MIL-STD-2071A(AS)
3.12 Processing - first level statistics. First level processing of RCS data involves calculating average values, statistical data, and other information or presentations where the inputs to the processing are the raw pulse-to-pulse RCS values. First level processing is done for each discrete chaff unit or a sample (a given number of consecutive pulses) of continuous chaff or very large chaff clouds.
3.13 Processing - percentile value. In RCS statistics, the percentile value is that value which a given percent of data points equal or exceed. As an example, a percentile value of 70 percent of
10 square meters mean that 70 percent of the data points would have an RCS value of 10 square meters or more. A data point in the first level statistics is the RCS value obtained on a given radar pulse, while a data point in the second level statistics is the average RCS value of a chaff unit or chaff sample.
3.14 Processing - second level statistics. Results from the first level processing are used as inputs to calculate average RCS values for each radar frequency, statistical data, or other information or presentations in the form of second level statistics for a group of similar units.
3.15 Processing - shadow graphs. Shadow graphs visually display RCS values as a function of time and range to pictorially show scintillation, physical cloud growth, homogeneity of the cloud, and other details. A printer or plotter is used to show pulse-to-pulse RCS values where a solid black line is calibrated to maximum RCS and white to no RCS. The various shades from black to white then show relative RCS values. Lines may be printed for each radar pulse, or spaced "N" pulses apart, where "N" may be any integer. The shadow graph may be presented on a color monitor where color may be used to increase the dynamic range of the presentation.
3.16 Processing - spectral data. Spectral data are used to present the unique spectral signature of a chaff cloud as observed by the measuring radar and is a function of the Fast
Fourier Transform algorithm applied to the pulse-to-pulse amplitude data. The data are presented graphically to display the power spectral density of the chaff cloud (volts2) relative to the frequencies of interest (0-500 Hz).
3.17 Radar cross-section (RCS). RCS is defined as the return signal to a radar where
RCS = = 4 Power reradiated by the target per steradian
Power incident on the target per unit of area
Physically, the RCS of a body is equal to the geometric cross-section of a sphere (large compared to wavelength) which would give the same return if placed at the same point in the radar antenna beam.
3.18 RCS frequency spectrum. The radars intended to be targeted by the chaff countermeasure fall in the range of 2-18 GHz and 35 GHz. This is considered the chaff RCS frequency spectrum to be measured.
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