Patent GB-1179417-A (GB)
Title: Multi-Sensor Correlation Apparatus particularly for Radar Systems
Inventor: KLEES ROBERT MOWERY
IPC: G01S13/86
Filed: 1966-09-08
Abstract: 1,179,417. Wave-energy position finding. NORTH AMERICAN AVIATION Inc. 8 Sept., 1966, No. 40253/66. Heading H4D. An improved target display signal is provided by correlating signals reflected and radiated from a target which is both reflective and radiative. As described, the system correlates the signals from an IR sensor with the signals from a monopulse radar to enable both the range and direction of the target to be resolved. The two sets of signals have different time bases and the system includes means for converting the IR signals to the time base of the radar signals, the means including a store for the IR signals, these signals being read out in accordance with the time base of the radar signals. As shown in Fig. 3 there is provided a monopulse radar system adapted for airborne use for providing signals having a magnitude indicative of the angle-off-bore-sight B of a reflective radar target and a periodic time occurrence (relative to the system trigger) indicative of the slant range or distance thereof. Such a radar system comprises a system trigger 22, a transmitter (not shown), a monopulse receiver 23, and a multi-aperture microwave antenna 24 in driven relationship to antenna drive means 25 for scanning the antenna in azimuth. By summing at a signal-summing means 26, the receiver signal indicative of the radar target angle-off-bore-sight B and a signal from an antenna elevation pick-off means 27 indicative of the antenna declination #, a signal is provided which is indicative of the elevation angle # of a detected monopulse radar target return, the time of occurrence thereof (relative to the system trigger response) being indicative of the range of the target. There is further provided a passive optical sensor 28 comprising an infra-red-sensitive point-scanning device. The optical axis of the receiver optics of the sensor 28 is bore-sighted substantially parallel to the bore-sight axis of the antenna 24, and is so mounted relative thereto that the azimuth scanning mode of the drive means 25 scans in common the antenna beam pattern (10) and the optical response pattern (12) in azimuth, Fig. 4 (not shown). There is further provided means 29 for adjusting the vertical view angle # of the response pattern (12) of the passive sensor 28 for vertical scanning within the vertical beam width (10) of the antenna 24. Such vertical scanning means may consist of a mirror drive or motor rotating a hexagonal element, the six equal sides of the hexagon being reflectively coated and the element being so disposed relative to the optical input of the sensor 28 as to vary cyclically the orientation of the sensitive direction thereof in a vertical direction which is contained within the azimuthal extent of the antenna beam width (10). A position pick-off 30 co-operates with the mirror drive to provide a signal indicative of the vertical angle 0 to which the response pattern of the sensor 28 is oriented. There is further provided a scan converter 31 for providing radar range correlation of the passive sensor response to different vertical view angles. A write-mode modulation input 32 and associated write-mode vertical sweep input 33 of the scan converter 31 are responsively connected to the respective outputs of the passive sensor 28 and pick-off 30. The gain, or amplitude level, of the pick-off angle signal is then so adjusted that a maximum angle of interest corresponds to and produces full deflection of the write-mode sweep of the scan converter 31. Because the scanning means 29 varies the elevation view angle # of the passive sensor at a constant rate, the time base of the stored IR signal traces is substantially a linear function of changes in the view angle #, Fig. 2a (not shown). A vertical read-sweep input 35 of the scan converter 31 is responsively connected to the source 26 of radar target angle signals. The radar target angle signal on the line 35 is scaled similarly to the pick-off angle signals on the line 33, whereby radar target angle signals corresponding to the same angles as those of the pick-off angle signals (for deflecting the " write " gun) produce a like deflection of the read gun. Hence, the read-out line 34 of a stored passive sensor signal corresponding to a given vertical view angle # occurs at a time interval (relative to the system trigger) associated with a radar return from such direction #, and which is indicative of the radar slant range of the reflective radar target in such direction. Because of the variable nature of the terrain profile, together with the selected angle # at which the antenna bore-sight is depressed, the radar target angle observed as a function of radar range time is not in general linear, Fig. 2c (not shown). However, because the radar target angle signal is used as the readsweep signal, the time base of the stored passive sensor signals is converted to that of the received radar returns for corresponding view angles. Also, because the scan converter converts the time scale of the stored passive sensor signals as a function of the view angle # to a function of radar range time, it is not necessary that the periodicity of the mirror drive means 29 be synchronized with the system trigger 22. It is only necessary that the read-out mode should read the stored image traces or lines at no greater rate than they are being generated by the write mode. Hence the system trigger 22 may be coupled to a periodic output of the mirror drive 29 to ensure a common speed for the write-in and read-out operations of the scanconverter 31. Also, horizontal " read " and " write " scan generators must be included for co-operation with the respective read-sweep and write-sweep inputs, whereby successive vertical data traces, corresponding to successive azimuth increments of the azimuthally scanning antenna 24 and associated passive sensor 28, may be separately processed, as shown in Fig. 5. Referring to Fig. 5, in addition to the read and write vertical sweep inputs, and the write gun input (shown in Fig. 3), there is further provided a read and write horizontal scan input 36 and 37 of the scan converter 31. The horizontal scan inputs 36 and 37 are responsively connected to respective ones of like scan generators 38 and 39, which are in turn responsively connected to the system triggers 22 (of Fig. 3). Interposed between the input from the system trigger 22 and the scan generators 38 and 39 is a frequency divider for providing an integer sub-multiple frequency, the integer of which corresponds to the number of traces or successive azimuth increments to be displayed as a data set on the storage element of the scan converter 31. Hence, if sixteen successive range traces, corresponding to sixteen successive azimuth increments, are to be read out of the time-scale converting means 31, then the integer of frequency divider 40 would be sixteen, and the integer sub-multiple would be <SP>1</SP>/ 16 . The time interval thus provided between successive data traces occurring at a given vertical line (i.e. the time interval occurring between every sixteenth data trace), coupled with the trace-attenuating action of the read mode in read-sweeping such a vertical line, ensures adequate " erase " action prior to writing a subsequent data trace at such a vertical line. The output on the line 34 is thus a periodic video output, the period of which corresponds to a selected azimuth, and the time phase of which relative to the system trigger corresponds to a selected slant range distance. Such output may be applied to the modulation input of a display element such as the PPI indicator 42 of Fig. 3. The range sweep input 43 of the indicator 42 may be connected to a range sweep generator 44 (which is synchronized with the system trigger 22), and the azimuth control input 45 of indicator 42 may be responsively connected to an azimuth pick-off 46 of the antenna 24.