WO2012020397A1

WO2012020397A1 - Method and system of measuring a distance

Info

Publication number: WO2012020397A1
Application number: PCT/IL2011/000592
Authority: WO
Inventors: Gadi Tivon
Original assignee: Gadi Tivon
Priority date: 2010-08-12
Filing date: 2011-07-24
Publication date: 2012-02-16
Also published as: IL207554A0

Abstract

A passive method of measuring a target distance includes a detector (detectors), which detects energy emitted by an object. This emitted radiation preliminary passes through optical multi-channel filtering block having several selecting channels. The quantity of these band-pass channels must be two at least. After the detector (detectors) a coupled programmed data processor calculates the distance to target using a special algorithm based on solving equations of transmittance through surrounding environment.

Description

METHOD AND SYSTEM OF MEASURING

A DISTANCE

Field of the Invention

This invention relates to aiming devices, cameras etc., and more particularly to the measuring of distance using the passive method.

Background of the Invention

In general, for passive distance measuring the following methods have been achieved:

- triangulation;

- focus manipulation (autocollimation, autoreflexivity etc);

detection of an object onto a region (or regions) in which one is expected to be located;

- by using changes on imaging surface (or surfaces) due to object displacement;

- by using the Doppler effect or phase changes;

- combination of the aforementional methods.

One particular application of the triangution approach was described in US Pat. No 5,914,7,75 issued to Hargrore et al, where triangulation rangefmder includes measuring an elevating angle being formed between reference axis and a line of sight between rangefmder and target.

To increase probability of target acquisition and tracking, US Pat. No 5,300,777, issued to Goodwin, proposed using two colour infrared detectors. For this purpose in US Pat. No 5,929,444, issued to Leicher, monitors rotations and angular displacement changes claimed.

Using two infrared responsive sensors spaced apart a predetermined distance from one another on the camera body with triangulation was assumed in US Pat. No 4,341,447, issued to Biber. As for the distance measuring using a focuse manipulation, in US Pat. No 5,923,910, issued to Nakahara et al, claimed apparatus with a pair of image lenses having variable focal length. Combined passive and active a distance measuring device with automatic focusing is described in US Pat. No 5,081,344, issued to Misawa.

Passive infrared bullet detection and tracking which is focused onto a region in which a projectile is expected, was described in US Pat. No 5,596,509, issued to Karr. Using a plurality of individual reflects to each required distance range of the passive infrared detectors we can see in US Pat. No 4,606,600, issued to Schmidt. To detect any motion onto a controlled regions, in US Pat. No 5,083,025, issued to Blomberg, a Fresnel lenses system coupled with passive infrared apparatus is disposed on horizontal surface, and target distance (and direction, velocity too) are determined by infrared rays scanning. Using distributed lenses and moving detector was described in US Pat. No 6,215,399, issued to Pinhas Shpater, to increase a probability acquisition and control area.

As example using changes on images surface (or surfaces), it was assumed in US Pat. No 5,781,281, issued to Miyano, where in finder lenses system (it was considered fifth lenses system), having a zooming function, a distance measuring infrared projection system having its own zooming function is disposed such that the beam diameter of the emitted ray becomes smaller in " telephotographic mode". Interesting US Pat. No 5,541,412, issued to Tanaka et al, in this direction, where it was described plurality micro-lenses system, and these micro-lenses are located to face the beams so that a convex portion of each of the micro-lenses is spaced from the top of each of beam by the same distance as a focal distance of the micro-lenses.

An example of a combination of the some abovementioned methods is reflected in US Pat. No 4,502,773, issued to Gaewsky et al, where two zone ranging systems were described with using principle of triangulation. A very interesting combination of triangulation method and GPS/Gyro device possibility was represented in EP Pat. 1, 876,413,A2, issued to Ash, William W..

The overall problem with existing methods and passive rangefinder is that they don't provide satisfactory precision for variable numerous applications. As a rule, they are limited or spectral region, or atmospheric conditions, or route extent. Sometimes they imply large optical base, moving blocks. Moreover, for practice apparatus it is very important that every new device or additional arrangement to ranging has been made compatible and incorporated into a known system for mass production and miniaturization.

