Processing of surface proton magnetic resonance signals using non-linear fitting

When performing proton magnetic resonance (PMR) soundings, the observed signal is the relaxation electromagnetic field from subsurface water molecules which have been energised by an electromagnetic pulse at the Larmor frequency. Using currently available instruments, this signal is detected through a synchronous detection analyser. The four basic unknowns then to be recovered from a given time record are the amplitude, the decay time constant and the phase of the relaxation decay, the frequency shift between the energising frequency, and the true Larmor frequency at the site. This is best performed using a global non-linear least square parameter fitting scheme in order to reduce possible bias from noise.