SURVEYS : Methods & Description


airborne_lidar_sm.jpg Remote: Airborne topographic LIDAR (LIght Detection And Ranging) data have been collected by SCBPS since 5/2002 under the direction of Dr R. Guterriez at the Bureau of Economic Geology (BEG), University of Texas at Austin.

Five of the initial surveys spanned from Point La Jolla to Dana Point, about 79 km, with the subsequent surveys covering from the Mexican Border to Long Beach, about 170 km.

The surveys cover a wide swath, including cliffs and adjacent wetlands. The width of the exposed beach, between the low tide waterline and the backbeach (e.g. highway, cliffs or dunes), ranges from less than 30m on eroded narrow beaches to several 100m on accreted wide beaches. The 170-km long surveys take 3-5 days to complete.

The quality of LIDAR surveys is influenced by clouds and GPS satellite coverage. Special care is required to reject LIDAR returns from the surface of waves running up the beach face, especially when when waves are energetic. The spatially extensive and dense (multiple data points per square meter) but temporally infrequent LIDAR surveys are supplemented with more frequent insitu surveys.


collage_sm.jpg In Situ: A beach nourishment (completed March 01 ) and adjacent control areas at Torrey Pines were monitored by SCBPS between Feb 01 and Apr 03. These pile of sand "POS" surveys, referred by Place_Keyword "TORREY" in the SCBPS database span about 3km alongshore and extend from the backbeach to about 8m depth.
Additional information available at the Torrey Pines Nourishment Study Page.

The Nearshore Canyon Experiment (NCEX ) was designed to identify and quantify wave shoaling processes near submarine canyons, and to investigate the associated wave-driven nearshore circulation. The experiment region, located a few km south of the Torrey Pines Nourishment Study area, was surveyed about 15 times between Aug 03 and Jan 04 between the backbeach and about 8m depth.

NCEX surveys are included in the SCBPS database because surveys in this area were continued by SCBPS.

Monthly surveys of a 5km-long region that includes both the Torrey Pines (2km) and NCEX (3km) regions were begun in Feb 04 (after NCEX ended).

Monthly surveys of a 4km-long beach at San Onofre, with different wave exposure than Torrey Pines (located about 40km north of Torrey Pines) began May 05.

Since then, three other insitu sites have been added to complement the LIDAR surveys: Camp Pendleton in Dec 06, Cardiff/Solana Beach in May 07 and Imperial Beach near the Tijuana rivermouth in April 08.

These sites have contrasting exposure to sea and swell. Surveys are obtained above the low tide waterline with a GPS-equipped all terrain vehicle (ATV). An ATV survey usually is completed during a single Spring low tide by driving on alongshore-oriented transects.

Twice a year, surveys at Torrey Pines - NCEX and San Onofre State Beach are extended to about 8-m depth (referred to as Theme_Keyword "ATV, DOLLY, JETSKI" in the SCBPS database and also known as "Jumbo" surveys locally) using a GPS-equipped personal water craft (PWC), ATV, and push dolly. Data is collected on cross-shore oriented transects, spaced between 20 and 100 m apart. The PWC surveys, conducted at high tide, are used to survey underwater bathymetry seaward of the surfzone (surfzone bubbles interfere with the acoustic depth finder). The ATV and push dolly low-tide surveys span from the backbeach to about waist deep water. The high- and low-tide surveys overlap when conditions are good (large tidal excursions and small waves), but sometimes contain gaps. These surveys usually take 3-5 days to complete.


Quality Control: LIDAR data are thoroughly examined to ensure data quality and accuracy:

  1. Pier Comparisons
  2. Insitu Beach Comparisons
  3. NGS and USGS Benchmark Comparisons

Vertical bias is usually less than 10 cm, with less than 10 cm standard deviation.


Metadata: Federal Geographic Data Committee (FDGC) metadata submissions can be made to SCBPS through the following form.

Metadata Submission Form


Beach Extraction: LIDAR data is collected across the entire coastal zone and extracting the beach region from all other LIDAR returns is accomplished in the following manner:

  1. Define & Digitize Back Beach boundary using the following resources for reference:
  2. Acquire tide and wave information
  3. Separate LIDAR data into individual passes
  4. Estimate waterline boundary using tides and wave heights
  5. Merge individual passes after extraction and calculate beach surface
    • Bin data calculating average of all points within 2m square areas
    • No need for interpolation due to high data density
  6. Experimenting with LIDAR Intensity return to designate Wet vs. Dry regions

 

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