Title :
Generalized coherences between vector data on two spacecraft
Author :
Thomson, David J.
Author_Institution :
Queen´´s Univ., Kingston, Ont.
Abstract :
This paper describes some methods to analyze relations between vector-valued time series in a plasma environment. Specifically, we study the propagation between ACE, a spacecraft located at the first Lagrange point; and wind, a spacecraft whose complex orbit includes both Earth and L1. Propagation in an inhomogeneous magnetoplasma, in near-field conditions, and at frequencies below the plasma cutoff frequency makes analytic (or even numerical) solutions extremely difficult. Thus, a major goal is to measure the wavelength as a function of frequency and hence infer the dispersion relations. A major problem is that both spacecraft measure B, but in a plasma, this is insufficient to determine the direction of propagation and polarization properties of the wave. Thus a new method of determining propagation properties is required. We propose to examine the angular offsets between apparent directions derived from principle components of B as a function of frequency on both spacecraft and from the canonical coherences between the two spacecraft. The principle components for both spacecraft and the canonical coherences between the two vector-valued magnetic fields can be efficiently computed by using three singular-value-decompositions (SVD\´s) at each frequency. The goal is to do three-dimensional "beamforming" from a pair of moving vector sensors in an uncertain propagation environment.
Keywords :
electromagnetic wave polarisation; plasma electromagnetic wave propagation; plasma magnetohydrodynamics; singular value decomposition; space vehicles; time series; SVD; inhomogeneous magnetoplasma; plasma cutoff frequency; plasma environment; polarization properties; propagation properties; singular-value-decompositions; spacecraft; three-dimensional beamforming; vector data; vector-valued magnetic fields; vector-valued time series; Cutoff frequency; Extraterrestrial measurements; Lagrangian functions; Magnetic analysis; Plasma measurements; Plasma properties; Plasma waves; Space vehicles; Time series analysis; Wavelength measurement;
Conference_Titel :
Sensor Array and Multichannel Processing, 2006. Fourth IEEE Workshop on
Conference_Location :
Waltham, MA
Print_ISBN :
1-4244-0308-1
DOI :
10.1109/SAM.2006.1706100