Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the 

U.S. Government

This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary between electronic plotters 

and between X and Y directions on the same plotter, and paper may change size due to atmospheric conditions; therefore, scale and 

proportions may not be true on plots of this map.

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://pubs.usgs.gov/sim/3302/

Suggested Citation: Dartnell, P., Phillips, E.L., Finlayson, D.P., Conrad, J.E., and Kvitek, R.G., 2014, Acoustic backscatter, Offshore of 

Coal Oil Point map area, California, sheet 3 in Johnson, S.Y., Dartnell, P., Cochrane, G.R., Golden, N.E., Phillips, E.L., Ritchie, A.C., 

Kvitek, R.G., Dieter, B.E., Conrad, J.E., Lorenson, T.D., Krigsman, L.M., Greene, H.G., Endris, C.A., Seitz, G.G., Finlayson, D.P., Sliter, 

R.W., Wong, F.L., Erdey, M.D., Gutierrez, C.I., Leifer, I., Yoklavich, M.M., Draut, A.E., Hart, P.E., Hostettler, F.D., Peters, K.E., Kvenvolden, 

K.A., Rosenbauer, R.J., and Fong, G. (S.Y. Johnson and S.A. Cochran, eds.), California State Waters Map Series—Offshore of Coal Oil 

Point, California: U.S. Geological Survey Scientific Investigations Map 3302, pamphlet 57 p., 12 sheets, scale 1:24,000, 

http://dx.doi.org/10.3133/sim3302.

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3302

US Army Corps

of Engineers

Figure 1. Map showing areas of multibeam-echosounder and bathymetric-sidescan surveys (pink shading), 

topographic-lidar surveys (orange diagonal lines), and publicly available interferometric synthetic aperture 

radar (ifSAR) topography (yellow shading). Also shown are data-collecting agencies (CSUMB, California 

State University, Monterey Bay, Seafloor Mapping Lab; FP, Fugro Pelagos; USACE, U.S. Army Corps of 

Engineers; USGS, U.S. Geological Survey) and dates of surveys if known.

USACE, 2009

USGS, 2006

CSUMB, 2007

Fugro Pelagos, 2008

Coal Oil Point

USGS, 2007

USGS, 2008

120° 119°55' 119°50'

34°25'

100

DISCUSSION 

This acoustic-backscatter map of the Offshore of Coal Oil Point map area in southern California was 

generated from backscatter data collected by the U.S. Geological Survey (USGS), by California State University, Monterey Bay (CSUMB), and by Fugro Pelagos (fig. 1). Most of the nearshore and shelf areas were 

mapped by the USGS in 2006, 2007, and 2008, using a combination of 117 kHz (2006, 2007) and 234.5-kHz 

(2008) SEA (AP) Ltd. SWATHplus-M phase-differencing sidescan sonars. A small area in the far-eastern 

nearshore and shelf was mapped by CSUMB in 2007, using a 244-kHz Reson 8101 multibeam echosounder. 

The outer shelf and slope were mapped by Fugro Pelagos in 2008, using a combination of 400-kHz Reson 

7125, 240-kHz Reson 8101, and 100-kHz Reson 8111 multibeam echosounders. These mapping missions 

combined to collect acoustic-backscatter data from about the 10-m isobath to beyond the 3-nautical-mile limit 

of California’s State Waters.

During the USGS mapping missions, differential GPS (DGPS) data (2006, 2007) and GPS data with 

real-time kinematic corrections (2008) were combined with measurements of vessel motion (heave, pitch, and 

roll) in a CodaOctopus F180 attitude-and-position system to produce a high-precision vessel-attitude packet. 

This packet was transmitted to the acquisition software in real time and combined with instantaneous soundvelocity measurements at the transducer head before each ping. The returned samples were projected to the 

seafloor using a ray-tracing algorithm that works with previously measured sound-velocity profiles. Statistical 

filters were applied to discriminate seafloor returns (soundings and backscatter intensity) from unintended 

targets in the water column. The backscatter data were postprocessed using USGS software (D.P. Finlayson, 

written commun., 2011) that normalizes for time-varying signal loss and beam-directivity differences. Thus, 

the raw 16-bit backscatter data were gain-normalized to enhance the backscatter of the SWATHplus system. 

The resulting normalized-amplitude values were rescaled to 16-bit and gridded into GeoJPEGS using GRID 

Processor Software, then imported into a geographic information system (GIS) and converted to GRIDs.

During both the CSUMB and the 2008 Fugro Pelagos multibeam mapping missions, an Applanix POS 

MV (Position and Orientation System for Marine Vessels) was used to accurately position the vessel during 

data collection, and it also accounted for vessel motion such as heave, pitch, and roll (position accuracy, ±2 m; 

pitch, roll, and heading accuracy, ±0.02°; heave accuracy, ±5%, or 5 cm). To account for tidal-cycle fluctuations, CSUMB used NavCom 2050 GPS receiver (CNAV) data, and Fugro Pelagos used KGPS data (GPS data 

with real-time kinematic corrections). In addition, sound-velocity profiles were collected with an Applied 

Microsystems (AM) SVPlus sound velocimeter. Soundings were corrected for vessel motion using the 

Applanix POS MV data, for variations in water-column sound velocity using the AM SVPlus data, and for 

variations in water height (tides) using vertical-position data from the CNAV receiver and also the KGPS data. 

