. Airborne radar. Airplanes; Guided missiles. 218 REFLECTION AND TRANSMISSION OF RADIO WAVES. Fig. 4-40 Geometrical Relations for Doppler Spectrum of Sea Return. Thus it is evident that the spread in cos x, and hence the width of the induced doppler spectrum, will be minimum along the ground track (00 = 0)- As an example, we consider an airborne X-band pulse radar (9400 Mc/sec) with a horizontal beamwidth of 3° (A = °), and an aircraft speed of 200 knots. Then from Equation 4-69,/i = kc. At grazing depression angles along the ground track {do = 0), the induced doppler spectrum has a ha
. Airborne radar. Airplanes; Guided missiles. 218 REFLECTION AND TRANSMISSION OF RADIO WAVES. Fig. 4-40 Geometrical Relations for Doppler Spectrum of Sea Return. Thus it is evident that the spread in cos x, and hence the width of the induced doppler spectrum, will be minimum along the ground track (00 = 0)- As an example, we consider an airborne X-band pulse radar (9400 Mc/sec) with a horizontal beamwidth of 3° (A = °), and an aircraft speed of 200 knots. Then from Equation 4-69,/i = kc. At grazing depression angles along the ground track {do = 0), the induced doppler spectrum has a half-power width of = cps, while at 45° to the ground track the half-power width is = 238 cps. In principle, the induced spectrum is known from information available at the radar and thus may be compensated, in part, by appropriate (though complicated) circuitry. There still remains the intrinsic spectrum, and a knowledge of this is necessary in order to determine the capabilities and limitations of doppler radar in target detection and tracking through clutter. Measurements of the intrinsic spectrum of sea clutter have been made by the Control Systems Laboratory of the University of Illinois.^^ These were made with a coherent airborne radar operating on a wavelength of cm. By making measurements along the ground track, the width of the induced spectrum was made small relative to that of the measured spectrum, so that the measurements yielded the intrinsic spectrum directly. By multiplying the frequencies by X/2 (see Equation 4-69) the results were converted to a velocity spectrum. ^iThe information on the intrinsic doppler spectrum of sea clutter was furnished through the courtesy of the Control Systems Laboratory, University of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the origina
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