Measurements of Slope Currents and Internal Tides on the 

Continental Shelf and Slope off Newport Beach, California 

Open-File Report 2014–1041

U.S. Department of the Interior

U.S. Geological Survey

Measurements of Slope Currents and Internal Tides on the 

Continental Shelf and Slope off Newport Beach, California 

By Kurt Rosenberger, Marlene A. Noble, and Benjamin K. Norris

Open-File Report 2014–1041

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment—visit 

http://www.usgs.gov or call 1–888–ASK–USGS

For an overview of USGS information products, including maps, imagery, and publications,

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Suggested citation:

Rosenberger, Kurt, Noble, M.A. and Norris, B.K., 2013, Measurements of Slope Currents and Internal Tides on the 

Continental Shelf and Slope off Newport Beach, California: U.S. Geological Survey Open-File Report 2014–1041, 

65 p., http://dx.doi.org/10.3133/ofr20141041.

ISSN 2331-1258 (online) 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report
iii

Contents

Abstract ......................................................................................................................................................................... 1

Introduction.................................................................................................................................................................... 1

Methods......................................................................................................................................................................... 1

Field Program ............................................................................................................................................................ 1

Instruments............................................................................................................................................................. 2

Mooring and Instrument Setup ............................................................................................................................... 3

Data Processing......................................................................................................................................................... 5

Data-File Identifiers and Formats ........................................................................................................................... 5

Time ....................................................................................................................................................................... 7

Current-meter Data................................................................................................................................................. 7

Optical Backscatter Sensor Data............................................................................................................................ 8

Transmissometer Data ........................................................................................................................................... 8

Results........................................................................................................................................................................... 8

Data Return................................................................................................................................................................ 8

Inner Shelf Site....................................................................................................................................................... 8

Shelf Break Site.................................................................................................................................................... 11

Slope Site............................................................................................................................................................. 11

Shallow Canyon Site ............................................................................................................................................ 11

Deep Canyon Site ................................................................................................................................................ 11

Ancillary Data ....................................................................................................................................................... 12

Discussion ................................................................................................................................................................ 12

Basic Statistics ..................................................................................................................................................... 12

Tidal Parameters .................................................................................................................................................. 13

Conclusions ................................................................................................................................................................. 14

References Cited......................................................................................................................................................... 15

Figures

1. Map of study area showing locations of USGS and OCSD mooring placements ................................. 16

2. Diagram of mooring and tripod placed on inner shelf of Newport Shelf (Inner Shelf site)..................... 17

3. Diagram of mooring and tripod placed on shelf break of Newport Shelf (Shelf Break site)................... 18

4. Diagram of mooring placed on the slope off Newport Shelf (Slope site)............................................... 19

5. Diagram of mooring placed in deep section of Newport Canyon (Deep Canyon site) .......................... 20

6. Diagram of the mooring placed in shallow section of Newport Canyon (Shallow Canyon site) ............ 21

7. Timeline of data acquired by USGS on Newport Shelf and slope, by platform and data type .............. 22

8. Low-pass filtered alongshore and cross-shore currents (Inner Shelf site) ............................................ 23

9. Surface-wave parameters measured by ADCP on bottom-mounted tripod (Inner Shelf site)............... 24

10. Near-bottom water properties and suspended sediment data (Inner Shelf site)................................. 25

11. Meteorological parameters (Inner Shelf site)...................................................................................... 26

12. Surface currents and water properties (Inner Shelf site)..................................................................... 27

13. Low-pass filtered alongshore and cross-shore currents (Shelf Break site)......................................... 28

14. Near-bottom water properties and suspended sediment data (Shelf Break site)................................ 29

15. Surface currents and water properties (Shelf Break site) ................................................................... 30

16. Water-column temperature data (Shelf Break site)............................................................................. 31
iv

17. Contours of water-column temperature data (Shelf Break site).......................................................... 32

18. Low-pass filtered alongshore and cross-shore currents (Slope site) .................................................. 33

19. Near-bottom water properties and suspended sediment data (Slope site)......................................... 34

20. Water-column temperature data (Slope site)...................................................................................... 35

21. Contours of water-column temperature (Slope site) ........................................................................... 36

22. Low-pass filtered alongshore and cross-shore currents (Shallow Canyon site).................................. 37

23. Near-bottom water properties and suspended sediment data (Shallow Canyon site)......................... 38

24. Low-pass filtered alongshore and cross-shore currents (Deep Canyon site)...................................... 39

25. Near-bottom and mid-water column properties and suspended sediment data (Slope site) ............... 40

26. Meteorological parameters (NOAA ocean buoy number 46025) ........................................................ 41

27. Surface-wave parameters (NOAA ocean buoy number 46025).......................................................... 42

28. Meteorological parameters (OCSD Plant2 and Balboa Peninsula personal weather station)............. 43

29. Daily mean river discharge data (USGS streamflow-gaging station number 11074000).................... 44

30. Profile plot of mean currents (Inner Shelf site).................................................................................... 45

31. Profile plot of mean currents (Shelf Break site) .................................................................................. 46

32. Profile plot of mean currents (Slope site)............................................................................................ 47

33. Profile plot of mean currents (Shallow Canyon site)........................................................................... 48

34. Profile plot of mean currents (Deep Canyon site)............................................................................... 49

35. Profile plot of mean currents (OCSD site M18)................................................................................... 50

36. Profile plot of mean currents (OCSD site M19)................................................................................... 51

37. Profile plot of mean currents (OCSD site M20)................................................................................... 52

38. Profile plot of mean currents (OCSD site M21)................................................................................... 53

39. Map of variance ellipses of low-pass filtered flow............................................................................... 54

40. Profile of tidal currents (Inner Shelf site)............................................................................................. 55

41. Profile of tidal currents (Shelf Break site) ........................................................................................... 56

42. Profile of tidal currents (Slope site)..................................................................................................... 57

43. Profile of tidal currents (Deep Canyon site)........................................................................................ 58

44. Profile of tidal currents (Shallow Canyon site) .................................................................................... 59

45. Profile of tidal currents (OCSD site M18)............................................................................................ 60

46. Profile of tidal currents (OCSD site M19)............................................................................................ 61

47. Profile of tidal currents (OCSD site M20)............................................................................................ 62

48. Profile of tidal currents (OCSD site M21)............................................................................................ 63

49. Map of M2 tidal ellipses of vector current-meter data.......................................................................... 64

50. Map of variance ellipses of vector current-meter data........................................................................ 65

Tables

1. List of moorings deployed, measurement goals, and deployment times and locations at 5 study sites ... 3

2. Summary of U.S. Geological Survey netCDF file-naming conventions. ................................................... 6

3. Detailed listing of data return for each instrument.................................................................................... 9
v

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

mile, nautical (nmi) 1.852 kilometer (km)

yard (yd) 0.9144 meter (m)

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

mile per hour (mi/h) 1.609 kilometer per hour (km/h) 

Mass

ounce, avoirdupois (oz) 28.35 gram (g) 

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Pressure

atmosphere, standard (atm) 101.3 kilopascal (kPa)

bar 100 kilopascal (kPa) 

Density

pound per cubic foot (lb/ft3) 16.02 kilogram per cubic meter 

(kg/m3)

pound per cubic foot (lb/ft3) 0.01602 gram per cubic centimeter 

(g/cm3)
vi
1

Measurements of Slope Currents and Internal Tides on the 

Continental Shelf and Slope off Newport Beach, California

By Kurt Rosenberger, Marlene A. Noble, and Benjamin K. Norris

Abstract

An array of seven moorings housing current meters and oceanographic sensors was deployed for 

6 months at 5 sites on the Continental Shelf and slope off Newport Beach, California, from July 2011 to 

January 2012. Full water-column profiles of currents were acquired at all five sites, and a profile of 

water-column temperature was also acquired at two of the five sites for the duration of the deployment. 

In conjunction with this deployment, the Orange County Sanitation District deployed four bottom 

platforms with current meters on the San Pedro Shelf, and these meters provided water-column profiles 

of currents. The data from this program will provide the basis for an investigation of the interaction 

between the deep water flow over the slope and the internal tide on the Continental Shelf. 