It's necessary to note that a passive method of determining a target distance, which involves determing the thermal radition emitted by the object, has to include possibility non-contact temperature measurements. Existing pyrometry methods (so called multiwavelength pyrometry methods) as a rule are based on Plank's equation solving, and these don't take into consideration enrovironments.

Thus, there is a long felt need for universal method for determining a target distance by a passive system.

Summary of the Invention

It is hence an object of the invention is to disclose a method of determining a target distance between an object and an electro-optical system (EOS). The aforesaid method comprises steps of: (a) filtering radiation emitted by the object in at least within two spectral bands; (b) detecting the filtered radiation emitted by the object in the at least within two spectral bands; the filtered radiation is detected by a multi-channel filtering block of the EOS; (c) transmitting a composite signal corresponding to the detected filtered radiation in all spectral bands to a coupled data processor; the coupled data processor is adapted to be pre-programmed for providing the colour temperature corresponding to the detected filtered radiation by minimizing the following expression:

. . φ, IMD A_d ,6f,A ,...)τ, . . . .

mm I ; 1, i, j = l,...n. , ι≠ j , where: <p, is a detector response, I_0i is target intensity, f_i is a function of EOS parameters: £>^* is specific detectivity of the detector, A_ap \^'s an area of a collection aperture, Af is an electronic frequency bandwidth, A_d is a detector area, r, is spectral atmospheric transmittance, n is a number of spectral bands, (d) calculating the target distance between the object and the EOS corresponding to the colour temperature obtained from each pair of filtered radiation; the distance is determined from the following equation:

where: r is the target distance, SNR_t is Signal Noise Ratio; (e) calculating an average value of the target distance over all obtained distances corresponding to each pair of filtered radiation.

Another object of the invention is disclose the method further comprising step of calculating an average value of the colour temperature is performed over values of colour temperatures corresponding to each spectral pair.

A further object of the invention is disclose the step of filtering performed be the filtering block embedded into the EOS and disposed at a location selected from the group consisting of before an optical block, behind the optical block, before a scanner, behind the scanner and any combination thereof.

A further object of the invention is disclose at the step of filtering, the radiation emitted by the object, relationship between of the chosen spectral bands characterized by one collocations selected from the group consisting of a separated collocation, a mutually intersecting collocation, one-band-inside-another collocation and any combination thereof.

A further object of the invention is disclose at the step of filtering, the radiation emitted by a moving target, bandwidth of the spectral band and a number thereof are variable.

A further object of the invention is disclose the step of calculating the distance further comprising correcting the distance according to transmittance with arbitrary functional dependence of a distance defined by

<Pi =

where ?, is unknown variable, and preliminary obtained colour temperature and distance to target, defined by φ, = /, (ΔΛ, , A_ap, A_d , Af, D' , a, γ ,...)r, ,

r

where α,γ are angles between source, detector and line of centres correspondently, so that the distance to target is obtained from an iteration process.

A further object of the invention is disclose the step of calculating the distance, for black body and/or grey body models of a target, comprising initial approximation of distance to target, obtained by solving equation transmittance defined by φ, = ^ f_i (Αλ_ί , A_ap ,A_d,Af, D' ,a, γ,...)τ, ,

r

whereby the colour temperature of an object and the target distance are obtained by iterations.

A further object of the invention is disclose the method further comprising steps of: (a) (a) using Bouguer-Lambert-Beer law for radiation transmittance, and black body (or grey body) model as initial approximation, (b) determining a distances to the target corresponding to chosen spectral pairs from the equation: r =— ln(-^-) ,

E hi I ¹0i where: ξ, is extinction coefficient, then for another chosen spectral pair a colour temperature is obtained, and then from arbitrary chosen spectral pair, and (c) determining the distance to target by iterations.