Backscatter data were postprocessed using both Geocoder version 3.2 (Fugro Pelagos modified test release 16) 

and Geocoder within Caris HIPS and SIPS software. Georeferenced Backscatter Rasters (GeoBaRs) were 

created for each survey line using the beam average or time series data type. Intensities were radiometrically 

corrected (including despeckling and angle-varying gain adjustments), and the position of each acoustic 

sample was geometrically corrected for slant range on a line-by-line basis. The contrast and brightness of some 

GeoBaRs were adjusted to better match the surrounding GeoBaRs. Individual GeoBaRs were mosaicked 

together at 2-m resolution using the auto-seam method. The mosaics were then exported as georeferenced 

TIFF images, imported into a GIS, and converted to GRIDs.

The acoustic-backscatter imagery from each different mapping system and processing method were 

merged into their own individual grids. These individual grids, which cover different areas, were displayed in 

a GIS to create this composite acoustic-backscatter map. On the map, brighter tones indicate higher backscatter intensity, and darker tones indicate lower backscatter intensity.The intensity represents a complex interaction between the acoustic pulse and the seafloor, as well as characteristics within the shallow subsurface, 

providing a general indication of seafloor texture and sediment type. Backscatter intensity depends on the 

acoustic source level; the frequency used to image the seafloor; the grazing angle; the composition and 

character of the seafloor, including grain size, water content, bulk density, and seafloor roughness; and some 

biological cover. Harder and rougher bottom types such as rocky outcrops or coarse sediment typically return 

stronger intensities (high backscatter, lighter tones), whereas softer bottom types such as fine sediment return 

weaker intensities (low backscatter, darker tones). The differences in backscatter intensity that are apparent in 

some areas of the map are due to the different frequencies of mapping systems, as well as different processing 

techniques. Note also that the straight lines of higher backscatter intensity that are visible throughout the map 

area are data-collection artifacts.

The onshore-area image was generated by applying an illumination having an azimuth of 300° and from 

45° above the horizon to the coastal airborne topographic-lidar data, as well as to publicly available, 3-mresolution, interferometric synthetic aperture radar (ifSAR) data, available from National Oceanic and Atmospheric Administration (NOAA) Coastal Service Center’s Digital Coast, at http://csc-s-maps-q.csc.noaa.gov/

dataviewer/viewer.html (last accessed April 5, 2011).

EXPLANATION

Backscatter intensity

High

Low

 Area of “no data”—Areas near shoreline not mapped owing to insufficient high-resolution 

seafloor mapping data; areas beyond 3-nautical-mile limit of California’s State Waters were 

not mapped as part of California Seafloor Mapping Program

3-nautical-mile limit of California’s State Waters

Bathymetric contour (in meters)—Derived from modified 10-m-resolution bathymetry grid. 

Contour intervals: 1–100 m water depth, 10 m; >100 m water depth, 50 m

CALIF.

0 4 8 Nautical Miles

Kilometers 0 5 10

120° 119°40' 119°20' 119°

34°

34°20'

MAP LOCATION

Ventura

Santa Barbara

Anacapa

Island

Santa Cruz Island Santa Rosa Island

Area of

Map

Santa Barbara Channel Limit of California’s

State Waters

1 

U.S. Geological Survey;

2 

California State University, Monterey Bay, Seafloor Mapping Lab

Acoustic Backscatter, Offshore of Coal Oil Point Map Area, California

By

Peter Dartnell,1 Eleyne L. Phillips,1 David P. Finlayson,1 James E. Conrad,1 and Rikk G. Kvitek2

2014

ONE MILE = 0.869 NAUTICAL MILES

BATHYMETRIC CONTOUR INTERVALS 10 and 50 METERS

1 .5 0 1 KILOMETER

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET

1 1/2 0 1 MILE

SCALE 1:24 000

APPROXIMATE MEAN

DECLINATION, 2014

MAGNETIC NORTH

12 / ° 1 2

TRUE NORTH

Acoustic-backscatter imagery collected by U.S. Geological Survey in 

2006, 2007, and 2008; by California State University, Monterey Bay, 

Seafloor Mapping Lab in 2007 (reprocessed by Peter Dartnell, 2010); 

and by Fugro Pelagos in 2008. Bathymetric contours by Andrew C. 

Ritchie, 2011

GIS database and digital cartography by Nadine E. Golden and Eleyne 

L. Phillips

Edited by Taryn A. Lindquist

Manuscript approved for publication June 2, 2014

Onshore elevation data from NOAA Coastal Services Center (data collected 

by EarthData International in 2002-2003) and from U.S. Army Corps of 

Engineers (data collected by Fugro Pelagos in 2009). California's State 

Waters limit from NOAA Office of Coast Survey

Universal Transverse Mercator projection, Zone 11N

NOT INTENDED FOR NAVIGATIONAL USE

10

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50

60

70

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100

90

150

200

250

250

Goleta

Isla Vista

Coal Oil Point

Goleta Point

34°25'

120° 119°55' 119°50'

34°30'

34°25'

120° 119°55' 119°50'

Scientific Investigations Map 3302

Sheet 3 of 12

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey