多偏極雷達影像斑駁減抑之研究

A Study of Speckle Reduction for Multi-polarization SAR Images

王志添(C. T. Wang) ； 陳錕山(K. S. Chen) ； 胡婕美(C. M. Hu)

《航測及遙測學刊》 10卷2期 (2005/06) Pp. 159-168

https://doi.org/10.6574/JPRS.2005.10(2).3

摘要

就SAR影像觀點而言，當地表粗糙度與雷達波波長相近時，雷達回波將有同調性干擾現象產生斑駁雜訊造成SAR影像判釋上的困難。多偏極資料係以交替改變偏極方式取像，其斑駁效應遠大於單偏極資料，因此斑駁雜訊減抑成為ENVISAT-1雙偏極雷達影像資料於應用方面之重要課題。
在斑駁減抑約制條件為不改變影像上均質目標平均值與降低影像斑駁雜訊，兼顧保有影像解析力，且在不同偏極間振幅差值應維持不變。因此在處理兩張偏極影像時，我們先分別對兩偏極影像作雷達特性統計模式分析，以線性化轉換作為多偏極斑駁減抑處理以降低兩偏極之相關雜訊。我們以ENVISAT-1於2003年6月16日所獲取之雙偏極(HH/HV)影像作為測試資料，經上述斑駁減抑處理後，兩張影像之等效觀點數皆由原約3觀點數提升至約6觀點數，同時在影像上仍能保有點目標地物特徵，說明本文提出之方法有效減抑斑駁雜訊，同時保有原空間解析力，改善交替偏極影像於目標辨識上應用。

關鍵字

ENVISAT-1 ； 斑駁雜訊 ； 濾波 ； 交替偏極Alternating Polarisation

並列摘要

Multi-polarization SAR imagery data are important for a wide range application such as retrieval of soil moisture, vegetation mapping, and terrain cover classification. How ever, these alternative polarization data suffer more serious speckle noise caused by the alternating scanning. Speckle noise is inherently induced from the coherent processing of the backscattered signals and substantially degrades the effectiveness of images interpretation and target recognition/identification. To facilitate scene interpretation and qualitative applications of such SAR images, the speckle noise must be reduced to an acceptable level while preserving the polarimetric properties between different polarization data.
In this article, we proposed an effective approach that stems from a processing a series of images. A linear transformation that decorrelates the multi-polarization was carried out, followed by the Lagrange multiplier method to find a set of optimal filtering weights that are related to local image statistics. The effectiveness of the method was verified using the ENVISAT-1 Alternating Polarisation Mode HH/HV images acquired on 16(superscript th) June 2003 over Taiwan. It is found that the equivalent number of looks (ENL) is greatly improved from 3 to 6, and the strong targets are well preserved without scarifying the spatial resolution.

並列關鍵字

ENVISAT-1 ； Speckle noise ； Filter ； Alternating ； Polarisation