DE3532085A1 - Device for using high-resolution, stabilized daylight level imaging, or weak-light level imaging, which has been made uniform, of a moving carrier - Google Patents

Abstract

The invention relates to improvements in monitoring arrangements which are used in daylight and are based on television cameras and a lens or lens group having a long focal length. The improvement to a large extent overcomes the difficulties resulting from vibration and atmospheric interference. The device comprises an amplifying, or image-intensifying, electrooptical imaging device and a suitable optical lens or lens group with an exposure control device, in such a manner that the sensor is exposed for a time duration or period which is much shorter than the normal scanning time of the sensor.

Description

The invention relates to a novel system or a novel Arrangement that is suitable, the disadvantages and overcome problems on a large scale which is caused by vibrations of the line of sight and certain atmospheric Effects on the resolution of an image be that via a television tube camera and an optical Lens or lens group, in particular with a lens or a long focal length lens group. The stabilization of such systems or arrangements is a serious problem, and this problem is solved by the novel system or the novel arrangement according to the invention overcome to a great extent.

The invention preferably relates to an educational and / or or surveillance system or a reconnaissance and / or Monitoring arrangement.

In particular, the invention relates to an electro-optical Arrangement that uses a reinforcing electro-optical (ultraviolet, visible light and infrared) imaging device and an exposure control device, in particular a shutter, and a synchronization circuit for use with a suitable optical Includes lens or lens group.

The arrangement is intended in particular in a High resolution stabilized daylight level real-time imaging arrangement and a moderate low-light level real-time imaging device for reconnaissance, surveillance and / or attack to be used.

In most cases, these are high order Magnification and a narrow field of view (lenses or lens groups  long focal length), their performance (Range of resolution) seriously due to shortcomings of the previous achieved line of sight stabilization and in the wide range arrangement also due to the atmospheric turbulence is hindered or disturbed.

The amplifying imaging device can be "in the sensor" intended electronic amplifier, as in a TV tube or television tube with low light levels and some solid state sensors, or it can be one be a two-part device consisting of an external amplifier, such as a microchannel plate amplifier or an MCP amplifier on a conventional imaging sensor tube or a solid-state sensor, in particular a CCD sensor or a CID sensor, attached or in Connection is provided.

The exposure control device can be a motorized one mechanical closure or an electro-mechanical Closure, in particular a solenoid closure, or a Closure operated by means of a device which is based on an electro-optical effect, or a Switching device on the amplification device (MCP) or acts on a solid-state sensor and an exposure shutter effect generated.

The synchronization circuit is needed for an accurate Period between successive openings maintain the shutter and / or open the Shutter and the beginning of the frame scan with each other to synchronize.

This sub-arrangement is proposed to be the stabilized one Performance of a stabilized real-time Daylight level high definition imaging arrangement (usually wide area) to improve.  

This novel arrangement is relatively simple and does it possible to overcome the constraints imposed on the capabilities of conventional imaging arrangements due to their previously achieved line of sight stabilization and to a certain extent also through the atmospheric Turbulence (in the wide range arrangement) inherent are.

The imaging performance in the moderate low light level range of the target or Target illuminance expanded.

The prior art is first explained below:

In each mapping arrangement, a movement or a "Dance" of the generated image on the sensor surface during the exposure period that the scene picture is beyond detection blurred, blurry and out of focus becomes.

The origin of this blurring, blurring and blurring can be:
(1) Random or statistical movements (tremors) of the line of sight around its nominal position, such as those caused by mapping non-stable platforms,
(2) each image "dancing" relative to time or parts of image dancing relative to each other and relative to time caused by atmospheric turbulence,
(3) rapid relative movements between the sensor and the scene, thereby causing:
(a) the sensor is "pivoted" in a search pattern,
(b) the sensor is on a fast moving vehicle,
(c) the sensor maps a fast moving scene.

The phenomenon of blurring, blurring and / or blurring, which has a dissolving effect, is known per se. The image resolution reduction is almost completely described and expressed or estimated by the optical transfer function, which is also referred to below as OTF , or the modulation transfer function, which is also referred to below as MTF and relates to the specific effects mentioned above.

The dissolution reducing effect is strongest or worst in high definition arrays.

