Device and method for 3D height-finding avian radar

Abstract

A height-finding 3D avian radar comprises an azimuthally scanning radar system with means of varying the elevation pointing angle of the antenna. The elevation angle can be varied by employing either an antenna with multiple beams, or an elevation scanner, or two radars pointed at different elevations. Heights of birds are determined by analyzing the received echo returns from detected bird targets illuminated with the different elevation pointing angles.

What is claimed is: 
     
       1. A 3D radar surveillance system for simultaneously tracking multiple targets, comprising: an antenna; means operatively connected to said antenna for varying an effective elevation pointing direction of said antenna; a radar transmitter operatively connected to said antenna, said transmitter generating a radar signal for emission via said antenna; a exactly one radar receiver operatively connected to said antenna; an azimuth scanner operatively coupled to said antenna for rotating said antenna about an axis during repeated azimuth scans, said receiver being configured to receive echo returns from all transmitted radar signals for all azimuth directions and effective elevation pointing directions of said antenna; and a processor operatively connected to said receiver, said processor being configured for contemporaneously detecting and localizing multiple airborne targets in azimuth and range for each of said azimuth scans, said processor being further configured for estimating a height above a ground surface of each detected an localized target based on relative, the estimated height being geometrically related to a respective, estimated target elevation angle, said processor being further configured for computing said estimated target elevation angle by mathematically combining amplitudes of temporally spaced echo returns as a function of from such detected and localized targets in response to respective temporally spaced transmit radar signals received at a minimum of two respective elevation pointing direction of said antenna. 
     
     
       2. The system defined in  claim 1  wherein said antenna includes means for generating at least two beams and said means for varying includes means for selecting a given beam for a given radar pulse. 
     
     
       3. The system defined in  claim 2  wherein said means for generating and said means for selecting includes a high-power RF switch that rotates with said antenna about said axis, said switch being operable to cause (a) said radar pulse to be transmitted via said given beam and (b) pulse echo returns associated with said radar pulse to be received via said given beam. 
     
     
       4. The system defined in.  claim 2  wherein said means for selecting includes a low-power RF switch that is stationary relative to said axis and does not rotate with said antenna, said switch being operable to direct pulse echo returns from said given beam to said receiver. 
     
     
       5. The system defined in  claim 2  wherein said antenna is a reflector, said means for generating including multiple feeds. 
     
     
       6. The system defined in  claim 2  wherein said antenna is a frequency-scanning antenna and said means for generating includes a variable-frequency transceiver that is tuned to generate said at least two beams. 
     
     
       7. The system defined in  claim 2  wherein said antenna is a phased-array antenna and said means for generating and said means for selecting include a beam forming network. 
     
     
       8. The system defined in  claim 2  wherein said antenna and said means for generating include two antennas oriented to provide respective beams with respective elevation pointing directions different from one another. 
     
     
       9. The system defined in  claim 2  wherein said at least two beams are vertically stacked pencil beams and said means for varying includes an RF switch. 
     
     
       10. The system defined in  claim 1  wherein said antenna is an elevation monopulse antenna and said radar receiver includes a dedicated receiver for each of a plurality of antenna receive channels, said means for varying including means for selecting from among the antenna receive channels for a given radar pulse. 
     
     
       11. The system defined in claim  10  1 wherein said antenna is a reflector with multiple feeds. 
     
     
       12. The system defined in  claim 10  wherein the dedicated receivers are non-coherent and the associated receive channels are from the upper and lower beams of said antenna. 
     
     
       13. The system defined in  claim 1  wherein said radar transmitter and said radar receiver are noncoherent. 
     
     
       14. The system defined in  claim 1  wherein said radar transmitter and said radar receiver are from a COTS marine radar. 
     
     
       15. The system defined in  claim 1  wherein said receiver has a digitized output. 
     
     
       16. The system defined in  claim 1  wherein said means for varying includes an elevation scanner. 
     
     
       17. The system defined in  claim 1  wherein said processor is a COTS PC. 
     
     
       18. The system defined in  claim 1  where said processor executes integration, interference suppression, clutter suppression, and adaptive thresholding. 
     
