Topographic migration of georadar data: Implications for acquisition and processing

Abstract

Application of conventional elevation static corrections and migration to wavefield data recorded on irregular surfaces may result in poor reconstructions of complex subsurface features. Particulary poor images may be obtained at locations where the depths to target structures are comparable to undulations in the surface topography. For example, topographic relief of only 1-2 m may be important for the processing of georadar data. We describe an algorithm that allows georadar data to be migrated directly from gently to highly irregular acquisition surfaces. When applied to a variety of complicated synthetic data sets, topographically migrated images are observed to be markedly superior to those produced by two standard processing schemes. Extensive tests demonstrate that topographic migration should be considered in regions characterized by surface gradients 10% (i.e., dips 6 • ). For effective topographic migration, lateral and vertical coordinates of the georadar antennas should be determined to better than 10% of the dominant georadar wavelength, and velocities should be known to within 10-20% (e.g., 0.01-0.02 m/ns) of their true values. When applied to data collected across a moderately dipping (∼14 • ) rock glacier in the Swiss Alps, georadar sections resulting from two standard processing schemes have reflectors with depths and dips that differ by a significant 10-15% from those in the topographically migrated images.

Geophysical imaging of alpine rock glaciers

“…For high-resolution investigations, antennas with dominant frequencies between 20 and 100 MHz have proven to be suitable (Arcone and others, 1998;Isaksen and others, 2000;Lehmann and Green, 2000;Berthling and others, 2003;Moorman and others, 2003). Proper coupling of the antennas to the ground is an important prerequisite for recording high-quality data.…”

“…If reliable speed information is available, migration may be used to convert the processed time sections to equivalent depth sections. To account for the effects of strong topographic relief, special-purpose topographic migration algorithms may be applied (Lehmann and Green, 2000;Heincke and others, 2005).…”

Reverse time migration from rugged topography to image ground-penetrating radar data in complex environments sounding.

“…Fisher et al (1992) gave perhaps the first example, where they utilized an acoustic algorithm and the exploding reflector model for post-stack migration of GPR data [2] . Sanada and Ashida (1999) developed an RTM post-stack algorithm from Maxwell's equations that includes the effect of conductivity.As described by Lehmann and Green (2000), topographic variation on the same order as depth of investigation can have serious consequences on kinematic reconstruction of GPR images when conventional processing strategies are applied, e.g. elevation statics followed by poststack [3,4] migration (Fig.1); an alternative processing Fig.1 Schematic of travel paths for a zero offset section, collected along a topographic surface, after correction to a datum.…”

“…Sanada and Ashida (1999) developed an RTM post-stack algorithm from Maxwell's equations that includes the effect of conductivity.As described by Lehmann and Green (2000), topographic variation on the same order as depth of investigation can have serious consequences on kinematic reconstruction of GPR images when conventional processing strategies are applied, e.g. elevation statics followed by poststack [3,4] migration (Fig.1); an alternative processing Fig.1 Schematic of travel paths for a zero offset section, collected along a topographic surface, after correction to a datum. The vertical dashed lines show the travel path which is implicitly assumed in a standard elevation static correction.…”

“…The assumed path is a poor approximation leading to failure of migration from datum after elevation statics corrections. (Source: Lehmann and Green, 2000) strategy must be employed under these conditions. We have extended the RTM post-stack approach for imaging in complex topography based on the exploding reflector concept.…”