JP2931616B2 - Infrared imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an infrared imaging apparatus using a two-dimensional IRCCD (infrared charge-coupled device) element, and more particularly, to a seeker mounted on a flying object. The present invention relates to a device that captures an infrared image transmitted through a dome of a forehead of a flying object and uses it for target detection or tracking.

(Prior Art) In a conventional infrared imaging apparatus mounted as a seeker on a flying object such as a missile, a two-dimensional IRCCD element having a highly sensitive light receiving surface such as InSb is often used. However, it is very difficult to uniformize the quality of the IRCCD element with the current technology, and not only has an offset for each pixel, but also varies in the photoelectric conversion output (sensitivity) with respect to the light intensity of incident infrared light. Therefore, even if a hot plate with a uniform temperature distribution is taken as a thermal image in the same state, the brightness does not become uniform like a snow noise image. Therefore, a pixel correction circuit is generally mounted on the infrared imaging device.

FIG. 2 shows a configuration of a conventional infrared imaging device mounted as a seeker on a missile. In FIG. 2, the infrared light transmitted through the IR dome 11 in the forehead of the missile is incident on the two-dimensional IRCCD image pickup unit (the number of pixels is i) 13 by the optical lens 12. Each pixel signal obtained by the imaging unit 13 is sequentially converted into a digital signal by an A / D (analog / digital) converter 14 and then input to a pixel correction circuit 15.

The pixel correction circuit 15 includes an offset correction unit and a gain correction unit. Offset correction unit subtractor 15 _1, the offset correction value setting switch 15 ₂ is composed of an offset correction value storing circuit 15 _3, the gain correction unit multiplier 15 _4, the gain coefficient memories 15 _5, the gain coefficient setting switch 15 ₆ consists of the gain coefficient calculation circuit 15 _7.

The offset correction is performed as follows. First,
The switch 15 ₂ is set to ON before the missile launch, I
A hot plate (not shown) held at a uniform temperature T ₁ [K] (generally, the same temperature as the background) is placed in front of the R dome 11 and an image is taken by the imaging unit 13. At this time, the digital signal Vi of each pixel output from the A / D converter 14 is set to an offset correction value.
Stored as V _T1 i to the area A ₁ of the memory circuit 15 _3. Next, the A / D conversion output Vi when an image is taken with a hot plate held at a temperature T ₂ (k) different from T ₁ [K] is stored in the area A ₂ as an offset correction value V _T2 i. Keep it. Similarly, stored in the temperature T ₃ [K] ... T _n offset correction value when placing the hot plate _{[K] V T3 i ... V} Tn i region A ₃ ... A _n.

When actually missile fire sets off the switch 15 _2. Detected temperature from the memory circuit 15 the temperature sensitive sensor attached to the tip of the _3, IR dome 11 (not shown)
The corresponding area _Ad is selected according to T _d [K] (d: 1 to n). Offset correction value V _Td i corresponding to A / D conversion output Vi from the selected region A _d is read out and sent to a subtractor 15 ₁ with Vi. V _Td i from Vi is subtracted for each pixel by the subtracter 15 _1, whereby the digital pixel signal Si offset correction has been performed is obtained.

On the other hand, gain correction is performed as follows. First,
Before missile launch, set the switch 15 ₆ ON, to connect the gain coefficient calculation circuit 15 ₇ and gain coefficient storage circuit 15 _5. Gain coefficient calculation circuit 15 ₇ offset correction value storage circuit 1
5 Offset correction values V _T2 i, V _T1 i stored in areas A ₂ and A ₁ of ₃
Reading, the average value V ₁ of the all the pixels to calculate the _{V T2 i-V T1 i =} ΔV 1 i, calculate the _{V 1 / ΔV 1 i = K} 1 i. Thereby, T ₁ [K] for each pixel signal
The gain coefficient K ₁ i of 〜T ₂ [K] is obtained. Storing the gain factor K ₁ i in a region B ₁ in the storage circuit 15 _5.

