Here is a cartoon of the concept from Klaus-Werner Gurgel.

© Klaus-Werner Gurgel, University of Hamburg, Germany

The University of Miami uses the WERA HF radar system. The WERA system transmits a frequency modulated continuous wave (FMCW) chirp and avoids the 3 km blind range in front of the radar (Essen et al., 2000). The horizontal resolution of WERA is a function of the the chirp characteristics as listed in the Table~2 for both a high-resolution and low-resolution version. For a transmission frequency of 16 and 30 MHz, Bragg wavelengths are 9.4 and 5 m, respectively. The transmitter is arranged to encompass about a 60 deg swath. WERA also has the flexibility to be configured into a DF array (such as CODAR) where 4 antennae may be set up in a square or a linear array can be set up consisting of 4n antennae or channels using BF techniques. According to representatives from the company, a long-range, high horizontal resolution version can be designed where the range would be O(100 km) and the horizontal resolution would be 600 to 750 m. This higher spatial resolution requires bandwidth of 200 to 250 KHz, and approval from the Federal Communication Center (FCC). Temporal sampling can be as low a few minutes as the system is FMCW as opposed to a pulsed radar (i.e. OSCR). This sampling feature make WERA particularly attractive in high current gradient regimes where time scales of surface current variability are less than an hour.

Capabilities of the WERA system High-Resolution Long-Range Operation range (km from radar site) 45 80 Range cell resolution (km) 0.3-0.6 0.6-1.2 Measurement depth (m) 0.4 0.8 Measurement cycle (min) < 10 < 10 Radial current (cm s -1) 2 2 Vector current (cm s -1) 5 5 Vector direction (°) ± 3 ± 3 Operating frequency (MHz) 30 16 Transmit elements (Yagi) 4 4 Receive elements (BF) 8-32 8-32 Receive elements (DF) 4 4 Transmitter Peak Power (W) 30 30