Method for the detection especially of small sea targets

• US 6,310,575 B1
• Filed: 12/10/1999
• Issued: 10/30/2001
• Est. Priority Date: 12/11/1998
• Status: Expired due to Fees

• Current Assignee: Thomson-CSF
• Original Assignee: Thomson-CSF
• Inventors: Chabah, Myriam, Quellec, Jean-Michel, Marchalot, Gabriel
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/458,815
• Time in Patent Office: 690 Days
• Field of Search: 342/89-104, 342/159-164, 342/175, 342/192-197, 342/134-137, 342/26, 342/27, 342/28
• US Class Current: 342/162
• CPC Class Codes: G01S 13/524 based upon the phase or frequency shift resulting from movement of objects, with reference to the transmitted signals, e.g. coherent MTi
• CPC Class Codes: G01S 7/2927 by deriving and controlling a threshold value

Abstract

A method for the detection of a target by a radar in the presence of noise, the detection being performed on M antenna rotations, comprises at least: a first step for the estimation of the Doppler frequency ({circumflex over (f)}) of the target; a detection step, the target being detected if an associated variable Z is greater than or equal to a predetermined threshold S, the variable Z being defined according to the following relationship: $Z=\underset{t\in D_t,f\in D_f}{\mathrm{MAX}}(\sum _{k=-N_d}^{N_d}\sum _{i=1}^{M-1}\frac{C_{z,z_i}^k\left(t,f,G\right)}{N\left(0,0,i,k\right)}+\sum _{k=-N_d}^{N_d}\sum _{l=-N_d}^{N_d}\sum _{i=1}^{M-1}\sum _{j=i+1}^{M-1}\frac{C_{z_{{,}_i}}^kz{,}_j^l\left(t,f,G\right)}{N\left(i,k,j,l\right)})$

D_t being the time domain [−t₀, t₀], t₀ being fixed as a function of the possible errors of framing of the signals from rotation to rotation; D being the frequency domain └{circumflex over (f)}_d−f₀, {circumflex over (f)}_d+f₀┘, f₀ fixed as a function of the possible errors of estimation of the Doppler frequency; z being the signal at the analyzed antenna rotation referenced “0”, at the analyzed range gate references “0”; z_i^k being the signal obtained by tracking at the rotation i of the signal z, in taking account of the tracking error in any, i.e., offset by k range gates with respect to the estimated range gate; C_z,_zf^k (t,f,G)being the Cohen transform of the signals z and z_i^k with a kernel G, computed at the time t and the frequency f; C_zi^k,zj^l(t,f,G) being the Cohen transform of the signals z_i^k and z_j^l of the kernel G, computed at the time t and at the frequency f; 2N_d+1 being the number of range gates taken into account, according to the tracking error if any; N(i, k, j, 1) being a standardization.

Claims

1. A method for the detection of a target by a radar in the presence of noise, the detection being performed on M antenna rotations, wherein it comprises at least:

a first step for the estimation of the Doppler frequency ({circumflex over (f)}_d) of the target;

a detection step, the target being detected if an associated variable Z is greater than or equal to a predetermined threshold S, the variable Z being defined according to the following relationship;

$Z=\underset{t\in <br><br>D_t,f\in <br><br>D_f}{\mathrm{Max}}<br><br>(\underset{k=-N_d}{\overset{N_d}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\underset{i=1}{\overset{M-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{<br><br>C_{z,z_i^k}<br><br>\left(t,f,G\right)<br><br>}{N<br><br>\left(0,0,i,k\right)}+<br><br><br><br>\underset{k=-N_d}{\overset{N_d}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\underset{l=-N_d}{\overset{N_d}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\underset{i=1}{\overset{M-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\underset{j=i+1}{\overset{M-1}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{<br><br>C_{z_i^k,z_j^l}<br><br>\left(t,f,G\right)<br><br>}{N<br><br>\left(i,k,j,l\right)})$

D_t being the time domain [−

t₀, t₀], t₀ being fixed as a function of the possible errors of framing of the signals from rotation to rotation;

D_f being the frequency domain [{circumflex over (f)}_d−

f₀, {circumflex over (f)}_d+f₀], f₀ being fixed as a function of the possible errors of estimation of the Doppler frequency;

z being the signal at the analyzed antenna rotation referenced “

0”

, at the analyzed range gate referenced “

0”

;

z_i^k being the signal obtained by tracking at the rotation i of the signal z, in taking account of the tracking error if any, i.e. offset by k range gates with respect to the estimated range gate;

C_z,zi^k (t,f,G) being the Cohen transform of the signals z and z_i^k with a kernel G, computed at the time t and the frequency f;

C_zi^k,zj^l (t,f,G) being the Cohen transform of the signals z_i^k and z_i^l of the kernel G, computed at the time t and at the frequency f;

2N_d+1 being the number of range gates taken into account, according to the tracking error if any;

N(i, k, j, I) being a standardization.

2. A method according to claim 1, wherein the kernel of the Cohen transform |A_s,s| is the modulus of the ambiguity function of the radar.

3. A method according to claim 1, wherein the estimated Doppler frequency {circumflex over (f)}_d is the argument that maximizes the variable M(f) defined according to the following relationship:

4. A method according to claim 1, comprising a tracking step following the first step on the M rotations to determine the resolution cells in which the target is located during the M rotations.

5. A method according to claim 1, wherein the first step is preceded by a step for the whitening of the noise.

6. A method according to claim 1, wherein the standardization N (i, k, j, l) is equal to 1.

7. A method according to claim 1, wherein the target is a target at sea in the presence of sea clutter.