GB2035007A

GB2035007A - Detecting and identifying a radiation source

Info

Publication number: GB2035007A
Application number: GB7937022A
Authority: GB
Original assignee: Licentia Patent Verwaltungs GmbH
Current assignee: Licentia Patent Verwaltungs GmbH
Priority date: 1978-10-30
Filing date: 1979-10-25
Publication date: 1980-06-11
Also published as: DE2847233A1; IT1124817B; GB2035007B; FR2440558A1; DE2847233C2; IT7926892A0

Abstract

A method of detecting and identifying a radiation source close to the horizon with an opti-electronic image receiver comprising an optical system (1), at least one detector array (2), a scanning device (3), a device to rotate the image receiver round a vertical axis and evaluating logic circuitry. For detecting radiation sources, the image receiver is rotated with the scanning device (3) at rest within the receiver and the region of the horizon imaged on the detector array (2) is searched by the image evaluating logic circuitry for punctiform radiation sources. For identification of the radiation sources, the image receiver is stopped, directed towards a radiation source and the scanning device (3) is actuated for repeated examination of the horizon image section surrounding the radiation source. When a moving source is to be identified, successive scans are compared. For the initial source detection, a memory stores the required image and this is correlated with the array output during the rotation of the image receiver. <IMAGE>

Description

SPECIFICATION Detecting and identifying a radiation source The present invention relates to a method of detecting and identifying a radiation source.

The risk posed by low-flying, that is horizontal means of attack, is continually on the increase. The problem of promptly recognizing this threat and, by identification of the attack means, of taking appropriate counter-measures, is itself known. It is possible either for specific characteristics in regard to space or time to be identified by filtering out, or in the case of very high range requirements, where the resolution of an image sensor not adequate for identifying the attack means, properties that vary with time can in certain circumstances be sought out. An example is a low-flying helicopter at a distance of 4 km and more. The hot rotor blades cause a characteristic modulation frequency of the thermal radiation.

Thus apparatures are known for locating aircraft and rockets which fly below the radar horizon. These devices comprise a revolving camera provided with a vertically disposed, linear detector array and they monitor a strip of a few degrees in the region of the horizon which is investigated for heat point targets (hot rocket heads, aircraft noses).

Thermal image cameras provided with scanning devices for obtaining thermal images are also known. Methods are also known in which movements are filtered out by forming differences between successive images.

These known apparatuses and methods suffer from the serious disadvantage that they require, for the recognition and identification, considerably complicated and expensive equipment, do not make any preselection possible by scanning the horizon and operate too slowly in identification.

According to the present invention there is provided a method of detecting and identifying a radiation source, comprising the steps of rotating an image receiver to provide an image on a detector array whilst maintaining a scanning device at rest, searching the array by image evaluating logic means to detect such a radiation source, stopping the rotation of the image receiver after detection of such radiation source, directing the image receiver towards the detected radiation source and actuating the scanning device to investigate the surroundings of the radiation source.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings in which Fig. 1 shows an image receiving device, Fig. 2 shows the image receiving device rotating for recognizing point targets, Fig. 3 shows a block diagram of image processing logic means for point target filtering, Fig. 4 shows the image receiving device at rest for identifying detected point targets, and Fig. 5 shows a block diagram of modulation filter ing logic means. Referring to the accompanying drawings, Fig. 1 shows an image receiving device (camera) comprising an objective (lens) 1, at least one vertically disposed, linear detector array 2 and a rotating prism 3 as an example of a scanning device.

The camera is mounted on a primarily stabilized platform 4 and can be set in rotation on this platform. Electronic detector signals can be transmitted via slip rings to image processing electronic logic means shown in Fig. 3.

For discovering approximately punctiform targets, the scanning device 3 is fixed, (Fig. 2), the camera is rotated and thus an annular strip 5, near to the horizon, of the scene surrounding the camera is sequentially imaged on the detector array. A portion of this panorama image is continuously, preferably digitally stored and is investigated on-line for point targets.

One possible image processing logic means for point target filtering is shown in a block diagram in Fig. 3. It comprises a memory 31, to which the portions of the scene are continuously supplied, and a further memory 32 for a pattern function of the point targets looked for. A cross-correlator 33, to which the memory contents from memories 31 and 32 are continuously supplied, filters out the position of all the point targets which have a similarity lying above a predeterminable minimum similarity to the point target pattern function. The correlator 33 emits a signal which corresponds to the position and similarity of detected targets. Components which suppress perturbing targets could possibly be included.

For subsequent identification, the rotation of the camera is stopped (Fig. 4) and the camera is directed successively onto the detected point targets. The scanning device 3 is now rotated so that the camera supplies on each occasion a complete series of image sections, following one another in time, around a suspicious point target.

Fig. 3 shows logic means in which image formation supplied by the scanning device 3 is supplied via an electronic switching device 50 alternately to a memory 51 for an image portion at time to and to a substracting element 52, which for all the succeeding image sections for each image point forms the difference from the stored image section. Thus, for example, each hundredth image section is input to the memory 51 and the succeeding 99 are substracted therefrom.If the scene is constant the difference is always zero. Afurther memory 53 stores a difference if this difference exceeds a minimum value, the associated image point co-ordinates and the time-sequential number of the image section and supplies this information to a freely programmable computer54 such as a microporcessor, which investigates the individual image point data for a modulation with time and fades in the results to a monitor 55, which also transmits the memory content from the memory 51.

