The Ames Sunphotometer/Satellite team, in collaboration with Battelle, Pacific Northwest Division, has been developing advanced instruments called Spectrometers for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR). Current 4STAR instruments include ground prototypes (4STAR-Ground) and an airborne instrument (4STAR-Air). The 4STAR instruments extend the capabilities of our airborne sunphotometer, AATS-14, in two ways:
- Sky scanning: By adding the capability to measure the angular distribution of sky brightness, 4STAR enables retrievals of aerosol type (via complex refractive index and shape) and aerosol size distribution extending to larger sizes than are possible with direct-beam sunphotometery alone. These capabilities, currently provided on the ground by NASA's AERONET network, would be extremely valuable in an airborne instrument.
- Wavelength resolution: By using a spectrometer in place of the discrete photodiodes and filters of AATS-14, 4STAR has potential to improve the accuracy of water vapor and ozone measurements, enable measurements of other gases (e.g., NO2) and improve accuracy of aerosol measurements via better aerosol-gas separation.
4STAR-Air made its first flights on the Battelle G-1 in September 2010, testing its Sun-tracking and spectroscopic abilities and obtaining airworthiness certification (See November 2010 presentation). In 2011, sky scanning and other capabilities will be added to 4STAR-Air, leading to a G-1 flight demonstration of its full science capability.
Above photos: show 4STAR-Air and 4STAR-Ground, along with data from 4STAR-Ground. Click on photos to enlarge.