Coastal ocean dynamics applications radar
[1] The system can be transported by vehicle and can operate from a portable power supply; for modern instrumentation a minimum capacity of 1050 Watts is recommended.
[4] The main equipment is cabled to the electronic segment, that is housed nearby in a sheltered environment and contains the system hardware, where information is stored.
A minicomputer controls the radar and processes the signals and the operator can communicate with the system through a portable keyboard terminal.
[5] However, the actual range can be limited by radio interference, high-ocean states and ground conditions in the vicinity of the antennas.
Main applications include coastal engineering and public safety projects, planning of navigational seaways, mitigation of ocean pollution, search and rescue operations, oil-spill mitigation in real time and larval population connectivity assessment.
Also, data obtained from CODAR are used as inputs for global resource monitoring and weather forecasting models and are particularly helpful for tidal and storm-surge measurements.
Interpreting the spectral returns for various transmit frequencies is the key to extracting information about the ocean [10] and, specifically, to measure surface currents.
The return signal is processed and its spectral analysis provides the sea-echo Doppler spectrum, where two dominant peaks at different frequencies can be recognized.
Displacement of these peaks away from their known frequencies is called the “echo Doppler shift” and allows one to assess the radial velocity of a surface current.
Exploiting Bragg’s Law, CODAR maximizes the scattered HF signal, given that the resonance will only occur for the given wavelength: λs = λt / (2 * cos(φ) ) where λs is the wavelength of surface ocean wave, λt is the wavelength of transmitted signal and φ is the angle of incidence between the signal and the ocean surface As the CODAR antennas are usually placed at sea level, the angle of incidence theta can be assumed to be zero.
[11] Then a further Doppler shift (Δf ) is observed and, by measuring it, it is possible to determine the radial velocity νs component of the surface current by using the Doppler formula: Δf = νs / λs The range to target is calculated starting from the time delay, which is obtained by subtracting the return signal time from the transmitted signal one.
[12] In 2010, retailers of modern CODAR equipments guarantee an accuracy typically < 7 cm/s of the total current velocity and 1–2 cm of the tidal component, in normal environment condition.
Here are presented the main practical limitations: As discussed before, for a given look angle, a single CODAR station can detect only the component of flow traveling toward or away from its location.
