Environmental Protection

Underwater Temperature Loggers

How to select and deploy them

Researchers and resource managers studying the water environment – whether it is on coral reef bleaching, industrial thermal loading, or modeling freshwater fish populations -- must have temperature data collection methods that are accurate, reliable, and practical for their particular field sites and studies.

Many researchers rely on electronic underwater temperature logging devices. The latest of these are small, rugged, inexpensive (between $39 and $130), and easy to use. Battery-powered, they can be programmed to gather data for months and will operate under a range of environmental conditions, including temperature fluctuations, rushing rocky streams, and ocean storms.

Underwater temperature loggers range from cigar-sized units to bite-sized pendulums, typically with anchoring holes at one end. The latest models feature precision sensors that can measure water temperatures from freezing to 50°C (122°F) in plastic housings and to 125°C (257°F ) in stainless steel housings.

While specific operating procedures vary, the process of using underwater temperature loggers involves logger configuration and launch; deployment; and data retrieval and analysis.

Configuration and launch
A logger is typically configured by connecting it with a cable to base station to a PC and selecting parameters for logging interval and start time. Once these selections are made, the user simply clicks a start button in the logger software, and the device is ready to start monitoring.

Data retrieval and analysis
After the logger has collected data for a period of time, the next steps are retrieving, offloading, and analyzing the data. Today’s loggers can transmit data optically to a waterproof pocket-sized data shuttle. This ensures that the data can be downloaded even when the logger is wet. Once the data is offloaded onto a PC directly or via a shuttle, data analysis can be performed using the supplied data logger software. These applications typically allow the user to quickly and easily generate graphs over the given data collection period.

Knowing how the devices will be used will help in choosing the correct underwater temperature loggers for the job. Generally, the logger should have a rugged, fully sealed enclosure that will withstand years of use in challenging conditions. A potential buyer should check device temperature and depth ranges and ask about saltwater deployment, if applicable.

Depending on measurement accuracy and legal requirements, a buyer may want to consider an underwater data logger from a manufacturer that offers National Institute of Standards & Technology (NIST) testing and certification services. These manufacturers can provide a certificate that indicates the logger’s temperature accuracy versus a NIST-traceable standard.

Finally, the software should enable users to configure parameters, launch the logger, and offload data. It also should offer data-plotting capabilities and enable users to export data to other programs for analysis. Buyers should note if the software needs to support both Windows and Macintosh operating systems.

As the demand for water temperature monitoring grows, so too will the need for instruments that make the process faster, cheaper, and more accurate. Underwater data loggers are the instruments of choice among researchers and resource managers because of their 24/7 operation, high-accuracy, ease-of-use, and PC-based analysis and reporting capabilities.

About the Author

Paul Gannett is product manager with Onset Computer Corp. He can be reached at 508.743.3149.

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