Water Quality

Aquatic environments are constantly changing. Regardless if you model effects of climate change on a global scale, operate an aquaculture facility, study the impact of human activities in the coastal zone, spreading of pollution, ecosystem changes or are involved in coastal or off-shore constructions measurements of relevant parameters are fundamental to understand ongoing changes and risks and make it possible to calibrate and verify mathematical models.

Occasional sampling is useful for quality control and for parameters that are difficult to measure but has often proven to have unsufficient resolution in time.

There is wide range of physical, chemical and biological sensors. It is crucial that the sensors in use are stable over time and provide accurate information, if not the value of the measurements will be limited. At Aanderaa we develop long-term stable accurate Smart Sensors. All sensors are multipoint calibrated, include high quality temperature measurements and makes the conversion from raw data to calibrated measurements internally on the fly. 

The SeaGuardII and SmartGuard platforms combined with a suite of Aanderaa sensors offers large flexibility to adapt to different missions. Sensors can be plug-and-play added/removed as desired on to the top plate of an instrument or cable connected or included in sensor strings. The Aanderaa Smart Sensors can also be used with any third party logger capable of reading serial Rs232 and/or Rs422.

One software, the Real Time collector, serve to communicate and set-up all Aanderaa platforms and smart sensors. It is also used to collect real-time data from multiple sensors and system simultaneously. If the sensors/instruments are used on-line the GeoView or the new Hydrosphere softwares are often selected for real-time presentation of the measurements and for database storage.

 In shallow waters fouling on the sensors might have negative effects on the sensor readings. In high fouling environments optical senors like turbidity could have issues already after some days, the conductivity/salinity after a week, the oxygen opcodes after two weeks while pressure and current sensors in general have low fouling sensitivity. To adress these issues we integrate UV light and recommend the usage of copper tape. Please contact us for recommendations.

 

Conductivity/Salinity: Conductivity is a key parameter for in-situ determination of salinity, density and speed of sound. The Aanderaa Conductivity Sensors are based on an inductive principle which provides stable measurement without electrodes. The sensors are 132 point calibrated and automatically switch between lower, below 10 psu, and higher salinities at which different methods to calculate salinity are used. Experiences from factory re-calibrations reveal that these sensor have a minimal drift in the field, less than 0.008 mS/cm-year. For field verification of the sensor functioning a multi-resistor loop is used.

Oxygen Optodes: Most chemical and biological processes are influenced by changes in dissolved oxygen. Consequently oxygen is a prime parameter to measure in aquatic studies. Aanderaa revolutionised natural water oxygen measurements with the introduction of oxygen optodes in 2002. The proven long-term stability (years) and reliability of these sensors have opened new possibilities in coastal and open ocean water monitoring, which are described in more than 150 scientific publications  The latest developments include new ultra stable and trace foils. The opcodes are forty-point calibrated with an absolute accuracy better than ±2 % over the whole range of oxygen concentrations and temperatures. Different sensor versions are rated from 100 to 12 000 m depth.

Pressure/Wave/Tide: In 2006 a new series of compact Pressure/Wave/Tide sensors based on silicon sensing elements using a piezoresistive measuring principle were introduced. These sensors are 20 point calibrated and have demonstrated excellent accuracy (0.01 %), resolution (0.1 mm) and stability (drift less than 0.01 % per year).  Also they consume little energy, can handle shock and are able to withstand 50% overpressure without damage and the need for recalibration. These sensor have outperformed quartz pressure sensors in several studies and are selected in application ranging from coastal wave measurements to mm movements of the seafloor in seismic areas and in off-shore oil and gas applications.

Turbidity: Turbidity is a proxy for water suspended mineralogenic particles like sand, silt and clay. The combination of turbidity measurements with acoustic backscatter from Doppler Current Profiling sensor is useful and gives high resolution information on the origins and distribution of Particles in the water column.

Currents: Aanderaa offers Acoustic Doppler Current Profiler (ADCP) and Single Point instruments  and Stand alone sensors that are used in a wide range of applications, from surface buoys to the deepest trenches, to measure currents, waves and particles.

Waves: At Aanderaa we have focused on three different methods for spot measurements of waves including:

  • Motion based waves: MOTUS, a stand-alone motion based directional wave sensor designed for surface platforms like buoys and autonomous vehicles.  
  • Acoustic Based Waves: Acoustic directional wave sensor that is mounted below the surface and use an upward facing ADCP (Acoustic Doppler Current Profiling) to measure directional wave and currents simultaneously.
  • Pressure based wave and tide sensors that are mounted below the surface. 

Integration of sensors from other manufacturers: For parameters that we do not offer we integrate sensors from other manufacturers to our systems including EXO units from YSI for shallow water applications with sensors for e.g. pH, Algae, CDOM, ORP/Redox, Blue green algae, Salinity, Temperature, Oxygen and with a wiper for anti-fouling. For deeper waters we integrate sensors from other manufacturers. 

 

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