Difference between revisions of "Instruments and sensors to measure environmental parameters"

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==Measurement of environmental parameters==
 
==Measurement of environmental parameters==
[[Image:Scales.png|550px|thumb|center|'''Figure 1 Temporal and spatial scales of ocean processes''']] The most simple approach to measure environmental parameters of water is to take samples and analyse them after returning to the laboratory. It is also a powerful approach as specialised laboratory equipment can be used to analyse a multitude of parameters. The main shortcoming of this approach is that only a limited number of measurements (samples) can be processed and the interval between samples taken at the same location (to gain information about the temporal variation) usually spans from weeks to months. Processes that occur on time-scales shorter than weeks or episodic and transient events are therefore not captured and the importance of these processes and events for the distribution of parameters cannot be assessed.
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[[Image:Scales.png|550px|thumb|center|'''Figure 1 Temporal and spatial scales of ocean processes''']] The simplest way in which on can measure the environmental parameters of water, is to take samples and then analyze them after returning to the laboratory. It is a powerful approach since specialized laboratory equipment can be used to analyze a multitude of parameters. The main shortcomings of this approach are that only a limited number of measurements (samples) can be processed and the time between samples taken at the same location (to gain information about the temporal variation) usually spans from weeks to months. Processes that occur on time-scales shorter than weeks or episodic and transient events are therefore not captured. As a result, the importance of these processes and events for the distribution of parameters cannot be assessed.
  
In oceanography there is a vast range of processes spanning many orders in time and space (see Figure 1). To investigate this range of processes a large volume of [[data]] has to be gathered on the appropriate time and space scales. To achieve this task [[oceanographic instrument|instruments]] are needed that measure environmental parameters automatically [[in situ]].
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In oceanography, there is a vast range of processes spanning many orders of time and space (see Figure 1). To allow for the investigation of these processes, a large volume of [[data]] must be gathered on the appropriate time and space scales. To achieve this task, [[oceanographic instrument|instruments]] are needed that measure environmental parameters automatically [[in situ]].
  
 
==Oceanographic instruments==
 
==Oceanographic instruments==
 
===Introduction===
 
===Introduction===
An oceanographic instrument generally consists of one or more [[sensors]] and a signal processing unit that converts the sensor signal and carries out scaling and conversion to engineering units and the output data protocol. Figure 2 shows a schematization of an oceanographic instrument. The analyte (property to be measured) interacts with the detector (in some cases after a stimulus has been exerted by the instrument). The detector produces a signal, that is transformed into an electrical signal by the transducer. Detector and transducer together constitute the sensor. The electrical signal is fed to the signal processing (and conditioning) unit that creates the signal output of the instrument.[[Image:Instrument schematic.jpg|thumb|700px|center|'''Figure 2 Schematization of a generalised oceanographic instrument''']]
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An oceanographic instrument generally consists of one or more [[sensors]] as well as a signal processing unit that converts the sensor signal and carries out scaling and conversion to engineering units and to the output data protocol. Figure 2 shows a schematization of an oceanographic instrument. The analyte (property to be measured) interacts with the detector (in some cases after a stimulus has been exerted by the instrument). The detector produces a signal, that is transformed into an electrical signal by the transducer. Detector and transducer together constitute the sensor. The electrical signal is fed to the signal processing (and conditioning) unit that creates the signal output of the instrument.[[Image:Instrument schematic.jpg|thumb|700px|center|'''Figure 2 Schematization of a generalised oceanographic instrument''']]
  
 
Oceanographic instruments can contain data loggers to store measurement data for readout after the deployment.  
 
