Langley Calibration Analysis of Solar Spectroradiometric Measurements: Spectral Aerosol Optical Thickness Retrievals

• Main Authors: Loftus, Adrian M., Pantina, Peter, Holben, Brent N., Swap, Robert J., Abuhassan, Nader, Butler, James J., Dimov, Alexander, Tsay, Si-Chee, Herman, Jay R., Jeong, Ukkyo
• Format: Other/Unknown Material
• Language: unknown
• Published: 2018
• Subjects: Earth Resources and Remote Sensing; Aerosol Robotic Network
• Online Access: http://hdl.handle.net/2060/20180003147

Aerosol optical thickness (tau(aer))) is a fundamental parameter for analyzing aerosol loading and associated radiative effects. Tau(aer) can constrain many inversion algorithms using passive/active sensor measurements to retrieve other aerosol properties and/or the abundance of trace gases. In the next wave of spectroradiometric observations from geostationary platforms, we envision that a strategically distributed network of robust, well-calibrated ground-based spectroradiometers will comprehensively complement spaceborne measurements in spectral and temporal domains. Spectral tau(aer) can be accurately obtained from direct-Sun measurements based on the Langley calibration method, which allows for the analysis of distinct spectral features of the calibration results. In this study, we present a spectral tau(aer) retrieval algorithm for an in-house developed, field deployable spectroradiometer instrument covering wavelengths from ultraviolet to near infrared (UV-Vis-NIR). The spectral total optical thickness obtained from the Langley calibration method is partitioned into molecular and particulate components by utilizing a least-squares method. The resulting high temporal-resolution tau(aer) and Angstrom Exponent can be used effectively for cloud screening. The new algorithm was applied to months-long measurements acquired from the rooftop at NASA Goddard Space Flight Center's Building 33. The retrieved tau(aer) demonstrated excellent agreement with those from well-calibrated Aerosol Robotic Network (AERONET) sunphotometers at all overlapping wavelengths (correlation coefficients higher than 0.98). In addition, empirical stray light corrections considerably improved tau(aer) retrievals at short wavelengths in the UV. The continuous spectrum of tau(aer) from UV-Vis-NIR spectroradiometers is expected to provide more informative constraints for retrieval of additional aerosol properties such as refractive indices, size, and bulk vertical distribution.