Introduction

In the summer of 2011, scientists of the U.S. Geological Survey (USGS) deployed seven moored 

platforms at five sites in the coastal ocean and slope off Newport Beach, California (fig. 1). The primary 

goal of the measurement program was to understand how internal tides on the narrow shelf to the south 

and east of Newport Beach differ from those previously observed on the wider shelf of San Pedro Bay 

(Noble and Xu, 2004), and subsequently, how sediment resuspension due to the internal tide may differ. 

Two secondary goals were (1) to understand how the internal tide on the shelf might be modulated by 

the flow over the slope, specifically by the California Undercurrent, and (2) to measure currents and 

sediment-transport events in Newport Canyon and to compare and contrast the flow and transport events 

in this canyon to those previously observed by USGS scientists in other canyons off the coast of 

California.

Concurrent with this measurement program, the Orange County Sanitation District (OCSD) 

placed four bottom platforms with acoustic Doppler current profilers on the San Pedro Shelf just to the 

north and west of Newport Beach, and the resulting data proved invaluable for comparison between the 

two shelves (fig. 1). The OCSD dataset consists of data from two deployments—the first was from May 

through October 2011, and the second was from October 2011 through January 2012. We present results 

from analyses of data collected during this second deployment period, when there is maximum overlap 

between the USGS and OCSD datasets.

Methods

Field Program

The following is a description of the instruments used in the program the platforms deployed at 

each site, the measurment goals, and which instruments were used to achieve those goals. 
2

Instruments

Acoustic Doppler Current Profilers 

An acoustic Doppler current profiler (ADCP) estimates current velocity in the water by sending 

an acoustic pulse into the water column and measuring the Doppler shift of the returned echo, which is 

reflected back by suspended particulate matter. The instrument can obtain a profile of current velocity 

by measuring the shift at different time lags, which correspond to different distances away from the 

instrument. The ADCPs used in this study, manufactured by Teledyne RD Instruments (TRDI), utilize 

proprietary broadband technology consisting of a pair of pulses sent together to achieve lower standard 

deviation of single pulses. This reduces the number of pulses per averaged ensemble required to attain a 

desired level of accuracy, thus allowing the user to collect ensembles at a higher sampling frequency. 

One disadvantage of the broadband technology, however, is that it reduces the overall profiling range of 

the instrument. The user has the option of setting the instrument in narrow-band mode to increase the 

range, at the expense of higher battery consumption, and thus the sampling frequency and (or) length of 

data record. One limitation of the ADCP, regardless of profiling mode, is that a certain percentage of the 

profile is potentially lost near boundaries, such as the surface or bottom, as a result of interference with 

side lobes of the acoustic beam. For the the TRDI ADCP used in this study, 6 percent of the water 

column is potentially affected. 

Single-Point Acoustic Doppler Current Meter 

A Nortek Aquadopp single-point acoustic Doppler current meter (AQD) was used on the surface 

buoy at each site to provide an independent measure of currents at the surface, where data on currents 

from the profiling ADCP could potentially be unusable. The Aquadopp also uses Doppler technology, 

by employing three acoustic beams to estimate water velocity at a single depth level.

Conductivity/Temperature Recorders 

Conductivity/temperature (CT) recorders measure water temperature and conductivity at the 

sensor location and record the values at specified intervals. From these measurements, salinity can be 

calculated by using the 1978 Practical Salinity Scale 

(http://www.seabird.com/application_notes/AN14.htm) (IEEE, 1980). 

Some CT recorders have the capability to log data from other sensors as well, such as pressure sensors, 

or analog external sensors that measure optical backscatter or fluorometry. A CT recorder with a 

pressure sensor installed (for measuring water depth) is referred to as a CTD. 

Temperature Loggers

A temperature logger (thermistor) measures temperature and records the data at programmed 

intervals. Typically, the thermistor is mounted on the exterior of the underwater housing, such that the 

instrument may respond more rapidly to rapid changes in water temperature. 

Optical Backscatter Sensors 

An optical baskscatter sensor (OBS) measures turbidity by sending a beam of infrared light into 

the water and then measuring the quantity of light that is reflected back to its sensor from suspended 

particles. The relationship between the raw OBS signal and the suspended-sediment concentration can 

be determined in the laboratory by calibrating the sensors with sediment collected in-situ. 
3

Transmissometers

A transmissometer measures the transmission of red collimated light (650 nm wavelength) from 

a light emitting diode (LED) along a fixed path through the water. Transmissometer data can be 

represented as a percentage of light transmission (from 0 to 100 percent, where 0 percent is completely 

occluded), or as light attenuation, or ‘beam-c’, in units of m-1 (utilizing another linear conversion). The 

advantage of presenting the data in light attenuation units is that the values increase as the suspended 

load increases. In addition, the usage of m-1 accounts for the path length of the instrument, thus making 

measurements from instruments of two different path lengths comparable. 

Mooring and Instrument Setup

Of the five USGS mooring sites, three were arranged in a cross-shelf transect from the slope up 

onto the shelf southeast of Newport Harbor (referred to here as the Newport Shelf), and two were in 

Newport Canyon (fig. 1, table 1). The shallowest site of the Newport Shelf array consisted of a tripod 

and surface-mooring pair in 15 m water depth, referred to here as the Inner Shelf site (fig. 2). The tripod 

(mooring ID NPT11IST) housed a 1,200-kHz TRDI Workhorse ADCP for measuring water-column 

profiles of currents and surface waves, a CTD that logged two LED transmissometers and a dissolvedoxygen sensor, and a second CTD for comparative purposes. The surface mooring (mooring ID 

NPT11ISS) housed a CTD, a single-point current meter positioned 1 m below the surface and a wind 

sensor for measuring windspeed and direction 2 m above the surface.

The two CTDs on the tripod use different methods for estimating the salinity of the water; the 

first measures conducitivity with an inductive coil, and the second measures conducitivity with an 

electrode conductivity cell. In addition, each transmissometer had a different mechanism for preventing 

fouling. The first transmissiometer (variable ATTN1) measured light attenuation through a volume of 

water in an enclosed flow-though tube that was connected to a plumbed system driven by the CTD 

pump. Incoming water samples to this transmissometer first passed through the CTD conductivity cell, 

and thus contain trace amounts antifoulant that should adequately prevent growth on the sensor face of 

the tranmissometer. The second transmissometer (variable ATTN2) was an open system that had an 

automated wiper, with brushes designed to wipe the sensor face clean on regular intervals. 

Table 1. List of moorings deployed, measurement goals, and deployment times and locations at the five study 

sites, Newport Beach, California. 

Site Platform Measurement Goal Latitude 

(North)

Longitude 

(West)

Depth 

(m)

Deployed

(GMT)

Recovered

(GMT)

NPT11IST

Inner Shelf

Small 

Tripod

Currents, suspended 

sediment, waves 33.572 117.845 14.2 7/21/2011, 

15:16:40

1/24/2012,

14:58:00

NPT11ISS

Inner Shelf

Surface 

Buoy

Winds, surface 

currents, temperature 33.572 117.844 15.2 7/21/2011, 

14:55:20

1/25/2012,

16:21:15

NPT11SBT

Shelf Break

Small 

Tripod

Currents, suspended 

sediment 33.560 117.857 85.2 7/20/2011, 

16:39:00

1/24/2012,

16:18:00

NPT11SBS

Shelf Break

Surface 

Mooring

Winds, surface 

currents, water 

column temperature

33.559 117.857 83.0 7/20/2011, 

16:08:00

1/24/2012,

18:13:00
4

Site Platform Measurement Goal Latitude 

(North)

Longitude 

(West)

Depth 

(m)

Deployed

(GMT)

Recovered

(GMT)

