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/of/2014/1214/

Suggested Citation: Bretz, C.K., Kvitek, R.G., Dartnell, P., and Phillips, E.L., 2014, Shaded-relief bathymetry, Offshore of Half Moon Bay 

map area, California, sheet 2 in Cochrane, G.R., Dartnell, P., Greene, H.G., Johnson, S.Y., Golden, N.E., Hartwell, S.R., Dieter, B.E., 

Manson, M.W., Sliter, R.W., Ross, S.L., Watt, J.T., Endris, C.A., Kvitek, R.G., Phillips, E.L., Erdey, M.D., Chin, J.L., and Bretz, C.K. (G.R. 

Cochrane and S.A. Cochran, eds.), California State Waters Map Series—Offshore of Half Moon Bay, California: U.S. Geological 

Survey Open-File Report 2014–1214, pamphlet 37 p., 10 sheets, scale 1:24,000, http://dx.doi.org/10.3133/ofr20141214.

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20141214

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

topographic-lidar surveys (yellow shading). Also shown are data-collecting agencies (CSUMB, California State University, Monterey Bay, Seafloor Mapping Lab; FP, Fugro Pelagos) and dates of surveys if 

known.

122°35' 122°30' 122°25'

37°30'

37°25'

Half Moon Bay FP, 

2006, 2007

CSUMB, 

2007

Photoscience,

2005

10

DISCUSSION

This shaded-relief bathymetry map of the Offshore of Half Moon Bay map area in northern California 

was generated from bathymetry data collected by Fugro Pelagos and by California State University, Monterey 

Bay (CSUMB) (fig. 1). Mapping was completed in 2006 and 2007, using a combination of 400-kHz Reson 

7125 and 244-kHz Reson 8101 multibeam echosounders. These mapping missions combined to collect 

bathymetry data from about the 10-m isobath to beyond the 3-nautical-mile limit of California’s State Waters.

During all the mapping missions, an Applanix POS MV (Position and Orientation System for Marine 

Vessels) was used to accurately position the vessels 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 watercolumn sound velocity using the AM SVPlus data, and for variations in water height (tides) using verticalposition data from the KGPS receivers. 

Processed soundings from the different mapping missions were exported from the acquisition or processing software as XYZ files and bathymetric surfaces. All the surfaces were merged into one overall 2-mresolution bathymetric-surface model and clipped to the boundary of the map area. An illumination having an 

azimuth of 300° and from 45° above the horizon was then applied to the bathymetric surface to create the 

shaded-relief imagery. Gray areas in map are gaps in data.

Bathymetric contours were generated at 10-m intervals from the merged 2-m-resolution bathymetric 

surface. The most continuous contour segments were preserved; smaller segments and isolated island polygons 

were excluded from the final output. Contours were smoothed using a polynomial approximation with 

exponential kernel algorithm and a tolerance value of 60 m.

The onshore-area image was generated by applying the same illumination (azimuth of 300° and from 45° 

above the horizon) to 1-m-resolution topographic-lidar data collected by Photoscience in 2005 for the U.S. 

Geological Survey and the County of San Mateo.

EXPLANATION

Amount of illumination

Illuminated (facing false sun)

In shadow (facing away from false sun)

Direction of illumination from false sun—Position of false sun is at 300° azimuth, 45° above 

horizon [arrow included in explanation for illustration purposes only; not shown on map]

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 2-m-resolution bathymetry grid. Contour 

interval: 10 m

Kilometers 0 5 10

0 5 10Nautical Miles

122°40' 122°20'

38°

37°40'

37°20'

San

Francisco

Bay

Area of

Map

Limit of California’s

State Waters

CALIF.

MAP LOCATION

1

California State University Monterey Bay, Seafloor Mapping Lab;

2

U.S. Geological Survey 

Shaded-Relief Bathymetry, Offshore of Half Moon Bay Map Area, California

By

Carrie K. Bretz,1 Rikk G. Kvitek,1 Pete Dartnell,2 and Eleyne L. Phillips2

2014

ONE MILE = 0.869 NAUTICAL MILES

BATHYMETRIC CONTOUR INTERVAL 10 METERS

1 .5 0 1 KILOMETER

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET

1 1/2 0 1 MILE

14°

SCALE 1:24 000

APPROXIMATE MEAN

DECLINATION, 2014

MAGNETIC 

 NORTH

TRUE NORTH

Onshore elevation data collected by Photoscience in 2005 for U.S. 

Geological Survey and County of San Mateo. California's State 

Waters limit from NOAA Office of Coast Survey

Universal Transverse Mercator projection, Zone 10N

NOT INTENDED FOR NAVIGATIONAL USE

Shaded-relief bathymetry by Peter Dartnell, 2012 (data collected by Fugro Pelagos in 2006 and 2007 and by 

California State University, Monterey Bay, Seafloor Mapping Lab in 2007). Bathymetric contours by Carrie K. 

Bretz, 2008

GIS database and digital cartography by Nadine E. Golden

Manuscript approved for publication October 2, 2014

Half Moon

 Bay

122°35' 122°30' 122°25'

122°35' 122°30' 122°25'

37°30'

37°25'

37°30'

37°25'

Open-File Report 2014–1214

Sheet 2 of 10

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey

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