JP2006162369A - Dual-wavelength ir image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of processing dual-wavelength IR images, capable of correctly obtaining the temperature of a target or temperature distribution of the target, by utilizing the IR rays of two wavelength regions if the the ratio of decay-rate of the two-wave length band IR rays, even if the decay-rates and the distance to the target are not known. <P>SOLUTION: By processing the dual-wavelength operations of each pixel or each pixel group of the target 1 photographed by the dual-wavelength IR camera 3 with the dual-wavelength IR image processing means 6, the temperature distribution of the target 1 can be calculated by making the ratio of the atmospheric attenuation ratios of the IR rays k<SB>1</SB>, k<SB>2</SB>be a certain known value, even if the distance to the target 1 and each atmospheric attenuation-ratio of the two wavelength IR rays k<SB>1</SB>, k<SB>2</SB>are not known. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, a two-wavelength infrared camera radiated from a target whose distance is unknown, propagated through the atmosphere and attenuated is picked up by a two-wavelength infrared camera, and a two-wavelength infrared image processing is performed. The present invention relates to a two-wavelength infrared image processing method capable of obtaining an accurate temperature distribution.

  In general, in order to measure the temperature distribution of a target whose infrared emissivity is known using an infrared image sensor, the infrared radiation from the target is captured by the infrared sensor, and the target infrared radiation amount captured by each pixel of the sensor is measured. In addition to measuring, calculate the infrared attenuation from the atmospheric attenuation rate and the distance to the target, add the attenuation to the measured infrared radiation, and calculate the target temperature distribution from the accurate infrared radiation emitted by the target. Have to ask. In other words, unless the atmospheric infrared attenuation rate and the distance to the target are known, the target temperature distribution cannot be measured accurately.

  However, in field measurements, it is often difficult to accurately determine the infrared attenuation rate of the atmosphere and the distance to the target. In that case, the infrared attenuation rate and the distance to the target are set to approximate values. Was measuring the target temperature. However, this method has a large error and it is difficult to accurately obtain the target temperature and temperature distribution.

  The following Patent Document 1 is known as an apparatus for acquiring a two-wavelength infrared image, and an accurate temperature distribution of the target is obtained by image processing of the two-wavelength infrared light emitted from a target whose distance is unknown. I don't see anything that aims to.

Japanese Patent Application Laid-Open No. 9-166400 “2-wavelength infrared image homing apparatus using a two-wavelength separation optical system”

  The present invention has been made to solve the above-described problems. By using infrared rays of two different wavelength bands, the infrared ray attenuation rate in the atmosphere and the distance to the target are unknown. It is an object of the present invention to provide a two-wavelength infrared image processing method capable of accurately obtaining a target temperature and further a temperature distribution if the ratio of the attenuation rate in the wavelength infrared band is known.

  Other objects and novel features of the present invention will be clarified in embodiments described later.

  In order to achieve the above object, a two-wavelength infrared image processing method according to the present invention performs a two-wavelength calculation process for each pixel or pixel group of a target image imaged by a two-wavelength infrared camera, so Even if the infrared atmospheric attenuation rate of each of the two wavelengths is unknown, the target temperature distribution is calculated with the ratio of the infrared atmospheric attenuation rates of the two wavelengths as a constant known value.

  In the two-wavelength calculation process, when the infrared atmospheric attenuation rate of at least one of the two wavelengths is known, the distance to the target can be calculated.

  According to the two-wavelength infrared image processing method of the present invention, even if the distance to the target is unknown and the infrared attenuation rate of the atmosphere is unknown, the ratio of the atmospheric attenuation rates of the two-wavelength infrared bands is known. Then, the target temperature distribution can be accurately obtained by obtaining the temperature for each target pixel (or each pixel group) imaged by the two-wavelength infrared camera. If the atmospheric attenuation rate is known, the distance to the target can be obtained.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a two-wavelength infrared image processing method will be described with reference to the drawings as the best mode for carrying out the present invention.

  1 and 2 show an embodiment of a two-wavelength infrared image processing method according to the present invention. FIG. 1 shows that infrared waves 4 and 5 in a two-wavelength band emitted from a target 1 are attenuated by the atmosphere 2. FIG. 2 is an explanatory diagram showing the radiant intensity of two wavelengths of infrared rays 4 and 5 immediately after being emitted from the target 1 and immediately before being incident on the infrared camera 3. In order to simplify the explanation, it is assumed that the infrared emissivity of the target 1 is 1 (black body). The two-wavelength infrared camera 3 acquires infrared images in two wavelength bands with the same angle of view and the same number of pixels. The output image from the camera 3 is captured in the subsequent stage of the two-wavelength infrared camera 3 and output for each corresponding pixel in each band of the two-wavelength infrared camera (for each corresponding pixel of the two-wavelength output image). A two-wavelength arithmetic processing means 6 is provided for obtaining a target temperature distribution (temperature of the target portion corresponding to the pixel) from the ratio between the value and the atmospheric attenuation rate of the two-wavelength infrared rays.