NPT11SLB

Slope

SubSurface 

Mooring

Water Column 

Currents and 

temperature, 

suspended sediment

33.545 117.866 358.0 7/18/2011, 

23:57:00

3/20/2012,

16:00:00

NPT11DCB

Deep 

Canyon

SubSurface 

Mooring

Water Column 

Currents, suspended 

sediment

33.548 117.927 390.0 7/18/2011,

15:10:00

1/25/2012,

21:00:00

NPT11SCB

Shallow 

Canyon

SubSurface 

Mooring

Water Column 

Currents, suspended 

sediment

33.582 117.928 215.0 7/18/2011, 

20:00:00

1/25/2012,

15:06

HBC11M18 Small 

Tripod

Water Column 

Currents 33.573 117.995 58.0 10/24/2011, 

18:50:00 

1/27/2012,

18:25:30

HBC11M19 Small 

Tripod

Water Column 

Currents 33.590 117.984 40.0 10/24/2011, 

17:49:00

1/27/2012,

19:01:00

HBC11M20 Small 

Tripod

Water Column 

Currents 33.607 117.972 20.0 10/26/2011, 

19:25:00

1/27/2012,

19:25:00

HBC11M21 Small 

Tripod

Water Column 

Currents 33.579 117.959 56.0 10/26/2011, 

17:31:00

1/27/2012,

18:13:30

Offshore of the Inner Shelf site, another bottom mounted tripod and surface-mooring pair were 

deployed on the shelf break in 85 m water depth, referred to here as the Shelf Break site (fig. 3). The 

tripod (mooring ID NPT11SBT) housed a 300-kHz RDI Workhorse ADCP that profiled the entire water 

column and a CTD that logged measurements of temperature, salinity, and light attenuation by using an 

external LED transmissometer. In addition, the tripod housed a broadband 5-beam ADCP for measuring 

high-resolution profiles of currents in the first 4 m above the tripod. The surface mooring (mooring ID 

NPT11SBS) had thermistors on the mooring wire at 10-m intervals, and the surface buoy housed a 

CTD, a single point current meter for measuring at 1 m water depth, and a wind sensor for measuring 

windspeed and direction 3 m above the surface. 

The deepest site of the Newport Shelf mooring array lay on the slope at about 350 m water 

depth, and consisted of one 247-m-tall subsurface mooring (mooring ID NPT11SLB), referred to here as 

the Slope mooring. This mooring had three 300-kHz RDI Workhorse ADCPs arranged vertically to 

measure currents throughout the water column, as well as a string of thermistors at 25-m intervals along 

the mooring wire (fig. 4). A CTD in an in-line frame 19 above the bed, logged light-attenuation data 

from an LED transmissometer. The purpose of this mooring was to detect the presence of the California 

Undercurrent in this region and to observe internal tides propogating onto the Newport Shelf. 

Two of the three ADCPs on the Slope mooring were mounted in an upward and downward 

configuration in a subsurface sphere at the top of the mooring at 170 m water depth. These two 

instruments were programmed in narrowband (or long-range ) mode, with 4-m vertical bins, to acquire 

longer current profiles than could be achieved with the standard broadband mode. The assumed 

maximum range for each was 150 m, thus covering 300 m of the water column. A Seabird SBE-39 

pressure and temperature recorder was also placed on the ADCP frame to monitor laydown of the 

mooring due to strong currents. The third ADCP was placed in a downward configuration measuring in 

standard broadband mode with smaller, 2-m bins, to provide more accurate measurements of nearbottom flow. This ADCP was conservatively placed 80 m above the bed, as the maximum range in this 

mode is 100 m. The planned water depth for this mooring was 380 m, and in anticipation that the long-
5

range ADCPs might not acquire data to the full extent specified by the manufacturer, a known gap 

between measurement volumes was built into the mooring design between the middle ADCP and the 

lower ADCP.

Two subsurface moorings were deployed in Newport Canyon to assess the potential for transport 

of sediment from the shelf down-canyon to the continental slope and rise. The deeper of the two 

moorings (mooring ID NPT11SLB) was of a similar configuration to that of the Slope mooring, except 

that it was shorter, at 217 m in height. It was deployed in 390 m water depth with three 300-kHz TRDI 

Workhorse ADCPs in a vertical configuration that collected profiles of current velocities throughout the 

water column (fig. 5). Although this mooring did not have a full string of thermistors as the Slope 

mooring did, there was a high-resolution thermistor on each ADCP frame and a Seabird SBE-37 CT 

logger and an RBR Branker logger recording measurements from a Wetlabs C-Star 25-cm 

transmissometer in a frame 19 mab. The canyon has slight relief at this water depth (that is, the canyon 

itself is not deep); the rim of the canyon is approximately 30 m above the canyon floor (fig. 1). 

A shorter, 90-m-tall mooring was deployed in the shallower section of Newport Canyon in 215 

m water depth (mooring ID NPT11SCB). This mooring consisted of two 300-kHz RDI Workhorse 

ADCPs in a paired upward-downward configuration to acquire profiles of currents throughout the entire 

water column (fig. 6). The downward-facing ADCP was programmed to broadband mode, collecting 

current data in 2-m vertical bins every 5 minutes, in order to better resolve the near-bed flows and any 

potential turbidity currents. The upward-facing ADCP was programmed in narrow-band mode, 

collecting profiles in 4-m vertical bins every 15 minutes. A Seabird SBE-39 pressure and temperature 

recorder was also placed on the ADCP frame to monitor laydown of the mooring due to strong currents. 

An SBE-16 CTD in an in-line mooring frame, 21 meters above bottom, measured temperature, salinity 

and pressure and logged data from a Wetlabs C-Star 10-cm transmissometer.

The OCSD dataset is presented here with permission from OCSD. The four sites occupied by 

OCSD during the USGS measurement program (M18, M19, M20, and M21) have been used by OCSD 

for many years to understand the flow on the San Pedro Shelf (SAIC, 2009). The USGS mooring IDs 

for these sites are HBC11M18, HBC11M19, HBC11M20 and HBC11M21. Each site consisted of an 

upward-facing ADCP mounted on a small, bottom tripod, approximately 1 mab; the first three sites had 

300-kHz RDI Workhorse ADCPs, and the last site, HBC11M20, in shallower water, had a 600-kHz RDI 

ADCP. The measurement program consisted of two deployments; the first lasted 5 months from lateMay until mid-October 2011, and the second lasted 3 months from late October 2011 until late January 

2012. We present data from the second deployment only in this report, because this period had greater 

overlap with the USGS deployment. 

Data Processing

Data-File Identifiers and Formats

An eight-character alpha-numeric mooring identification number (mooring ID) is assigned to 

each mooring or tripod and is used to identify all files containing time-series data recorded by 

instruments mounted on that platform. The mooring ID is the key to identifying and(or) locating data 

records in the USGS Pacific Coastal & Marine Science Center (PCMSC) time-series data-management 

system. In this identification scheme, the first three characters denote the project (in this case, ‘NPT’ for 

Newport Shelf), the next two characters identifiy the year, and the last three characters denote the site 

name and platform type. For example, NPT11IST denotes the Newport 2011 project Inner Shelf Tripod. 

Each instrument placed on the platform is then given a two-digit identifier, usually numbered according 

to the vertical position on the mooring or tripod. This two-digit identifier is appended to the end of each 
6

mooring ID to provide unique identifier for every instrument deployed in the ocean by PCMSC. Thus, 

NPT11IST01 identifies the topmost instrument on mooring NPT11IST; NPT11IST02 identifies the next 

instrument down on mooring NPT11IST, and so on. As data files are processed, additional identifiers 

are added to the ten-digit identifier to indicate sensors and any additional processing steps, such as 

averaging, that have been performed on the data. Table 2 summarizes the file-naming system.

Raw data files downloaded from each instrument were translated from the manufacturer’s data 

format into the netCDF data-file format using instrument-specific toolboxes developed in Matlab by 

USGS scientists. The netCDF data file format, developed by the Unidata Corporation 

(http://www.unidata.ucar.edu/software/netcdf/), is a compact binary format compatible with most 

computer systems that stores both the data and the metadata in the file.

Table 2. Summary of U.S. Geological Survey netCDF file-naming conventions. 

Mooring ID Instrument 

Identifier

Sampling 

Scheme 

(optional)

Data Type 

(optional) Version File Extension

USGS 

Instrument ID

First three digits identify program, next two digits the year, next three digits the site name, and last two the 

instrument number.

mc MicroCat temperature and salinity data

adc ADCP water flow data

adv ADV and accessory sensor data

pca PCADP and accessory sensor data

abs ABS statistics data

bt Brancker temperature data

sc Seacat temperature and salinity data

att Transmissometer data

1 First sampling scheme when multiple schemes are used

2 Second sampling scheme when multiple scheme are used

 b Burst data for instruments with burst and statistics 

files 

 q Quality data for instruments with flagging recorded 

in separate files

-a USGS best basic version

.nc

netCDF file 

extension

Example file names

Instrument ID Instrument 

Identifier

Sampling 

Scheme 

(optional)

Data Type 

(optional) Version File Extension

NPT11SLB15 bl -a .nc

.nc

Instrument ID Instrument 

Identifier

Sampling 

Scheme 

(optional)

Data Type 

(optional) Version File Extension

NPT11IST01 wh Wvs-p -a .nc

The USGS uses the Equatorial Pacific Information Collection conventions for organizing and 

naming oceanographic data variables developed by the National Oceanic and Atmospheric 
7

Administration Pacific Marine Environmental Laboratory. The data were processed using qualitycontrol procedures developed for all oceanographic data by the USGS. Files generated during the first 

processing step (which involved conversion to engineering units and quality-assurance calculations) 

were stored in netCDF format with ‘.cdf’ suffixes. Subsequent data-processing steps can include the 

application of calibration coefficients, coordinate transformations, rotation into geographic coordinates, 

and averaging of good data. Final versions of the processed data variables are stored in netCDF format 

with ‘.nc’ extensions. All of the final statistics data are in EPIC-compliant netCDF format. 

