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搭载在月球侦察轨道器(Lunar Reconnaissance Orbiter,LRO)上的微型无线电频率(Miniature Radio Frequency,Mini-RF)合成孔径雷达(Synthetic Aperture Radar,SAR)观测系统主要通过以固定入射角观测所得的圆极化比(Circular Polarization Ratio,CPR)来研究月球表面的物理性质.然而值得注意的是,在许多Mini-RF CPR影像中都可以发现沿距离向存在着明显的梯度.对于一个具有15 km刈宽的典型Mini-RF CPR影像,CPR沿距离向的系统性增长会达到0.2–0.3,这可能会对雷达影像的地质解译带来误导.更进一步的研究表明,这种系统性的CPR梯度有可能是由原本被认为固定的、但实际上沿距离向变化的局部入射角引起的.为了消除这种由入射角引起的CPR梯度,本文首先提出了三种模型用以拟合CPR与入射角的变化关系,接着再用一种基于沿距离向入射角的校正模型进行影像校正.以月球北极地区Baillaud撞击坑坑底的CPR影像为例,校正结果表明本文所提出的方法在保证原有CPR影像统计特征不变的情况下有效减少了系统性的梯度.这一方法可以为较大区域CPR影像的无缝镶嵌以及更为准确地解译月表的地球物理性质提供帮助.
The Miniature Radio Frequency (Mini-Radio) Synthetic Aperture Radar (SAR) observation system mounted on Lunar Reconnaissance Orbiter (LRO) is mainly based on the observation of the circular pole Circular Polarization Ratio (CPR) is used to study the physical properties of the lunar surface. However, it is noteworthy that a significant gradient along the distance can be found in many Mini-RF CPR images. Of the typical Mini-RF CPR images, the systematic increase of CPR along the distance will reach 0.2-0.3, which may mislead the geological interpretation of radar images.Further research shows that this systematic CPR gradient has May be caused by the local angle of incidence which is supposed to be fixed, but in fact changes along the distance.In order to eliminate this CPR gradient caused by the incident angle, we first propose three models to fit the CPR and the angle of incidence , And then use a correction model based on the incident angle along the distance for image correction.Using the CPR image of the bottom of the lunar Baillaud impact crater as The results show that the method proposed in this paper can effectively reduce the systematic gradient while keeping the original statistical characteristics of CPR images unchanged.This method can be used for seamless mosaic of CPR images in a large area and more accurately Interpretation of the geophysical properties of the lunar surface to help.