WAVELENGTH AND DIRECTION FILTERING BY MAGNETIC MEASUREMENTS AT SATELLITE ARRAYS - GENERALIZED MINIMUM-VARIANCE ANALYSIS

The main goal of the Cluster mission, consisting of four identical spa cecraft, is the spatial resolution of plasma structures. For the deter mination of the wave vectors of a wave field from four positions, clas sical Fourier analysis is inappropriate. We develop a generalized mini mum variance technique which gives a high wave vector resolution thoug h the spatial grid is restricted to only a few sampling positions. Thi s technique uses the amplitude and phase information of the magnetic f ield from the four satellite positions and determines the optimum wave field corresponding to the measured data. The components of the magne tic field are assumed to be normally distributed. The divergence-free nature of the magnetic field is used as a constraint. Using the magnet ic data measured at four positions allows up to seven different wave v ectors at one frequency to be uniquely resolved.