Nebraska State Climatology Office develops weather sensor calibration lab at School of Natural Resources
To provide people with accurate data about rainfall, temperature, wind speed and much more, state climatologists lead strategic installations of research-grade weather stations across their states. Weather stations are finely tuned machines, expected to record key data within finite margins of error. But even high-tech systems need a tune-up once in a while, said Nebraska State Climatologist Martha Shulski. Those calibrations can be time-consuming, she said. Four different companies manufacture the different sensors on a typical U.S. weather station, she said, meaning a state office has to send parts away to multiple companies that all often have backlogs. The State Climate Office at the University of Nebraska-Lincoln School of Natural Resources is stepping in to consolidate and streamline the process.
Starting this summer, the Nebraska State Climate Office began offering weather station sensor calibration services for research-grade equipment that is being used in other states. The program began with a shipment from the North Dakota Agricultural Weather Network, which sent a set of 17 temperature and humidity sensors from weather stations to Hardin Hall. There, in a basement lab, senior Nebraska Mesonet technician Glen Roebke ran the meteorological instruments through a battery of tests with instruments that can calibrate air temperature, humidity, barometric pressure readings and more. The instruments that need recalibration can receive it at the Nebraska lab in lieu of being sent back to a manufacturer.
The calibration center is an extension of the work that the Nebraska State Climate Office (NSCO) has long done for weather station sensors that are part of its statewide Nebraska Mesonet weather monitoring network, Shulski said.
"We’ve always calibrated our instrumentation in-house," Shulski said. " Now we’re opening up this service to other state weather networks. We’ve got the expertise. Glen has been doing this for roughly 20 years. He looked at what manufacturers do when you ship sensors to them for calibration tests, and determined what we could replicate here in the lab. He looked at what other weather networks use for their sensors and equipment, and developed techniques based on that."
That effort led to the development of, among other tools, an indoor solar calibration table that is now located in the basement lab. Roebke has had the capacity to test the solar readings of its NSCO’s pyranometers, which measure solar radiation, but only during a finite window of time. Before the table was installed, you could find Roebke in the Hardin Hall elevators every spring, bringing pyranometers up to be tested on a platform on the 10-story building’s roof, where a precision spectral pyranometer was installed.
"We've done a study in the past on when the best time of year to calibrate is, and the magic month is May, " Roebke said. " There are a lot of things that go into it. We want clear days, but there are a lot of clouds in the month of May, so it limits the number of days we can use it. And the other thing that's a huge variable is temperature. Temperature affects how these instruments work. So we don't want to do it in late July or the middle of August, because temperature changes the output. We want to stabilize it."
The indoor solar calibration table, then, allows any time in the basement lab to simulate a sunny day in May, as far as a weather station’s pyranometer is concerned. And the lab, Shulski said, now features equipment that can test each of the typical sensors that would have normally been sent to a manufacturer when they required calibration.
A weather station in Nebraska observes air temperature, relative humidity, wind speed and direction, barometric pressure, solar radiation, warm season liquid precipitation every minute, and soil temperature and soil moisture at five depths, every hour. Checking equipment once a year, Roebke said, helps the Nebraska Mesonet sensors to stay within a half a percent margin of error, rather than drifting 2%-4% off as equipment can when it’s not checked over two- or three-year stretches.
"It's a huge difference in the world of meteorology, " he said.
It costs about $2,600 a year per weather station to run the equipment, and that includes calibration, Shulski said. The stations are often sponsored by natural resource districts, and the equipment is in service for about a decade before its components are all replaced.
Some maintenance still requires field trips, she said. Lightning, gophers and coyotes are among a weather station’s natural enemies. If, for instance, rain is measured in an area surrounding one of the weather stations but not at that station, there’s a good chance that a spider web has been constructed atop its precipitation gauge. (Shulski said they spray vinegar on the gauges to prevent that.) Nebraska Mesonet’s 63 stations get inspected (and the grass around it mowed) at least four times a year.
The information collected from the sensors feeds into critical weather information systems, like the National Weather Service. It is used to determine when to issue flood warnings and when to declare drought emergencies. It helps ag producers make irrigation decisions and parents decide whether their kids need coats at recess. It helps track the changing climate over time. Shulski said it’s imperative to make sure the weather stations are providing readings that are as accurate as possible.
Shulski said that the University of Nebraska has the people, knowledge and gear to offer calibration services to states that don’t have similar in-house setups. The calibration services help augment operational funding for the Nebraska Mesonet, Shulski said, and could help contribute to continued expansion of the network. Currently,47 of the state’s 93 counties have weather stations installed in them. While the current collection provides strong spatial representation of what’s going on with Nebraska weather, Shulski said, a goal of hers is to install at least one weather station in each of the remaining counties that don’t yet feature one. As more states utilize Nebraska’s calibration lab, the revenue that the project brings in will allow for students to learn on-the-job calibration training in the lab, while also testing new equipment and sensors as weather station technology evolves.
"The calibration facility is part of our long-term vision for the Mesonet, and it’s quite exciting to see it come to fruition in such a short time, " Shulski said.
—Cory Matteson, SNR Communications