Kourosh Arfa-Kaboodvand

Geopotential Reconstruction, Decomposition, Fast Computation, and Noise Cancellation by Harmonic Wavelets

Harmonic wavelets are introduced within the framework of the Sobolev-like Hilbert space H of potentials with “square-integrable restrictions” to the Earths (mean) sphere ΩR. Basic tool is the construction of H-product kernels in terms of an (outer harmonics) orthonormal basis in H. Scaling function and wavelet are defined by means of so-called H-product kernels. Harmonic wavelets are shown to be “building blocks” that decorrelate geopotential data. A pyramid scheme enables fast computations. Multiscale signal-to-noise thresholding provides suitable denoising. Multiscale modelling of the Earths anomalous potential from EGM96-model data is illustrated by use of bandlimited harmonic wavelets, i.e. Shannon and CP-wavelets.

On High Frequency Polar Motion and Length of Day Variations

The 0.042-day Earth rotation data (diurnal and semidiurnal) computed by the International GPS Service were used to analyze the daily/sub-daily variations of polar motion (PM) and length of day (LOD). Systematic and advanced spectral analytical investigations of the degree of periodic variability have been carried out. They show that the prominent periodical components can be found at the tidal frequencies of zonal, tesseral and sectorial waves. These investigations should give better insight into the physical processes, which influence Earth orientation ( i.e. due to the atmospheric and oceanic motions, tidal forces etc. ). It should be the basis for the detailed modeling of excitation functions in the sub-diurnal range of the high-frequency spectrum.

On Subdiurnal Effects in Earth Rotation

More than two years of almost continuous polar motion data (obtained by reprocessing GPS-Observations) have been used to analyse the daily/subdaily variations in Earth rotation based on the complex Wavelet-Technique. Systematic and spectral analytical investigations of the degree of variability of periods including tidal have been carried out. Relevant indications of oceanic effects, besides atmospheric components, have been observed.