USGS-OWQ: NFM 6.1.3.B: Temperature measurement of surface water
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Official Method Name
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Temperature measurement in surface water. |
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Current Revision
| Revision in progress; 6/27/2005 |
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Media
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WATER |
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Instrumentation
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Thermometer |
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Method Subcategory
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Physical |
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Method Source
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Citation
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Brief Method Summary
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Temperature measurement in natural waters must be made on-site and in situ and in accordance with the designated sampling protocol and data use. Refer to TWRI Book 9 Ch. A6.0 and Ch.A4 for isokinetic and nonisokinetic sampling methods and guidance. Do not remove sensor from water during measurement. To determine stream variability, running a cross-sectional profile is recommended. Measure temperature in those stream sections that represent most of the water flowing in the reach. If the goal is a measurement that represents the stream temperature in a given reach, do not measure temperature in or directly below turbulent flow or from the stream bank. Immerse the thermometer to the selected depth and hold there for at least 60 seconds to allow thermometer to equilibrate with stream temperature. Record the median of at least 3 to 5 sequential measurements. WADEABLE STREAM -- Wade to the measurement location and stand so that a shadow is cast where the thermometer will be immersed. NONWADEABLE STREAM -- Attach thermistor thermometer to a weighted cable and lower it into the representative portion or segments of the stream from the bridge or cableway. STILL WATER -- Measure temperature at multiple depths at several points in the cross section. Make three sequential readings and record the median |
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Scope and Application
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In-situ measurement of temperature in wadeable and nonwadeable streams |
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Applicable Concentration Range
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-5 to +45 degrees C, minimum range |
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Interferences
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Rapid changes in environmental conditions, on the order of seconds to minutes. Avoid measuring in or directly below stream sections with turbulent flow or from stream bank, unless required by data-collection objectives. Direct solar radiation on the section being measured can cause erroneous readings. |
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Quality Control Requirements
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Water temperature must be measured in situ with a thermometer having a calibration certification within 12 months of use. For calibration procedures, refer to section 6.1.2 of the Source citation. In general, the field thermometer (liquid-in-glass or thermistor type) must be certified for accuracy (calibrated) within a 0-to-45 degree C range against a standard NIST-traceable thermometer at least annually or more frequently, as recommended by the manufacturer and depending on frequency of use and environmental conditions to which the thermometer is exposed. |
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Sample Handling
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Temperature of stream water is measured in situ, using either a liquid-in-glass or a thermistor thermometer that has been calibrated according to USGS protocol NFM 6.1.2. To prevent erroneious readings casued by direct solar radiation, stand so that a shadow is cast where the measurement is being made. Allow sensor to equilibrate with ambient water temperature before recording readings. |
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Maximum Holding Time
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zero holding time |
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Relative Cost
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Unknown |
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Sample Preparation Methods
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none |