A further object of the invention is disclose the method a further comprising a step of calculating the distance to target using the obtained colour temperature of the object,

A further object of the invention is disclose the step of calculating the distance performed according to the following equation:

A further object of the invention is disclose a system for determining a target distance between an object and an electro-optical system (EOS). The aforesaid method comprises steps of: (a) filtering means adapted for radiation emitted by the object in at least within two spectral bands; (b) detecting means adapted for the filtered radiation emitted by the object in the at least within two spectral bands; the filtered radiation is detected by a multi-channel filtering block of the EOS; (c) a coupled data processor pre-programmed for providing the colour temperature corresponding to the detected filtered radiation by minimizing the following expression:

= l,...n. , i≠ j ,

<Pj _{j j} (^D ,A_d , Af, A_ap ,...)Tj where: <p_t is a detector response, I_0j is target intensity, f_t is a function of EOS parameters: D^* is specific detectivity of the detector, A_ap is an area of a collection aperture, f is an electronic frequency bandwidth, A_d is a detector area, τ_ί is spectral atmospheric transmittance, n is a number of spectral bands, the processor adapted for calculating the target distance between the object and the EOS corresponding to the colour temperature obtained from each pair of filtered radiation; the distance is determined from the following equation:

where: r is the target distance, SNR_t is Signal Noise Ratio; and for calculating an average value of the target distance over all obtained distances corresponding to each pair of filtered radiation.

A further object of the invention is disclose the system further adapted for calculating an average value of the colour temperature is performed over values of colour temperatures corresponding to each spectral pair.

A further object of the invention is disclose the filtering means embedded into the EOS and disposed at a location selected from the group consisting of before an optical block, behind the optical block, before a scanner, behind the scanner and any combination thereof.

A further object of the invention is disclose the filtering means adapted for filtering the radiation emitted by the object so that relationship between of the chosen spectral bands is characterized by one of collocations selected from the group consisting of a separated collocation, a mutually intersecting collocation, one-band-inside-another collocation and any combination thereof.

A further object of the invention is disclose the filtering means adapted for filtering the radiation emitted by a moving target such that bandwidths of the spectral bands and a number thereof are variable.

A further object of the invention is disclose the processor adapted for correcting the distance according to transmittance with arbitrary functional dependence of a distance defined by

where β is unknown variable, and preliminary obtained colour temperature and distance to target, defined by

where a, γ are angles between source, detector and line of centres correspondently, so that the distance to target is obtained from an iteration process.

A further object of the invention is disclose the processor adapted for calculating the distance according to black body and/or grey body models of a target, initial approximation of distance to target, obtained by solving equation transmittance defined by i '

A further object of the invention is disclose the processor adapted for (a) using Bouguer- Lambert-Beer law for radiation transmittance, and black body (or grey body) model as initial approximation, (b) determining a distances to the target corresponding to chosen spectral pairs from the equation: r =— ln(^-) ,

E I where: ξ_ί is extinction coefficient, then for another chosen spectral pair a colour temperature is obtained, and then from arbitrary chosen spectral pair, and (c) determining the distance to target by iterations.

A further object of the invention is disclose the processor adapted for calculating the distance to target using the obtained colour temperature of the object,

A further object of the invention is disclose the processor adapted for calculating the distance according to the following equation:

Brief Description of the Drawings

In order to understand the invention and to see how it may be implemented in practice, a plurality of embodiments is adapted to now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

FIG. la, lb are schematic diagrams of arrangements of the Electro Optical System provided with the filtering block;

FIG. 2a, 2b, 2c and 2d are schematic diagrams of possible locations of spectral intervals; FIG. 3 is a schematic diagram of an object and a detector disposition and an example of radiative transfer between them;

FIG. 4a, 4b are schematic representations of the algorithms to define distance to target by first approach;

FIG. 5a, 5b are schematic representations of the algorithms to define distance to target by first approach when atmospheric characteristics are unknown;

FIG. 6 is a schematic representation of the algorithm to define distance to target by second approach;

FIG. 7a, 7b are schematic representations of the algorithms when colour temperature of an object is known;

FIG. 8 depicts some results of experimental validation of the invention.

Detailed Description of the Invention

The following description is provided, alongside all chapters of the present invention, so as to enable any person skilled in the art to make use of said invention and sets forth the best modes contemplated by the inventor of carrying out this invention. Various modifications, however, are adapted to remain apparent to those skilled in the art, since the generic principles of the present invention have been defined specifically to provide a method of passively measuring a target distance.

The invention relates to calculation (measurement) of distance to an object by installing the filters block and programmed data processor to use special algorithm obtained by solving equations of optical transmittance onto rangefinder.