Next, the arithmetic circuit 15 ₇ offset correction value from the offset correction value storing circuit _{15 3 V T3 i, V T2} i _{reads, V T3 i-V T2 i} = average value of all pixels to calculate the [Delta] V ₂ i V ₂ and calculate V ₂ / ΔV ₂ i = K ₂ i. Thereby, T ₃ [K] for each pixel signal
The gain coefficient K ₂ i of TT ₂ [K] is obtained. Storing the gain factor K ₂ i in the area B ₂ of the memory circuit 15 _5. Similarly, T
_{4 [K] ~T 3 [K} ], ... T n [K] ~T n-1 [K] of the gain coefficient _{K 3 i, ..., K n} -1 it is obtained. The gain factor _{K 3 i, ..., K n} -1 i the memory circuit 15 _fifth region B _3, and stored in the ... B _n-1.

When the actual missile is fired, it is set to turn off the switch 15 _6. Detected temperature T _d [K] corresponding region B _d according to from the storage circuit 15 ₅ wherein the temperature detection sensor is selected. Gain factor K _d i corresponding from the selected region B _d to the A / D conversion output Vi is read out, sent to the multiplier 15 ₄ together with the output Si of the subtractor 15 _1, wherein the Si for each pixel Gain coefficient K _d i
And it is multiplied, whereby it is possible to gain correction to obtain a digital pixel signal (thermal pixels) S _OUT which has been subjected.

However, the conventional infrared imaging device having the above configuration has the following problems when used as a seeker.

That is, when the flying object is made to fly, an air stagnation layer is formed around the IR dome in the forehead due to adiabatic compression of air (atmosphere), and this layer becomes high in temperature as the flying speed increases. Therefore, the imaging device is equivalent to viewing the target through the hot atmosphere. This leads to the misconception that the background temperature has increased.In particular, the temperature change of the stagnation layer depends on the air altitude such as flight altitude and atmospheric pressure. If an offset correction value, and thus a gain coefficient, is selected, an erroneous correction will be made. In such a case, the photocontrast with the target deteriorates, and it becomes difficult to detect the target.

Generally, the stagnation point temperature T is given by T = T _Q (1 + 0.2γM ² ) [K] T _Q : Ambient temperature [K] γ: Surface recovery factor 0.85 M: Flight speed [Mach] For example, when T _Q = 300 [K] and M = 2 [Mach], the stagnation point temperature T becomes about 500 [K]. Three
At 00 [K] and 500 [K], in the wavelength range of 3 to 5 μm, the blackbody radiation photon emittance is 1.3 × 10 ¹⁶ [phots ⁻¹ / cm ² ] 1.11 × 10 ¹⁸ [phots ⁻¹ / cm ² ] And there is a difference of about 100 times.

(Problems to be Solved by the Invention) As described above, in the conventional infrared imaging device mounted on a flying object and functioning as a seeker, when the flying object flies at a high speed, the temperature of the stagnation layer generated in the forehead is aerodynamic. It changes due to heating, and the temperature change depends on the air density such as flight altitude and atmospheric pressure.Therefore, it is necessary to calculate and store the offset correction value and gain coefficient in consideration of the temperature change of the stagnation layer before flight. No. Such an operation is very difficult and complicated, and the storage capacity is enormous, which is almost impossible.

The present invention has been made in order to solve the above problem, even if the flying object flies at a high speed and the temperature of the stagnation layer changes, it is possible to automatically and properly perform offset correction and gain correction, It is an object of the present invention to provide an infrared imaging device capable of improving the contrast between a flying background and a target.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the apparatus of the present invention captures an infrared image transmitted through a forehead dome of a flying object by an infrared imaging unit having a two-dimensional pixel array. An infrared imaging device for target detection and tracking; a first storage unit for storing an offset correction value for sensitivity correction corresponding to each pixel of the infrared imaging unit, which is obtained in advance before the flying object flies; A gain coefficient calculator for calculating the gain coefficient for sensitivity correction based on the offset correction value stored in the first memory; a second memory for storing the gain coefficient obtained by the calculator; For each pixel output of the infrared imaging unit, a corresponding offset correction value is read from the first storage unit, the offset correction value is subtracted, a gain coefficient is read from the second storage unit, and the gain coefficient is calculated. And a sensitivity correction unit that performs sensitivity correction for all pixels, and extracts and averages output signals of a plurality of elements having an average sensitivity among all the pixels of the infrared imaging unit, and averages the average value. A reset offset correction value calculation unit for sequentially obtaining a reset offset correction value by dividing by the gain coefficient of each pixel read out in the above-mentioned manner. Switching means for rewriting the storage contents of the first storage unit.