In FIG. 1, it is assumed that infrared rays 4 having a wavelength λ01 and infrared rays 5 having a wavelength λ23 are emitted from a target 1. Each infrared ray is propagated by a propagation distance L and is detected by the two-wavelength infrared camera 3. It is assumed that infrared rays are attenuated during propagation through the atmosphere 2 by the respective atmospheric attenuation rates k ₁ and k ₂ .

FIG. 2 shows the infrared radiation intensity before and after attenuation. Infrared radiation intensity of the wavelength λ01 immediately emitted to A ₁ from the target 1, A infrared radiation intensity of the _two wavelengths λ23 immediately after being emitted from the target 1, S ₁ 2-wavelength infrared camera 3 attenuated after air propagating infrared radiation intensity of the wavelength λ01 immediately before entering the S ₂ to the infrared radiation intensity of the wavelengths λ23 just before entering the two-wavelength infrared camera 3 attenuated after atmospheric propagation in.

(1)式及び(2)式は赤外線放射強度が大気中を指数関数的に減少することを示している。 Assuming that the atmosphere is uniform at the same temperature and humidity, the attenuation rates k ₁ and k ₂ are constant, and assuming that the infrared rays have propagated by the distance L, equations (1) and (2) are established.

Equations (1) and (2) indicate that the infrared radiation intensity decreases exponentially in the atmosphere.

(1)式、(2)式、(3)式から伝搬距離Ｌ、減衰率ｋ_１、ｋ_２を消去すると

If the ratio of the attenuation rates k ₁ and k ₂ in Equations (1) and (2) is a,

When the propagation distance L and attenuation factors k ₁ and k ₂ are deleted from the equations (1), (2) and (3)

Ｓを(5)式のように定義するとＳは観測値であり、既知である。そこで(4)式は

とおくことができる。 In the equation (4), the infrared radiation intensity S ₁ and S ₂ immediately before entering the two-wavelength infrared camera are values that can be measured using the two-wavelength infrared camera. In addition, the attenuation rates k ₁ and k _{2 in} equation (3) are values that vary depending on the atmospheric conditions (temperature, humidity, etc.), but since the respective rates of variation are considered to be empirically equal, the ratio a is constant. Is considered a known value. Therefore

If S is defined as in equation (5), S is an observed value and is known. So equation (4) is

It can be said.

Next, the sensitivity of the two-wavelength infrared camera 3 is assumed as shown in FIG. In the two-wavelength infrared camera, the sensitivity on the short wavelength side is in the range of wavelengths λ0 to λ1. The sensitivity on the long wavelength side is in the range of wavelengths λ2 to λ3. In this wavelength range, the respective infrared atmospheric attenuation rates k ₁ and k ₂ are constant (when they vary, an average is taken). The sensitivity of the infrared camera with respect to the wavelength λ is w (λ). If the target temperature is T (absolute temperature), the infrared radiation intensity measured by the two-wavelength infrared camera when there is no atmospheric attenuation (L = 0) matches A ₁ and A ₂ respectively. ,

ここで、Ａ_１及びＡ_２はそれぞれm1次数（m1：正整数）、m2次数（m2：正整数）のＴの多項式関数となるが、(9)式及び(10)式の係数ａ_ｉ及びｂ_ｊは、実験室内（Ｌ＝０と見なすことができる）で温度Ｔを変えながら目標を２波長赤外線カメラで撮像し、その時の温度に対応するＡ_１及びＡ_２を測定し、最小二乗法から決定することができる。またm1及びm2は十分満足な近似が可能な値として設定するものとする。 When formulas (7) and (8) are approximated with a polynomial of T for simplification of calculation,

Here, A ₁ and A ₂ are polynomial functions of T of m1 order (m1: positive integer) and m2 order (m2: positive integer), respectively, and the coefficients a _i and (9) and (10) b _j is an image of a target with a two-wavelength infrared camera while changing the temperature T in the laboratory (which can be regarded as L = 0), and measures A ₁ and A ₂ corresponding to the temperature at that time, and the least square method Can be determined from In addition, m1 and m2 are set as values that allow sufficiently satisfactory approximation.

