CN102759729A - Full-frequency-range RCS (Radar Cross-Section) value pre-estimating and correcting method based on atmospheric absorption loss - Google Patents

Abstract

The invention relates to a full-frequency-range RCS (Radar Cross-Section) value pre-estimating and correcting method based on an atmospheric absorption loss, which can utilize a loss caused by oxygen absorption and steam absorption under an atmospheric environment in an electromagnetic wave transmission process to correct a target RCS. In order to grasp scattering properties of each target under the atmospheric environment, the method can provide reference evidences for accurate remote sensing and detection.

Description

Full frequency band target RCS value based on atmospheric absorption loss is estimated modification method

Technical field

The present invention relates to a kind of full frequency band target RCS value and estimate modification method based on atmospheric absorption loss; Calculating through to the full frequency band atmospheric absorption loss can be estimated correction to the RCS of target; Be to hold the scattering properties of all types of target under atmospheric environment, accurately carry out ground remote sensing, detection provides reference frame.

Background technology

There is absorbing phenomenon as a kind of medium in atmosphere for electromagnetic wave propagation, and just there is the certain absorption loss in the electromagnetic wave of therefore propagating.At present, basically all be under the free space environmental baseline for the radar scattering sectional area of each class targets (RCS is called for short in the back) pre-estimating technology, do not consider the loss influence of Atmospheric Absorption.Along with the extension of detection range, the influence of atmospheric absorption loss increases gradually, does not consider that this factor will influence the precision of estimating of target RCS.

Summary of the invention

The technical matters that the present invention will solve is to defective a kind of full frequency band target RCS discreet value modification method based on atmospheric absorption loss to be provided; Can with under the atmospheric environment during electromagnetic wave propagation oxygen absorption and water vapor absorb caused loss and be reflected in the discreet value of target RCS through correction; Be to hold the scattering properties of all types of target under atmospheric environment, accurately carry out ground remote sensing, detection provides reference frame.

For solving the problems of the technologies described above, the technical scheme that the present invention adopts is:

A kind of modification method of the full frequency band target RCS discreet value based on atmospheric absorption loss; It is characterized in that: under the prerequisite of confirm at detection range, the antenna gain of detection radar, emissive power, look-in frequency are known; Confirm or known distance parameter, radar performance parameter are calculated in the electromagnetic wave propagation process oxygen and water vapor absorption coefficient and absorption loss respectively by above-mentioned; Then according to the absorption loss of oxygen and water vapor and the relevance between radar equation, the target RCS discreet value correction of the full frequency band that imposes a condition down.

By technique scheme, said full frequency band is: near the 22.235GHz with 100GHz above or K wave band with millimere-wave band, 60GHz is neighbouring or the THz wave band.

By technique scheme, mainly comprise the steps:

(1) according to electromagnetic theory, in conjunction with the specific absorption frequency of oxygen and water vapor, provide oxygen and water vapor separately to any specific frequency absorption of electromagnetic wave coefficient, calculate the absorption loss of whole detection process then by the absorption coefficient of each frequency band;

A) oxygen to any CF f absorption of electromagnetic wave coefficient does

$\begin{array}{cc}{\mathrm{\ξ}}_{O_2}\left(h\right)=2.0058{\mathrm{PT}}^{-3}{f}^2\underset{N}{\mathrm{\Σ}}{A}_N& (\mathrm{dB}/\mathrm{km})\end{array}---\left(1\right)$

Parameter declaration is following: h is a detection range, and P is an air pressure, and T is a temperature, and f is a frequency; The sum term that each resonance is counted N does

$A_N=(F_{N+}{{\mathrm{\&mu;}}^2}_{N+}+F_{N-}{{\mathrm{\&mu;}}^2}_{N-}+{\mathrm{<figure-callout\; id="0"\; label="F"\; filenames="120713113509.png"\; state="\{\{state\}\}">F</figure-callout>}}_0{{\mathrm{\&mu;}}^2}_{N_0})\exp (-e_n/T)---\left(2\right)$

Wherein

${{\mathrm{\&mu;}}^2}_{N+}=\frac{N(2N+3)}{N+1},$ ${{\mathrm{\&mu;}}^2}_{N-}=\frac{(N+1)(2N-1)}{N}$

${{\mathrm{\&mu;}}^2}_{{\mathrm{<figure-callout\; id="0"\; label="N"\; filenames="120713113509.png"\; state="\{\{state\}\}">N</figure-callout>}}_0}=\frac{2(N^2+N+1)(2N+1)}{N(N+1)},$ e _n=2.06844N(N+1)

