Government Solutions: Helping Astronomers Collect More Accurate Images of the Sky

Case Study

Helping Astronomers Collect More Accurate Images of the Sky

The brightness of stars and galaxies seen through a telescope can vary from day to day because of atmospheric variability. The sky's inconsistency is due to the presence of atmospheric aerosols -- seen as haze -- that scatter and absorb some of the light from the stars and distort what is seen through the telescope.

To address this problem, researchers at the Georgia Tech Research Institute (GTRI) developed a device to accurately assess the impact of this variability on light traveling through the Earth's atmosphere. The tool was developed in collaboration with the University of New Mexico and supported by the National Science Foundation.

"Until now, astronomers never had an independent way to measure the transparency of the atmosphere," says Gary Gimmestad, a GTRI principal research scientist. "They always had to compare their measurements to the standard star catalog, which was itself created without having this atmospheric information."

The device developed by Gimmestad, senior research scientist David Roberts and senior research engineer John Stewart is called the Astronomical Lidar for Extinction (ALE). It scans the entire sky to probe for cirrus clouds and accurately measures the transmission of the atmosphere by taking measurements at multiple angles above the horizon.

"ALE provides real-time continuous and unattended monitoring, and measurements of the amount of atmospheric extinction -- the absorption or scattering of light -- as well as its cause, whether low-lying aerosols, dust or smoke," says Roberts.

When activated, the device transmits rapid pulses of eye-safe green laser light into the atmosphere, which are scattered back to two detectors. Measuring the scatter provides a distance-resolved profile of gas, particles and clouds that allows astronomers to calculate precisely the amount of light lost in traversing the atmosphere at a specific moment.

Using that information, the researchers calculate extinction coefficients, which are applied to the telescope's photometric data to correct the photometric images for the light loss in the atmosphere. The result is more accurate stellar photometry along with a precision profile of the structure of Earth's atmosphere.

The Astronomical Lidar for Extinction system is currently in use at the University of New Mexico campus observatory.