HF radar ship detection through clutter cancellation

High-frequency over-the-horizon (HF-OTH) radar uses ionospheric refraction to detect targets at thousands of kilometers. A timely surveillance of large areas requires relatively short dwells (coherent integration times) of less than 10 seconds. The resulting resolution in the Doppler Fourier transform is sufficient for detecting fast targets such as aircraft, but slow targets such as ships require integration times 12-30 seconds long to distinguish the ship peaks from the much more powerful ocean clutter. By modeling the first-order clutter as sinusoidal and subtracting it, we are able to expose ships in dwells as short as 3 seconds that would otherwise be masked by the mainlobe spread of the clutter. This technique is applied to data from the US Navy's relocatable OTHR (ROTHR). This approach is an alternative to superresolution techniques and may sometimes be more robust.