Originating Technology/NASA Contribution

A stunning red sunset or purple sunrise is an aesthetic treat with a scientific explanation: The colors are a direct result of the absorption or reflectance of solar radiation by atmospheric aerosols, minute particles (either solid or liquid) in the Earth’s atmosphere that occur both naturally and because of human activity. At the beginning or end of the day, the Sun’s rays travel farther through the atmosphere to reach an observer’s eyes and more green and yellow light is scattered, making the Sun appear red. Sunset and sunrise are especially colorful when the concentration of atmospheric particles is high. This ability of aerosols to absorb and reflect sunlight is not just pretty; it also determines the amount of radiation and heat that reaches the Earth’s surface, and can profoundly affect climate.

Stratton Park Engineering Company Inc. (SPEC) installed its Cloud Particle Imager (CPI) on NASA’s High Altitude Research Program aircraft. Research facilities around the world have since used the commercially available CPI to further atmospheric study.
In the atmosphere, aerosols are also important as nuclei for the condensation of water droplets and ice crystals. Clouds with fewer aerosols cannot form as many water droplets (called cloud particles), and consequently, do not scatter light well. In this case, more sunlight reaches the Earth’s surface. When aerosol levels in clouds are high, however, more nucleation points can form small liquid water droplets. These smaller cloud particles can reflect up to 90 percent of visible radiation to space, keeping the heat from ever reaching Earth’s surface.

The tendency for these particles to absorb or reflect the Sun’s energy—called extinction by astronomers—depends on a number of factors, including chemical composition and the humidity and temperature in the surrounding air; because cloud particles are so small, they are affected quickly by minute changes in the atmosphere. Because of this sensitivity, atmospheric scientists study cloud particles to anticipate patterns and shifts in climate.

Until recently, NASA’s study of atmospheric aerosols and cloud particles has been focused primarily on satellite images, which, while granting large-scale atmospheric analysis, limited scientists’ ability to acquire detailed information about individual particles. Now, experiments with specialized equipment can be flown on standard jets, making it possible for researchers to monitor and more accurately anticipate changes in Earth’s atmosphere and weather patterns.


Boulder, Colorado-based Stratton Park Engineering Company Inc. (SPEC) has won 16 Phase I Small Business Innovation Research (SBIR) contracts and 11 Phase II contracts with NASA since 1990. These contracts all related to developing atmospheric instrumentation and included: a Phase II Small Business Technology Transfer (STTR) contract in 1996 from Langley Research Center for cloud radiation measurement; a Phase II SBIR in 1999 from Jet Propulsion Laboratory for cloud particle imagers; a Phase I SBIR in 2001 from Goddard Space Flight Center for in situ lidar for cloud and aerosol radiation studies; a Phase II SBIR in 2003 for cloud micro-sensors from Goddard; and a Phase I SBIR in 2008 from Wallops Flight Facility and Goddard for advanced cloud particle probes.

Developed with funding from the 1999 SBIR, the SPEC Cloud Particle Imager (CPI) was installed on NASA’s High Altitude Research Program aircraft, the two WB-57s based at Ellington Field near Johnson Space Center. Research facilities around the world have since used the commercially available CPI to further atmospheric study. SPEC has sold its CPIs to the National Center for Atmospheric Research, the University of Washington, the University of North Dakota, and Sandia National Laboratories, in addition to other agencies and institutions in the United States, Australia, and Canada.

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