     
       19. The system defined in  claim 1  wherein said means for varying an effective elevation pointing direction includes components taken from the group consisting of mechanical components and electrical components. 
     
     
       20. The system defined in  claim 19  wherein said means for varying an effective elevation pointing direction includes components taken from the group consisting of a plurality of vertically stacked feed horns, an RF switch for switching among a plurality of beams of different fixed elevation angles, a rotary joint for conveying signals from said antenna during rotation thereof in elevation, a dual-channel rotary joint and a hybrid, frequency-scanning apparatus, a beam forming network, a plurality of receive channels, a channel selector, and an elevation scanner. 
     
     
       21. The system defined in  claim 1  wherein said means for varying an effective elevation pointing direction are means for varying the effective elevation pointing direction of said antenna while said antenna rotates about said axis. 
     
     
       22. A 3D radar surveillance method of contemporaneously determining the heights of multiple airborne targets above a ground surface, comprising: operating a radar system over successive azimuth scans to illuminate and detect the targets in a search volume including a plurality of range-azimuth cells, said radar system having a at least one radar antenna; during the operating of said radar system, varying an antenna elevation pointing angle of said radar antenna; and detecting and localizing multiple targets on a plane in respective range-azimuth cells, and estimating the height above a ground surface for each detected and localized target from, the estimated height being geometrically related to a respective, estimated target elevation angle, the estimating of said height including computing a value for said estimated target elevation angle by mathematically combining the amplitudes of temporally spaced echo returns thereof received from said radar antenna pointed along at least two different elevation pointing angles, the estimating of the height including computing height estimates from relative amplitudes of said echo returns as a function of said elevation pointing angles from such detected and localized target in response to respective temporally spaced illumination signals received at a minimum of two respective elevation pointing directions of said antenna. 
     
     
       23. The method defined in  claim 22  wherein said varying comprises emitting a plurality of beams via said antenna. 
     
     
       24. The method defined in  claim 23  wherein radar transmission and reception is alternated between said beams from pulse to pulse. 
     
     
       25. The method defined in  claim 23  wherein radar transmission and reception is through all of said beams on every transmission pulse. 
     
     
       26. The method defined in  claim 23  where said beams are vertically stacked pencil beams. 
     
     
       27. The method defined in  claim 22  wherein said varying comprises operating an elevation scanner. 
     
     
       28. The method defined in  claim 22  wherein said radar system includes at least two radar subsystems proximate to one another, said varying comprising operating said at least two radar subsystems so that each radar subsystem is pointed at a different elevation angle. 
     
     
       29. The method defined in  claim 22  further comprising operating a processor to track the detected airborne targets. 
     
     
       30. The method defined in  claim 22  wherein said estimating includes interpolating in elevation. 
     
     
       31. The method defined in  claim 22  wherein said estimating includes using target tracks in an association process to identify tracks in different beams belonging to a common target, thereby enabling a smoothing and improving of height estimates. 
     
     
       32. The method defined in  claim 22  further comprising using the height estimates further to estimate target radar cross-section. 
     
     
       33. The method defined in.  claim 22  further comprising using the height estimates further for target classification. 
     
     
       34. The method defined in  claim 22  further comprising distributing height information to a network. 
     
     
       35. The method defined in  claim 22  further comprising automatically notifying or alerting users of hazards or situations of interest. 
     
     
       36. The method defined in  claim 22  further comprising combining target height and range estimates and radar echo intensities to form accurate estimates of radar cross-sections. 
     
     
       37. The method defined in  claim 22  farther comprising continually updating estimated dynamics vectors, including speed, heading, position, and height for each of said targets. 
     
     
       38. The method defined in  claim 22  wherein said estimating is carried out for all targets detected in said search volume, to provide 3D localization of such targets. 
     
     
       39. The method defined in  claim 22  wherein the operating of said radar system is continuous so that the search volume is scanned repeatedly at regular time intervals, causing targets to be repeatedly illuminated and detected. 
     