Time

Times are reported in Universal Time [(UT, equivalent to Greenwich Mean Time (GMT)]. We 

checked for drift of instrument clocks by comparing instrument times with accurate times [(from the 

GPS, or from clocks synchronized with the National Institute of Standards and Technology in Boulder, 

Colorado (http://tf.nist.gov/)], before and after deployments. The observed offsets were small compared 

to the sample intervals (typically ~10), so no adjustments to any instrument times in this data set were 

made.

Time is recorded in the netCDF files as two variables, named time1 and time2, in compliance 

with EPIC standards to allow precise storage of time in integer format. Time1 is the Julian day, where 

midnight on May 23, 1968, equals 2,440,000, and time2 is the elapsed time on that day, in milliseconds 

since midnight. Thus, time in decimal Julian days is computed as time1+time2/(1,000 x 3,600 x 24). 

Current-meter Data

Instrument Orientations

Each of the current meters had internally mounted flux-gate compasses. These compasses were 

calibrated prior to deployment according to manufacturer’s recommendations. Raw current data were 

recorded in beam coordinates for instruments mounted on the bottom (that is, they were not freely 

moving) and the data were transformed into earth coordinates (corrected for pitch, roll, and heading) 

during post processing. Velocity data was recorded in earth coordinates for instruments mounted on 

subsurface or surface moorings, whereby the instrument performs the coordinate transformation in real 

time for each ensemble. It was necessary to do this for these moorings because the frames on the 

mooring lines were able to rotate and pitch. 

All data were rotated to true geographic coordinates (positive axes toward east, north, and up) 

using instrument compasses and tilt sensors and correcting for local magnetic variation (12.4o east of 

true North). For some of the results and discussions, the horizontal components of current velocity have 

been rotated into alongshore and cross-shore coordinates, with the positive alongshore axis oriented 

toward 300o True. Flow in the positive alongshore direction (toward Los Angeles) is described as 

upcoast or poleward, whereas flow in the negative alongshore direction (toward San Diego) is described 

as downcoast or equatorward. 

Acoustic Doppler Current Profiler Data

The ADCP data were processed according to standard USGS procedures by using ADCP Tools, 

a collection of Matlab routines written to read in and process raw ADCP data and to create netCDF files 

of the raw and processed data. The toolbox is described in USGS Open-File Report 00–458. Raw data 

files from the ADCPs were converted to netCDF format and checked for clock accuracy by comparing 

in-and-out-of-water times to the mooring log and checking for linear-time progression. Data were 

despiked, with gaps replacing bad data points. The clocks, ADCP calibrations, and internal compasses 
8

of nearby instruments were compared for consistency. Automatic algorithms were used to check for 

high-intensity reflection indicative of fish or other beam obstructions. Bad values were masked both 

manually and automatically and, where possible, a three-beam solution was used to fill in gaps caused 

by one compromised beam. Data above the water surface were masked; since the water depth at the site 

varies with the stage of the tide, there are periods when some bins above the water surface are retained 

within the file. Data collected before the instrument was on bottom or after it was recovered were 

trimmed. Finally, the data were rotated from beam coordinates into geographic coordinates. The final 

processed versions of these data were stored in EPIC-compliant netCDF format.

Aquadopp Single-point Current-meter Data

Raw current-velocity data measured by the Aquadopp single-point current meters were first 

converted into netCDF format These instruments were set to record velocity data in Earth coordinates as 

while they were mounted on freely-rotating surface platforms. The data were screened for quality using 

standard thresholds for acoustic correllation and return-echo intensity, and then they were rotated into 

geographic coordinates using the local magnetic variation. 

Optical Backscatter Sensor Data

The Nortek Aquadopp data logger converts raw optical backscatter sensor (OBS) voltage 

measurements to counts with a 16-bit analog-digital converter. Data were converted from counts back to 

volts (a linear conversion) in the processing so that the data could be calibrated to sediment 

concentration using laboratory-derived calibration coefficients. The Seabird SBE-16 Seacat logs the 

analog voltages from the OBS directly. The data are available in the netCDF ‘.nc’ file for the instrument 

to which the OBS was connected (Seabird Seacat or Nortek Aquadopp). As there are no standards for 

screening bad data values for this data type, no quality/-control procedure has been applied, and 

determining quality of the data is at the discretion of the researcher.

Transmissometer Data

Seabird SeaCAT CTD loggers and RBR Brancker loggers were used to log raw voltage data 

from the transmissometers. Processing of the data from these loggers includes converting the raw 

voltage values into values of light attenuation (beam-c) in units of m-1. The final data are available in the 

.nc file for the instrument with which the transmissometer was deployed (RBR Branker logger or 

Seacat).

Results

Data Return

The following is a discussion of the data return for each platform deployed. A detailed listing of 

the data return for each instrument is provided in table 3, and a timeline of the data return (for USGS 

data only) by data type and platform is presented in figure 7. 

Inner Shelf Site

The tripod at the Inner Shelf site (NPT11IST) collected a complete record of water-column 

currents and waves (as recorded by the ADCP) and water properties (temperature and salinity) from one 

CTD. A second CTD that was logging data from two transmissometers and an oxygen sensor stopped 
9

recording on November 14, 2011. Low-pass, filtered (to remove tidal fluctuations) alongshore and 

cross-shore current velocity data from three depth levels are plotted in figure 8, and directional-wave 

parameters are plotted in figure 9. Water properties, as measured by the two CTDs on the tripod and 

measurements of light attenuation (made by the two individual transmissometers), are plotted in figure 

10. 

Table 3. Detailed listing of data return for each instrument. Values for depth(s) listed represent the depth(s) that 

the instrument made measurements, not necessarily the depth of the instrument itself.

[Abbreviations of parameters: T, temperature; S, salinity; SS, suspended sediment; CP, current profile; D, directional wave 

data; W, non-directional wave data; Met, meteorologic data]

Mooring Instrument Depth 

(Height)

Parameters 

Measured

Sampling 

Scheme Processed File(s) Date Ranges

NPT11IST - Inner Shelf Tripod - 15.2m

NPT11IST01 RDI 1200 kHz ADCP 2.4-14.4 CP/T/W 3 minute NPT11IST01wh.nc 7/21/11-1/24/12

NPT11IST02 RBR XR-420 CTD 14.1 S/T/D 5 minute NPT11IST02ctd.nc 7/21/11-1/24/12

NPT11IST03

Seabird SBE16+/Trans/OBS 14.4 CP/T 6 minute NPT11IST03sc.nc 7/21/11-11/14/11

NPT11ISS - Inner Shelf Surface Mooring - 14.3m

NPT11ISS01 Airmar Met PB-200 2 Met 3 minute NPT11ISS01met.nc 11/12/11-1/24/12

NPT11ISS02 RBR XR-420 CTD 1 S/T/D 5 minute NPT11ISS02ctd.nc 7/21/11-1/2/12

NPT11ISS03 Nortek Current Meter 1 CP/T 3 minute NPT11ISS03aq-cal.nc 7/21/11-1/24/12

NPT11SBS - Shelf Break Surface Buoy - 83m

NPT11SBS01 Airmar Met PB-200 2 Met 3 minute NPT11SBS01met.nc 7/20/11-7/31/11

NPT11SBS02 RBR XR-420 CTD 1 S/T/D 5 minute NPT11SBS02ctd.nc 7/20/11-1/24/12

NPT11SBS03 Nortek Current Meter 1 CP/T 3 minute NPT11SBS03aqcal.nc 7/20/11-1/24/12

