Method of processing a radar image

• US 7,714,766 B2
• Filed: 12/22/2008
• Issued: 05/11/2010
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Sauvageot, Henri, Artis, Jean-Paul, Costes, Clementine
• Primary Examiner(s): Sotomayor; John B
• Application Number:
  US12/341,271
• Publication Number:
  US 20090167596A1
• Time in Patent Office: 505 Days
• Field of Search: 342/26.R, 342 26 A- 26 D, 342/159, 342/162, 342/195
• US Class Current: 342/26.00R
• CPC Class Codes: G01S 13/426 Scanning radar, e.g. 3D radar G01S13/66 takes precedence
• CPC Class Codes: G01S 13/44 Monopulse radar, i.e. simultaneous lobing
• CPC Class Codes: G01S 13/953 mounted on aircraft
• CPC Class Codes: G01S 7/062 in which different colours are used
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

Embodiments of the invention process a radar image arising from a radar antenna, by reading the reflectivity information associated with each pixel forming the radar image, processing the reflectivity information, pixel by pixel, with the aid of a first procedure. The method further includes a second processing of the radar image using a second procedure that includes extracting objects from the radar image, then calculating the extent and the position of each object, with the aid of an angular aperture between two signals. For each part of the radar image processed by the first procedure, corresponding to an extracted object, pixel within the result of the first procedure are replaced by corresponding pixels of the radar image processed by the second procedure, if the reflectivity value associated with the second pixel is greater than the reflectivity value of the first pixel, the parts of the radar image corresponding to zones situated at a distance greater than a given threshold from the radar antenna.

Claims

1. Method of processing a radar image from a radar antenna, the radar image comprising a plurality of pixels having an associated reflectivity value, the method comprising the steps of:

pre-processing the radar image by a first predetermined procedure, to produce a first pre-processed image comprising a plurality of first pixels;

pre-processing the radar image by a second predetermined procedure, to produce a second pre-processed image comprising a plurality of second pixels, the second predetermined procedure comprising the steps of;

extracting an object from the radar image, to produce an extracted object;

calculating an extent and a position of the extracted object by use of an angular aperture between two predetermined signals; and

determining an associated reflectivity value for the second pixels of the extracted object;

for each extracted object, replacing each of the plurality of the first pixels of the first pre-processed image with the corresponding second pixel of the second pre-processed image, if the reflectivity value associated with the second pixel is greater than the reflectivity value of the first pixel,

wherein the replaced pixels correspond to zones situated at a distance greater than a predetermined threshold from the radar antenna.

2. The method according to claim 1, wherein the predetermined threshold is equal to 80 nautical miles.

3. The method according to claim 1, wherein the position of an object is given by a position of its summit.

4. The method according to claim 1, wherein the first predetermined procedure comprises the steps of:

removing ground clutter; and

minimizing, for each pixel of the image, a square error between a reflectivity value of the pixel and a reflectivity value estimated on the basis of a pattern of the radar antenna and of reflectivity values of pixels surrounding the pixel.

5. The method according to claim 1, wherein the second predetermined procedure determines the angular aperture corresponding to an extent in a plane of the extracted object, the extracted object being situated at a predetermined distance from the radar antenna, by performing the steps of:

measuring echoes in directions

${\mathrm{\theta <br><br>}}_p-\frac{\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{\theta <br><br>}}{2}<br><br><br><br>\mathrm{and}<br><br><br><br>{\mathrm{\theta <br><br>}}_p+\frac{\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{\theta <br><br>}}{2}$

 

of the plane, where θ

_p is a variable angle corresponding to directions of the plane and Δ

θ

is a predetermined angular aperture;

calculating pairwise differences between the echo measurements taken in the directions

${\mathrm{\theta <br><br>}}_p-\frac{\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{\theta <br><br>}}{2}<br><br><br><br>\mathrm{and}<br><br><br><br>{\mathrm{\theta <br><br>}}_p+\frac{\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{\theta <br><br>}}{2},$

 

to produce calculated differences; and

determining a slope at a value θ

_p of a function e of θ

_p interpolated between the calculated differences,

wherein the angular aperture is calculated from the slope.

6. The method according to claim 5, wherein the slope of the function e is determined at the value of θ

_p for which the function e substantially vanishes.

7. The method according to claim 5, wherein the angular aperture which corresponds to the extent of the object at the predetermined distance is extracted from a correspondence base associating angular aperture values with slope values, the slope of the function e at the value of θ

_p for which the function e vanishes having previously been calculated on the basis of measurements performed on a synthetic object of variable angular aperture.

8. The method according to claim 6, in which the plane is the horizontal plane.

9. The method according to claim 6, in which the plane is the vertical plane.

10. The method according to claim 1, wherein the radar is a meteorological radar, and the angular aperture corresponds to a height of a cloud.

11. The method according to claim 5, wherein the value of θ

_p for which the function e vanishes points to a center of a cloud, an altitude of the center of the cloud being calculated by trigonometry, using a predetermined distance between the radar antenna and the cloud.

12. The method according to claim 11, wherein an altitude of a summit of the cloud is calculated by adding half of a height of the cloud to the altitude of the center of the cloud.

13. The method according to claim 10, wherein the meteorological radar is airborne.