An emitted energy flux which is incident on a detector may be written down as:

λ,+δ, /2

^ f _ji r cosacos ^ , . . . _/1

λ,-δ, /2 A ^r where r, is spectral atmospheric transmittance, A is detector area, λ, is average wavelength in 5_j interval, r is distance to target, J, is wavelength interval, I₀ is target intensity, n is number of channels (spectral zones), α,γ are angles between source, detector and line of centres correspondently, ^ is Electro Optical System (EOS) transmittance. This equation is often used to obtain limit distance - so-called range equation.

The spectral transmittance r, follows from radiative transfer equation dL » dl, , . k_t r

cdt Br Απ . (2) k_t = k_{i s} + k_{i a};i = \,...,n where: Ω is solid angle, k_{i s} , k_{i a} are scattering and absorption coefficients, j_t and is emission coefficient. Thus, there are two variables: target temperature T and ranger , which may be determine by solving equation systems (1), (2).

From abovementioned two methods to determine a distance follows:

a) the first approach is minimization of the functional

To minimize the functional (3) the range equation (1) is represented in the form

From equations (4) for /^', j channels follows

which must be minimized to obtain the colour temperatures for every , j pair. Here, SNR is signal noise ratio, £>^* is detector parameter (specific detectivity of a detector), A is area of the collection aperture (entrance pupil area), A_d is detector area, Δ/ is electronic frequency bandwidth, / and is function of EOS parameters only. The object intensity may be represented by Planck's function

,j_{( /2} ^[exp(_C2 /A, ) - l]

Where: c_{,c₂ are Planck's coefficients.

After obtaining the colour temperatures from relations (5), the distance to target follows from range equation as

Of course, here the spectral atmospheric transmittance τ_{ is a known in advance.

If the colour temperature is known in advance too, or one determined parallel by device (pyrometer, spectrometer etc) was used, then the atmospheric patameters r, is found under condition of minimum of the functional (5). Then, the distance target is obtained from range equation (7)

the second path is functional minimization

And now equations (1) will be used as boundary conditions.

Functional minimizations (3), (8) demand complicated computational algorithms, overcoming numerous numerical problems. Therefore often taking into consideration that change target rate is less than light speed, and atmospheric parameters are not influenced by object intensity, from equation (2) follows the well-known Lambert-Bouguer-Beer law

7, = /_0i exp(-£r) , (9) where ξ_ί is extinction coefficient. That is minimization algorithm for functional (3) reduces to simple relations among channels

But here at first step the gray body model must be used (if again the colour temperature is not known in advance), and after determining a target intensities from Lambert-Bouguer- Beer law distance to target expressed as

Thus, in both first and second cases the distance measurement includes two steps: at first the object temperature must be determined and the distance by second step. Temperature determination carried out solving functionals: (5) - first method -or functional (10) for second method, and distance will be obtained from equation (6) -first method or from relation (1 1) for second method.

Any function in the form ® λ Τ) may be used, where variables temperature and wavelength are separate instead Planck's function (6) for object intensity I_0i .

Reference is now made to FIG. la, lb, presenting the schematic diagrams of an EOS of a rangefinder. They include the optical scanning block (4), detector (detectors) and detector's electronics (5), electronic block (6), programmed data processor (computer) (7), recording or any another data storage block (8). Abovementioned blocks (4-8) have been used in numerous different uses. For the sake of clarity, in these figures an object and track of surrounded atmosphere (blocks 1, 2) are presented too. A core feature of the current invention is the multi-channel filtering block (3) which is disposed either before the optical block (4) - FIG. la- or after the optical block - FIG. lb, or at both aforesaid locations. This filtering block (3) includes, at least, two optical channels (i.e. n > 2). Emitted energy flux emitted by the object (1) passes through the filter block (3) characterized by signal to noise ratio (SNR) sufficient for reception. Then the energy flux is detected by detector (detectors) of the block (5). The filtering block can be provide with different glass (or plastic) filters (bandpass, colour substrate, dichroic etc), mirrors, prisms etc and any combinations thereof. Moreover, spectral regions of these filters may be separated from each other without intercrossing (FIG. 2a), or some wavelength intervals have common zones, particularly intercrossing (FIG. 2b), or one spectral interval is situated inside another (FIG. 2c), and combined variant (FIG. 2d). Wavelength intervals and its numbers are designated as 6j , 5_j , ...,δ_η . As shown by FIG. 3, choice of spectral zone is defined by EOS parameters, target and atmospheric characteristics.