NPT11SBS04 RBR TR-1050 

Temperature 10 T 1 minute NPT11SBS04bt.nc 7/20/11-1/24/12

NPT11SBS05 RBR TR-1050 

Temperature 20 T 1 minute NPT11SBS05bt.nc 7/20/11-1/24/12

NPT11SBS06 RBR TR-1050 

Temperature 30 T 1 minute NPT11SBS06bt.nc 7/20/11-1/24/12

NPT11SBS07 RBR TR-1050 

Temperature 40 T 1 minute NPT11SBS07bt.nc 7/20/11-1/24/12

NPT11SBS08 RBR TR-1050 

Temperature 50 T 1 minute NPT11SBS08bt.nc 7/20/11-1/24/12

NPT11SBS09 RBR TR-1050 

Temperature 60 T 1 minute NPT11SBS09bt.nc 7/20/11-1/24/12

NPT11SBS10 RBR TR-1050 

Temperature 70 T 1 minute NPT11SBS10bt.nc 7/20/11-1/24/12

NPT11SBS11 RBR TR-1050 

Temperature 80 T 1 minute NPT11SBS11bt.nc 7/20/11-1/24/12

NPT11SBT - Shelf Break Tripod - 85.2m

NPT11SBT01 RDI 300 kHz ADCP 9.2-81.2 CP/T 3 minute NPT11SBT01wh.nc 7/20/11-1/24/12

NPT11SBT02 RDI 1200 kHz 5-

Beam BBADCP 84 CP/T 7.5min bursts 

NPT11SBT03 Seabird SBE16+/Trans/OBS 84 S/T/D/SS 5 minute NPT11SBT03sc.nc 7/20/11-1/24/12

NPT11SLB - Slope Subsurface Mooring - 358m

NPT11SLB01 RDI 300 kHz ADCP 6.8- CP/T 15 minute NPT11SLB01wh.nc 7/19/11-12/23/12
10

Mooring Instrument Depth 

(Height)

Parameters 

Measured

Sampling 

Scheme Processed File(s) Date Ranges

106.8

NPT11SLB02 Seabird SBE-39 TP 97 T/CP 5 minute NPT11SLB02pr.nc 7/19/11-3/20/12

NPT11SLB03 RDI 300 kHz ADCP 119.1-

275.1 CP/T 15 minute NPT11SLB03wh.nc 7/19/11-12/23/12

NPT11SLB04 Star Oddi 

Temperature 117 T 1 minute NPT11SLB04st.nc 7/19/11-3/18/12

NPT11SLB05 Star Oddi 

Temperature 142 T 1 minute NPT11SLB05st.nc 7/19/11-3/18/12

NPT11SLB06 Star Oddi 

Temperature 167 T 1 minute NPT11SLB06st.nc 7/19/11-3/18/12

NPT11SLB07 Star Oddi 

Temperature

192 T 1 minute NPT11SLB07st.nc 7/19/11-3/20/12

NPT11SLB08 Star Oddi 

Temperature 217 T 1 minute NPT11SLB08st.nc 7/19/11-3/18/12

NPT11SLB09 Star Oddi 

Temperature 242 T 1 minute NPT11SLB09st.nc 7/19/11-3/18/12

NPT11SLB10 Star Oddi 

Temperature 267 T 1 minute NPT11SLB10st.nc 7/19/11-3/18/12

NPT11SLB11 RDI 300 kHz ADCP 292.2-

354.2 CP/T 15 minute NPT11SLB11wh.nc 7/19/11-3/20/12

NPT11SLB12 RBR TR-1050 

Temperature 272 T 1 minute NPT11SLB12bt.nc 7/18/11-3/20/12

NPT11SLB13 Star Oddi 

Temperature 292 T 1 minute NPT11SLB13st.nc 7/18/11-3/20/12

NPT11SLB14 Star Oddi 

Temperature 317 T 1 minute NPT11SLB14st.nc 7/18/11-3/20/12

NPT11SLB15 RBR Logger/ Seatech 

Trans 323 SS 10 minute NPT11SLB15bl.nc 7/18/11-2/29/12

NPT11SLB16 Seabird SBE-37 CT 323 S/T 5 minute NPT11SLB16mc.nc 7/19/11-3/18/12

NPT11DCB - Deep Canyon Subsurface Mooring - 390m

NPT11DCB01 RDI 300 kHz ADCP 10.8-

166.8 T/S 15 minute NPT11DCB01wh.nc 7/18/11-1/25/12

NPT11DCB02 Seabird SBE-39 TP 173 T/CP 3 minute NPT11DCB02pr.nc 7/19/11-1/25/12

NPT11DCB03 RDI 300 kHz ADCP 174.1-

330.1 T/S 15 minute NPT11DCB03wh.nc 7/18/11-1/25/12

NPT11DCB04 RDI 300 kHz ADCP 324.2-

386.2 T 15 minute NPT11DCB04wh.nc 7/18/11-1/25/12

NPT11DCB05 RBR TR-1050 

Temperature 320 T 3 minute NPT11DCB05bt.nc 7/18/11-1/25/12

NPT11DCB06 Seabird SBE-37 CT 371 T/S 3 minute NPT11DCB06mc.nc 7/19/11-1/25/12

NPT11DCB07 RBR Logger/ Seatech 

Trans 371 T 3 minute NPT11DCB07bl.nc 7/18/11-1/25/12

NPT11SCB - Shallow Canyon Subsurface Mooring - 215m

NPT11SCB01 RDI 300 kHz ADCP 12.8-

136.8 CP/T 15 minute NPT11SCB01wh.nc 7/18/11-1/25/12

NPT11SCB02 Seabird SBE-39 TP 144 T/CP 5 minute NPT11SCB02pr.nc 7/19/11-1/25/12

NPT11SCB03 RDI 300 kHz ADCP 147.2-

205.2 CP/T 15 minute NPT11SCB03wh.nc 7/18/11-11/1/11

NPT11SCB04 Seabird SBE-16 CT 187 S/T 5 minute NPT11SCB04sc-aq.nc 7/18/11-1/25/12

NPT11SCB05 Sequoia LISST-25 187 SS 5 minute NPT11SCB05ls.nc
11

The instrumentation on the surface mooring at the Inner Shelf site (NPT11ISS) collected a 

mostly complete record for the deployment period. The meteorological station data logger did not 

record time for the first few months of the deployment, rendering those data unusable. The data logger

began recording time on November 18, 2011, and continued through the end of the deployment period 

(fig. 11). The single-point Aquadopp current meter acquired a complete record of currents and optical 

backscatter, and the CTD recorded water properites through January 2, 2012 (fig. 12). 

Shelf Break Site

The ADCP and the CTD on the Shelf Break tripod (NPT11SBT) collected data for the entire 

deployment period. The high-resolution ADCP collected burst data on currents for one month, however 

the data are not presented here because they are experimental. Low-pass filtered alongshore and crossshore current velocity data from three depth levels are plotted in figure 13. Water properties 

(temperature and salinity), light attenuation, and optical backscatter data are plotted in figure 14. 

The surface mooring at the Shelf Break site (NPT11SBS) collected a complete record of nearsurface currents, temperature, and salinity (fig. 15), as well as water-column temperature data (figs. 16 

and 17). The meteorological station at this site stopped recording data after one week; therefore, the data 

are not presented here. 

Slope Site

The mooring at the Slope site (NPT11SLB) did not return to the surface when the initial 

recovery was attempted in January 2012; subsequently, USGS personnel returned to the site in March 

2012 to recover the mooring with grappling hooks. Although this mooring collected a longer dataset 

than the rest, some instruments stopped prior to recovery as a result of battery failure, including the two 

ADCPs in the upper water column (both stopped on December 24, 2011) and the bottom 

transmissometer logger (NPT11SLB15, ending on February 29, 2012). All other instruments collected a 

full record for the duration of the deployment. 

Low-pass filtered alongshore and cross-shore currents at several depth levels from the three 

ADCPs are plotted in figure 18, and near-bottom water properties (temperature and salinity) and light 

attenuation data are plotted in figure 19. Raw temperature readings from the thermistor string, ranging 

from 97 to 323 m water depth are shown in figure 20, and a contour plot of these data is presented in 

figure 21. 

