DATA ACQUISITION SYSTEM FOR A CABLED OCEAN BOTTOM SEISMOMETER (OBS) Tomasz Rogalski, Shahram Shariat-Panahi, J. Del Río, A. Mànuel SARTI Research Group. Electronics Dept. Universitat Politècnica de Catalunya (UPC), Rambla Exposició 24, 08800 Vilanova i la Geltrú, Spain. Phone: +(34) 938967200, Fax: +(34) 938967201 Abstract- Ocean Bottom Seismometers (OBS) are highly used to monitor seismic activities at sea. They are also used to detect tsu- namis and generate warning alarms. This paper presents a data acquisition system built for an OBS with capability to synchronize time through IEEE-1588 protocol. This acquisition system provides real time data through the Ethernet making it suitable for OBSs de- ployed at seafoor observatories. Introduction Today Ocean Bottom Seismometers (OBS) are very popular and used in many places all around the world to detect seismic activities at the sea bottom. It is enough to mention scientifc institutes in United States, Japan, Norway, Germany etc. The seismometer is a detector that is placed in direct contact with the earth to convert very small motions of the earth into electri- cal signals, which are recorded digitally [1]. In general, OBSs are used to study the sea bottom to detect earthquakes, tsunamis or to fnd oil reservoirs. In order to monitor continuous seismic activities in the ocean, OBSs are installed in seafoor observato- ries. OBSEA is a cabled seafoor observatory located 4 kilometers from Vilanova i la Geltru (Spain) in a fshing protected area. The main advantage of this observatory is its uninterrupted power supply to scientifc instruments. It allows permanent power supply and avoids problems with battery powered systems. This way, OBSEA can perform real-time observation of multiple pa- rameters in the marine medium. [2] The acquisition system Following tools were used in the design of the OBS acquisition system: •DK-LM3S9B96 - board equipped with many modules as: SSI, GPIO, GPTM, UART etc. [3]. Used for executing the main pro gram, acquiring data from the ADC board and sending it trough the UDP protocol for monitoring. •CS5372-76A – analog-digital converter equipped with a 1 to 4 channel modulator and a digital decimation flter which is required to acquire the correct data. [4] (Left) Figure 1: DK-LM3S9B96 board Figure 2: Connection between DK-LM3S9B96 and CS5376A •CodeSourcery G++ - compiler where the C code was written. This software was also used to upload and debug programs to the Luminary Micro board. •LabVIEW – graphical programming environment used to vi sualize data transferred through UDP protocol. The main program is described in the following fow-chart: As the fow-chart shows, frst the system clock was enabled as well as all peripherals as SSI, GPIO bases, timers etc. The next step is to confgure GPIO pins for all tasks needed. Later lwIP library was used to set MAC and IP addresses. Another step is to confgure a flter in the ADC board to acquire correct data. The last step is to enable interrupts. Interrupt handler func- tion can be divided into four parts: sending data to ADC board through SSI protocol, acquiring data from ADC board through SSI protocol, processing data (creating frame contains time, date and data), sending data through UDP for monitoring. Visualization was made by LabVIEW. The data is extracted from the main frame and data for each channel is shown in separate graphs. Instrumentation Viewpoint / 10 / Winter 38