Wherein, μ ² _N+, μ ² _N-With

Be respectively forward resonance coefficient, reverse resonance coefficient and disresonance coefficient; e _nBe temperature coefficient;

The disresonance component

$F_0=\frac{\mathrm{\&Delta;f}}{f^2+{\left(\mathrm{\&Delta;f}\right)}^2}---\left(3\right)$

The resonance line shape function

$F_{N\&PlusMinus;}\left(f\right)=\frac{\mathrm{\&Delta;f}}{{(f_{N\&PlusMinus;}-f)}^2+{\left(\mathrm{\&Delta;f}\right)}^2}+\frac{\mathrm{\&Delta;f}}{{(f_{N\&PlusMinus;}-f)}^2-{\left(\mathrm{\&Delta;f}\right)}^2}---\left(4\right)$

Wherein

Oxygen difference on the frequency factor △ f=0.1895g (h) P/T;

Being defined as of height coefficient g (h) in the formula: $g\left(h\right)=\left\{\begin{array}{cc}0.640& 0\&le;h\&le;8\mathrm{Km}\\ 0.3026+0.04218h& 8\&le;h\&le;25\mathrm{Km}\end{array}\right.;$

B) water vapor to any CF f absorption of electromagnetic wave coefficient is:

$\begin{array}{cc}{\mathrm{\&xi;}}_{22}\left(h\right)=0.002535\left({\mathrm{fP}}_w{\left(\frac{300}{T}\right)}^{3.5}\exp \left(20144(1-\frac{300}{T})\right)F\right)& (\mathrm{dB}/\mathrm{km})\end{array}---\left(5\right)$

ξ _res(h)=0.007347ρPT ^-2.5f ²(dB/km) （6）

Wherein, ξ ₂₂(h) near the absorption coefficient the expression 22.235GHz, ξ _Res(h) the above absorption coefficient of expression 100GHz;

Power factor $P_w=\frac{\mathrm{\&rho;\; T}}{288.75}---\left(7\right)$

Wherein, parameter ρ is a density;

The frequency ratio factor

$F=\frac{f}{f_r}(\frac{\mathrm{\&Delta;f}}{{(f_r-f)}^2+{\left(\mathrm{\&Delta;f}\right)}^2}+\frac{\mathrm{\&Delta;f}}{{(f_r+f)}^2+{\left(\mathrm{\&Delta;f}\right)}^2})---\left(8\right)$

The water vapor difference on the frequency factor $\mathrm{\&Delta;\; f}=0.01799(P_w\frac{300}{T}+0.20846(0.75P-P_w){\left(\frac{300}{T}\right)}^{0.63})---\left(9\right)$

Therefore, the absorption loss of whole detection process does

(2) according to the absorption loss of whole detection process the detection radar echo power is revised, provided the echo power P that radar can receive under the revised Atmospheric Absorption environment _r

For monostatic radar, the received power of target echo with the relational expression of propagating absorption loss does

10lgP _r=10lgP ₀-2L _atm （11）

Wherein, P ₀Be the target echo power at radar receiving antenna place under the free space condition, for treating modified value through what predicting means was known;

(3) according to radar equation, the echo power P that can receive in conjunction with radar under the revised Atmospheric Absorption environment _r, the target RCS value is revised;

Radar equation is:

${\mathrm{\&sigma;}}^r=\frac{{\left(4\mathrm{\&pi;}\right)}^3{P}_{r}R}{P_t{G}^2{\mathrm{\&lambda;}}^2}---\left(12\right)$

Wherein, σ ^rModified value for the target RCS value; R is a detection range; λ is a wavelength, with the radar detection frequency relation be λ=c ₀/ freq; G is a radar antenna gain; P _tBe known radar emission power;

The echo power P that radar under the revised Atmospheric Absorption environment can be received _rSubstitution radar equation (12) can obtain the modified value of target RCS value.

Principle of the present invention is:

Comprise oxygen (O in the principal element of general atmosphere layer to electro-magnetic wave absorption ₂) absorb with water vapor and absorb, wherein mainly near the 22.235GHz and more than the 100GHz (being K wave band and millimere-wave band), and oxygen is to absorption of electromagnetic wave mainly near 60GHz (being the THz wave band) to absorption of electromagnetic wave for water vapor.The present invention is based on main absorption frequency, atmospheric loss is revised.