An advantage of the above described embodi ment is that both detection and also identification can be carried out with one and the same image receiving device and that a possibility is provided for determiningthe modulation frequency.

1. A method of detecting and identifying a radia tion source, comprising the steps of rotating an image receiver to provide an image on a detector

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Detecting and identifying a radiation source The present invention relates to a method of detecting and identifying a radiation source. The risk posed by low-flying, that is horizontal means of attack, is continually on the increase. The problem of promptly recognizing this threat and, by identification of the attack means, of taking appropriate counter-measures, is itself known. It is possible either for specific characteristics in regard to space or time to be identified by filtering out, or in the case of very high range requirements, where the resolution of an image sensor not adequate for identifying the attack means, properties that vary with time can in certain circumstances be sought out. An example is a low-flying helicopter at a distance of 4 km and more. The hot rotor blades cause a characteristic modulation frequency of the thermal radiation. Thus apparatures are known for locating aircraft and rockets which fly below the radar horizon. These devices comprise a revolving camera provided with a vertically disposed, linear detector array and they monitor a strip of a few degrees in the region of the horizon which is investigated for heat point targets (hot rocket heads, aircraft noses). Thermal image cameras provided with scanning devices for obtaining thermal images are also known. Methods are also known in which movements are filtered out by forming differences between successive images. These known apparatuses and methods suffer from the serious disadvantage that they require, for the recognition and identification, considerably complicated and expensive equipment, do not make any preselection possible by scanning the horizon and operate too slowly in identification. According to the present invention there is provided a method of detecting and identifying a radiation source, comprising the steps of rotating an image receiver to provide an image on a detector array whilst maintaining a scanning device at rest, searching the array by image evaluating logic means to detect such a radiation source, stopping the rotation of the image receiver after detection of such radiation source, directing the image receiver towards the detected radiation source and actuating the scanning device to investigate the surroundings of the radiation source. An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings in which Fig. 1 shows an image receiving device, Fig. 2 shows the image receiving device rotating for recognizing point targets, Fig. 3 shows a block diagram of image processing logic means for point target filtering, Fig. 4 shows the image receiving device at rest for identifying detected point targets, and Fig. 5 shows a block diagram of modulation filter ing logic means. Referring to the accompanying drawings, Fig. 1 shows an image receiving device (camera) comprising an objective (lens) 1, at least one vertically disposed, linear detector array 2 and a rotating prism 3 as an example of a scanning device. The camera is mounted on a primarily stabilized platform 4 and can be set in rotation on this platform. Electronic detector signals can be transmitted via slip rings to image processing electronic logic means shown in Fig. 3. For discovering approximately punctiform targets, the scanning device 3 is fixed, (Fig. 2), the camera is rotated and thus an annular strip 5, near to the horizon, of the scene surrounding the camera is sequentially imaged on the detector array. A portion of this panorama image is continuously, preferably digitally stored and is investigated on-line for point targets. One possible image processing logic means for point target filtering is shown in a block diagram in Fig. 3. It comprises a memory 31, to which the portions of the scene are continuously supplied, and a further memory 32 for a pattern function of the point targets looked for. A cross-correlator 33, to which the memory contents from memories 31 and 32 are continuously supplied, filters out the position of all the point targets which have a similarity lying above a predeterminable minimum similarity to the point target pattern function. The correlator 33 emits a signal which corresponds to the position and similarity of detected targets. Components which suppress perturbing targets could possibly be included. For subsequent identification, the rotation of the camera is stopped (Fig. 4) and the camera is directed successively onto the detected point targets. The scanning device 3 is now rotated so that the camera supplies on each occasion a complete series of image sections, following one another in time, around a suspicious point target. Fig. 3 shows logic means in which image formation supplied by the scanning device 3 is supplied via an electronic switching device 50 alternately to a memory 51 for an image portion at time to and to a substracting element 52, which for all the succeeding image sections for each image point forms the difference from the stored image section. Thus, for example, each hundredth image section is input to the memory 51 and the succeeding 99 are substracted therefrom.If the scene is constant the difference is always zero. Afurther memory 53 stores a difference if this difference exceeds a minimum value, the associated image point co-ordinates and the time-sequential number of the image section and supplies this information to a freely programmable computer54 such as a microporcessor, which investigates the individual image point data for a modulation with time and fades in the results to a monitor 55, which also transmits the memory content from the memory 51. An advantage of the above described embodi ment is that both detection and also identification can be carried out with one and the same image receiving device and that a possibility is provided for determiningthe modulation frequency. CLAIMS

1. A method of detecting and identifying a radia tion source, comprising the steps of rotating an image receiver to provide an image on a detector array whilst maintaining a scanning device at rest, searching the array by image evaluating logic means to detect such a radiation source, stopping the rotation of the image receiver after detection of such radiation source, directing the image receiver towards the detected radiation source and actuating the scanning device to investigate the surroundings of the radiation source.

2. A method as claimed in claim 1, wherein the image receiver is rotated about a vertical axis.

3. A method of detecting and identifying a radiation source, substantially as hereinbefore described with reference to the accompanying drawings.