Recognizing the need to analyze cloud particles from close range, SPEC designed its CPI to be mounted to airplane exteriors; this robust design allows the CPI to operate in most airspeeds, altitudes, and air pressures, and to withstand vibrations and extreme temperatures as low as -70 °C. The system can also be adapted for harsh ground studies, and has been used at locations at the South Pole and New Hampshire’s Mount Washington.
As a research aircraft flies through clouds, the externally mounted CPI captures digital images of cloud particles. As they enter the CPI’s detection subsystem, particles cause light to scatter from two overlapping laser beams. That scattered light hits detectors and triggers the CPI’s imaging system to capture a high-resolution digital photograph of the particles using a 1-megapixel charge coupled device camera, which can image between 75 and 500 frames per second, depending on camera upgrades. The CPI captures images of particles that range in size from 15 to 2,500 micrometers, and the high-resolution images have a nominal resolution of 2.3 micrometers, displaying unprecedented detail for researchers. After capturing a particle’s image, the system transmits the information to a computer and SPEC’s CPI software, which crops and compresses the images. The system then stores the images and information for further analysis.
SPEC’s customized post-processing software, CPIView, performs some analysis automatically, calculating perimeters, areas, lengths, and volumes. It also creates graphical displays to show researchers certain distributions, such as patterns over time and in certain locations.
With such long-term studies and histograms of particle sizes, SPEC’s CPI system can help alert scientists to how the Earth’s climate is changing, and how quickly. SPEC president and CEO, Dr. Paul Lawson, explains that clouds and cloud particles have a major impact on global climate change: “If we change the mean size of cloud particles by a micron, a millionth of a meter, then that’s the same as doubling the concentration of carbon dioxide in the atmosphere,” thereby drastically increasing the lower atmosphere’s tendency to trap heat on Earth’s surface.
The company is now developing extremely small instruments that can image cloud particles continuously for up to 24 hours. Under the 2008 Wallops and Goddard SBIR agreement, SPEC has designed a small version of its CPI, the Micro-CPI, for small Uninhabited Aerial Vehicles (UAVs) which span fewer than 6 feet across. NASA and other agencies are using UAVs for atmospheric measurements because, among other reasons, they can fly in extremely cold or oxygen-poor altitudes. Micro-CPI—like the original CPI—measures the properties of ice crystals and water droplets, records the data onboard the UAV, and then sends them back to a computer.
SPEC also continues to develop the other particle imaging products funded by SBIR and STTR contracts, including the in situ lidar. This instrument can measure the absorption in liquid clouds with sampling volumes of millions of cubic meters. In this technique, a laser sends out pulses of light horizontally from an aircraft inside an optically thick cloud. Meanwhile, wide field-of-view detectors measure the time series of the number of photons returned. The ultimate use of these instruments is to provide a large volume of high-quality data about clouds for climate prediction models.
For its own studies and research using the CPI, the Micro-CPI, and the in situ lidar, SPEC makes the collected data available to the scientific community for analysis and further study, helping promote a better understanding of the Earth’s climate.