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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).
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.
Remote sensing as we know it today started with the first earth orbiting satellite Landsat 1 in 1973. [10] Landsat 1 delivered the first multi-spectral images of features on land and coastal zones all over the world and already showed effectiveness in oceanography, [11] although not specifically designed for it.
Ships and planes are metal, and reflect radio waves. The radar measures the distance to the reflector by measuring the time of the round trip from emission of a pulse to reception, dividing this by two, and then multiplying by the speed of light. To be accepted, the received pulse has to lie within a period of time called the range gate. The ...
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The difference between these two time intervals causes the blind range area which is given by , where is the speed of light in free space. If the PRI is uniform, blind ranges will remain unchanged along azimuth, and after compression in azimuth, the image would have blind strips of width c 0 ∗ τ {\displaystyle c_{0}*\tau } .