6.3 Environmental and oceanographic sensors

Underwater robots use a variety of sensors to gather crucial data about the marine environment. These include temperature, salinity, and conductivity sensors, which provide insights into water properties and ocean circulation patterns.

Current meters and Doppler velocity logs measure water flow and robot motion, aiding navigation and studying ocean dynamics. Turbidity sensors and fluorometers monitor water quality and biological activity, helping researchers understand ecosystem health and productivity.

Marine Robotics Sensors

Environmental and Oceanographic Sensors

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• Temperature sensors measure the temperature of the surrounding water, providing data on thermal gradients and heat exchange processes
• Salinity sensors determine the salt content of the water, which affects the density and buoyancy of the underwater environment
• Conductivity sensors measure the electrical conductivity of the water, which is related to the salinity and temperature of the water
• Current meters and Doppler velocity logs (DVLs) measure the speed and direction of water flow, as well as the velocity of the robot relative to the water
• Turbidity sensors measure the clarity of the water by detecting the amount of suspended particles, which can indicate water quality and sediment transport
• Fluorometers measure the concentration of chlorophyll and other pigments in the water, providing information on the presence and distribution of phytoplankton and other microorganisms
• Dissolved oxygen sensors measure the amount of oxygen dissolved in the water, which is essential for aquatic life and can indicate the health of the ecosystem
• pH sensors measure the acidity or alkalinity of the water, which can affect the distribution and behavior of marine organisms

Sensors for Underwater Environments

Temperature, Salinity, and Conductivity Sensors

• Temperature sensors provide data on the thermal structure of the water column, including thermoclines and mixed layers, which can influence the distribution and behavior of marine organisms
  • Temperature data can also help identify water masses, currents, and upwelling zones, which are important for understanding ocean circulation patterns (Gulf Stream, Kuroshio Current)
• Salinity sensors measure the amount of dissolved salts in the water, which affects the density and buoyancy of the water and can influence the vertical stratification of the water column
  • Salinity data can help identify different water masses, as well as freshwater inputs from rivers or melting ice, which can affect the physical and chemical properties of the underwater environment (Amazon River plume, Arctic sea ice melt)
• Conductivity sensors provide an indirect measurement of salinity, as the electrical conductivity of water is proportional to the concentration of dissolved ions
  • Conductivity data can be used in conjunction with temperature data to calculate the density and sound velocity of the water, which are important parameters for underwater acoustics and navigation

Measuring Water Flow and Robot Motion

Current Meters and Doppler Velocity Logs

• Current meters measure the speed and direction of water flow at a fixed point, providing data on the local hydrodynamic conditions
  • Current data can help identify tidal flows, ocean currents, and turbulent eddies, which can affect the movement and distribution of marine organisms and sediments (Gulf Stream eddies, tidal currents in coastal regions)
• Doppler velocity logs (DVLs) use acoustic signals to measure the velocity of the robot relative to the water or the seafloor, providing data on the robot's motion and position
  • DVLs can measure the velocity of the robot in three dimensions, allowing for accurate navigation and positioning in the underwater environment
• By combining current meter and DVL data, researchers can study the interaction between the robot and the surrounding water flow, which can help optimize the robot's performance and energy efficiency
  • Current and velocity data can also be used to estimate the transport of water masses, nutrients, and pollutants in the underwater environment, which is important for understanding the functioning of marine ecosystems (nutrient transport in upwelling zones, oil spill tracking)

Monitoring Water Quality and Biology

Turbidity Sensors and Fluorometers

• Turbidity sensors measure the amount of suspended particles in the water, such as sediment, organic matter, and microorganisms, by detecting the scattering or absorption of light
  • Turbidity data can provide information on water clarity, sediment transport, and the presence of pollutants or algal blooms, which can affect the health and productivity of marine ecosystems (sediment plumes from dredging, harmful algal blooms)
  • High turbidity levels can reduce light penetration and photosynthesis, while also clogging the gills of fish and other aquatic organisms
• Fluorometers measure the concentration of chlorophyll and other pigments in the water by detecting the fluorescence emitted by these compounds when excited by light
  • Chlorophyll is a key pigment in phytoplankton, which form the base of the marine food web and play a crucial role in the global carbon cycle
  • Fluorometer data can provide information on the abundance and distribution of phytoplankton, as well as the primary productivity of the ecosystem (spring phytoplankton blooms, upwelling-driven productivity)
• By combining turbidity and fluorometer data, researchers can study the relationships between water quality, light availability, and biological activity in the underwater environment
  • Monitoring changes in turbidity and chlorophyll levels over time can help detect the onset and development of harmful algal blooms or the impact of human activities on marine ecosystems (eutrophication, coral reef degradation)