Temperature Profiling


Surface waters including lakes and oceans commonly undergo seasonal temperature changes from factors like currents, wind and sun heating the water surface. Temperature affects water density and can result in stratification, with warmer upper layers separated from colder, denser lower layers. Temperature profiling involves deployment of thermistor strings with multiple sensors in the water column to measure and track such gradients.

Water Column Temperature

The annual cycle of freshwater lakes in many parts of the world includes seasonal stratification and turnover. In oceans, stratification can affect heat transfer and nutrient transport and even lead to effects such as more powerful hurricanes fed by warm surface waters.
During the summer, lakes often stratify as the sun warms surface layers and creates a thermocline between the surface and colder, denser lower layers.
Cooling surface waters in the fall eventually sink, resulting in more uniform temperatures in the lake and transfer of dissolved oxygen to the bottom.
Dams with multiple release points can utilize temperature profile data to avoid sudden changes in downstream temperature and DO levels.
In the ocean, stratification can prevent transfer of oxygen and carbon dioxide to deeper layers and have a negative impact on aquatic life.
Warming of ocean waters decreases the density and thereby increases the volume, which contributes to sea level rise.
Temperature profiling can also be useful in some industrial applications, for example in discharge waters or liquids stored in tanks.

Typical Temperature Profiling System

Temperature profiling strings are most commonly deployed from data buoy platforms, which are easy to deploy and relocate as needed and offer flexible mooring options for deployment in almost any location.

The NexSens CB-450 buoy is an ideal platform for temperature profiling. It is light enough to be deployed from most small boats, yet large and powerful enough with its on-board battery and three solar panels for continuous operation and potential expansion with weather and water quality sensors. It supports an M550 solar marine light for nighttime visibility.

NexSens manufactures two types of temperature profiling strings. T-Node FR systems have interchangeable sensors and cables with waterproof UW connectors which allow the user to build and modify strings. TS210 temperature strings provide similarly high accuracy, but with thermistors built into a fully-sealed, marine-grade cable at user-specified depths. Both can be securely fixed to mooring lines with TS-Clamp mooring clamp kits.

The X3 environmental data logger simplifies sensor connections and transmission of real-time data via 4G LTE cellular or Iridium satellite telemetry to the WQData LIVE web datacenter, where data can be viewed and alarms configured to provide notice when critical thresholds are exceeded. Multiple waterproof sensor ports and automatic sensor detection simplify startup and expansion with various sensor types.

Contact a NexSens Applications Engineer today to discuss your temperature profiling application.

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Case Studies


Managing Plant Discharge Temperatures

The Southern Illinois Power Cooperative operates a power plant near Lake of Egypt around the clock to produce energy for its customers. All the activity can stress the plant’s infrastructure, so key to continuing its operations is minimizing that stress as much as possible. One of the main issues that plant managers encounter in overseeing operations is keeping equipment from overheating. They routinely pump in water from the lake to cool generators and ensure reliable power generation in the long term. Through being used as a cooling agent, the water is heated up considerably, and then must be condensed and cooled before it can be discharged back into the reservoir.

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Washington Reservoir Temperature Changes

There are many major rivers flowing through the Pacific Northwest. Like others around the country, they are outfitted with various dams and reservoirs that are used to control their movements, provide energy and maintain drinking water supplies for those living around them. The U.S. Army Corps of Engineers (USACE) plays a big hand in managing and maintaining the structures that corral these rivers. Of significance for engineers with the USACE’s Walla Walla District are the Columbia, Snake and North Fork Clearwater Rivers.

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Lake Temperature Profile

The Carleton College Department of Geology is enhancing classroom learning and student/faculty research with real-time water quality data. A National Science Foundation Grant funded the purchase and deployment of a water quality buoy on Upper Lyman Lake. The new buoy logs temperature data at four depths every 15 minutes. Once per hour, the data is transmitted by radio telemetry to the college’s geology lab. Temperature profile data is posted to a website for student and professor access.

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