Feature imaging and adaptive focusing for synthetic aperture processor

• US 6,088,295 A
• Filed: 12/29/1998
• Issued: 07/11/2000
• Est. Priority Date: 12/29/1998
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Altes, Richard A.
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US09/222,635
• Time in Patent Office: 560 Days
• Field of Search: 367/87, 367/88, 367/100, 367/7, 367/103, 342/179, 342/195, 342/25
• US Class Current: 367/103
• CPC Class Codes: G01S 15/8904 using synthetic aperture techniques

Abstract

A feature imaging and adaptive focusing synthetic aperture processing met provides improved sharpness and easier classification of images derived from radar and sonar echo data by applying adaptive focusing and feature imaging to a sequence of echo data.

Claims

1. A feature imaging and adaptive focusing synthetic aperture process comprising the steps of:

predicting expected echo delays between a sensor and a target for each pixel coordinate of an image representative of the target and its environment formed from echo data;

calculating possible perturbations to the expected echo delays;

beamforming image data of an echo sequence and constructing a test image for each possible or hypothesized echo delay perturbation at each pixel coordinate;

calculating the mean square bandwidth of each test image;

selecting the best test image having the largest value of mean square bandwidth resulting in the best local focus for each image pixel;

subtracting the predicted expected echo delays from the perturbed delays of the best test image for each image pixel;

estimating relative motion of the sensor with respect to each point of the imaged target and its environment;

and constructing a motion compensated image from the best test image of the echo sequence.

2. The feature imaging and adaptive focusing synthetic aperture process of claim 1 wherein the echo data is sonar echo data.

3. The feature imaging and adaptive focusing synthetic aperture process of claim 1 wherein the echo data is radar echo data.

4. A feature imaging and adaptive focusing synthetic aperture process comprising the following steps:

identifying peaks or local maxima at the output of a whiten-and-match filter in a small delay interval around a selected range sample or pixel wherein each peak has a maximum peak amplitude;

normalizing each peak by dividing each peak amplitude by the maximum peak amplitude;

finding an echo feature representation by estimating peak sharpness from a second derivative of the whiten-and-match filter output evaluated at the peak;

replacing the original whiten-and-match filtered echo by the maximum normalized peak sharpness within each small delay interval;

and constructing a noncoherent synthetic aperture image from the echo feature representation.