Shallow Canyon Site

The mooring placed in the shallow section of Newport Canyon (NPT11SCB) collected a 

complete record of currents and water properties for the deployment period. The upward facing ADCP 

collected water-column velocity data from 126 m water depth to the surface in 4 m vertical bins, while 

the downward facing ADCP collected velocity data from 136 m water depth to the bottom of the canyon 

at 194 m in 2 m bins. Low-pass, filtered current-meter data, rotated into alongshore and cross-shore 

orientations at several depth bins through the water column are plotted in figure 22. Data from the 

CTD/transmissometer package 17 m off the bottom and from the pressure/temperature logger mounted 

on the ADCP frame are plotted in figure 23.

Deep Canyon Site

The mooring placed in the deeper section of Newport Canyon (NPT11DCB) collected a 

complete record of currents and water properties for the deployment period. The top ADCP collected 
12

current data from 10 to 166 m water depth, the middle ADCP collected data from 180 to 324 m water 

depth (both in 4 m vertical bins), and the bottom ADCP collected data from 318 to 380 m water depth 

(in 2 m vertical bins). Low-pass filtered alongshore and cross-shore currents at several depth bins 

throughout the water column are plotted in figure 24. Data from the CTD/transmissometer package 17 

m off the bottom and from as well as the pressure/temperature logger mounted on the ADCP frame are 

plotted in figure 25. 

Ancillary Data

Data from other agencies were gathered for analysis in conjunction with the USGS data. 

Meteorological and wave data for the deployment period were acquired from NOAA buoy 46025, 33 

nautical miles west-southwest of Santa Monica, in the Santa Monica Basin 

(http://www.ndbc.noaa.gov/station_page.php?station=46025) (figs. 26 and 27). Wind data on shore 

were acquired from two sources: (1) the OCSD Plant 2 near Talbot Marsh, and (2) a personal weather 

station on the Balboa Penisula at the entrance to Newport Harbor, downloaded from Weather 

Underground 

(http://classic.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KCANEWPO17) (fig. 28).

River discharge data were acquired from USGS streamflow-gaging station 11074000 on the Santa Ana 

River (2001) and were plotted in figure 29. We also obtained data on mean sea level for the duration of 

the deployment from NOAA’s National Ocean Service water-level station number 9410660 at the 

entrance to Los Angeles Harbor (http://co-ops.nos.noaa.gov/waterlevels.html?id=9410660). 

Discussion

An assesment of the data quality involves an examination of basic statistics and standard 

oceanographic parameters to place the data in context with data previously acquired from the region and 

our current undertstanding of the important oceanographic processes. Here we focus on examining the 

profiles of current-meter data, the primary objective of this study. 

Basic Statistics

Basic statistics were run on the current meter data to assess data quality and to compare to other 

available data (in particular, the OCSD current meter-data). The current-meter data are stored in the 

final format as eastward and northward vector components, and mean profiles of these components were 

computed for the entire deployment period. Alongshore and cross-shore components of the data were 

determined by rotating the current data to align with the coastline. This is often done individually for 

each moored platform, however for this presentation of the data, a single rotation value of 60 degrees 

was used to rotate all of the data into alongshore and cross-shore constituents. Profiles of mean 

alongshore and cross-shore velocity and speed and direction for the five USGS sites and the four OCSD 

sites are plotted in figures 30–38. 

Mean flow through the region is predominantly poleward (upcoast) at depth and equatorward 

(downcoast) near the surface, as has been observed in previous studies in the central southern California 

Bight (Noble and Xu, 2004; Hamilton and others, 2006; Noble and others 2009; Rosenberger and 

others, 2011). The depth of the surface layer that flows downcoast (as well as the percentage of the 

water column) varies with distance from shore. On the San Pedro Shelf, the surface layer is 9 m deep 

(42 percent of the water column) inshore at site M20 (fig. 37) and 12 m deep (21 percent of the water 

column) at the southwestern end of the shelf at site M21 (fig 38), but it is not present mid-shelf (site 

M19) or at the southern end of the shelf (site M18). Both the Shallow Canyon and Deep Canyon sites 
13

exhibit downcoast flow at the surface that is 25 m deep (12 percent) and 50 m deep (13 percent), 

respectively. On the Newport Shelf to the southeast, most of the water column flows downcoast in 14 m 

water depth at the Inshore site (90 percent). Farther offshore this surface layer is 30 m deep (35 percent) 

at the Shelf Break site and ~45 m deep (13 percent) at the Slope site.

A slight discontinuity in current direction, at ~110 m water depth at the Slope site (fig. 32) and at 

~175 m water depth at the Deep Canyon site (fig. 34), suggest suggests a slight difference in compassdirection readings between the upward-looking and downward-looking ADCP’s at each site. Although 

the compass for each instrument is calibrated for magnetic- field disturbance (primarily by the internal 

battery) at the beginning of the deployment, that disturbance can change over time as the battery is 

depleted. Unfortunately there is no way to account for this change, however, the difference is minor. 

In addition to the profiles of the mean alongshore and cross-shore currents, it is instructive to 

examine the variance of the low-pass filtered (subtidal) data to ensure the patterns match the expected 

flow in the region. To achieve this we performed a principal components analysis (PCA) on the lowpass, filtered vector data, which resulted in ellipse parameters of the data variance (elucidating the 

primary orientation of the low-pass, filtered flow, the inclination of the major axis). PCA ellipses at 

several depths in the water column at each site are plotted in figure 39. 

The PCA current ellipses are consistent with results from other measurement programs in the 

region (Hamilton and others, 2006; Rosenberger and others, 2011), demonstrating that the near-bottom 

current ellipses orient with the bathymetry, whereas the near-surface ellipses orient with the general 

trend of the coastline. The near-bottom ellipses the Shallow Canyon and Deep Canyon sites appear to be 

normal to the bathymetry; however, they are aligned with the canyon axis, as is evident in the mean 

profiles.

The time-series plots of the low-pass filtered currents show the variability of the flow with time 

and season. Although near-bottom flow tends to be upcoast on each shelf, this is not exclusively true, as 

is exemplified at the Shelf Break site, where the entire water column can flow downcoast for weeks (fig. 

13). At the deeper sites (Slope and Deep Canyon), this upcoast flow is constrained to the middle of the 

water column and can be transient (figs. 18 and 24). These observations could indicate the presence of 

the Davidson Undercurrent (or California Counter-current), although more analysis is required to 

confirm this possibility. 

Tidal Parameters

A harmonic tidal analysis was performed on the current-meter data at each site as another 

measure to determine quality of data. This was accomplished with the t_tide package in Matlab 

(Pawlowicz, and others, 2002), which is based on the original routines of Foreman (1978). A tidal 

analysis on vector current data provides ellipse parameters of each constituent used in the analysis 

(major-and minor-axis amplitude and inclination of major axis with respect to north), as well as a vector 

tide fit to the data reconstructed from each constituent. The four major constituents for this region are 

the M2 and S2 in the semidiurnal band, and the O1 and K1 in the diurnal band (Noble and Xu, 2004). 

Vertical profiles of the major axis amplitude and inclination of the tidal ellipses for these four 

constituents at each USGS and OCSD site are plotted in figures 40–48. 

Tidal parameters on the San Pedro Shelf from the OCSD moorings (figs. 45–48) are consistent 

with results from previous measurement programs on this shelf (Noble and Xu, 2004) and other sections 

of the California Continental Shelf (Rosenberger and others, 2011). Amplification of the M2 tide toward 

the bottom is observed at sites near the shelf break (M18 and M21, figs. 45 and 48) and the mid-shelf 

(M19, fig. 46). Orientation of the M2 tidal ellipses shift from alongshelf near the surface to cross-shelf 

near the bottom. Noble and Xu (2004) show that this is due to the internal tide propogating onto the 
14

shelf from offshore. This amplification and rotation near the bottom is not observed on the Newport 

Shelf and Slope, (figs. 40–42), suggesting that the internal tides are not as strong in this region. Both 

canyon moorings show significant amplification of the M2 tide near the bottom (figs. 43 and 44) . This 

phenomenon occurs below the canyon rim at each location, and thus it is not clear if this is due to 

internal tides or simply a funnelling of the barotropic tide along the canyon. 

The tidal ellipses for each constituent can also be plotted on a map of the region to elucidate the 

eccentricity (ratio of major axis to minor axis) and orientation of the ellipses at differernt depths, with 

respect to the topography of the region. Figure 49 shows the tidal ellipses from the M2 constituent at 

several depth levels in the water column at each site. Rather than plot each constituent separately, figure 

50 shows the results of a principal components analysis on the combined vector tide fit, with the the 

variance ellipses plotted.

The eccentricity of the M2 tidal ellipses (major-axis amplitude/minor-axis amplitude) illustrate 

how focused the energy is in a particular direction (fig. 49). For instance, the near-bottom tidal currents 

in the canyon are very focused in the along-canyon direction. Similarly, the near-bottom and mid-depth 

tidal currents are highly focused alongshore at the Inner Shelf and Shelf Break sites. In contrast, the 

near-bottom currents near the shelf break at M18 are highly focused cross-shore, demonstrating the 

importance of the internal tide at this site. Site M21 shows strong M2 tidal currents near the bottom as 

well, although not as focused as at M18. Near-bottom tides decrease with magnitude and rotate 

alongshelf as one moves inshore to site M20 in 19 m water depth. 

Conclusions

Six months of data on water-column current speed and direction were obtained by the USGS at 

five sites in water depths ranging from 15 to 390 m off the coast of southern California in 2011–12. The 

data were processed using standard quality-assurance/quality-control procedures to ensure completeness 

and quality. These data will provide invaluable insights to the overall flow patterns in a region of 

complex bathymetry. These data will also allow for investigations on the interaction between offshore 

and inshore flow and understanding how these flow patterns influence the transport of sediments and 

pollutants in the coastal ocean. 

Initial results show differences in internal tidal energy between the San Pedro Shelf and the 

Newport Shelf, as well as variability in this energy between seasons. Future investigations will attempt 

to elucidate the processes responsible for these differences. The variability of internal tides on 

continental shelves is not well understood. The full water-column profiles at the Slope and Deep 

Canyon site suggest the presence of the Davidson Undercurrent and provide a unique opportunity to 

study how the undercurrent may influence the propogation of internal tides onto the Continental Shelf. 

 
15

References Cited

Foreman, M.G.G, 1977, Manual for tidal height analysis and prediction: Sidney, British Columbia, 

Institute of Ocean Sciences Technical Report, Pacific Marine Science Report 77–10. 

Foreman, M.G.G., 1978, Manual for tidal current analysis and prediction: Sidney, British Columbia, 

Institute of Ocean Sciences Technical Report, Pacific Marine Science Report 78–6. 

National Oceanic and Atmospheric Administration, Pacific Marine Environmental Laboratory, EPIC 

netCDF General Conventions, http://www.epic.noaa.gov/epic/document/convention.htm. 

National Oceanic and Atmospheric Administration, National Data Buoy Center database, 

http://www.ndbc.noaa.gov. 

National Oceanic and Atmospheric Administration, National Ocean Service, Center for Operational 

Oceanographic Products and Services, http://co-ops.nos.noaa.gov. 

Noble, M.A and Xu, J.P., 2004, Huntington Beach Shoreline contamination investigation, phase III: 

U.S. Geological Survey Open File Report 2004–1019. 

Noble, M. A., Rosenberger, K.J., Hamilton, P., and Xu, J.P., 2009, Coastal ocean transport patterns in 

the central Southern California Bight, in Lee, H.J., and Normark, W.R., eds., Earth science in the 

urban ocean: The Southern California continental borderland: Boulder, Colo., The Geological Society, 

Special Paper 454, p. 193–226. 

Hamilton, P., Noble, M.A, Largier, J., Rosenfeld, L.K., and Robertson, G., 2006, Cross-shelf subtidal 

variability in San Pedro Bay during summer, 2001: Continental Shelf Research, v. 208, p. 681–702. 

IEEE, 1980, 1978 practical salinity scale equations: Institute of Electrical and Electronics Engineers 

Journal of Oceanic Engineering, OE-5, no. 1, 14 p. 

Pawlowicz, P., Beardsley, B., and Lentz, S., 2002, Classical tidal harmonic analysis including error 

estimates in MATLAB using T_TIDE: Computers and Geosciences, v. 28, p. 929–937. 

Rosenberger, K.J., Noble, M.A., Sherwood, C.R., Martini, M.M., Ferreira, J.T., and Montgomery, 

Ellyn, 2011, Palos Verdes Shelf oceanographic study; data report for observations December 2007–

April 2008: U.S. Geological Survey Open-File Report 2010–1240, 118 p., 

http://pubs.usgs.gov/of/2010/1240/.

Science Applications International Corporation (SAIC), 2009, Orange County Sanitation District ocean 

current studies: Analysis of inter- and intra-annual variability in coastal currents: San Diego, 

California, prepared by Science Applications International Corporation for Orange County Sanitation 

District, SAIC Report, 62 p. 

U.S. Geological Survey, 2001, National Water Information System (NWISWeb): U.S. Geological 

Survey database, available at http://waterdata.usgs.gov/nwis/. 

University Corporation for Atmospheric Research, Unidata Program Center, 2013, NetCDF Users 

Guide, https://www.unidata.ucar.edu/software/netcdf/docs/user_guide.html.

Weather Underground, 1995, Personal Weather Station database, http://classic.wunderground.com. 
16

Figure 1. Map of study area showing Orange County Sanitation District and U.S. Geological Survey moorings in 

the Newport Shelf program and their locations relative to the San Pedro Shelf, Newport Beach, California. 

Contours are plotted every 10 m from 0 to 100 m depth, and every 50 m deeper than 100 m.
17

Figure 2. Diagram of the mooring and tripod placed on the inner shelf of the Newport Shelf (Inner Shelf site), 

Newport Beach, California. Mooring depth, 14 m. 
18

Figure 3. Diagram of the mooring and tripod placed on the shelf break of the Newport Shelf (Shelf Break site), 

Newport Beach, California. Mooring depth, 85 m.
19

Figure 4. Diagram of mooring placed on the slope off the Newport Shelf (Slope site), Newport Beach, California. 

Mooring depth, 358 m.
20

Figure 5. Diagram of mooring placed in the deep section of Newport Canyon (Deep Canyon site), Newport 

Beach, California. Mooring depth, 380 m.
21

Figure 6. Diagram of mooring placed in the shallow section of Newport Canyon (Shallow Canyon site), Newport 

Beach, California. Mooring depth, 215 m.
22

Figure 7. Timeline of data acquired by the U.S. Geological Survey on the Newport Shelf and slope, by platform 

and data type, Newport Beach, California.
23

Figure 8. Low-pass filtered currents measured at several depth levels in the water column at the Inner Shelf site, 

Newport Beach, California. A, Alongshore currents. B, Cross-shore currents. The alongshore direction is 

determined using a depth-averaged value of major axis inclination from a principal components analysis of the 

current-meter data from the acoustic Doppler current profilers.
24

Figure 9. Surface-wave parameters measured by the ADCP on the bottom-mounted tripod at the Inner Shelf site, 

Newport Beach, California. A, Significant wave height and maximum wave height. B, Mean wave period and 

peak wave period. C, Mean wave direction. D, Water depth.
25

Figure 10. Near-bottom water properties and suspended sediment data at the Inner Shelf site, Newport Beach, 

California. A, Temperature. B, Salinity. C, Light attenuation. D, Dissolved oxygen.
26

Figure 11. Meteorological parameters at the Inner Shelf site, Newport Beach, California. A, Wind speed. B, Wind 

direction (blowing from). C, Vector components of winds (alongshore and cross-shore). D, Air temperature.
27

Figure 12. Surface currents and water properties at the Inner Shelf site, Newport Beach, California. A, Low-pass 

filtered alongshore and cross-shore currents. B, Water temperature. C, Salinity.
28

Figure 13. Low-pass filtered currents measured at several depth levels in the water column at the Shelf Break site. 

A, Alongshore currents. B, Cross-shore currents. The alongshore direction is determined using a depthaveraged value of major axis inclination from a principal components analysis of the current-meter data from 

this site.
29

Figure 14. Near-bottom water properties and suspended sediment data at the Shelf Break site, Newport Beach, 

California. A, Temperature. B, Salinity. C, Light attenuation (third panel). D, Optical backscatter.
30

Figure 15. Surface currents and water properties at the Shelf Break site, Newport Beach, California. A, Low-pass 

filtered alongshore and cross-shore currents. B, Water temperature. C, Salinity.
31

Figure 16. Water-column temperature data at the Shelf Break site, Newport Beach, California.
32

Figure 17. Contours of water-column temperature data at the Shelf Break site, Newport Beach, California.
33

Figure 18. Low-pass filtered currents measured at several depth levels in the water column at the Slope site, 

Newport Beach, California. A, Alongshore and B, Cross-shore. The alongshore direction is determined using a 

depth averaged value of major axis inclination from a principal-components analysis of the current-meter data 

at this site.
34

Figure 19. Near-bottom water properties and suspended sediment data at the Slope site, Newport Beach, 

California. A, Pressure. B, Temperature. C, Salinity. D, Light attenuation. 
35

Figure 20. Water-column temperature data at the Slope site, Newport Beach, California.
36

Figure 21. Contours of water-column temperature at the Slope site, Newport Beach, California.
37

Figure 22. Low-pass filtered currents measured at several depth levels in the water column at the Shallow Canyon 

site, Newport Beach, California. A, Alongshore currents. B, Cross-shore currents. The alongshore direction is 

determined using a depth-averaged value of major axis inclination from a principal components analysis of the 

current-meter data for a given instrument at this site.
38

Figure 23. Near-bottom water properties and suspended sediment data at the Shallow Canyon site, Newport 

Beach, California. A, Temperature. B, Salinity. C, Light attenuation. 
39

Figure 24. Low-pass filtered currents measured at several depth levels in the water column at the Deep Canyon 

site, Newport Beach, California. A, Alongshore. B, Cross-shore. The alongshore direction is determined using a 

depth-averaged value of major axis inclination from a principal components analysis of the current- meter data 

for a given instrument at this site.
40

Figure 25. Near-bottom and mid-water column water properties and near-bottom suspended sediment at the Slope 

site, Newport Beach, California. A, Temperature. B, Salinity. C, Light attenuation. 
41

Figure 26. Meteorological parameters measured by the National Oceanic and Atmospheric Administration metocean buoy number 46025 in the Santa Monica Basin, 33 nautical miles west-southwest of Santa Monica, 

California. A, Wind speed. B, Wind direction (blowing from). C, Barometric pressure. 
42

Figure 27. Surface-wave parameters measured by the National Oceanic and Atmospheric Administration metocean buoy number 46025 in the Santa Monica Basin, 33 nautical miles west-southwest of Santa Monica, 

California. A, Significant-wave height. B, Mean wave period and peak wave period. C, Mean wave direction.
43

Figure 28. Meteorological parameters measured by the Orange County Sanitation District meteorological station at 

Plant2 and a personal weather station on the Balboa Peninsula at the entrance to Newport Harbor, Newport 

Beach, California. A, Wind speed. B, Wind direction (blowing from). C, Alongshore component. D, Cross-shore 

component. 
44

Figure 29. Daily mean river discharge data for the deployment period from the USGS streamflow-gaging station 

number 11074000 on the Santa Ana River, feeding into Newport Harbor, Newport Beach, California. Discharge 

is measured in cubic feet per second.
45

Figure 30. Profile plot of mean currents at the Inner Shelf site, Newport Beach, California, computed over the 

entire deployment period. A positive alongshore flow is directed upcoast, and a positive cross-shore flow is 

directed onshore. A, Mean alongshore, mean cross-shore and mean speed. B, Mean direction.
46

Figure 31. Profile plot of mean currents at the Shelf Break site, Newport Beach, California, computed over the 

entire deployment period. A positive alongshore flow is directed upcoast, and a positive cross-shore flow is 

directed onshore. A, Mean alongshore, mean cross-shore, and mean speed. B, Mean direction.
47

Figure 32. Profile plot of mean currents at the Slope site, Newport Beach, California, computed over the entire 

deployment period. A positive alongshore flow is directed upcoast, and a positive cross-shore flow is directed 

onshore. A, Mean alongshore, mean cross-shore, and mean speed. B, Mean direction.
48

Figure 33. Profile plot of mean currents at the Shallow Canyon site, Newport Beach, California, computed over the 

entire deployment period. A positive alongshore flow is directed upcoast, and a positive cross-shore flow is 

directed onshore. A, Mean alongshore, mean cross-shore, and mean speed. B, Mean direction.
49

Figure 34. Profile plot of mean currents at the Deep Canyon site, Newport Beach, California, computed over the 

entire deployment period. A positive alongshore flow is directed upcoast, and a positive cross-shore flow is 

directed onshore. A, Mean alongshore, mean cross-shore, and mean speed. B, Mean direction.
50

Figure 35. Profile plot of mean currents at the Orange County Sanitation District site M18, Newport Beach, 

California, computed over the entire deployment period. A positive alongshore flow is directed upcoast, and a 

positive cross-shore flow is directed onshore. A, Mean alongshore, mean cross-shore, and mean speed. B, 

Mean direction.
51

Figure 36. Profile plot of mean currents at the Orange County Sanitation District site M19, Newport Beach, 

California, computed over the entire deployment period. A positive alongshore flow is directed upcoast, and a 

positive cross-shore flow is directed onshore. A, Mean alongshore, mean cross-shore, and mean speed. B, 

Mean direction.
52

Figure 37. Profile plot of mean currents at the Orange County Sanitation District site M20, Newport Beach, 

California, computed over the entire deployment period. A positive alongshore flow is directed upcoast, and a 

positive cross-shore flow is directed onshore. A, Mean alongshore, mean cross-shore, and mean speed. B, 

Mean direction.
53

Figure 38. Profile plot of mean currents at the Orange County Sanitation District site M21, Newport Beach, 

California, computed over the entire deployment period. A positive alongshore flow is directed upcoast, and a 

positive cross-shore flow is directed onshore. A, Mean alongshore, mean cross-shore, and mean speed. B, 

Mean direction.
54

Figure 39. Map of the variance ellipses of the low-pass filtered flow from principal components analysis at several 

depth levels in the water column at each site, Newport Beach, California.
55

Figure 40. Profile of tidal currents at the Inner Shelf site, Newport Beach, California, computed over the entire 

deployment period. A, Major-axis ellipse amplitude. B, Major-axis inclination, in degrees clockwise from north.
56

Figure 41. Profile of tidal currents at the Shelf Break site, Newport Beach, California, computed over the entire 

deployment period. A, Major-axis ellipse amplitude. B, Major-axis inclination, in degrees clockwise from north.
57

Figure 42. Profile of tidal currents at the Slope site, Newport Beach, California, computed over the entire 

deployment period. A, Major-axis ellipse amplitude. B, Major-axis inclination, in degrees clockwise from north.
58

Figure 43. Profile of tidal currents at the Deep Canyon site, Newport Beach, California, computed over the entire 

deployment period. A, Major-axis ellipse amplitude. B, Major-axis inclination, in degrees clockwise from north.
59

Figure 44. Profile of tidal currents at the Shallow Canyon site, Newport Beach, California, computed over the entire 

deployment period. A, Major-axis ellipse amplitude. B, Major-axis inclination, in degrees clockwise from north.
60

Figure 45. Profile of tidal currents at the Orange County Sanitation District site M18, Newport Beach, California, 

computed over the entire deployment period. A, Major-axis ellipse amplitude. B, Major-axis inclination, in 

degrees clockwise from north.
61

Figure 46. Profile of tidal currents at the Orange County Sanitation District site M19, Newport Beach, California, 

computed over the entire deployment period. A, Major-axis ellipse amplitude. B, Major-axis inclination, in 

degrees clockwise from north.
62

Figure 47. Profile of tidal currents at the Orange County Sanitation District site M20, Newport Beach, California, 

computed over the entire deployment period. A, Major-axis ellipse amplitude. B, Major-axis inclination, in 

degrees clockwise from north.
63

Figure 48. Profile of tidal currents at the Orange County Sanitation District site M21, Newport Beach, California, 

computed over the entire deployment period. A, Major-axis ellipse amplitude. B, Major-axis inclination, in 

degrees clockwise from north.
64

Figure 49. Map of the M2 tidal ellipses calculated from a harmonic tidal analysis of the vector current-meter data at 

several depth levels in the water column, Newport Beach, California.
65

Figure 50. Map of the variance ellipses calculated from a principal components analysis of the harmonic tidal fit of 

the vector current-meter data at several depth levels in the water column, Newport Beach, California.