Reference is now made to FIG. 3 depicting in an exemplary manner the flux emitted by the object which is detected for wavelength interval Δλ] at distance n only (of course, for the given SNR), and for zones Δλ₂, Alk at ranges r₂, ¾, respectively. That is, these intervals are used - or may be used - when distance decreases (target and EOS converge). On the other hand, in the same spectral in FIG.3 depicted by Δλ;, A j, ...,Akn, the SNR may have critical minimum value due to target removal. It is important to note that the number of working channels and size of wavelength intervals 5j may be both constants and variable.

To explain the first approach in detail, the equations (4) are written down in the form: φ, = ^-f_i (A _i , A_ap , A_d , Af, D' ,a,r,...)T_i . (12) for each region λ_ί - δ_ί Ι2 < Αλ_Λ≤ λ_ί + 5 2 . Here φ_ί may be signal voltage, produced by the detector, or SNR simple, or contrast characteristic etc. The object intensity I_0i is a function of wavelength 2, , temperature T , and often represented by Planck's function (6) or any other approximations. N relations follows from the equation (12):

^®, =— --Γ ^» = ^«. i≠j . (13)

Here number relations N equals to N = «!/ 2/(n - 2)! . Taking into consideration that functions f_t , f_j are known parameters of EOS, and values Γ,. , Τ . are obtained atmospheric characteristics in advance, then, for each pair zones Αλ, , A j , the colour temperature of object Ty can be determined by minimizing | <o_t] \ . That is from equation (13) N values of colour temperature Ty have been obtained, and further averaging these colour temperatures and having T^c , from equation (12) the distance to target for each - channel will be determined. Again, averaging distance plurality r, we obtain required distance to the target r . The described algorithm is shown in FIG. 4a.

Reference is now made FIG. 4b, presenting another alternative algorithm where colour temperatures have not been averaged, but using N values of T^* from equation (1),

N values of distances r_y for each spectral pair are obtained and then distance r is obtained by averaging over the aforesaid values of distances r_tj . Note, if environment extinction characteristics are equal, ( r, = r■ ), which it is probable for neighbouring intervals, the equation (13) and the algorithms in FIGS. 4a and 4b are simplified.

If precision of a distance determination is not satisfactory (variance, confidence interval etc exceed boundaries) then it is preferable to use other averaging methods for parameters T ⁰ , r . For example, if at the first, the arithmetic means for averaging has been done, i.e.

T^C =∑T' /N, r =∑r_y /N, (14) as it is rather to try geometric averaging, or "weight" scheme

which is convenient for a previously known colour distribution of object. Of course, any other averaging methods may be used. However, if, after applying the aforesaid approach, the precision of the obtained distance value is not satisfactory, the most probable reason of the given error is incorrect knowledge of atmospheric characteristics. In this case we present equation (12) in following view:

where: β_ί is unknown variable, and so the n equations with n + 3 unknown values take place. As first step earlier obtained significances T ^c , r for β_ί = 2 must be used for zero initial estimate T_Q = T ^C , r₀ = r . Again N equations follow from equation (16), which for convenience is written down for i, j,...,n channels in the form:

ω^ - ^-τ^ , (17b)

<Pn n *^Tn

Here parameters r, , r . , z_n were chosen for the initial significances when order β_ί equals ?, = 2. Taking r » r₀ and ?,⁽⁰⁾ « 2 , and well /?j⁰⁾ « β.⁰⁾ + e_t , where ε₍ is small values and index (0) is zero estimate, then from equation (17a), the first approximation for colour temperature is determined. Further, a zero approximation ?„⁽⁰⁾ follows from equation (17b), and then from equation (17c) another, next approximation distance to target r_x will be obtained. That is for the given algorithm at least three channels must exist. For n = 4 (four channels) we have two values of colour temperatures and ranges r, etc. This algorithm is shown in FIG. 5a. If again the variance, confidence interval etc. exceed boundaries, then part of algorithm in FIG.5a which has been marked by dotted lines must be repeated, where, again an approximation Τ^_ ₎ follows from equation (17a), further an order ? *⁾ will be obtained from equation (16), and the colour temperature T£ will be found from equations (17a, 17b, 17c), and next approximation r_k follows from equation (16) etc. Here, k is iteration number.

