FINE RESOLUTION RADAR FOR FOLIAGE PENETRATION

• US 3,614,778 A
• Filed: 11/18/1965
• Issued: 10/19/1971
• Est. Priority Date: 11/18/1965
• Status: Expired due to Term

• Current Assignee: Keeve M. Siegel, Robert R. Graham, Weston E. Vivian
• Original Assignee: Keeve M. Siegel, Robert R. Graham, Weston E. Vivian
• Inventors: Vivian, Weston E., Graham, Robert R., Siegel, Keeve M.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US04/508,731
• Time in Patent Office: 2,161 Days
• Field of Search: 343/5W,100.3
• US Class Current: 342/25.00A
• CPC Class Codes: G01S 13/9027 Pattern recognition for feature extraction
• CPC Class Codes: G01S 7/025 involving the transmission of linearly polarised waves
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures

Abstract

A method and apparatus for detecting by airborne radar the presence of a ground object hidden beneath foliage or the like. The radar signal is transmitted at a frequency having a wavelength relatively long with respect to the dimensions of the foliage and the like so that the scatter of the transmitted signal wave due to foliage is minimized and the transmitted wave passes through the foliage to be reflected from the ground object back to the airborne radar set. The optimum frequency range has been determined to be 100 to 1,000 mHz. The transmitted radar beam forms a radar path on the ground and it has been discovered that the optimum incidence angles measured in the vertical plane of the beam at the patch are in the range of 30* to 60* . The radar beam is transmitted at right angles to the direction of motion of the airborne radar set. The radar beam is preferably horizontally polarized to eliminate or minimize a scatter from vertical clutter such as tree trunks.

Claims

1. In the method of radar object detection by means of a focused, synthetic-aperture, coherent, fine resolution, airborne radar wherein recurrent pulses of electromagnetic waves at a predetermined phase and predetermined frequency are transmitted by a transmitter moving through successive positions along a predetermined path, one of said pulses being transmitted at a corresponding one of said positions, reflected waves from each of said transmitted pulses are received after reflection from said object, bipolar signals indicative of the relative phase between said transmitted and said received waves corresponding to each of said pulses at each of said positions are derived, and said signals are summed vectorially, that improvement comprising transmitting said waves at only a single frequency having a wavelength relatively long with respect to dimensions of foliage and the like so that scatter of the transmitted wave due to foliage is minimized and said transmitted wave propagates through said foliage so as to be reflected from said object when said object is disposed beneath said foliage.

2. The method set forth in claim 1 wherein said waves are transmitted at only a single frequency in the range of 100 to 1, 000 megacycles/second.

3. The method set forth in claim 1 wherein said radar is side-looking and airborne, said transmitted wave is in the form of a beam defining a radar patch on the ground, and the incidence angles measured in the vertical plane of said beam at said patch are in the range of from 30* to 60*.

4. In a fine resolution radar of the foCused, synthetic-aperture, coherent, side-looking airborne type for object detection and having means for transmitting recurrent pulses of electromagnetic waves at a predetermined phase and frequency while said transmitting means is moved through successive positions along a predetermined path, one of said pulses being transmitted at a corresponding one of said positions, means for receiving reflected waves of each of said transmitted pulses after reflection from said object, means for deriving bipolar signals indicative of the relative phases between said transmitted and said received waves corresponding to each of said pulses at each of said positions, and means for summing said signals vectorially, that improvement comprising means for transmitting said pulses at a predetermined frequency having a wavelength relatively long with respect to dimensions of foliage and the like so that scatter of the transmitted wave due to foliage is minimized and said transmitted wave propagates through said foliage so as to be reflected from said object when said object is disposed beneath said foliage.

5. The device set forth in claim 4 wherein said predetermined frequency is in the range of 100 to 1,000 megacycles/sec.

6. The device set forth in claim 4 wherein said transmitted wave is in the form of a beam defining a radar patch on the ground, and the incidence angles measured in the vertical plane of said beam at said patch are in the range of from 30* to 60*.

7. The device set forth in claim 4 wherein said transmitted wave has substantially only a horizontal polarization.

8. In a method of detecting an object by directing a transmitted radar beam toward an object and comparing the transmitted and reflected beams, the improvement for detecting an object hidden by foliage comprising directing toward the hidden object a transmitted radar beam whose wavelength is much greater than the dimensions of the individual components of the foliage behind which the object is hidden, whereby the radar beam penetrates the foliage with relatively little attenuation to impinge upon the hidden object and be reflected thereby.

9. The method set forth in claim 8 wherein said radar beam is transmitted from an airborne radar apparatus and directed to an object on the ground, which object is hidden by foliage and other ground cover, and said radar beam is horizontally polarized further to reduce attenuation by vertical components of the foliage and ground cover.

10. The method as set forth in claim 9 wherein the frequency of the radar beam is in the range of 100 to 1,000 megacycles/second.