The full frequency band target RCS value based on atmospheric absorption loss that adopts the present invention to propose is estimated modification method; Can calculate according to the atmospheric absorption loss of the parameters such as distance between target and detection radar, and revise according to the RCS of result of calculation to target to the radar wave propagation process.This estimates the RCS that modification method will help accurately to hold target, helps more accurately target being carried out remote sensing and detection.

Description of drawings

(solid line is 0 degree corresponding to the elevation angle to Fig. 1, and dotted line is 2 degree corresponding to the elevation angle according to standard aerial oxygen absorption loss curve map in the inventive method implementation process; The enforcement implementation condition is under the conditions such as typical frequencies, atmospheric pressure, temperature).

Embodiment

Below in conjunction with embodiment and accompanying drawing the present invention is described further, but does not limit the present invention.

Embodiment 1:

Suppose a certain target range detection radar 200km, look-in frequency is 22.235GHz, and P is 1 atmospheric pressure, and T is 300k, and the RCS under this acquisition mode is 8.7dB.According to said method, because research frequency spectrum f=22.235GHz, therefore the loss of whole detection process is main with water-vapour absorption loss, and the absorption loss value is:

$L_{\mathrm{atm}}=\mathrm{Lw}={\&Integral;}_0^h({\mathrm{\&xi;}}_{22}\left(h\right)+{\mathrm{\&xi;}}_{\mathrm{res}}\left(h\right))\mathrm{dh}=0.18\mathrm{dB}$

So the modified value of echo power is about 2L _Atm=0.36dB.

The RCS unit of target is square metre in the formula (12), when getting the dB value, has:

${\mathrm{\&sigma;}}_{\mathrm{dB}}^r=10\log \left(\frac{{\left(4\mathrm{\&pi;}\right)}^{3}R}{P_t{G}^2{\mathrm{\&lambda;}}^2}\right)+10\log \left(P_r\right)$

Convolution (11),, under the situation of considering water-vapour absorption loss, the RCS modified value of target is:

${\mathrm{\&sigma;}}_{\mathrm{dB}}^r=10\log \left(\frac{{\left(4\mathrm{\&pi;}\right)}^{3}R}{P_t{G}^2{\mathrm{\&lambda;}}^2}\right)+10\log P_r=10\log \left(\frac{{\left(4\mathrm{\&pi;}\right)}^{3}R}{P_t{G}^2{\mathrm{\&lambda;}}^2}\right)+10\log P_0-2L_{\mathrm{atm}}$

$=10\log \left(\frac{{\left(4\mathrm{\&pi;}\right)}^3{P}_{0}R}{P_t{G}^2{\mathrm{\&lambda;}}^2}\right)-2L_{\mathrm{atm}}={\mathrm{\&sigma;}}_{\mathrm{dB}}-2L_{\mathrm{atm}}=8.7\mathrm{dB}-0.36\mathrm{dB}=8.34\mathrm{dB}.$

Claims (3)

1. modification method based on the full frequency band target RCS discreet value of atmospheric absorption loss; It is characterized in that: under the prerequisite of confirm at detection range, the antenna gain of detection radar, emissive power, look-in frequency are known; Confirm or known distance parameter, radar performance parameter are calculated in the electromagnetic wave propagation process oxygen and water vapor absorption coefficient and absorption loss respectively by above-mentioned; Then according to the absorption loss of oxygen and water vapor and the relevance between radar equation, the target RCS discreet value correction of the full frequency band that imposes a condition down.

2. method according to claim 1 is characterized in that said full frequency band is: near the 22.235GHz with 100GHz above or K wave band with millimere-wave band, 60GHz is neighbouring or the THz wave band.

3. method according to claim 1 and 2 is characterized in that mainly comprising the steps:

(1) according to electromagnetic theory, in conjunction with the specific absorption frequency of oxygen and water vapor, provide oxygen and water vapor separately to any specific frequency absorption of electromagnetic wave coefficient, calculate the absorption loss of whole detection process then by the absorption coefficient of each frequency band;

A) oxygen to any CF f absorption of electromagnetic wave coefficient does

$\begin{array}{cc}{\mathrm{\&xi;}}_{O_2}\left(h\right)=2.0058{\mathrm{PT}}^{-3}{f}^2\underset{N}{\mathrm{\&Sigma;}}{A}_N& (\mathrm{dB}/\mathrm{km})\end{array}---\left(1\right)$

Parameter declaration is following: h is a detection range, and P is an air pressure, and T is a temperature, and f is a frequency;