Oceanographic instruments can contain data loggers to store measurement data for readout after the deployment.  
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===Important properties===
 
===Important properties===
 
:* '''Accuracy''': deviation of the measured value from the true value
 
:* '''Accuracy''': deviation of the measured value from the true value
:* '''Precision''': deviation of a measured value from another measured value of the same quantity (but at different environmental conditions (e.g. the two measurements taken at different temperatures)
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:* '''Precision''': deviation of a measured value from another measured value of the same quantity (but at different environmental conditions (e.g. the two measurements taken at different temperatures))
 
:* '''Resolution''': smallest change in the measured quantity that can be detected by the instrument
 
:* '''Resolution''': smallest change in the measured quantity that can be detected by the instrument
:* '''Measurement rate''': number of measurements that can be carried out per time unit (e.g. measurements/hour)
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:* '''Measurement rate''': number of measurements that can be carried out per unit time (e.g. measurements/hour)
:* '''Power consumption''': mean of electrical power uptake during deployment (usually in Watts [W])
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:* '''Power consumption''': mean of electrical power uptake during deployment (usually measured in Watts [W])
 
:* '''Deployment time''': time period for which the instrument can be deployed (usually depends on environmental conditions, such as [[biofouling]], or on stored energy and power consumption)
 
:* '''Deployment time''': time period for which the instrument can be deployed (usually depends on environmental conditions, such as [[biofouling]], or on stored energy and power consumption)
  
 
==Sensors==
 
==Sensors==
 
===Introduction===
 
===Introduction===
In an [[oceanographic instrument]] the stimulus can either interact directly with the detector (e.g. in a temperature, pressure or light sensor) or a stimulus is exerted by the instrument, then is modified by the property to be measured and the modified stimulus then interacts with the detector. For example, a [[Fluorescence sensors | fluorometer]] that sends out a light pulse (stimulus), which is transformed by chlorophyll fluorescence in the water (modification of stimulus); the transformed light (modified stimulus) then is interacting with the detector.
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In an [[oceanographic instrument]] the stimulus can interact either directly with the detector (e.g. in a temperature, pressure or light sensor) or a stimulus can be exerted by the instrument. The stimulus is then modified by the property to be measured and then interacts with the detector, such as a [[Fluorescence sensors | fluorometer]] that sends out a light pulse (stimulus), which is transformed by chlorophyll fluorescence in the water (modification of stimulus). The transformed light (modified stimulus) then interacts with the detector.
  
If the detector signal is of a property (such as colour) it can be converted to an electrical signal by a not an electrical signal (e.g. an optical signal or the change transducer). Detector and transducer together form the sensor.  
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If the detector signal is of a property (such as color) it can be converted to an electrical signal by a not an electrical signal (e.g. an optical signal or the change transducer). The sensor is made up of both the detector and the transducer.  
  
 
===Types of sensors===
 
===Types of sensors===
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''Examples of specialized sensor systems are''
 
''Examples of specialized sensor systems are''
:* [[Nutrient analysers]]
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:* [[Nutrient analyzers]]
:* [[Trace metal analysers]] (Theme 9 wanted page)
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:* [[Trace metal analyzers]] (Theme 9 wanted page)
 
:* [[Measuring instruments for fluid velocity, pressure and wave height]]
 
:* [[Measuring instruments for fluid velocity, pressure and wave height]]
 
:* [[Measuring instruments for sediment transport]]
 
:* [[Measuring instruments for sediment transport]]
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===Important properties===
 
===Important properties===
:* '''Sensitivity''': The smallest change in the property to be measured that leads to a measurable change in the detector signal.
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:* '''Sensitivity''': The smallest change in the property being measured that leads to a measurable change in the detector signal.
:* '''Selectivity''': In how far the change of other properties than the one to be measured leads to a change in the detector signal. High selectivity sensors exhibit little influence of detector signal from changes in properties other than the one to be measured.
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:* '''Selectivity''': How those properties, other than the one being measured, lead to changes in the detector signal. High selectivity sensors exhibit little change in the detector signal from properties other than the one being measured.
:* '''Range''': The span between the extremes of the property to be measured at which no further change in detector signal occurs.
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:* '''Range''': The span between the extremes of the property being measured, at which no further change in the detector signal occurs.
:* '''Linearity''': A measure that represents in how far equal amounts of change in the property to be measured lead to equal amounts of change in detector signal.
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:* '''Linearity''': A measure of how far equal amounts of change in the property being measured, lead to equal amounts of change in the detector signal.
  
