Mass Storage Digital Ocean Bottom Seismometer and Hydrophone (DOBSH) Controlled by Micro-processors Using ADPCM Voice Synthesizing.

A DOBSH (Digital Ocean Bottom Seismometer and Hydrophone) and PDER (Portable Digital Event Recorder) have been newly developed. Main features are : storage of a large number of events, namely, 750 events on 4 channels, 2-minutes each and 100 Hz sampling rate ; including ADPCM (Adaptive Differential Pulse Code Modulation) speech synthesis ; a long (4 minutes max. on 4 channels) buffer size for the pre-event-delay using two 8 bit CMOS micro-processors. Events are identified by the event triggering algorithm. 100 Hz or 200 Hz samplings are used. On collecting data, the length of one sampling is compressed from 12 bit to 4 bit by ADPCM-IC and the compressed data are stored on digital tape. Records on the tape are synthesized by ADPCM-IC, or soft-ware on a mini-computer. By use of the ADPCM method, the total amount of data that can be put on a tape is practically increased fourfold. One cartridge tape (555-feet tape length) can store 72 MB of data when the data are synthesized. The time information is from a clock processor which can be adjusted at any time by a one minute pulse supplied from a precision clock or a 40 kHz standard time radio. Two field experiments showed the DOBSH worked correctly and proved its usefulness