Synthetic aperture radar hybrid-quadrature-polarity method and architecture for obtaining the stokes parameters of radar backscatter
A synthetic aperture radar hybrid-quadrature-polarity method and architecture comprising transmitting both left and right circular polarizations (by alternately driving, at the minimum (Nyquist) sampling rate, orthogonal linear feeds simultaneously by two identical waveforms, +/−90° out of phase), and receiving two orthogonal linear polarizations, coherently. Once calibrated, the single-look complex amplitude data are sufficient to form all Stokes parameters, which fully characterize the radar backscatter.
1. A method for obtaining the four Stokes parameters representing a backscattered field from a polarimetric synthetic aperture radar (SAR) comprising:
transmitting either a left-circularly polarized (L) field or a right-circularly polarized (R) field by the SAR;
receiving coherently two orthogonal linear polarizations for the backscattered field after each transmission; and
using data embedded in the received backscattered field to obtain the Stokes parameters.
2. The method as recited in claim 1 , wherein the transmissions are alternated at a minimum (Nyquist) sampling rate, thereby the SAR becoming fully (quadrature) polarimetric.
3. The method as recited in claim 2 , wherein the transmitting step comprises the step of driving two orthogonal linear feeds simultaneously by two identical waveforms, the waveforms being 90 degrees out of phase.
4. The method as recited in claim 2 , further comprising the step of applying a decomposition methodology to analyze the data using the Stokes parameters.
5. The method as recited in claim 4 , the applying a decomposition methodology step comprising the step of calculating a 3×3 or 4×4 coherency matrix.
6. The method as recited in claim 1 , wherein the transmitting step comprises the step of driving two orthogonal linear feeds simultaneously by two identical waveforms, the waveforms being 90 degrees out of phase.
7. The method as recited in claim 1 , further comprising the step of applying a decomposition methodology to analyze the data using the Stokes parameters.
8. The method as recited in claim 7 , the applying a decomposition methodology step comprising the step of calculating a 2×2 coherency matrix.
9. The method as recited in claim 7 or 4 , the calculating step further comprising calculating a degree of polarization and a relative phase.
10. The method as recited in claim 7 or 4 , the calculating step further comprising calculating derived quantitative norms dependent on the values of the Stokes parameters.
11. A partial polarimetric synthetic aperture radar (SAR) for obtaining the Stokes parameters representing a backscattered field comprising:
a dual linearly-polarized antenna comprising two orthogonal linear feeds;
a transmitter operatively connected to the antenna;
a +/−90 degree hybrid operatively connected to the transmitter and the antenna for simultaneously driving the feeds 90 degrees out of phase and −90 degrees out of phase thereby causing the antenna to radiate, respectively, a left-circularly polarized field or a right circularly polarized field;
a receiver operatively connected to the antenna for receiving two orthogonal linear polarizations for the backscattered field after each transmission; and
a processor operatively connected to the receiver for obtaining the Stokes parameters from data embedded in the backscattered field.
12. The method as recited in claim 11 , wherein the transmissions are circularly polarized of opposite senses alternated at a minimum (Nyquist) sampling rate.
13. The SAR as recited in claim 12 , wherein the SAR is operated in ScanSAR mode thereby achieving simultaneously wide swath coverage and polarimetric measurements.
14. The SAR as recited in claim 12 , wherein the antenna comprises an active array of transmit/receive modules, each module comprising two orthogonal feeds which on transmit are driven simultaneously 90 degrees out of phase by nominally identical signals.
15. The SAR as recited in claim 14 , wherein the SAR is operated in ScanSAR mode thereby achieving simultaneously wide swath coverage and polarimetric measurements.
16. The SAR as recited in claim 12 , further comprising a decomposition methodology for analyzing the data using the Stokes parameters.
17. The SAR as recited in claim 16 , wherein the decomposition methodology comprises calculating a 4×4 coherency matrix.
18. The SAR as recited in claim 16 , wherein the decomposition methodology comprises calculating one of a degree of polarization and a relative phase.