Polarimetric selectivity method for suppressing cross-track clutter in sounding radars

• US 7,570,202 B2
• Filed: 05/16/2008
• Issued: 08/04/2009
• Est. Priority Date: 05/16/2007
• Status: Active Grant

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Raney, Russell K.
• Primary Examiner(s): Sotomayor; John B
• Application Number:
  US12/121,841
• Publication Number:
  US 20080284640A1
• Time in Patent Office: 445 Days
• Field of Search: 342/25.R, 342 25 A- 25 F, 342159-162, 342/188
• US Class Current: 342/188
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06
• CPC Class Codes: G01S 13/9076 Polarimetric features in SAR
• CPC Class Codes: G01S 7/026 involving the transmission of elliptically or circularly polarised waves

Abstract

Methods for suppressing cross-track clutter in a sounding radar utilize polarimetric selectivity in two ways: (1) transmitting full-beam circular polarization and separating the desired signal of interest from the clutter based on the signal and clutter having different polarizations, and (2) transmitting and receiving circular polarization at the radar'"'"'s nadir and elliptical polarization at the radar'"'"'s off-nadir regions and filtering out the elliptical polarization.

Claims

1. A method for suppressing cross-track clutter in a sounding radar comprising the steps of:

transmitting a circularly polarized electromagnetic (EM) field over a full beamwidth of an antenna pattern;

receiving a coherently dual-polarized backscattered field containing cross-track clutter and a desired signal having different polarizations;

using data embedded in the received backscattered field to calculate Stokes parameters that characterize the receive backscattered field;

using the calculated Stokes parameters to identify the polarizations of the desired signal and the cross-track clutter; and

suppressing the cross-track clutter using the difference in polarization between the cross-track clutter and the desired signal.

2. The method as recited in claim 1, wherein in the using data and using the calculated Stokes parameters steps, instead of the Stokes parameters, a 2×

2 coherency matrix is calculated and used to identify the polarizations.

3. The method as recited in claim 1, wherein in the using data and using the calculated Stokes paramters steps, instead of the Stokes parameters, a representation that is a complete embodiment of the observable properties of the received backscattered field is calculated and used to identify the polarizations.

4. A method for suppressing cross-track clutter in a sounding radar comprising the steps of:

transmitting an electromagnetic (EM) field, having a first polarization at the radar'"'"'s nadir and an EM field having a second polarization;

at the radar'"'"'s off-nadir regions;

receiving a coherently dual-polarized backscattered field, wherein backscatter received from the nadir retains the first polarization and backscatter received from the off-nadir regions retains the second polarization;

using data embedded in the received backscattered field to calculate the Stokes parameters;

using the calculated Stokes parameters to distribute the data according to the extent of the second polarization; and

suppressing the second polarization using a passband centered on the first polarization.

5. The method as recited in claim 4, wherein the first polarization is circular and the second polarization is elliptical.

6. The method as recited in claim 4, wherein in the using data and using the calculated Stokes parameters steps, instead of the Stokes parameters, a 2×

2 coherency matrix is calculated and used to distribute the data according to the extent of the second polarization.

7. The method as recited in claim 4, wherein in the using data and using the calculated Stokes parameters steps, instead of Stokes parameters, a representation that is a complete embodiment of the observable properties of the received backscattered field is calculated and used to distribute the data according to the extent of the second polarization.