In most cases these are high magnification arrangements and narrow field of vision (lenses or lens groups long focal length).

The present invention relates in particular to a high-resolution arrangement, which is carried on a vehicle unstable platform (earth, air or marine vehicle).

The instability of such a platform can be mechanical Interference that is inherent to the vehicle (engines, internal resonances and / or natural resonances) or them can result from mechanical disturbances caused by environmental factors or by interaction between environmental factors and the vehicle (winds, currents, roads etc.) are caused. Such mechanical disturbances can act directly on the arrangement platform (winch and  Marginal or boundary air flow in an aircraft environment) or as a thrust or warp on the vehicle body or such a mechanical fault can be a rash, a Rejection, a feed, a stroke, a push or the like Be vehicle body.

There is a known method of reducing one Blurring, blurring and / or blurring of one Image, which is characterized by rapid relative movements between the sensor and the scene. This method is to shorten the exposure time and it is used in fast film photography as well as in the fast event / Real time photography applied by using pulsed active lighting and gate controlled sensors are used.

For a first reason it is clear that the principle of Shortening the exposure time for an image does not improve the resolution brings that by blurring, blurring and / or blurring is impaired, its origin is the tremor of the line of sight of an arrangement that is on an inappropriately stabilized platform, or with an image caused by atmospheric turbulence is impaired.

This is because there is almost no positive effect is if it is so that the frequency of the line of sight tremor or the picture dancing higher or equal to that Reciprocal of the reduced exposure time is. So far all efforts to improve the imaging performance (resolution / Distance) from high resolution stabilized imaging assemblies to improve, focused and focused to achieve a higher level of stabilization.

The highest level of stabilization achieved so far or so far is about 40 microadians or 40 microbow units  Tip-to-tip, and even this high level of stabilization (achieved at high cost) is not appropriate to achieve the full resolution that the eye uses or exploit if you try to use lenses with a Use a focal length that is longer than about 900 mm. It as a result, there is a limitation on system expansion - The usable area of the system or Arrangement.

The arrangement according to the invention enables a real-time imaging device high resolution available too the image blur caused by stabilization, - blur and / or become blurred by shortening exposure time can be significantly reduced can.

The arrangement enables a real-time imaging arrangement at daylight level and with a short exposure time to operate. As a result, it is possible that on other way insurmountable performance limitation (Resolution / distance) to overcome such Real-time imaging arrangements of high resolution through that or subject to achievable stabilization levels are.

In summary, the invention in particular one Monitoring arrangement for use in daylight reconnaissance and for use in the moderate low light target lighting area made available.

The novel arrangement is based on the processing capabilities a stabilized television imaging device high resolution. The new arrangement according to The invention is based on the projection of the image onto one suitable TV sensor for a period of time or  period that is significantly shorter than the conventional sampling time of the sensor, and on evaluating the on this Wise image obtained. It is at this point noted that with the term "sensor" also and in particular a sensor arrangement, in particular a flat one Sensor arrangement as used for capturing an image individual pixels is required to be understood should. By reducing the exposure time of one Low level television sensor per scan of the general assumed or planned period of 1/30 second a period or period that is significantly shorter, especially up to about 1/10000 second, many of the inherent disadvantages of such arrangements that by themselves the most expensive and sophisticated as well as technically sophisticated mechanical stabilization arrangements are not can be overcome, avoided to a high degree, which is a considerably increased image resolution and one considerably increased stabilization-free system area or a considerably increased stabilization-free system removal range has the consequence.

The novel arrangement, which is particularly suitable for use in optical surveillance, reconnaissance and / or attack systems mounted on a moving support a low level television sensor, a suitable optical one Lens or lens group and a device for exposure of the sensor with the target image over the lens or Lens group during a period of time that is essential shorter than the normal sampling time of the sensor, in particular is significantly shorter than 1/30 second. The facility, between the lens or lens group and the A suitable closure or sensor can be inserted any other facility with the same result as can be achieved with a closure, a switching device or the amplifier or a switching device of the amplifier etc.  

