Pre-inversion Corrections and Analysis of Radar Tomographic Data

Abstract
Pre-inversion corrections and analysis of transmission radar data is important for producing reliable tomographic images. In order to extract high-resolution, quantitative information from radar tomographic data, it is important to process the data as accurately as possible. This is especially true when analyzing data collected in a time-lapse mode, where changes in geophysical attributes with time may be less than a few percent, or when the spacing between acquisition wells is on the order of several meters. Using high-resolution tomographic radar data collected in a variety of geological environments, this study illustrates how different pre-inversion travel time and amplitude processing steps affect the velocity and attenuation estimates. In some cases, the distortion caused from incorrect processing can lead to severe artifacts in the tomogram including the appearance of anisotropy. This paper presents methods for recognizing and correcting the raw data for errors caused by incorrect station geometry and zero time, geometric spreading, transmitter radiation pattern, transmitter amplitude, and high angle raypaths, and also addresses the spectral variability of the transmitted radar signal as a function of borehole properties. The examples presented here suggest that analyses and corrections should be routinely performed prior to inverting transmission radar data.