About HF Radar


High frequency (HF) radar systems measure the speed and direction of ocean surface

currents in near real time by combining the radial velocities on polar coordinate grid points 

centered by more than two antenna locations. These radars provide two-dimensional maps 

of currents over a large region of the coastal ocean, from a few kilometers offshore up to 200

km, resolving spatial scales of about 0.5 to 6 km, and can operate under any weather

conditions. They are located near the water’s edge, and need not be situated atop a high

point of land.  High frequency radars are unique in their ability to measure surface currents in

large areas at once with the detail required for important ecological, economic, and safety



 about hf radar 01.jpg     WERA-Newsletter-2010-Fig.jpg

<HF radar Antennas of crossed-loop (left) and phased-array type (right)>



<HF radar-derived surface currents by KNU in the Saemangeum coastal sea>


The underlying physiscs of surface current and wave measurements by HF radar is concerned 

with radar backscattering from a moving rough sea surface (Bragg scattering). First-oder

Bragg scattering is due to surface gravity waves of half of transmitted HF wave-length

propagating towards or away from the radar site. The Doppler shift of the received signal

determines the phase velocity of scattering waves which is composed of the theoretically

known portion of surface waves in non-moving water and a contribution from underlying

currents. The difference between the measured and theoretical phase velocity is attributed to

the radial velocity of the surface current. While first-order scattering yields information on the

scattering only, second-order scattering reflects the full two dimensional wave spectrum within

certain continuous spectral bands.



<Bragg Scattering and Doppler shift of sea echo by current>


Ocean currents determine the movement of surface waters and are equivalent to winds in the

atmosphere. Presently, ocean current measurements are not as readily available as winds, in

large part due to the expense and difficulty of measuring ocean currents at many locations. 

In order for coastal managers, emergency responders, and marine scientists to perform most

effectively, they require access to near-real time surface current measurements that cover a

large area continuously over time. Existing oceanographic monitoring systems are insufficient

to provide the level of detail required by scientists and forecasters to measure surface current

speed and direction. 


 about HF radar 05new.jpg


HF radars can resolve ocean features that satellites cannot resolve and can provide two-

dimensional maps of ocean velocity that are not possible with moorings and drifting buoys.  

HF radar is recognized as a cost-effective solution to expand the existing system of in situ

measurements and to provide increased spatial and temporal resolution of surface current

velocity measurements.


about hf radar 03.jpg     KHOA.jpg 

<HF radar-derived surface currents by KHOA in the YeoSu and Korea Strait>


The ocean currents carry any floating object, nutrients as well as pollutants, so it is important

to know the currents for ecological and economic reasons. Because ocean currents determine

the movement of surface waters, the ability to collect data on their direction and speed

provides critical information to support pollutant tracking, search and rescue, harmful algal

bloom monitoring, navigation, coastal zone planing and management and ecosystem


HF radar systems potentially have additional capabilities to observe surface waves and

tsunami and to detect and track vessels. Emerging uses of HF radar data include ingestion into

numerical model, ecosystem and climate where working together will accelerate the research in

these area.


  Visit to CODAR and WERA sites for more information.    



<Application fields of HF radar data>