Design of a Low-cost Acoustic Modem for Moored Oceanographic Applications

1
Design of a Low-cost Acoustic Modem for Moored
Oceanographic Applications

• Bridget Benson, Grace Chang, Derek Manov, Brian
  Graham, Ryan Kastner
• University of California Santa Barbara
• WUWNet Presentation
• September 25th 2006

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Outline

• Motivation
• Requirements
• Design
• Experimental Results
• Meeting the Requirements for the SB CHARM
• Future Work

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Motivation

• To understand the ocean we must be able to
  observe large regions for long periods of time
• Such data could help predict earthquakes,
  tsunamis, or spread of a toxic algal bloom
• Platforms to measure large sets of data for long
  periods have been and are being established

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Cabled Observatories
Marthas Vineyard Coastal Observatory
LEO
NEPTUNE
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Moorings

• MBARI Ocean Observing System (MOOS)
• EOM cable in this mooring system parted in a
  storm on December 15, 2002.

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Mooring Modem Requirements

• Sensor to Modem Interfacing

• Packaging

• Power

• Low Cost

• Data Transmission Range

• Data Transmission Rate

• Oceanic Motion Resistance

• Acoustic Interference

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Mooring Modem Design
Transmitter
Receiver
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Mooring Modem Specifications

• Power Supply 12 V
• Sampling Frequency 8 kHz
• Data Rate 80 bps
• Carrier Frequency 50 kHz
• Frequency Separation 320 Hz
• Transducer Beam Width 20o

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Experimental Set-Up
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Experimental Results
Distance (ft) Direction Bit Errors Data Errors BER DER
4 Vertical 2 1 0.002 0.033
9 Vertical 10 10 0.010 0.333
10 Horizontal 0 0 0.000 0.000
17 Horizontal 4 4 0.004 0.133
19 20 Degrees 10 4 0.010 0.133
25 Horizontal 17 6 0.018 0.200
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Experimental Results
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SB CHARM
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Meeting the Requirements for the SB CHARM
Requirement SB CHARM Mooring Modem
Sensor-to-Modem Interfacing RS-232 Data Protocol X
Packaging Water proof and biofoul resistant X
Power Mooring batteries must last 6 months X
Low-Cost Minimum 9 modems 9 x 100.00 900.00
Data Transmission Range 6 meters (20 ft) 25 ft
Data Transmission Rate 200 bps 80 bps
Oceanic Motion Resistance Speeds of 1 m/s contribute to frequency deviation of 1 40 Hz Bandpass Filters designed to withstand 40Hz deviation
Acoustic Interference ADCP operates at 300 kHz Fmark1040 Hz Fspace1360 Hz Fc 50 kHz
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Future Work

• Determine actual power consumption and battery
  life of mooring modems
• Reduce size of the Mooring Modem design and
  waterproof the electronics
• Implement error correcting codes to reduce the
  BER
• Determine how to network the Mooring Modems
• Interface the Mooring Modem with oceanographic
  sensors using RS-232 protocol
• Test the Mooring Modem on the SB CHARM at depths
  0, 4, 10, and 22m

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Acknowledgements

• W.M Keck Foundation
• Hua Lee and Ronald Iltis