Cassini imaging of Saturn's rings. II. A wavelet technique for analysis of density waves and other radial structure in the rings
Cassini imaging of Saturn's rings. II. A wavelet technique for analysis of density waves and other radial structure in the rings
复制标题
卡西尼号对土星环的成像。
DOI：
10.1016/j.icarus.2006.12.025
复制
发表时间：
2006
期刊：
影响因子：
3.2
通讯作者：
C. Porco
中科院分区：
文献类型：
--
作者：
M. Tiscareno;J. Burns;P. Nicholson;M. Hedman;C. Porco
我们描述了一个强大的信号处理方法，连续小波变换，并用它来分析卡西尼国际空间站的土星环图像的径向结构。小波分析在频率空间中局部地分离信号分量，使得许多难以用肉眼观察的结构变得明显。密度波是在土星卫星在环外（或环内）的共振下产生的，特别适合于这种分析。我们确定了一些以前未观察到的弱波，并证明了小波变换的能力，隔离叠加在彼此之上的多个波。我们还提出了两个波浪状结构，我们无法最终确定。在一个多步骤的半自动化的过程中，我们从清晰观察到的弱螺旋密度波中恢复了四个参数：局部环表面密度，局部环粘度，精确的共振位置（用于指向图像，并可能用于改进土星天体测量），以及波振幅（可能对扰动卫星的质量提供新的约束）。我们推导出的表面密度比以前的测量，来自更强的非线性波的散射少，并建议从内部到中间的A环的表面密度的温和的线性增加。我们发现，环粘度不断增加，从卡西尼司向外恩克差距。环厚度的有意义的上限可以设定在卡西尼环（在r = 118，800 km时为3.0 m，在r = 120，700 km时为4.5 m）和内A环（在r<127，000 km时为10-15 m）。
We describe a powerful signal processing method, the continuous wavelet transform, and use it to analyze radial structure in Cassini ISS images of Saturn's rings. Wavelet analysis locally separates signal components in frequency space, causing many structures to become evident that are difficult to observe with the naked eye. Density waves, generated at resonances with saturnian satellites orbiting outside (or within) the rings, are particularly amenable to such analysis. We identify a number of previously unobserved weak waves, and demonstrate the wavelet transform's ability to isolate multiple waves superimposed on top of one another. We also present two wave-like structures that we are unable to conclusively identify. In a multi-step semi-automated process, we recover four parameters from clearly observed weak spiral density waves: the local ring surface density, the local ring viscosity, the precise resonance location (useful for pointing images, and potentially for refining saturnian astrometry), and the wave amplitude (potentially providing new constraints upon the masses of the perturbing moons). Our derived surface densities have less scatter than previous measurements that were derived from stronger non-linear waves, and suggest a gentle linear increase in surface density from the inner to the mid-A Ring. We show that ring viscosity consistently increases from the Cassini Division outward to the Encke Gap. Meaningful upper limits on ring thickness can be placed on the Cassini Division (3.0 m at r∼118,800 km, 4.5 m at r∼120,700 km) and the inner A Ring (10–15 m for r<127,000 km).