(Operation) In the infrared imaging device having the above configuration, sensitivity correction is performed with the offset correction value and the gain coefficient which are initially set in the first and second storage units immediately after the flying object flies, and after the flight, all the infrared imaging units perform the correction. The output signals of a plurality of elements having the average sensitivity among the pixels are taken out and averaged, and the average value is sequentially divided by the gain coefficient of each pixel to obtain a reset offset correction value. Determine the reset gain coefficient from the values, and perform sensitivity correction with these reset offset correction values and gain coefficients, so that the aerodynamic heating offset during flight, the speed of the flying object, the density of the atmosphere, the heating of the IR dome It allows for dynamic sensitivity correction to the overall radiation, including some thermal radiation.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG. However, in FIG. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals, and different parts will be mainly described here.

Figure 1 is shows the configuration, the storage capacity of the offset correction value storage circuit 15 ₃ used here two frames of the output of the imaging unit 13, the storage capacity of the gain coefficient memories 15 ₅ may be one frame . Offset correction value write input of the offset correction value storing circuit 15 ₃ is carried out through the mode switch 15 _8.

The switch 15 ₈ flight before writing mode a, write stop mode b, and has a switchable set of flight after writing mode c. The output Vi of flying before writing mode a the A / D converter 14 is led to the storage circuit 15 _3. In flight after write mode c output from the reset offset correction value calculating circuit 15 ₉ described below is derived in the memory circuit 15 _3. In the write stop mode b, no output is derived. This switch 15 ₈
Can be manually set to the pre-flight write mode a, and can be automatically switched to the write stop mode b and the post-flight write mode c by the switching control signal CS.

The reset offset correction value calculating circuit 15 ₉ takes in the output of the A / D converter 14, the average value calculated by extracting the output of the pixel near the four corners of the all the pixels, a gain and the average value by sequentially rebate that a gain coefficient for each pixel read from the coefficient memory circuit 15 _5, and calculates the reconfiguration offset correction value.

The operation method of the above configuration will be described below.

First, before the projectile fired, set the switch 15 ₈ to flight before writing mode a, by the method described above, the expected temperature T ₁ [K] immediately after firing, each pixel of one frame when the T ₂ [K] offset correction value V _T1 i, and stores the V _T2 i in the memory circuit 15 ₃ for the. Further, by setting the switch 15 ₆ ON,
In a gain factor calculating circuit 15 ₇ calculates a _{V T2 i-V T1 i =} ΔV 1 i, calculate the _{V 1 / ΔV 1 i = K} 1 i further from the mean V ₁ of the all pixels, T for each pixel signal ₁ obtains the gain factor K ₁ i of _{[K] ~T 2 [K]} , and stores it in the storage circuit 15 _5.
After stored sets the switch 15 ₈ to write stop mode b, a standby state is set to turn off the switch 15 _6.

After launching a flying object, by a command from the ground or a command inside the flying object, for example, when the flying object reaches a predetermined speed,
Upon reaching a predetermined altitude, at the same time the switching control signal CS in such as when entering the target detectable range and ON control signal, which is set to fly after write mode c is sent to switch 15 _8, the switch 15 ₆ And set it to the ON state. At this time, resetting the offset correction value calculation circuit 15 ₉ takes one frame output Vi of the A / D converter 14, the fourth of all the pixels
Extracting pixel output V ₁ ~V ₄ near the corners and the average value V _A1 determined sequentially rebate with a gain factor K ₁ i of each pixel to be read and the average value V _A1 of the gain coefficient memories 15 ₅ it allows to calculate the re-setting the offset correction value _{V t1 i (= V A1 /} K 1 i).

