Navigation Filtering

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The 1-Hz DGPS and 100-Hz INS navigation data were logged with the Kongsberg Simrad EM1002 software. The Simrad Bottom Detection Unit (BDU) time stamps the depth and sidescan telegrams and was slaved to a shipboard SUN Sparc 20 workstation that itself was synched to the GPS 1 PPS. The navigation telegrams were externally stamped by the Trimble 4000 GPS receiver. The receiver antenna positions were shifted to the transducer position according to the X and Y offsets using the POS/MV output (Table 3).

Every 1-Hz navigation fix was checked for gross time and/or distance jumps by graphical examination during data processing. Outliers were interactively interrogated for time, flagged and rejected (or re-accepted). All navigation jumps greater than 20 s were automatically flagged as uninterpretable.