Wind compensation (MTI)
The wind compensation is a sub-assembly in a Störschutzsystem an air defense radar. Radar devices with a moving target indicator (MTI), a system for the detection of moving objects in flight , have a problem with weather clutter or chaff clouds if they move with the wind speed and therefore cause a Doppler shift in the transmission frequency of the radar device, just like objects in flight . These disturbances, moving at the speed of the wind, would create an area of high brightness on the screen, within which the detection of aircraft is difficult. The system used to suppress these special disturbances is called wind compensation.
A technical solution to this problem with analog radar devices is to modulate the coherent oscillator of the MTI system with an additional frequency that corresponds to the Doppler frequency of the radial speed of the wind. Thus, the targets moving at wind speed are suppressed.
This principle is mainly used in analog weapon control and target tracking radar devices. Since the radar antenna is constantly directed in the direction of the target, the radial speed of the wind is relatively constant. The wind compensation is then only a manually operated controller, which detunes the coherent oscillator slightly until the disturbances are suppressed. The disadvantage is that the fixed targets can no longer be suppressed and appear as bright light spots on the screen.
If the antenna rotates, as is usual with air surveillance radar devices, then the radial speed of the wind also changes periodically depending on the current angle of the antenna. From the history of radar, applications in analog broadcast radar devices are known that nevertheless used wind compensation. The interference protection system of the P-12 ("Spoon Rest") and its successor, the P-18 , were equipped with such wind compensation. Here the change in the reference frequency was implemented by a resolver , which generated an amplitude of a sinusoidal voltage corresponding to the angle of rotation of the antenna. The envelope of this sinusoidal voltage was used to detune the coherent oscillator. The close range with strong fixed targets could be excluded from this disgruntlement.
In modern 3D radar devices with digital target signal recognition, the moving target indication works completely without wind compensation. The targets are distinguished here on the basis of their Doppler frequency spectrum, determined by a Fast Fourier Transformation, in front of a passive disturbance (cloud or chaff) moving at wind speed.