Each picture is taken during the conventional scan time, in particular during 1/30 second, sampled. If any Vibration occurs during this period blurring, blurring and / or blurring, which results in low image quality, even can be without any value. Conventional stabilization arrangements are complicated and expensive and it is practical impossible to achieve a degree higher than one 40 µ radian peak-to-peak stabilization or a 40 µ-arc unit tip-to-tip stabilization is. If such an arrangement, for example on an airplane or is attached to another carrier, cause the vibrations serious malfunctions of the engine and / or the wing, Difficulties or the like. When light goes a long way has to go through low altitudes, blurring occurs, Blurring and / or blurring also due to atmospheric turbulence.

Generally you have to have a 6-line pair according to the Johnson criteria have on the target to identify this. Conventional The dimensions of the sensors are 6.6 × 8.8 mm or 9.9 × 11.6 mm (2/3 ″ or 1 ″ dimension); there are solid state sensors with about 800 × 800 sensor elements or 380 × 525 sensor elements.

The arrangement according to the invention has capabilities result, which is only achieved with a degree of stabilization would not, or through conventional facilities is almost impossible to achieve. It is possible to cross the border stabilization on the order of about 40 µ Overcoming radian-to-peak, and that enables the effective use of optical lenses or lens groups of very large focal length instead of 900 mm focal length, which is currently in use and what focal length is currently the limit for good resolution.  

The basic feature of the arrangement is the projection of the image on the sensor (which is also connected to a self-amplification device is coupled or to a conventional image intensifier is coupled) during a period of time, which is much shorter than the conventional sampling time of the sensor (generally 1/30 second), and this Image is then taken during the conventional scanning period mentioned scanned. Because a gain of 1000 times is easy to achieve, the exposure time of the sensor be short, in the order of up to about 1/10000 second if necessary, whatever still an adequate quality of the thus obtained Result.

As a result, a device for use in high resolution stabilized daylight level monitoring Real-time imaging arrays and to some extent Extent a facility for use in high resolution stabilized low-light level reconnaissance real-time imaging arrangements made available. These mapping arrangements are generally for surveillance, reconnaissance and / or attack purposes.

The arrangement comprises a novel electro-optical system, which enables high-resolution stabilized real-time Prepare daylight level mapping arrangements or to make them more powerful, their maximum performance (Resolution / distance) otherwise through their stabilization level are limited.

For example, it is possible to arrange very high resolution to get that a 2000 mm lens or lens with a focal length of 2000 mm and a Vidicon 1 ″ television tube TV receiver tube and stabilization the almost incredible value of 40 micro radians  Has peak-to-peak residual tremors and it is essential to improve.

It is assumed that the permeability of the insulators, on which the arrangement is attached, at 20 Hz to 50% descends and at 40 Hz to 10%, as is the case for example if you have very effective Barry S-44 isolators chooses.

For reasons of simplification, the following calculation is only carried out for the 20 Hz dither frequency. In order to be cautious about the performance improvement achieved by the invention, the MTF calculation of linear image motion is applied here even to the normal case where the 1/20 Hz dither frequency and the 1/30 Hz frame period are relatively close together lie.

The MTF of the linear motion case is given by:

MTF ( SF ) = sinc ( π SFD ),

wherein
U = image speed on the photo surface or on the light-sensitive surface
SF = spatial frequency or frequency in line pairs per mm
D = U · T = maximum image shift on the photo surface or on the light-sensitive surface, which is given by:

D = 2 · X · sinc (ω T / 2)

T = exposure time
ω = angular velocity of the tremor
X = amplitude of the tremor shift on the photo surface or on the light-sensitive surface.

For a 10% MTF of this tremor, the maximum spatial frequency or frequency is:

The 1 ″ photo surface resolution required to use normal eye resolution is SF = 26 LP / mm.

Using the aforementioned MTF (10%) equation, for the normal arrangement, which is stabilized on 40-micro-radian peak-to-peak residual jitter, a limiting spatial frequency or frequency of:

SF = 13 LP / mm

which means an overall insufficient resolution.

According to the invention, the 1 ″ Vidicon television tube is passed through a reinforcing 1 ″ imaging device that replaces a Low light level television tube or television reception tube can be (for example, SIT tube, SEBIR tube, one SER tube or other reinforcing tube) or a CCD sensor or CID sensor that optically connects to an amplification device, in particular a microchannel plate reinforcement device is coupled.