If the object may be presented as a grey body model, then we have from equation (16):

At the first step of the algorithm (FIG. 5a), the initial colour temperature is absent, and this algorithm has changes. As shown in FIG. 5b, in accordance with the second approach to the distance measurement, the functional co^{( )} must be used. The calculation process has iterative character (see FIG. 6), where for first approximation, the model of grey body is applied. The zero estimate follows from pair wavelength intervals ΔΛ,- ,ΔΛ . , so the colour temperature T{_0)kn will be obtained from another pair, for example A _k , Αλ_η , and again, the range r_x may be determined from pair ΔΛ,· , A _j using value T^_)kn . Instead pair Δ Ι, , Δ ^ intervals ( ΔΑ, , Δ^ ) or (Δ 1, ,Δ/Ι_η ) etc. may be used. Thus, according to the second approach, at least three channels are required (« > 3 ).

If the colour temperature is known in advance, or determined in parallel by means of an external device (pyrometer, spectrometer etc), then both first and second approaches algorithm will be simpler. The simplified algorithms corresponding to the first and second approaches are shown in FIG. 7a and 7b, respectively.

After distance determination in the form of a set r(t) , the target velocity u(t) is defined as simple derivative with time . Alternative way includes using equation (12)

with following averaging. Here u(t) is the target velocity. In FIGs. 4a, 4b and 7a, the velocity determination is shown as a last block.

To validate this invention, the first method of determining a distance to target by solving the functional (3) is used. The EOS was realized according to the scheme shown in FIG. la, where a pair of blue and red filters is embedded into the filter block. The collector has one lens only, the detector was a matrix-like. The following main EOS parameters were realized: A_d = 820mm² , A_ap = 3800mm² , SNR≥ 3.0 . Filament lamps of power ranged between 25 and 100W and provided with bulbs of different colours are used. In FIG. 8 some results for distances 5÷15m are shown.

Claims

Claims:

1. A method of determining a target distance between an object and an electro-optical system EOS; said method comprising steps of:

a. filtering radiation emitted by said object in at least within two spectral bands;

b. detecting said filtered radiation emitted by said object in said at least within two spectral bands; said filtered radiation is detected by a multichannel filtering block of said EOS;

c. transmitting a composite signal corresponding to said detected filtered radiation in all spectral bands to a coupled data processor; said coupled data processor is adapted to be pre-programmed for providing the colour temperature corresponding to said detected filtered radiation by minimizing the following expression:

. . φ, iMD A_{d i}tf_tA ,...)r_t , . . .

mm I ; 1, i, j = Ι,.,.η. , ι≠ j ,

<P_{j j}f_j iP ,A_d , Af,A_ap ,...)Tj where: φ_ί is a detector response, I_0i is target intensity, /, is a function of EOS parameters: D^* is specific detectivity of said detector, A is an area of a collection aperture, Δ/ is an electronic frequency bandwidth, A_d is a detector area, r, is spectral atmospheric transmittance, n is a number of spectral bands,

d. calculating said target distance between said object and said EOS corresponding to said colour temperature obtained from each pair of filtered radiation; said distance is determined from the following equation:

where: r is said target distance, SNR_f is Signal Noise Ratio; e. calculating an average value of said target distance over all obtained distances corresponding to each pair of filtered radiation.

2. The method according to claim 1, further comprising step of calculating an average value of said colour temperature is performed over values of colour temperatures corresponding to each spectral pair.

3. The method according to claim 1, wherein said step of filtering is performed be said filtering block embedded into said EOS and disposed at a location selected from the group consisting of before an optical block, behind said optical block, before a scanner, behind said scanner and any combination thereof.

4. The method according to claim 1 wherein at said step of filtering said radiation emitted by said object, relationship between of said chosen spectral bands is characterized by one collocations selected from the group consisting of a separated collocation, a mutually intersecting collocation, one-band-inside-another collocation and any combination thereof.

5. The method according to claim 1, wherein at said step of filtering said radiation emitted by a moving target, bandwidth of said spectral band and a number thereof are variable.

6. The method according to claim 1, wherein said step of calculating said distance further comprises correcting said distance according to transmittance with arbitrary functional dependence of a distance defined by

where ?, is unknown variable, and preliminary obtained colour temperature and distance to target, defined by

<Pi = ^rf_t (Δ , A , A_d , Af, D^* ,α,γ,...)τ, ,

f

where α,γ are angles between source, detector and line of centres correspondently, so that said distance to target is obtained from an iteration process.

