QT inversion — Comprehensive use of the complete surface NMR data set

Abstract

The technique of surface nuclear magnetic resonance (surface NMR) is the only geophysical exploration method providing direct and nondestructive information on subsurface aquifer properties due to the method’s unique sensitivity to hydrogen protons. The method combines the information content accessible via nuclear magnetic resonance (NMR) measurements and the nondestructive approach to derive subsurface information from surface-based measurements. Because of this, surface NMR became a useful tool for hydrogeophysics during the last decade. Two different inversion schemes exist. The initial value inversion (IVI) extracts the water content distribution from the surface NMR information content by estimating a sounding curve from surface NMR data. The time step inversion (TSI) extracts the distribution of both water content and decay time by separating the surface NMR data into several time steps. Both solve the inverse problem using independent steps and by separating subdata sets from the complete data. In this paper, a new inversion scheme — the QT inversion (QTI) — is found to solve to inverse problems by taking the complete surface NMR data set into account at once. QTI extracts water content and decay time and satisfies the complete data set jointly. We examine and compare QTI to IVI and TSI by a synthetic data set and a field data set. Our results find that the QT inversion approach increases both spatial resolution of the subsurface decay time distribution and stability of the inverse problem.

Detecting unfrozen sediments below thermokarst lakes with surface nuclear magnetic resonance

“…Raw data were imported, band-pass filtered, and digital noise compensation was applied. The applied QT inversion scheme fits all pulse moments, signal amplitudes, and T 2 * values simultaneously (see Müller-Petke and Yaramanci [2010]). Four-layer blocky inversions (an optimization approach for sharp boundaries) were used for the lake data sets because of the expected sharp transitions between stratigraphic layers with different water contents: (1) ice, (2) water, (3) saturated sediments, and (4) permafrost.…”

Hydraulic properties at the North Sea island of Borkum derived from joint inversion of magnetic resonance and electrical resistivity soundings

“…This class of inversion is therefore referred to as QT inversion. Mueller-Petke and Yaramanci (2010) discretise the subsurface in the spatial (depth) and spectral (decay time) dimension and achieve a smooth distribution of T * 2 for each of the depth layers. However, very often the subsurface consists of distinct layers of constant properties, and a mono-exponential decay is a valid assumption for many unconsolidated sediments (Hertrich, 2008).…”

Uncertainty estimates for surface nuclear magnetic resonance water content and relaxation time profiles from bootstrap statistics

“…Following this procedure, the first step is to conduct a synthetic experiment where surface NMR data is simulated. Using a simple subsurface structure consisting of three layers of contrasting water content and T 2 * and a survey employing a 25 m diameter loop and sixteen q's logarithmically sampled on the interval [0.28 13.56] [A s], we generate a single synthetic surface NMR data set using the forward modeling framework within the open source surface NMR processing software MRSMatlab (Müller-Petke and Yaramanci, 2010). Briefly, this process involves using a known set of w(z) and T 2 *(z) in combination with the set of survey parameters (loop size, list of pulse moments) to simulate a data set V(q,t) using Eq.…”