Light amplification of such devices is common higher, namely about a thousand times that a normal Vidicon tube, with a 10-fold gain is usually enough for the present case.

Between this 1 ″ image intensifier and the normal System lens or lens group (in the case in which the imaging device has no automatic gain control or regulation or no sufficient automatic Gain control or regulation, can there is a need to replace a lens with an auto IRIS or with an automatic iris diaphragm or a suitable one  optically neutral density or brightness filter to be used) you insert a chopper that works at a frequency of 30 Hz with an exposure time of 1/140 second.

This will decrease the amount of light by 140/30 = 4.6 (6), keeping in mind that 100 times the gain is available.

If one uses the MTF (10%) equation, then for the improved arrangement one obtains a limiting spatial frequency or frequency of:

SF = 26 LP / mm

what is the resolution required by the eye.

It is clear that the improvement is less effective Isolator is more spectacular, especially with lenses or long focal length lens groups.

It is further clear that there is a wide range of exposure time options is available from which one can Optimization according to the special system and Can carry out task or application data: focal length, Stabilization level, isolator transfer function, target lighting levels, Height and relative target sensor movement.

In order to ensure normal television pictures at an exposure time that is shorter than the reciprocal of the special television standard frame rate (30 Hz, 25 Hz or another frequency), one of the two following conditions must be fulfilled.
(a) The shutter frequency control must be better than the line scan time, which means that the frequency control must be better than 0.07% in a 30 Hz system. This can be achieved in a mechanically rotating closure by means of a suitable coding and speed control loop. In electro-magnetic or electro-optical closures and in a switching device with a locking effect, this can be achieved by a synchronization signal,
(b) synchronization:
(1) between the opening of the shutter and the start of the television frame scan (with a reasonable delay),
(2) between the end of the straight field scan or the scan of the flat field and the opening of the shutter. This synchronization can be done by using the synchronization signals of the television camera (or the main clock in a solid-state camera), and in the first case also by using a position measuring sensor on the shutter (mechanical or electro-mechanical).

Figure 1 is a schematic block diagram of an imaging arrangement based on the system of the invention.

The advantages of the new arrangement and the fact that related operating concept according to the invention in particular in that this arrangement enables the incomparable conventional stabilization restrictions, due to the stabilization level in real-time daylight High resolution, long distance imaging arrays are set to overcome.

Because of the use of a television camera with low light levels in the new arrangement it is possible as  Byproduct of the main goal is the imaging capabilities part of the low light area to extend the target lighting. This by-product increases also the "good mapping" area of the arrays high resolution and long distance because of such arrangements usually due to atmospheric turbulence severely hindered or disturbed. The atmospheric Turbulence is minimal in the early morning, in a situation in which the target lighting level is too low around for an image with a normal conventional arrangement to be sufficient.

Shortening the exposure time can be part of the blurring, Being blurred and / or out of focus atmospheric turbulence has been caused to take away, because the phenomena that a "dancing" of the picture on the Photo surface or on the light-sensitive surface cause, are sometimes a time-dependent effect.

The new arrangement and the related operational concept is of crucial importance for tasks and operations of air reconnaissance, surveillance and air strikes. Daylight and near-infrared imaging arrangements used in these tasks and uses are typically limited in stabilization performance (resolution / distance) for one of two reasons:
(a) A limited level of stabilization is accepted because of the cost, complexity, and maintainability required to achieve an adequate level of stabilization; for example mini RPV surveillance payloads,
(b) Inaccessible (however large the cost) stabilization levels required for high resolution, long distance tasks and missions (long focal length optics).

The arrangement can be in connection with lenses or lens groups of very long focal length can be used and there Light resolution images or high resolution images.

The device according to the invention takes away the limitations away from the level of stabilization and allows better ones Abilities at a lower stabilization level to achieve.

It also extends the scope of tasks and deployment in the area of target lighting with low light and makes it possible to avoid the turbulence effect by that the orders operated early in the morning will.

The invention also directly reduces part of the Turbulence blurring effect on image quality caused by atmospheric turbulence is caused.

The accompanying single figure, designated as Fig. 1, is a block diagram of an imaging arrangement in accordance with the invention.

