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In fact, “waves moving toward the receiver increase the return frequency, while waves moving away decrease the return frequency”. [11] Then a further Doppler shift (Δf ) is observed and, by measuring it, it is possible to determine the radial velocity ν s component of the surface current by using the Doppler formula: Δf = ν s / λ s
A typical case is wave measurements from an offshore platform in deep water, where swift currents could make mooring a wave buoy enormously difficult. Another interesting case is a ship under way, where having instruments in the sea is highly impractical and interference from the ship's hull must be avoided.
Marine radar has performance adjustment controls for brightness and contrast, also manual or automatic adjustment of gain, tuning, sea clutter and rain clutter suppression, and interference reduction. Other common controls consist of range scale, bearing cursor, fix/variable range marker (VRM) or bearing/distance cursor (EBL).
Nautical charting may take the form of charts printed on paper (raster navigational charts) or computerized electronic navigational charts. Recent technologies have made available paper charts which are printed "on demand" with cartographic data that has been downloaded to the commercial printing company as recently as the night before printing.
If the target is rotated through large angles, the Doppler frequency history of a scatterer becomes non-linear, following a sine wave trajectory. This Doppler history can not be processed directly by a Fourier transform because of the smeared Doppler frequency history resulting in the loss of cross range resolution.
The sea surface height is then the difference between the satellite's altitude relative to the reference ellipsoid and the altimeter range. The satellite sends microwave pulses to the ocean surface. The travel time of the pulses ascending to the oceans surface and back provides data of the sea surface height.
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SARs produce a two-dimensional (2-D) image. One dimension in the image is called range and is a measure of the "line-of-sight" distance from the radar to the object. Range is determined by measuring the time from transmission of a pulse to receiving the echo from a target. Also, range resolution is determined by the transmitted pulse width.