Aeromagnetic Gradiometers-a Perspective

Transformations between aeromagnetic gradients in frequency domain

“…This expression for computing vertical gradient is discussed and used by many authors, and all of them considered that the good results can be obtained (Oruç and Keskinsezer, 2008;Nabighian et al, 2005;Guo, 2004;Shearer and Li, 2004;Cowan et al, 1995;Nelson, 1994Nelson, , 1988. Cowan et al (1995) concluded that although the noise level of the survey system was relatively high, it was feasible to calculate the vertical from the transverse and longitudinal gradients by using the Hilbert transform. Guo (2004) used theoretical data of models and illustrated the accuracy and reliability of method.…”

“…At first, there are three types of gradiometer systems, that is, horizontal, vertical, and triaxial gradiometer systems. At present, only the first two types are widely used (Zhang and Fan, 2007;Doll et al, 2006;Mushayandebvu and Davies, 2006;Scott Hogg, 2004;Cowan et al, 1995). However, three gradients are necessary for many techniques of data enhancement or direct interpretation, such as analytic signal and Euler deconvolution methods.…”

“…Secondly, checking the validity of measured gradients can be achieved by transforming between any two gradients. Furthermore, in some cases, the quality of calculated gradients may be better than measured (Doll et al, 2006;Mushayandebvu and Davies, 2006;Cowan et al, 1995). Cowan et al (1995) pointed that the vertical gradient can be derived from the longitudinal and traverse horizontal gradients with probably lower noise levels than the measured vertical gradient.…”

“…Furthermore, in some cases, the quality of calculated gradients may be better than measured (Doll et al, 2006;Mushayandebvu and Davies, 2006;Cowan et al, 1995). Cowan et al (1995) pointed that the vertical gradient can be derived from the longitudinal and traverse horizontal gradients with probably lower noise levels than the measured vertical gradient. Doll et al (2006) compared the analytic signal maps computed from measured gradients and calculated gradients from total magnetic anomaly and from the vertical gradient; only the analytic signal map that was computed from gradients obtained from measured vertical gradient showed all the test targets.…”

“…Practical advantages of measured gradients include elimination of the diurnal problem, removing of the main field of the earth, suppression of regional anomalies due to deep sources, and improving spatial resolution of shallow features and closely spaced sources (Nabighian et al, 2005;Jin, 2004;Guan et al, 2002;Cowan et al, 1995;Paterson and Reevesj, 1985). Aeromagnetic gradient surveys have improved dramatically over the past three decades with advances in both data acquisition and processing techniques.…”