As illustrated in this figure, the arrangement comprises in combination a television tube camera 11 (in particular a CCD camera or a CID camera) or some type of LLTV camera (ie a low-light television camera or a low-light television camera).

As an optional feature, this can have an automatic gain control (AGC), and the camera is aligned on the optical axis with an exposure control device 12 , with an optional neutral density or brightness filter 13 and with an optical lens or lens group 14 .

The television camera can be used in conjunction with the optionally coupled or inserted image intensifier (MPC) 15 . Exposure control device 12 may be a mechanical shutter, an electro-mechanical shutter (solenoid) and a device based on electro-optical effects. The exposure control device 12 is not necessary if an amplifier 15 or an image intensifier with fast switching capabilities is used. The lens group 14 may be a long focal length, the focal length may exceed that currently present due to the limitations of blurring, blurring and / or defocusing due to the various causes noted above are used or used to the maximum. Focal lengths well above the 900 mm range can be used without any problems in terms of image quality.

It is clear that any other structure of components or Components used to form an image on the sensor (e.g. TV tube or television camera tube) during a time period that is much shorter than that of conventional scanning, in combination with a suitable lens or lens group can be used, an arrangement according to the invention To make available or used as an arrangement according to the invention can be.

It is also within the scope of the invention to brief exposure of the television tube or television camera tube  (or an equivalent) to resort to and a scan at a higher speed than usual with the condition that the 40µ radian Peak-to-peak stabilization or less stabilization is achieved.

It should be noted that the abbreviations used above have the following meanings:
CCD - charge coupled device
CID - charge injected facility
LP - line pairs
PTP - tip-to-tip
SIT - silicon or silicon intensifier target tube or image intensifier tube with silicon target
auto IRIS - automatic iris, especially automatic iris
RPV - remote pilot vehicle or remote-controlled vehicle
MPC - microchannel plate

It should also be noted that as a television recording tubes with low light level in the arrangement according to the invention especially secondary electron effect television recording tubes can be used.

Claims (7)

1. Device for use for high-resolution stabilized daylight level imaging or moderate low-light level imaging of a movable carrier, characterized in that the system or arrangement ( 11, 12, 13, 14 ) has a reinforcing electro-optical imaging device ( 11 ) and a suitable optical lens ( 14 ) or lens group ( 14 ) with an exposure control device ( 12 ) which is suitable for exposing the sensor or the sensor arrangement to the target image for a period of time which is substantially shorter than the conventional scanning time of the sensor. 2. Device according to claim 1, characterized in that the image projection control device ( 12 ) is a shutter. 3. Device according to claim 1 or 2, characterized in that a synchronization device for the synchronization of the image projection and the scanning of the sensor ( 11 ) or the sensor arrangement ( 11 ) is provided. 4. Device according to one of claims 1 to 3, characterized in that the sensor ( 11 ) or the sensor arrangement ( 11 ) is selected from television tubes with a low light level, which comprise an amplification device ( 15 ), or solid-state sensors, in particular CCD sensors or CID sensors, combined with a microchannel plate amplifier (MCP amplifier), or another amplifier ( 15 ) which is attached to a conventional imaging sensor tube ( 11 ) or a solid-state sensor ( 11 ) or with a conventional imaging sensor tube ( 11 ) or a solid-state sensor ( 11 ) is combined. 5. Device according to one of claims 1 to 4, characterized in that the exposure control ( 12 ) is an electro-mechanical or electro-optical shutter or a switching device which acts on the amplification device ( 15 ), or a solid state sensor, which produces an exposure shutter effect. 6. Device according to one of claims 1 to 5, characterized in that it is suitable for achieving a performance which is a stabilization of better than 50 µ-arc units tip-to-tip, wherein the exposure time of the sensor ( 11 ) or the sensor arrangement ( 11 ) is shorter than the normal sampling time, namely up to 1/10000 second. 7. Device, in particular according to one of claims 1 to 6, characterized in that it is a monitoring system or a monitoring arrangement, the one or the television tube ( 11 ) or another television sensor or another television sensor arrangement low light levels or a television recording tube ( 11 ) or another television recording sensor or other television recording sensor arrangement of low light level, as well as a lens ( 14 ) or lens group ( 14 ) and a closure device ( 12 ).