(uncountable, slang) Noise on an A-scope or similar type of radar display.
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_:vb6316015
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The problem in radar detection is to have a signal to noise ratio that will allow the echo to be seen through the grass on the radar screen. The use of a long pulse allows a greater average signal strength to be returned in the target echoes.
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1960, Radarman 3 & 2, volume 1, United States. Bureau of Naval Personnel, page 49:
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Some of the scattered waves can be picked up by the receiver and may show up as "grass" on the radar presentation. Weather radars make use of this phenomenon to chart the progress of storms.