The equivalent number of looks (ENL) is an important parameter in the multilook statistical model of polarimetric synthetic aperture radar (Pol-SAR). Recently, the maximum likelihood (ML) method was proposed and gave a good performance in the Gaussian model case by using the full covariance matrix instead of the intensity of Pol-SAR data, but it generated underestimates in the product model case. In this paper several novel ENL estimators are presented via certain cumulants of the log-determinant of the sub-matrices of the multilook polarimetric covariance matrix. The texture effect to the ENL estimates is eliminated, and the analytic estimators are derived. The estimators use the full covariance matrix and sub-matrices information, rather than the intensities of polarization channels. All the novel estimators are suitable for any texture model and thus provide more accurate results than many existing ones. Experiments using simulated data and real data are presented to evaluate the performance of different estimators. The results show that the second log-determinant moment (SLDM3)-based method is the best one among the novel estimators. At the same time this estimator has much less computational complexity. In addition, a novel distribution classification method is proposed by coloring the image via second- and third-order log-cumulants of the covariance matrix (MLC), which is helpful to assess the estimation result.
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Anfinsen S N, Doulgeris A P, Eltoft T. Estimation of the equivalent number of looks in polarimetric synthetic aperture radar imagery. IEEE Trans Geosci Remote Sens, 2009, 47: 3795–3809
Oliver C, Quegan S. Understanding Synthetic Aperture Radar Images. 2nd ed. Raleigh: Sci Tech Publishing, 2004
Cumming I G, Wong F H. Digital Processing of Synthetic Aperture Radar Data: Algorithms and Implementation. Norwood: Artech House, 2005
Lee J-S, Grunes M R, Kwok R. Classification of multilook polarimetric SAR imagery based on complex Wishart distribution. Int J Remote Sens, 1994, 15: 229–231
Lee J-S, Grunes M R, Ainsworth T L, et al. Unsupervised classification using polarimetric decomposition and the complex Wishart distribution. IEEE Trans Geosci Remote Sens, 1999, 37: 2249–2259
Kersten P R, Lee J-S, Ainsworth T L. Unsupervised classification of polarimetric synthetic aperture radar images using fuzzy clustering and EM clustering. IEEE Trans Geosci Remote Sens, 2005, 43: 519–527
Frery A C, Correia A H, Freitas C C. Classifying multifrequency fully polarimetric imagery with multiple sources of statistical evidence and contextual information. IEEE Trans Geosci Remote Sens, 2007, 45: 3098–3109
Doulgeris A P, Anfinsen S N, Eltoft T. Classification with a non-Gaussian model for PolSAR data. IEEE Trans Geosci Remote Sens, 2008, 46: 2999–3009
Conradsen K, Nielsen A A, Schou J, et al. A test statistic in the complex Wishart distribution and its application to change detection in polarimetric SAR data. IEEE Trans Geosci Remote Sens, 2003, 41: 4–19
Lee J-S, Schuler D L, Lang R H, et al. K-distribution for multi-look processed polarimetric SAR imagery. In: Proceedings of the IEEE International Geoscience Remote Sensing Symposium (IGARSS’94), Pasadena, 1994, 4: 2179–2181
Liu T, Cui H G, Xi Z M X, et al. Texture-invariant estimation of equivalent number of looks based on trace moments in polarimetric radar imagery. IEEE Geosci Remote Sens Lett, 2014, 11: 1129–1133
Doulgeris A P, Anfinsen S N, Eltoft T. Automated non-Gaussian clustering of polarimetric synthetic aperture radar images. IEEE Trans Geosci Remote Sens, 2011, 49: 3665–3676
Liu T, Cui H G, Gao J. Statistics of the determinant of the Wishart distributed matrix and its application to parameter estimation. Acta Electron Sinica, 2013, 41: 1231–1237
Anfinsen S N, Eltoft T. Application of the matrix-variate Mellin transform to analysis of polarimetric radar images. IEEE Trans Geosci Remote Sens, 2011, 49: 2281–2295
Eltoft T, Anfinsen S N, Doulgeris A P. A multitexture model for multilook polarimetric synthetic aperture radar data. IEEE Trans Geosci Remote Sens, 2013, 52: 2910–2919
Maaref A, Aissa S. Joint and marginal eigenvalue distribution of (non)central complex Wishart matrices and PDFbased approach for characterizing the capacity statistics of MIMO Ricean and Rayleigh fading channels. IEEE Trans Wirel Commun, 2007, 6: 3607–3619
Lee J-S, Hoppel K, Mango S A. Unsupervised estimation of speckle noise in radar images. Int J Imaging Syst Tech, 1992, 4: 298–305
Foucher S, Boucher J M, Benie G B. Maximum likelihood estimation of the number of looks in SAR images. In: Proceedings of the International Conference of Microwave, Radar and Wireless Communications, Wroclaw, 2000, 2: 657–660
Cui Y, Zhou G, Yang J, et al. Unsupervised estimation of the equivalent number of looks in SAR images. IEEE Geosci Remote Sens Letts, 2011, 8: 710–714
Xu B, Cui Y, Zhou G, et al. Unsupervised speckle level estimation of SAR images using texture analysis and AR model. IEICE Trans Commun, 2014, 97: 691–698
Anfinsen S N, Doulgeris A D, Eltoft T. Goodness-of-fit tests for multilook polarimetric radar data based on the Mellin transform. IEEE Trans Geosci Remote Sens, 2011, 49: 2281–2295
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Liu, T., Cui, H., Xi, Z. et al. Novel estimators of equivalent number of looks in polarimetric SAR imagery based on sub-matrices. Sci. China Inf. Sci. 59, 062309 (2016). https://doi.org/10.1007/s11432-015-5480-x
- radar polarimetry
- synthetic aperture radar
- parameter estimation
- moment methods