An SLS4 Longitude System Based on a Tracking Filter Analysis of the Rotational Modulation of Saturn Kilometric Radiation
An SLS4 Longitude System Based on a Tracking Filter Analysis of the Rotational Modulation of Saturn Kilometric Radiation
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基于土星千米辐射旋转调制跟踪滤波分析的 SLS4 经度系统
DOI：
10.1553/pre7s51
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
G. Fischer
中科院分区：
文献类型：
--
作者：
D. Gurnett;J. Groene;T. Averkamp;W. Kurth;S. Ye;G. Fischer
众所周知，三十多年来，土星一直在千米波长发出强烈的射电辐射，称为土星千米辐射(SKR)，这种辐射受到行星自转的调制。虽然这种调制的周期最初被认为代表了行星的自转周期，但现在人们知道，辐射有两个截然不同的旋转调制周期，在几年的时间尺度上，这两个周期的变化约为1%。一种主要来自北极光地区，另一种主要来自南极光地区。调制周期的差异被认为是由于磁层相对于行星内部的滑移在纬度上的变化，显然是由土星旋转轴倾斜的季节变化控制的。由于其他磁层现象表现出相似的复杂的旋转调制效应，因此需要根据两个半球内可变的SKR调制周期来定义南北经度系统。由于航天器接收到的SKR信号通常包括这两个分量，因此有时很难区分这两个分量的相位。本文描述了一种基于跟踪滤波法确定两个相位的方法，该方法可以分别跟踪两个分量的调制波形。然后，可以使用这两个波形的相位来为北部和南部分量定义新的经度系统，我们称之为SLS4经度系统。这是以前的SLS2和SLS3经度系统的延伸，后者只描述了南分量的位相变化。
Saturn has been known for over thirty years to emit an intense radio emission at kilometer wavelengths called Saturn Kilometric Radiation (SKR) that is modulated by the rotation of the planet. Although the period of this modulation was initially thought to represent the rotation period of the planet, it is now known that the radiation has two distinctly different rotational modulation periods that vary by on the order of one percent on times scales of years. One component originates primarily from the northern auroral region, and the other originates primarily from the southern auroral region. The differences in the modulation periods are believed to be due to latitudinal variations in the slippage of the magnetosphere relative to the interior of planet, apparently controlled by the seasonal variation in the tilt of Saturn’s rotational axis. Since other magnetospheric phenomena display similar complicated rotational modulation effects, there is a need to define north and south longitude systems based on the variable SKR modulation periods in the two hemispheres. Because the SKR signal received by the spacecraft often includes both components it is sometimes difficult to separate the phases of the two components. In this paper we describe a method of determining the two phases based on a tracking filter approach that can separately track the modulation waveforms of the two components. The phases of the two waveforms can then be used to define a new longitude system for the northern and southern components that we call the SLS4 longitude system. This is an extension of the previous SLS2 and SLS3 longitude systems, which only described phase variations of the southern component.