     
       40. The method defined in.  claim 22  further comprising rotating or scanning said radar antenna in azimuth. 
     
     
       41. The system defined in claim 1 wherein an antenna beam is associated with each of said elevation pointing directions, and wherein said processor includes a multi-target tracker that is configured to track each target for each beam and identify associated tracks across beams for each target. 
     
     
       42. The system defined in claim 41 wherein said processor is configured to record, for each target track, an amplitude from each detection used in the formation of such track, said processor being further configured to perform at least one additional operation taken from the group of (i) smoothing such amplitudes to form a more accurate target amplitude estimate within each beam, and (ii) smoothing noisy per detection height estimates over multiple scans using said associated tracks to thereby produce better height estimates. 
     
     
       43. The system defined in claim 1 wherein said processor is further configured to compute a radar cross section estimate for each target using the estimated target elevation angle to improve the radar cross section estimate. 
     
     
       44. The method defined in claim 22 wherein the varying of said antenna elevation pointing angle means steering its associated beam to said elevation pointing angle, and wherein the detecting and localizing multiple targets includes performing multi-target tracking on detected targets to generate target tracks for each beam, and associating tracks across beams belonging to the same target. 
     
     
       45. The method defined in claim 44 wherein for each target track, an amplitude from each detection used in the formation of such track is recorded, and where at least one additional operation is performed taken from the group of (i) smoothing such amplitudes to form a more accurate target amplitude estimate for a given beam, and (ii) smoothing noisy, per detection height estimates over multiple scans using said associated tracks to produce better height estimates. 
     
     
       46. The method defined in claim 22, further comprising computing a radar cross section estimate for each target using the estimated target elevation angle to improve the radar cross section estimate. 
     
     
       47. A 3D radar surveillance system comprising:
 an antenna provided with means for varying its effective pointing direction in elevation to enable multiple elevation beams;   a radar transmitter operatively connected to said antenna for generating a radar signal for emission via said antenna and over said beams;   a radar receiver operatively connected to said antenna;   an azimuth scanner operatively coupled to said antenna for rotating same about an azimuth axis for repeated scans; and   a processor operatively connected to said receiver, said processor being configured for contemporaneously estimating a height above a ground surface of each of a plurality of detected targets localized in azimuth and range, wherein the height estimate for any given detected target is geometrically related to a respective, estimated target elevation angle, said processor being configured to compute said respective estimated target elevation angle by mathematically combining amplitudes of echo returns from such given detected target received from at least two respective elevation beams of said antenna, said processor including a multi-target tracker that tracks target detections in each beam retaining their echo return amplitudes, said processor further configured to determine which of those tracks across said beams belong to the same target in order to identify respective target relative amplitude pairs for said estimating of target heights.   
     
     
       48. The system defined in claim 47 where said processor is further configured to reduce the noise associated with height estimates computed for each detected target by smoothing the relative amplitudes retained in said tracks over multiple scans. 
     
     
       49. The system defined in claim 47 where said processor is further configured to compute radar cross section estimates for each target utilizing the target elevation estimate to improve said radar cross section estimate. 
     
     
       50. A radar surveillance method of contemporaneously determining the heights of multiple airborne targets above a ground surface, comprising:
 operating a radar system over successive scans to illuminate and detect the targets in a search volume including a plurality of range-azimuth cells, said radar system having at least one radar antenna;   during the operating of said radar system, forming multiple elevation beams of said at least one radar antenna centered at respective elevation pointing angles; and   detecting and localizing airborne targets in said range-azimuth cells, estimating a height above a ground surface of each detected and localized target, said height being geometrically related to a respective, estimated target elevation angle whose value is computed by mathematically combining relative amplitudes of echo returns from such detected and localized target received from at least two respective elevation beams of said antenna, said estimating of target height further including tracking target detections from said targets in each beam, retaining their respective echo return amplitudes and determining those tracks across said beams belonging to the same target in order to identify respective target relative amplitude pairs for said estimating of target heights.   
     
     
       51. The method defined in claim 50 where said estimating of target height further includes reducing the noise associated with height estimates computed for each detected target by smoothing the relative amplitudes retained in said tracks over multiple scans. 
     
     
       52. The method defined in claim 50 wherein said target elevation estimate is further used to estimate radar cross section for said target.