The sum term that each resonance is counted N does

$A_N=(F_{N+}{{\mathrm{\&mu;}}^2}_{N+}+F_{N-}{{\mathrm{\&mu;}}^2}_{N-}+F_0{{\mathrm{\&mu;}}^2}_{N_0})\exp (-e_n/T)---\left(2\right)$

Wherein

${{\mathrm{\&mu;}}^2}_{N+}=\frac{N(2N+3)}{N+1},$ ${{\mathrm{\&mu;}}^2}_{N-}=\frac{(N+1)(2N-1)}{N}$

${{\mathrm{\&mu;}}^2}_{N_0}=\frac{2(N^2+N+1)(2N+1)}{N(N+1)},$ e _n=2.06844N(N+1)

Wherein, μ ² _N+, μ ² _N-With

Be respectively forward resonance coefficient, reverse resonance coefficient and disresonance coefficient; e _nBe temperature coefficient;

The disresonance component

$F_0=\frac{\mathrm{\&Delta;f}}{f^2+{\left(\mathrm{\&Delta;f}\right)}^2}---\left(3\right)$

The resonance line shape function

$F_{N\&PlusMinus;}\left(f\right)=\frac{\mathrm{\&Delta;f}}{{(f_{N\&PlusMinus;}-f)}^2+{\left(\mathrm{\&Delta;f}\right)}^2}+\frac{\mathrm{\&Delta;f}}{{(f_{N\&PlusMinus;}-f)}^2-{\left(\mathrm{\&Delta;f}\right)}^2}---\left(4\right)$

Wherein

Oxygen difference on the frequency factor △ f=0.1895g (h) P/T;

Being defined as of height coefficient g (h) in the formula: $g\left(h\right)=\left\{\begin{array}{cc}0.640& 0\&le;h\&le;8\mathrm{Km}\\ 0.3026+0.04218h& 8\&le;h\&le;25\mathrm{Km}\end{array}\right.;$

B) water vapor to any CF f absorption of electromagnetic wave coefficient is:

$\begin{array}{cc}{\mathrm{\&xi;}}_{22}\left(h\right)=0.002535\left({\mathrm{fP}}_w{\left(\frac{300}{T}\right)}^{3.5}\exp \left(20144(1-\frac{300}{T})\right)F\right)& (\mathrm{dB}/\mathrm{km})\end{array}---\left(5\right)$

ξ _res(h)=0.007347ρPT ^-2.5f ²(dB/km) （6）

Wherein, ξ ₂₂(h) near the absorption coefficient the expression 22.235GHz, ξ _Res(h) the above absorption coefficient of expression 100GHz;

Power factor $P_w=\frac{\mathrm{\&rho;\; T}}{288.75}---\left(7\right)$

Wherein, parameter ρ is a density;

The frequency ratio factor

$F=\frac{f}{f_r}(\frac{\mathrm{\&Delta;f}}{{(f_r-f)}^2+{\left(\mathrm{\&Delta;f}\right)}^2}+\frac{\mathrm{\&Delta;f}}{{(f_r+f)}^2+{\left(\mathrm{\&Delta;f}\right)}^2})---\left(8\right)$

The water vapor difference on the frequency factor $\mathrm{\&Delta;\; f}=0.01799(P_w\frac{300}{T}+0.20846(0.75P-P_w){\left(\frac{300}{T}\right)}^{0.63})---\left(9\right)$

Therefore, the absorption loss of whole detection process does

(2) according to the absorption loss of whole detection process the detection radar echo power is revised, provided the echo power P that radar can receive under the revised Atmospheric Absorption environment _r

For monostatic radar, the received power of target echo with the relational expression of propagating absorption loss does

10lgP _r=10lgP ₀-2L _atm （11）

Wherein, P ₀Be the target echo power at radar receiving antenna place under the free space condition, for treating modified value through what predicting means was known;

(3) according to radar equation, the echo power P that can receive in conjunction with radar under the revised Atmospheric Absorption environment _r, the target RCS value is revised;

Radar equation is:

${\mathrm{\&sigma;}}^r=\frac{{\left(4\mathrm{\&pi;}\right)}^3{P}_{r}R}{P_t{G}^2{\mathrm{\&lambda;}}^2}---\left(12\right)$

Wherein, σ ^rModified value for the target RCS value; R is a detection range; λ is a wavelength, with the radar detection frequency relation be λ=c ₀/ freq; G is a radar antenna gain; P _tBe known radar emission power;

The echo power P that radar under the revised Atmospheric Absorption environment can be received _rSubstitution radar equation (12) can obtain the modified value of target RCS value.

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