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Geophysical Prospecting, 1998, 46, 141–151 iSPITM – the improved source parameter imaging method1 Richard S. Smith,2 Jeffrey B. Thurston,2 Ting-Fan Dai3 and Ian N. MacLeod3 Abstract Interpretation of an anomalous magnetic response involves determining the parameters that characterize the source of the anomaly. The depth to the top of the structure is a parameter that is commonly sought, and the Source Parameter ImagingTM (SPITM) method is one way of determining this depth estimate. One advantage of the SPI method is that the depths can be displayed on an image. Typically there can be one image for an assumed contact (fault) model and another image for an assumed dipping thin sheet (dike) model. The depth estimate obtained will depend on the model assumed. An improvement to the source parameter imaging method extends the method to horizontal cylinders and at the same time allows the most appropriate model to be determined automatically. This model can be displayed on an image and the correct depth estimate for each anomaly can also be determined. The depth estimates can therefore be summarized on one map independent of an assumed model. The images generated from synthetic and field data show that the improved SPI method makes the task of interpreting magnetic data significantly easier. Introduction A large number of automatic methods exists for interpreting magnetic data. These methods can be applied to profile data (Hartman, Tesky and Friedberg 1971; Naudy 1971; Nabighian 1972; Jain 1976; Thompson 1982; Atchuta Rao, Ram Babu and Sanker Narayan 1981) or grid data (Reid et al. 1990; Roest, Verhoef and Pilkington 1992; MacLeod, Jones and Dai 1993; Hsu, Sibuet and Shyu 1996). All the techniques assume a certain model and then determine the parameters which characterize the source subject.