A robust method for lining up tomographic records

The fronts of acoustic arrivals are usually estimated by a human operator. The present author proposes a robust detection and estimation method for this purpose. The detection is based on a well-known entropy function that computes automatically the thresholding parameters. The first front of the main arrivals is then roughly estimated. The originality of the method is to perform a line up of the whole image so that tidal effects and mooring motions are removed. A replica of the received signals is computed by averaging the lined up image column by column. Each received signal is then intercorrelated with this coherent replica in order to compute a finer estimation of time arrivals. A new line up is performed to build a more coherent replica. Another intercorrelation of this replica with the received signal gives the finest estimation of time arrivals