of the 60 sample areas each containing on average 1311 common points was 18.5 cm.

In comparisons of another ATM LIDAR data set for a small geographic region to various ground surveys the differences are between +/- 15 to 20

centimeters. The accuracy of the majority of this data set is estimated to be consistent with the above stated results.

None

Not applicable.