 
==See also==
 
==See also==

Revision as of 11:09, 28 October 2009

Category:References

This article does not contain any cited references.

This article explains why instruments are needed to investigate oceanographic processes. It also explains the properties of available oceanographic instruments and sensors.

Measurement of environmental parameters

Figure 1 Temporal and spatial scales of ocean processes
The simplest way in which on can measure the environmental parameters of water, is to take samples and then analyze them after returning to the laboratory. It is a powerful approach since specialized laboratory equipment can be used to analyze a multitude of parameters. The main shortcomings of this approach are that only a limited number of measurements (samples) can be processed and the time between samples taken at the same location (to gain information about the temporal variation) usually spans from weeks to months. Processes that occur on time-scales shorter than weeks or episodic and transient events are therefore not captured. As a result, the importance of these processes and events for the distribution of parameters cannot be assessed.

In oceanography, there is a vast range of processes spanning many orders of time and space (see Figure 1). To allow for the investigation of these processes, a large volume of data must be gathered on the appropriate time and space scales. To achieve this task, instruments are needed that measure environmental parameters automatically in situ.

Oceanographic instruments

Introduction

An oceanographic instrument generally consists of one or more sensors as well as a signal processing unit that converts the sensor signal and carries out scaling and conversion to engineering units and to the output data protocol. Figure 2 shows a schematization of an oceanographic instrument. The analyte (property to be measured) interacts with the detector (in some cases after a stimulus has been exerted by the instrument). The detector produces a signal, that is transformed into an electrical signal by the transducer. Detector and transducer together constitute the sensor. The electrical signal is fed to the signal processing (and conditioning) unit that creates the signal output of the instrument.
Figure 2 Schematization of a generalised oceanographic instrument

Oceanographic instruments can contain data loggers to store measurement data for readout after the deployment.

Important properties

  • Accuracy: deviation of the measured value from the true value
  • Precision: deviation of a measured value from another measured value of the same quantity (but at different environmental conditions (e.g. the two measurements taken at different temperatures))
  • Resolution: smallest change in the measured quantity that can be detected by the instrument
  • Measurement rate: number of measurements that can be carried out per unit time (e.g. measurements/hour)
  • Power consumption: mean of electrical power uptake during deployment (usually measured in Watts [W])
  • Deployment time: time period for which the instrument can be deployed (usually depends on environmental conditions, such as biofouling, or on stored energy and power consumption)

Sensors

Introduction

In an oceanographic instrument the stimulus can interact either directly with the detector (e.g. in a temperature, pressure or light sensor) or a stimulus can be exerted by the instrument. The stimulus is then modified by the property to be measured and then interacts with the detector, such as a fluorometer that sends out a light pulse (stimulus), which is transformed by chlorophyll fluorescence in the water (modification of stimulus). The transformed light (modified stimulus) then interacts with the detector.

If the detector signal is of a property (such as color) it can be converted to an electrical signal by a not an electrical signal (e.g. an optical signal or the change transducer). The sensor is made up of both the detector and the transducer.

Types of sensors

There are numerous sensors in oceanographic work:

Some of the most commonly used are

Secchi disk
Optical backscatter point sensor (OBS)
Optical transmissiometers (Theme 9 wanted page)

Less common are

Examples of specialized sensor systems are

Important properties

  • Sensitivity: The smallest change in the property being measured that leads to a measurable change in the detector signal.
  • Selectivity: How those properties, other than the one being measured, lead to changes in the detector signal. High selectivity sensors exhibit little change in the detector signal from properties other than the one being measured.
  • Range: The span between the extremes of the property being measured, at which no further change in the detector signal occurs.
  • Linearity: A measure of how far equal amounts of change in the property being measured, lead to equal amounts of change in the detector signal.

See also

References

The main authors of this article are Schroeder, Friedhelm and Prien, Ralf
Please note that others may also have edited the contents of this article.