OBSAPS data acquisition system : operator's manual and system overview

Abstract

On the Ocean Bottom Seismometer Augmentation to the Philippine Sea Experiment (OBSAPS, April-May, 2011, R/V Revelle), a VLA and six OBSs were deployed to listen to an active acoustic source, a J15-3. This report describes the hardware and software used to control and record the acoustic transmissions from the source. Some significant features of the system are: 1) The system transmits general user-defined source functions, such as Msequences (.SIO files). 2) In addition to controlling the source waveform, the system also records six real-time channels in binary files with user-selectable lengths: the monitor hydrophone mounted near the source, the power amplifier voltage and current, the depth of the source, sonobuoy data (when deployed) and an IRIG-B time reference. Files are output in .AUV format with a precision GPS-based time stamp in the file name. 3) The transmission start time along with ADC and DAC sample rates are disciplined to GPS time. 4) A convenient, Labview based, user interface provides real-time source control and monitoring. 5) The software provides parsing and logging of gyro and GPS NMEA sentences. The system, which was based on an earlier system from Scripps MPL, worked well on OBSAPS and is available for future projects.