(11)式において、ａ_ｉ、ｂ_ｊ、ａ、Ｓは既知であるから、(11)式は非線形方程式を解くためのアルゴリズムとして知られるニュートン法または二分法を用いて目標温度Ｔに関して解くことができる。つまり、目標を撮像した２波長赤外線カメラの２波長出力画像における対応する画素同士の出力値を処理することにより、目標の正確な温度分布（各画素に対応した目標部分の温度）を求めることができる。 Substituting Equation (9) and Equation (10) into Equation (6)

In equation (11), a _i , b _j , a, and S are known, so equation (11) is solved for target temperature T using Newton's method or bisection method known as an algorithm for solving nonlinear equations. Can do. That is, by processing the output values of the corresponding pixels in the two-wavelength output image of the two-wavelength infrared camera that images the target, the target accurate temperature distribution (the temperature of the target portion corresponding to each pixel) can be obtained. it can.

  If the target infrared emissivity ε is known and smaller than 1, the black body temperature can be easily converted to the target temperature using Planck's equation or the like.

In the embodiment of FIGS. 1 and 2, the two-wavelength calculation processing means 6 takes in the observation values S ₁ and S ₂ of the two-wavelength infrared camera 3 and calculates the equations (5), (6), and (11). Thus, the target temperature T can be obtained for each pixel of the target image. Instead of calculating the target temperature T for each pixel, a plurality of adjacent pixels may be considered as one pixel group, and the target temperature T may be calculated for each pixel group.

(12)式から目標までの距離Ｌを求めることができる。本実施の形態においては、２波長演算処理手段６で減衰率ｋ_１を既知として(12)式を演算することで距離Ｌを得ることができる。なお、減衰率ｋ_２が既知であれば、Ａ_１，Ｓ_１，ｋ_１の代わりにＡ_２，Ｓ_２，ｋ_２を用いて距離Ｌを求めることができる。 Although it is possible to obtain the target temperature T by the above method, (9) A ₁ is obtained in decreasing expression, k ₁ is equal known in air propagation constant, by modifying the equation (1),

The distance L to the target can be obtained from the equation (12). In the present embodiment, the distance L can be obtained by calculating the equation (12) with the attenuation factor k ₁ known by the two-wavelength calculation processing means 6. If the attenuation rate k ₂ is known, the distance L can be obtained using A ₂ , S ₂ , k ₂ instead of A ₁ , S ₁ , k ₁ .

  According to this embodiment, the following effects can be obtained.

(1) For each pixel or pixel group of the target image captured by the two-wavelength infrared camera 3, the two-wavelength calculation processing means 6 performs two-wavelength calculation processing (using observed values S ₁ and S ₂ (5), (6) , (11) calculation), even if the distance L to the target 1 and the infrared atmospheric attenuation rates k ₁ and k ₂ of the two wavelengths are unknown, the ratio a of the infrared atmospheric attenuation rates of the two wavelengths is constant. As a known value, it is possible to calculate the temperature distribution of the target 1.

(2) In the two-wavelength operation processing, if the at least one of the infrared atmospheric attenuation factor of two wavelengths k ₁ or k ₂ are known, it is possible to calculate the distance L to the target 1.

  Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.

FIG. 2 is an explanatory diagram of an embodiment of a two-wavelength infrared image processing method according to the present invention, in which infrared rays in a two-wavelength band emitted from a target are attenuated by the atmosphere and incident on a two-wavelength infrared camera . In this Embodiment, it is explanatory drawing which shows the infrared radiation intensity | strength of two wavelengths immediately after radiating | emitting from a target and immediately before injecting into an infrared camera. It is a graph which shows the sensitivity curve in each wavelength band of a 2 wavelength infrared camera.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Target 2 Air | atmosphere 3 2 wavelength infrared camera 4,5 Infrared 6 2 wavelength arithmetic processing means L Propagation distance

Claims (2)

  Even if the distance to the target and the infrared atmospheric attenuation for each of the two wavelengths are unknown by performing the two-wavelength calculation processing for each pixel or pixel group of the target image captured by the two-wavelength infrared camera, the infrared atmospheric attenuation of the two wavelengths is unknown. A two-wavelength infrared image processing method, characterized in that the target temperature distribution is calculated with a ratio of a constant and a known value.   2. The two-wavelength infrared image processing method according to claim 1, wherein, in the two-wavelength calculation process, when the infrared atmospheric attenuation rate of at least one of the two wavelengths is known, the distance to the target is calculated.

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