Ground-based sun photometers provide an important consistent global long-term aerosol data record that is used to better understand aerosol impact on climate, improve aerosol transport models and bound lidar-derived aerosol products. Since sun photometers only provide aerosol information during the day, even though there is scientific interest, there is very little information on aerosols at night. Innovative Imaging and Research proposes Angstrom, an affordable easily deployable multiband wide field of view (FOV) imaging star photometer that measures aerosol optical depth (AOD) and the Angstrom parameter across the night sky using stars. It can be used to augment traditional sun/lunar photometer networks and significantly improve atmospheric monitoring.
Angstrom applies state-of-the-art image processing techniques to imaging systems that make use of emerging high quantum efficiency, low read noise CMOS sensors and high-quality machine vision optics. Early simulations and test data suggest these types of imaging systems can acquire dim star fields at a relatively high signal-to-noise ratio to produce traditional sun/lunar photometer AOD and Angstrom parameter measurements using stars instead of the sun or moon.
Imaging star photometry acquires large regions of sky and can measure near-instantaneous spatial variability not possible with traditional narrow FOV photometers. By imaging multiple stars in a portion of sky covering a wide range of air mass or by continuously imaging stars moving through varying air mass, Angstrom can take advantage of traditional Langley calibration or multi-star methods.
Angstrom tracks stars though image processing, eliminating complex precision moving mechanisms. It also uses the relative positions of stars to determine its orientation simplifying upfront, installation and maintenance costs allowing it to be more easily deployed on ships, UAVs and fixed terrestrial locations where historically it has been difficult to obtain measurements.
Angstrom supports atmospheric studies by providing additional nighttime aerosol measurements to atmospheric models. It also supports Decadal Survey recommended ACCP and TEMPO satellite missions and is directly relevant to numerous field campaigns that measure and monitor aerosols. This is significant as aerosols have been identified as the largest contributor to climate model uncertainty. Angstrom data also assists scientists that require atmospherically corrected products from night imaging remote sensing instruments such as the VIIRS DNB.
Emerging remote sensing applications that require nighttime aerosol measurements include mapping artificial lights and estimating power usage, important economic measures as we emerge from COVID-19. Angstrom will be compatible with and complement the widely utilized Aeronet ground network of Cimel solar/lunar photometers to fill current nighttime data gaps to support these new applications.