Study On Calibration Methods For Simultaneous Measurement Polarimetric Radar

The adequate use of polarization information can remarkably improve theperformance of radar in the aspect of clutter suppression, target detection, targetidentification and recognition, and anti-jamming, etc. Therefore, the accurateacquirement of targets’ polarimetric characteristics, which is a basis and preconditionfor target identification and recognition, clutter suppression, and anti-jamming of radar,owns an important meaning in theory and practice. Under the background of airsurveillance, missile defence, and weather target exploration, this paper, closesurrounding the main line of how to precisely obtain targets’ polarimetric scatteringcharacteristics, deeply studies on the methods of the measurement-waveformnon-orthogonality suppression, the kinematic error compensation, the passive and activecalibration of polarimetric radar system error and the polarimetric-radar cluttersuppression, etc., based on the simultaneous measurement scheme. The main contentsof the dissertation are as follows:For the simultaneous measurement polarimetric radar, the modification of errorsdue to the unideal orthogonality of measurement waveforms and target kinesi in themulti-polarimetric channels during the measurement of the polarization scatteringmatrix (PSM) is studied. The effect of the velocity and acceleration on the waveformisolation of the opposite slope linear frequency modulated signals is quantitativelydescribed by defining the range-velocity-acceleration ambiguity function matrix. Afterthe cross-channel interference produced by the frequency-modulated continuous-wavefull-polarimetric radar using the de-ramping processing to obtain the PSM is analyzed,the interference suppression method based on the fractional Fourier transform isproposed. Compared with the traditional method, the proposed method can achievelower peak sidelobe levels and integrated sidelobe levels in range profiles, which canobviously improve the polarimetric measurement performance of weak targets formulti-targets and weak polarimetric scattering components for a single target. After theerror due to the target kinestate is analyzed for the full-polarimetric radar during thePSM measurement, the estimation and compensation method of the kinetic parametersbased on the fractional Fourier transform is proposed. The simulative results show thatthe accuracy of the proposed method is higher than the conventional method.The point-target passive polarimetric calibration technique is studied. Afull-polarimetric radar system error model during PSM measurement is established. Thepolarimetric calibration performances of several typical point-target passivepolarimetric calibration algorithms are compared under different antenna polarizationisolations. After the disadvantage of the traditional passive calibration algorithms in thepractical application is founded, a new polarimetric calibration algorithm based on the Pauli-basis decomposition is proposed. Any three targets satisfying the orthogonalcondition can be chosen as calibrators to calibrate the full-polarimetric radar, whichbroaden the limitation to PSM of calibrators in the traditional calibration algorithms.The validity of the proposed method is proved by the out-field calibration experimentalresult of the PARSAX (Polarimetric Agile Radar S-And X-band) polarimetric weatherradar developed by the Delft University of Technology in the Netherlands. After theexternal calibration, the maximum amplitude and phase relative errors of the relativePSM are-22.04dB and1.40°, respectively.For the polarimetric calibration with the theory and practical engineering problemof the giant aperture antenna radar, the dynamic polarimetric calibration algorithmbased on the digital polarimetric active radar calibrator (PARC) is studied. The newPARC systems with two antennas and a single antenna are designed based on the digitalradio frequency memory, respectively. The frequency-domain dynamic polarimetriccalibration algorithm is proposed by the uniform-speed rotation of the PARCs’ antennasto modulate receive signals of the polarimetric radar. The unknowns in the system errormodel of the full-polarimetric radar are resolved in the frequency domain. The proposedmethod can eliminate the errors due to a set of measurements and the initial angles ofPARCs’ antennas in the traditional static calibration methods. The simulative resultsshows that the calibration performance of the dynamic polarimetric calibrationalgorithm based on the digital PARC is better than the traditional static polarimetriccalibration algorithms, such as the Target Spinor Calibration (TSC) and the FullPolarimetric Calibration Technique (FPCT), etc.The clutter suppression technique for the polarimetric characteristic measurementof atmospheric targets is studied. A new polarimetric clutter suppression method basedon the mathematical morphology method and double spectral linear depolarizationratios (SLDRs) is proposed. A binary mask matrix is constructed by using mathematicalmorphology operators via the analysis of statistical properties of the doublerange-Doppler spectral linear depolarization ratios of atmospheric targets and theground clutter. Using the atmospheric target data acquired by the PARSAX polarimetricradar in the simultaneous measurement mode, the analysis of calculation results of theatmospheric target data after clutter suppression in the range-Doppler spectrogram, thereflectivity, the mean Doppler velocity, and the Doppler width show the efficiency ofthe proposed method. Compared with the results of the traditional method, results of theproposed method verify its improvement and advantage.The research results of this dissertation help to promote the application of thepolarimetric radar technology and possess an important meaning to improve theperformance of target identification and recognition, clutter suppression andanti-jamming in the application area of the air surveillance, missile defence, weatherobservation and ground reconnaissance.