Method for improving SAR system sensitivity in the presence of RF interference

• US 5,850,202 A
• Filed: 07/29/1997
• Issued: 12/15/1998
• Est. Priority Date: 07/29/1997
• Status: Expired due to Fees

• Current Assignee: ERIM International, Inc. (Altarum Institute)
• Original Assignee: ERIM International, Inc. (Altarum Institute)
• Inventors: Schneider, Ronald A., Goodman, Ron S.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/902,422
• Time in Patent Office: 504 Days
• Field of Search: 342/25, 342/196, 342/159, 342/162
• US Class Current: 342/25.00A
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 7/023 Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques auxiliary means for detecting or identifying radar signals or the like G01S7/021; means for anti-jamming G01S7/36
• CPC Class Codes: G01S 7/2927 by deriving and controlling a threshold value

Abstract

The sensitivity of a synthetic aperture radar (SAR) system employing stretch processing is improved in the presence of radio-frequency interference (RFI). The sequence of data processing operations initially uses a high number of bits to digitize radar echoes plus RFI, then uses floating-point arithmetic to perform range deskewing to "compress" RFI tones, followed by threshholding and nulling the primary RFI contributors, and finally re-quantizes the resulting radar signal to a lower number of bits and appropriately allocating these bits over the range of signal levels.

Claims

1. A method of improving the sensitivity of a synthetic aperture radar (SAR) system, comprising the steps of:

receiving a digital SAR signal exhibiting b1 bits per sample;

range deskewing and threshold nulling the signal using floating-point arithmetic; and

re-quantizing the signal using a number of bits per sample which is less than b1.

2. The method of claim 1, wherein the threshold nulling is constant.

3. The method of claim 1, wherein the threshold nulling is dynamic.

4. In a synthetic aperture radar (SAR) system, the method of improving sensitivity in the presence of radio-frequency interference, comprising the steps of:

receiving a dechirped analog SAR signal

performing an analog-to-digital conversion of the dechirped analog SAR signal utilizing b₁ bits per sample to yield a plurality of digitized signal samples;

converting the digitized signal samples into floating point data;

range deskewing the floating point data;

nulling the floating point data on a per-sample basis using an intensity value greater than a threshold value; and

re-quantizing the result of the above steps utilizing a number of bits per sample which is lower than b₁.

5. The method of claim 4, wherein, in the step of nulling the floating point data on a per-sample basis, the threshold value is a constant.

6. The method of claim 4, wherein, in the step of nulling the floating point data on a per-sample basis, the threshold value is a variable.