7. The method according to claim 6. wherein said step of calculating said distance, for black body and/or grey body models of a target, comprises initial approximation of distance to target, obtained by solving equation transmittance defined by

whereby said colour temperature of an object and said target distance are obtained by iterations.

8. The method according to claim 1 , further comprising steps of:

(a) using Bouguer-Lambert-Beer law for radiation transmittance, and black body (or grey body) model as initial approximation,

(b) determining a distances to said target corresponding to chosen spectral pairs from the equation: r =— ln(-½-) , where: ξ_ι is extinction coefficient, then for another chosen spectral pair a colour temperature is obtained, and then from arbitrary chosen spectral pair, and

(c) determining said distance to target by iterations.

9. The method according to claim 1, further comprising a step of calculating said distance to target using said obtained colour temperature of said object,

10. The method according to claim 9, wherein said step of calculating said distance is performed according to the following equation: r =— ln(^) .

11. A system for determining a target distance between an object and an electro-optical system EOS; said system comprising: a. filtering means adapted for radiation emitted by said object in at least within two spectral bands; b. detecting means adapted for detecting said filtered radiation emitted by said object in said at least within two spectral bands; said filtered radiation is detected by a multi-channel filtering block of said EOS; c. a coupled data processor pre-programmed for providing the colour temperature corresponding to said detected filtered radiation by minimizing the following expression:

!_>···«· , '≠ J ,

<Pj jfj iP , 4,, 4 4* »^■··)*^■, where: <p_t is a detector response, I_Qi is target intensity, is a function of

EOS parameters: D' is specific detectivity of said detector, A is ³¹¹ area of a collection aperture, Af is an electronic frequency bandwidth, A_d is a detector area, r, is spectral atmospheric transmittance, n is a number of spectral bands, said processor adapted for calculating said target distance between said object and said EOS corresponding to said colour temperature obtained from each pair of filtered radiation; said distance is determined from the following equation: r _ . ^D i^Aap^Ti /2

^kJ * SNR_i where: r is said target distance, SNR_i is Signal Noise Ratio; and for calculating an average value of said target distance over all obtained distances corresponding to each pair of filtered radiation.

12. The system according to claim 1 1, further adapted for calculating an average value of said colour temperature is performed over values of colour temperatures corresponding to each spectral pair.

13. The system according to claim 11 , wherein said filtering means is embedded into said EOS and disposed at a location selected from the group consisting of before an optical block, behind said optical block, before a scanner, behind said scanner and any combination thereof.

14. The system according to claim 11, said filtering means is adapted for filtering said radiation emitted by said object so that relationship between of said chosen spectral bands is characterized by one of collocations selected from the group consisting of a separated collocation, a mutually intersecting collocation, one-band-inside-another collocation and any combination thereof.

15. The system according to claim 11, wherein said filtering means is adapted for filtering said radiation emitted by a moving target such that bandwidths of said spectral bands and a number thereof are variable.

16. The system according to claim 1 1, wherein said processor is adapted for correcting said distance according to transmittance with arbitrary functional dependence of a distance defined by

(H , A_ap , A_d , f, D^* ,α,γ,...^ ,

r

where ,γ are angles between source, detector and line of centres correspondently, so that said distance to target is obtained from an iteration process.

17. The system according to claim 16, wherein said processor is adapted for calculating said distance according to black body and/or grey body models of a target, initial approximation of distance to target, obtained by solving equation transmittance defined by φ, =^ f_i (ΔΑ,. , A , A_d , Af, D' ,a, ,

r whereby said colour temperature of an object and said target distance are obtained by iterations.

18. The system according to claim 1 1, wherein said processor is adapted for

(b) determining a distances to said target corresponding to chosen spectral pairs from the equation:

where: ξ, is extinction coefficient, then for another chosen spectral pair a colour temperature is obtained, and then from arbitrary chosen spectral pair, and

(c) determining said distance to target by iterations.

19. The system according to claim 11 , wherein said processor is adapted for calculating said distance to target using said obtained colour temperature of said object,

20. The system according to claim 19, wherein said processor is adapted for calculating said distance is performed according to the following equation: