Instrument Type: CODAR Ocean Sensors SeaSonde HF Radar System

Sea surface current data is measured with SeaSondes, compact HF radars designed by CODAR Ocean Sensors, Ltd. They use patented FMCW (frequency modulated continuous wave) signal processing and crossloop direction finding to measure ocean surface currents and wave parameters of the coastal ocean. Each station consists of a transmitter, receiver, 2 antennas, and data acquisition and processing computers. A transmitter broadcasts a frequency modulated radio frequency pulse at 2Hz (two pulses per second). The Doppler shifted return signal (sea echo) is detected with a compound cross loop/monopole receive antenna and the signal is processed into estimates of surface current speed and direction and wave heights, period and direction. BML's three 12 MHz stations have a spatial resolution of 2 km and create hourly maps of surface currents out to a distance of 30-50 km (20-30 miles) along a 65 km (40 mile) length of shore. Onshore wave directional spectral data are also produced. Total coverage area for the 3- radar array is approximately 2800 km2. BML's two 5 MHz stations have a spatial resolution of 5 km and create hourly maps of surface currents out to a distance of 90-200 km (55-125 miles). Onshore wave directional spectral data are also produced.

Sea Surface Current Plots and Visualizations >

Ocean Currents

Ocean currents are most commonly observed by several methods including drifters, radar and current profilers. Drifters are used to measure surface currents, which are mainly driven by wind and tide. When deployed, drifters are allowed to move freely with the current, logging position data to an internal GPS unit. Upon recovery, the path of the drifter can be plotted and information gained about the movement of the surface water.

Acoustic Doppler Current Profilers (ADCP’s) use sonar techniques and the Doppler Effect and are used to study currents throughout the water column. These measurements can be made at a stationary location, such as an oceanographic mooring, or from a sensor mounted on the hull of a vessel. ADCP’s can be installed on the seafloor in an upward looking orientation, or from a buoy or boat in a downward looking orientation. Transmitting sound waves into the water, the instrument listens for echoes scattered back off particles suspended in the water column. Assuming that these particles are moving with the ocean current, the Doppler shift of the return signal can be used to determine the magnitude and direction of motion. Below the surface layer, currents are mainly influenced by tides and the rotation of the Earth.

High Frequency Radar is used to measure the currents at the ocean surface, called sea surface currents. Similar to ADCPs a radar transmitter sends a signal out to sea and the conductive seawater surface returns a signal that measures the Doppler shift to determine the velocity and direction. High frequency radar instruments are deployed on shore and are generally operated in pairs.

Researchers are interested in ocean currents for several reasons: the flow of water affects the transport of nutrients and organic matter, as well as pollutants. Currents also affect the settlement locations of many larval species. The larvae of organisms such as mollusks and crustaceans are transported to habitat by the current. Fresh water run-off and the pollution it can carry also move with the current. The analysis of currents may have predictive value for the settlement of these organisms.

Upwelling is a seasonal current effect. Caused by strong offshore winds, upwelling refers to the movement of the normally deep, nutrient rich waters up toward the surface. Plankton blooms generally follow a period of upwelling. It is useful for researchers to know when upwelling occurs, so that residual effects such as changes in the food web can be studied.

The ocean is in constant motion and this movement of water helps to regulate global climate through the transfer of heat. Warm equatorial waters move toward the poles, cool and move back toward the equator in a circular motion called a gyre. Understanding this motion is important to researchers studying the Earth’s climate.

Learn more about the benefits of sea surface current observations

High Frequency Radar: Sea Surface Current and Wave Sensors

Instrument Type: CODAR Ocean Sensors SeaSonde HF Radar System

Description: High-frequency (HF) radar uses radio-wave backscatter to map surface currents over wide swaths of the coastal ocean. These sensors are commonly referred to by the trade name "CODAR" (Coastal Ocean Dynamics Applications Radar) and take advantage of the propagation of radio waves over large distances out and back across the surface of the conducting sea water, and they have resonant interactions with ocean surface waves (i.e., the ones that can make people seasick). Back at the shoreline, a measurement of the frequency offset (i.e., Doppler shift) of the reflected radio waves provides a remotely sensed measurement of the speed of the ocean waves and surface currents.

Locations:

• 5 MHz - Bodega Marine Laboratory: 38°19.169'N,123°04.417'W - Installed: 2007
• 5 MHz - Point Arena: 38°55.706'N,123°43.666'W - Installed: 2007
• 5 MHz - Fort Bragg: 39°26.281'N,123°48.967'W - Installed: 2010
• 5 MHz - Shelter Cove: 40°02.002'N,124°04.732'W - Installed: 2008
• 5 MHz - Trinidad: 41°04.414'N,124°09.467'W - Installed: 2008
• 12 MHz - Bodega Marine Laboratory: 38°19.039'N,123°04.348'W - Installed: 2001
• 12 MHz - Point Reyes: 38°2'49.7"N,122°59'20.9"W - Installed: 2001
• 12 MHz - Salt Point State Park: 38°34'0.5"N,123°19'53.7"W - Installed: 2002
• 12 MHz - Slide Ranch: 37°52.350'N,122°35.855'W - Installed: 2008
• 12 MHz - Commonweal: 37°54.710'N,122°43.690'W - Installed: 2006
• 25 MHz - Point Bonita: 37°48.929'N,122°31.794'W

Specifications - Surface currents:

Map spatial resolution: 2 x 2 km
Map temporal interval: hourly; currents averaged over one hour
Map area coverage: 65-200 km along shore x 30 km offshore, variable
Map vector accuracies: speed < 7 cm/s, direction < 10°

Specifications - Waves:

Target range: 3 km from coast around each radar
Significant wave height accuracy: 7 to 15%
Dominant on-shore direction accuracy: 5° to 12°
Dominant wave period accuracy: 0.6 s
Minimum detectable significant wave height: 1 m
Wave temporal interval: hourly; waves averaged over one hour

Specifications - Radiated signal:

Output radiated power: 80 watts peak, 40-60 watts average
Operating frequency range: 4-14 MHz

HFR Progs Supplement: Matlab routines to perform QA/QC on high frequency radar (HFR) data and calculate temporal and spatial statistics.

Contact: John Largier Ph.D.

The zipped archives linked below contain Matlab routines to calculate temporal and spatial statistics for HF radar data, and perform QA/QC on the data. The processing methods are described in the technical report "HF Radar Processing Using “Nearest-Neighbor” Statistics, A Technical Report" [PDF], developed for the California Coastal Conservancy for the Coastal Ocean Currents Monitoring Program by Chris Halle. Please reference the paper and/or acknowledge this website if using these routines or statistics.

StatsAndUsefulScripts

The two folders in the StatsAndUsefulScripts folder (HF_Scratch and HFR_Progs_Supplement) both contain the scripts that actually calculate the statistics and qa/qc the radials and totals. These are as yet somewhat unorganized, so the routines can be found in either folder.  In general, script names generally follow a naming convention (1) scripts starting with “Get” – calculate the statistics, (2) script starting with “Clean” – qa/qc the radials or totals using the previously calculated statistics and user-specified totals, and (3) scripts starting with “Inv” – use the previously calculates stats and allow the user to interactively investigate the effects of setting different screening levels for the statistics.

SampleDrivingScripts

The scripts in the SampleDrivingScripts folder contain examples of how to call the processing routines.  The ReadMe file in the SampleDrivingScripts folder indicates the proper order of processing.  Please note that the scripts have not been optimized for speed, and can be repetitive. Updates will be posted as available.

The scripts set up the radials and totals in monthly files for processing and storage.

HFRosePlotRoutines

Current Rose Routines for HFR Data: prompt driven routines that allow the user to specify the date search range, etc, and generate plots similar to this sample plot.

Also see HFR_Progs Matlab Toolbox

High Frequency Radar Sea Surface Current Data

For special data requests contact bmldata@ucdavis.edu, please see the Data Disclaimer and terms of use.

Principal Investigator, Research: John Largier, Ph.D.

Download High Frequency Radar sea surface currents via CeNCOOS >

Tips for using the CeNCOOS data download tool:

For currents at a specific point - to download a .CSV file:

1. Choose the data set you are interested in (500 m, 2 km, 6 km, etc.)

• HF Radar Hourly Surface Currents (2km) For Northern CA - 2 km coverage area ends @ Bodega Bay, CA
• HF Radar Hourly Surface Currents (6km) 6 km surface current data for most of California and Orgeon
• HF Radar Hourly Surface Currents (500m) High Resolution Currents for SF Bay only

2. Select "Portal"

3. Use the mouse to move the map to your area of interest
4. Click once on an area within the data set that you are interested in (there must be sea water velocity data in the area of your choice)

5. You may need to wait several minutes while the viewer loads your graph and data set
6. Once the graph is completed, choose download from the data view window to save the file.
7. The resulting download is a timeseries file (csv) that includes the direction and speed for seawater at the lat/lon you chose.

For currents across a large area, to download a NetCDF file:

1. Choose the data set you are interested in (500 m, 2 km, 6 km, etc.)

• HF Radar Hourly Surface Currents (2km) For Northern CA - 2 km coverage area ends @ Bodega Bay, CA
• HF Radar Hourly Surface Currents (6km) 6 km surface current data for most of California and Orgeon
• HF Radar Hourly Surface Currents (500m) High Resolution Currents for SF Bay only

2. Select "Download"

3. The next screen will offer you some options you must select:

4. Be patient, a large area or date range can take some time to download, then save your file.