Spinoff is NASA's annual publication featuring successfully commercialized NASA technology. This commercialization has contributed to the development of products and services in the fields of health and medicine, consumer goods, transportation, public safety, computer technology, and environmental resources.
One common hazard facing airplanes is ice — not just on the ground, but in the air, where it can coat wings or engines. But how do you know when icing conditions exist in the clouds? NASA has been working for years to build better models, and the tools it's helped develop are turning out to be useful well beyond passenger planes.
One of the best ways to determine how much supercooled liquid water — the culprit behind airborne icing — is lurking in the skies is by sending up a sophisticated sensor on a specially equipped research aircraft. Although the probes work extremely well for research, instrumented aircraft are not flown day-to-day to provide real-time icing hazard information, which is what pilots and operators could use to improve flight safety.
NASA's ground-based Icing Remote Sensing System (NIRSS) consists of a vertically pointing Ka-band radar that measures the size of water drops in the air, a lidar ceilometer that uses laser pulses to measure cloud base height, and a radiometer that measures temperature at different altitudes and integrated liquid water. In order to prove the system works, NASA needed to compare the NIRSS prediction with what's happening in the air, but instrumented aircraft are expensive. So in the early 2000s, NASA put out a call for something new to act as a backup and a way to gather preliminary data — a lightweight, inexpensive sensor that could be sent into the clouds on weather balloons.
John Bognar, founder of Anasphere Inc. (Bozeman, MT), had previously built lightweight meteorological instruments to help get chemical measurements for his research, and set about using the same principles to build the sensor NASA needed.
As the sensor rises through the atmosphere, it encounters supercooled liquid water, which freezes onto the wire sensor. That accumulating ice causes the wire vibrations to change, and the sensor registers those changes and reports them back to the ground station. By analyzing that information, scientists can determine the content of supercooled liquid water. While the original sensor called for electromagnets and magnetic coils to produce and measure the vibrations, Bognar turned instead to piezoelectric elements, which can convert physical movement or pressure into electricity, and vice versa.
The piezoelectric transducer didn't work as well to create the vibration, but Bognar was able to use a mechanical actuator to pluck the wire instead. Anasphere was awarded a second NASA contract to produce the sensor for its weather balloon studies.
Outside of NASA, the Department of Energy (DOE) is also using the vibrating wire sensors in its studies of cloud formation in the lower levels of the Arctic atmosphere. The DOE is working to understand the effects of clouds on climate: how they reflect and absorb heat energy, and how that impacts the radiation balance on Earth. Multiple sensors can be deployed at once to see upper and lower altitudes simultaneously.
The DOE also uses Anasphere's tethersondes — instead of floating away, the devices are attached to long lines that can be reeled back in. The supercooled liquid water sensors are sold as a separate add-on to the tethersonde package. The Anasphere sensors are also being marketed to farmers. The sensors can sound a warning when icing conditions near the ground show signs of danger for crops, such as when a very cold fog gathers.