Geophysical survey
The magnetic and gravitational fields emanating from the Earth's interior hold essential information concerning seismic activities and the internal structure.
Geophysical surveys may use a great variety of sensing instruments, and data may be collected from above or below the Earth's surface or from aerial, orbital, or marine platforms.
Geophysical surveys have many applications in geology, archaeology, mineral and energy exploration, oceanography, and engineering.
The data collected from a geophysical survey is analysed to draw meaningful conclusions out of that.
Analysing the spectral density and the time-frequency localisation of any signal is important in applications such as oil exploration and seismography.
In such cases, specialized magnetometers such as the superconducting quantum interference device (SQUID) are used.
Jim Zimmerman co-developed the rf superconducting quantum interference device (SQUID) during his tenure at Ford research lab.
Jim Zimmerman pioneered the development of SQUID by proposing a new approach to making the Josephson junctions.
The diffraction gratings are nano fabricated materials with a separation of a quarter wavelength of light.
As the name suggests, the gravitational and electromagnetic waves in the analog domain are detected, sampled and stored for further analysis.
[9] The STFT is mathematically written as: The Wavelet transform is defined as A variety of window functions can be used for analysis.
The wavelet transform techniques offer a way to decompose the signals as a linear combination of shifted and scaled version of basis functions.
In other words, the beamformer output is formed by averaging weighted and delayed versions of receiver signals.
[13] The spectral estimates can be obtained by finding the square of the magnitude of the Fourier transform also called as Periodogram.
This problem is resolved using techniques that constitute the classical estimation theory.
[14] 2.Welch's method suggested to divide the measurements using data window functions, calculate a periodogram, average them to get a spectral estimate and calculate the power spectrum using Fast Fourier Transform.
Wider the main lobe of the smoothing spectrum, smoother it becomes at the cost of frequency resolution.
[13] For further details on spectral estimation, please refer Spectral Analysis of Multi-dimensional signals The method being discussed here assumes that the mass distribution of the underground objects of interest is already known and hence the problem of estimating their location boils down to parametric localisation.
Say underground objects with center of masses (CM1, CM2...CMn) are located under the surface and at positions p1, p2...pn.
A maximum likelihood procedure is followed and Cramér–Rao bound (CRB) is computed to assess the quality of location estimate.
Various sensors located on the surface of Earth spaced equidistantly receive the seismic waves.
The method of volume rendering is an important tool to analyse the scalar fields.
Data inside the 3-d dataset is projected to the 2-d space (display screen) using various techniques.
