We're doing a bathymetric survey with our Biosonics DT-X next week. Here are a couple of good links about split-beam technology:
Simrad reference manual 2006. Simrad ES-60 Fish Finding Echosounder Reference Manual.
Ehrenberg and Torkelson 1996. Application of dual-beam and split-beam target tracking in fisheries acoustics. ICES Journal of Marine Science, 53: 329-334.
Gunderson 1993. Surveys of fisheries resources. John Wiley and Sons, Inc. New York.