Here, the output V ₁ ~V ₄ pixels close to the four corners, the actual background clouds in projectile flight, scenery, unless the image of the target or the like is not spread to the entire field of view of the imaging unit 13, the outputs of all the pixels It is almost equal to the average gain. Therefore, it is approximately equal to determine the average of all the pixels for obtaining the average of the four pixel output V ₁ ~V _4. Reset offset correction value obtained in this way
V _t1 i is sent to the memory circuit 15 ₃ via a switch 15 _8, V _T1 i
Is rewritten as

When the rewriting of the offset correction value is performed, the gain coefficient calculation circuit _{15 7 V t1 i-V T2} i = a [Delta] V ₂ i calculates, V ₂ / [Delta] V ₂ further from the average value V ₂ of all pixels i = K the ₂ i is calculated, it obtains a gain factor K ₂ i of _{T 2 [K] ~T t1 [} K] for each pixel signal, again stores it in the storage circuit 15 _5.
Thus, each memory circuit 15 _3, 15 _5, the offset correction value corresponding to the temperature of the stagnant layer that occurs forehead in flight
V _t1 i and gain coefficient K ₂ i are stored. Therefore, storage circuit 1
5 Read the reset offset correction value _Vt1i from ₃ and
By subtracting the A / D conversion output in the subtractor 15 _1, it is possible to perform a highly accurate offset correction, the memory circuit 15
The gain factor K ₂ i which is re-set from ₅ reads, multiplier 15 ₄
In by multiplying the output Si of the subtractor 15 _1, it is possible to perform a highly precise gain correction. If the speed, altitude, etc. of the flying object further change, they may be reset at appropriate intervals.

Therefore, the infrared imaging device according to the above configuration enables dynamic sensitivity correction for the overall radiation including the aerodynamic heating offset, the speed of the flying object, the density of the atmosphere, and the thermal radiation due to the heating of the IR dome during the flight. The contrast between the flying background and the target can be improved.

In the above embodiment, the switching control signal CS, has been described as being suitably reconfigured in flight, always switch 15 ₈ and flying after rewriting mode c after flying, set the switch 15 ₆ ON If, for example, the offset correction value and the profit-taking coefficient are reset every ten frames, a highly accurate sensitivity correction can be performed in real time. In addition, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[Effects of the Invention] As described above, according to the present invention, even if the flying object flies at a high speed and the temperature of the stagnation layer changes, it is possible to automatically and properly perform offset correction and gain correction, and It is possible to provide an infrared imaging device capable of improving the contrast between an inside background and a target.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an infrared imaging apparatus according to the present invention, and FIG. 2 is a block diagram showing a configuration of a conventional infrared imaging apparatus. 11… IR dome, 12… Optical lens, 13… 2D IRCC
D imaging unit, 14 A / D converter, 15 pixel correction circuit, 15 ₁
...... Subtractor, 15 ₂ ...... Offset correction value setting switch, 1
5 ₃ …… Offset correction value storage circuit, 15 ₄ …… Multiplier, 15 ₅
...... gain factor storage circuit, 15 ₆ ...... gain factor setting switch, 15 ₇ ...... gain coefficient calculation circuit, 15 ₈ ...... mode switch, 15 ₉ ...... resetting the offset correction value calculation circuit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01S 3/78-3/789 H04N 7/18

Claims (3)

(57) [Claims] 1. An infrared imaging apparatus for capturing an infrared image transmitted through a frontal dome of a flying object by an infrared imaging unit having a two-dimensional pixel array and for performing target detection and tracking, wherein the infrared image is obtained in advance before the flying object flies. A first storage unit storing an offset correction value for sensitivity correction corresponding to each pixel of the infrared imaging unit; and a gain for the sensitivity correction based on the offset correction value stored in the first storage unit. A gain coefficient calculating unit for calculating a coefficient; a second storing unit for storing the gain coefficient obtained by the calculating unit; and a corresponding offset correction from the first storing unit for each pixel output of the infrared imaging unit. A sensitivity correction unit that reads a value, subtracts the offset correction value, reads a gain coefficient from the second storage unit, multiplies the gain coefficient, and performs sensitivity correction for all pixels; The output signals of a plurality of elements having an average sensitivity among all the pixels are taken out and averaged, and the average value is sequentially divided by the gain coefficient of each pixel read out by the sensitivity correction means to reset offset correction. A reset offset correction value calculating unit for determining a value, and switching means for rewriting the storage content of the first storage unit to the offset correction value calculated by the calculating unit after the flying object has been flying. apparatus. 2. The infrared imaging apparatus according to claim 1, wherein said sensitivity correction means extracts and averages output signals of elements near four corners of all pixels of said infrared imaging section. . 3. An infrared imaging apparatus according to claim 1, wherein said switching means is executed in frame units of the output of said infrared imaging section.