September 2008 Scripps Institute of Oceanography (SIO) Lidar of the Southern California Coastline: Long Beach to US/Mexico Border

This lidar point data set was collected during low tide conditions along an approximately 500-700 meter wide strip of the Southern

California coastline within an area extending south from Long Beach to the US/Mexico border. Data were collected in Los Angeles, Orange

and San Diego counties from south of the Downtown Long Beach Marina in Long Beach, California to Leucadia, California on September 30,

2008 between 20:46 and 23:25 UTC. Data were collected in Orange and San Diego counties from Dana Point, California to south of the United

States-Mexico border near Playas de Tijuana, Baja California, Mexico on September 29, 2008 between 20:08 and 23:08 UTC. Data set features

include water, beach, cliffs, and top of cliffs. The all points data set contains the complete point cloud of first and last return elevation

and laser intensity measurements recorded during the fall 2008 airborne lidar survey conducted semi-annually by the University of Texas at

Austin for the Southern California Beach Processes Study.

The data set was generated by the processing of laser range, scan angle, and aircraft attitude data collected using an Optech Inc. Airborne

Laser Terrain Mapper (ALTM) 1225 system and geodetic quality Global Positioning System (GPS) airborne and ground-based receivers. Instrument

settings and parameters during survey were:

Nominal on-ground beam diameter: 25 cm

Pulse rate: 25 kHz

Maximum number of returns recorded: 2

Minimum separation between detected returns from a single pulse: 4.3 m

Laser wavelength: 1064 nm

Frequency of GPS sampling: 1 Hz

Frequency of IMU sampling: 50 Hz; Scan angle: +/- 20 degrees

Nominal height of instrument above ground: 1100 m

Nominal single-swath pulse density: 2 m

Nominal aggregate pulse density: 0.75

Nature of vertical control: Kinematic and static GPS points

Original contact information:

Contact Name: Roberto Gutierrez

Contact Org: University of Texas at Austin Center for Space Research

Title: Research Associate in Geodesy and Geophysics

Phone: 512.471.5573

Email: oskar@mail.utexas.edu

The data described in this document will be compared with previous and forthcoming data sets to determine rates of shoreline change along

the Southern California coastline. The SCBPS program is designed to improve the understanding of beach sand transport by waves and currents,

thus improving local and regional coastal management.

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The University of Texas at Austin Center for Space Research operated an Optech Inc. Airborne Laser Terrain Mapper (ALTM) 1225 system

installed in a single engine Cessna 206 to collect lidar data for the survey. Global Positioning System (GPS) data were collected

simultaneously with three geodetic quality Ashtech Z-12 receivers installed in the aircraft and at two temporary base stations operated

during the survey. An Inertial Measurement Unit (IMU) used three orthogonal accelerometers and gyroscopes to collect in-flight

instrument orientation information. The Cessna 206 aircraft used in the survey is owned and operated by the Texas Department of Transportation.

The ALTM 1225 (SN#99d118) lidar instrument has the following specifications: operating altitude = 410-2,000 m AGL; maximum laser pulse

rate = 25 kHz; laser scan angle = variable from 0 to +/-20deg from nadir; scanning frequency = variable, 28 Hz at the 20deg scan angle;

and beam divergence: narrow = 0.2 milliradian (half angle, 1/e). The ALTM 1225 records the range and backscatter intensity of the first

and last laser reflection using an Avalanche Photo diode constant-fraction discriminator and two Timing Interval Meters (TIM).

ALTM elevation points are computed using three sets of data: laser ranges and their associated scan angles, platform position and orientation

information, and calibration data and mounting parameters (Wehr and Lohr, 1999). Global Positioning System (GPS) receivers in the aircraft

and on the ground provide platform positioning. The GPS receivers record pseudo-range and phase information for post-processing.

Platform orientation information comes from an Inertial Measurement Unit (IMU) containing three orthogonal accelerometers and gyroscopes.

An aided-Inertial Navigation System (INS) solution for the aircraft's attitude is estimated from the IMU output and the GPS information.

A footprint of this data set may be viewed in Google Earth at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/571/supplemental/Scripps_September_2008_Lidar_Long_Beach_to_Mexico_Border.kmz

Any conclusions drawn from analysis of this information are not the responsibility of the Scripps Institution of Oceanography, the UT Center for

Space Research, the Bureau of Economic Geology, The University of Texas at Austin or the NOAA Office for Coastal Management or its partners.

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

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These data were collected to support the Southern California Beach Processes Study. Any conclusions drawn from analysis of this information are

not the responsibility of the Scripps Institution of Oceanography, the UT Center for Space Research, the Bureau of Economic Geology, or the

University of Texas at Austin. Interested parties are advised to review metadata contents prior to use. These data are best used at scales

appropriate for raster or gridded data collected at a nominal resolution of 1-2 meters (approximately 1:12000). 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 base critical applications on this data set without full awareness of potential limitations.

Maximum allowable PDOP using a 15 degree elevation mask during data collection was 3.5. The lidar data is estimated to have a horizontal

error of less than or equal to 1.0 m. To assess horizontal accuracy, selected portions from each lidar data set (last return only) were

used to generate a 1m x 1m digital elevation model (DEM). Data from ground surveys conducted using kinematic GPS techniques and estimated

to have a horizontal accuracy of 0.01-0.03 m were superimposed on the lidar DEM and examined for any mismatch between the horizontal

position of the ground GPS and the corresponding feature on the lidar DEM. Horizontal agreement between the ground kinematic GPS and the

lidar was within the resolution of the 1m x 1m DEM.

(North) The September 30, 2008, lidar data were compared to kinematic GPS ground survey points collected along an approximately 2 kilometer

long stretch of the East Pacific Coast Highway near Laguna Beach. The September 30, 2008, lidar data set was sorted to find data points

that fell within 1 m of the GPS points.

(South) The September 29, 2008, lidar data were compared to 17 GPS ground survey points collected throughout a parking lot adjacent to the

North Torrey Pines Road. The September 29, 2008, lidar data set was sorted to find data points that fell within 2 m of the GPS points.

For each survey area (north and south), the mean elevation difference between the selected lidar points and their respective GPS points

was used to estimate and remove elevation bias from the lidar. The standard deviation of the elevation differences provided estimates

of the lidar precision. The bias was removed so that mean lidar elevations have a vertical accuracy of 0.10 m RMSE.

This data set contains data within a narrow strip (~700 m) of the Southern California coastline. A decimated dataset was visually inspected for

completeness. Some beach edges may be missing. Data collected west of the northwestern corner of the Downtown Long Beach Marina

(Longitude 118d11m0.63s W) and south of the US-Mexico border at Playas de Tijuana (Latitude 32d32m1.80s N) may be of poor quality and should

not be used for analysis. Data collected during the third pass of September 29 (pass 27308C) were noisier than desirable. Unacceptable data

points were removed from that pass.

Data points lacking either first or last return values were removed from the data set. An automated method was used to remove obvious outliers.

Only data points with vertical values greater than or equal to -20 m and less than or equal to 250 m were retained in the all points data set.