Discrimination of geomagnetic quasi-periodic signals by using SSA Transform

Discrimination of geomagnetic quasi-periodic signals by using SSA Transform Palangio1, L. Santarelli 1 1Istituto Nazionale di Geofisica e Vulcanologia L’Aquila3Istituto Nazionale di Geofisica e Vulcanologia Roma Correspondence to: lucia.santarelli@ingv.it AbstractIn this paper we present an application of the SSA Transform to the detection and reconstruction of very weak geomagnetic signals hidden in noise. In the SSA Transform multiple subspaces are used for representing and reconstructing signals and noise. This analysis allows us to reconstruct, in the time domain, the different harmonic components contained in the original signal by using ortogonal functions. The objective is to identificate the dominant subspaces that can be attributed to the signals and the subspaces that can be attributed to the noise, assuming that all these subspaces are orthogonal to each other, which implies that the signals and noise are independent of one another. The subspace of the signals is mapped simultaneously on several spaces with a lower dimension, favoring the dimensions that best discriminate the patterns. Each subspace of the signal space is used to encode different subsets of functions having common characteristics, such as the same periodicities. The subspaces identification was performed by using singular value decomposition (SVD) techniques, known as SVD-based identification methods classified in a subspace-oriented scheme.The quasi-periodic variations of geomagnetic field has been investigated in the range of scale which span from 22 years to 8.9 days such as the Sun’s polarity reversal cycle (22 years), sun-spot cycle (11 years), equinoctial effect (6 months), synodic rotation of the Sun (27 days) and its harmonics. The strength of these signals vary from fractions of a nT to tens of nT. Phase and frequency variability of these cycles has been evaluated from the range of variations in the geomagnetic field recorded at middle latitude place (covering roughly 4.5 sunspot cycles). Magnetic data recorded at L'Aquila Geomagnetic observatory (geographic coordinates: 42° 23’ N, 13° 19’E, geomagnetic coordinates: 36.3° N,87°.2 E, L-shell=1.6) are used from 1960 to 2009.