Solar Aureole Method - Atmospheric Almucantar and Limb Remote Sensing
Atmospheric aerosols can interact with incoming solar radiation, primarily through scattering processes; in doing so, they can directly redistribute solar energy. Aerosols can also have an indirect effect on the earth-atmosphere system, through ever-changing cloud formation in a circulation system of complex spatial and time scales. In these ways, aerosols play very important roles in atmospheric radiative transfer (ART), and profoundly affect the heat budget of the earthâ€™s climate system. Advancement in both data analysis and measurement techniques is essential to improve the understanding of atmospheric aerosol properties. The focus of the present work is on two distinct aerosol measurement techniques directly related to solar aureole features. One is the measurement technique referred to as Solar Aureole Almucantar Radiance Scan (SAARS), originally conceived by Dr. Alex E. S. Green. The other is the Solar Aureole Atmospheric Constant-Altitude Multi-Angle Limb Scattering System (ACAMALSS).
Several unique features of this work merit emphasis at this point:
(1) First, it demonstrates that all its complicated computations could be done by using a lap-top (MacBook Pro). Even though it took much longer to perform the calculations, it still yielded accurate results, thereby relegating a supercomputer to simply speeding up the calculations.
(2) Secondly, it shows that the Photographic Solar Aureole Method was an inexpensive method, affordable by even a high school student with a digital camera, to determine the columnar aerosol size-distribution (CASD) while the Sun is visible, thereby leading one to assume that, in principle, the Sunâ€™s aureole could be replaced by the Moonâ€™s aureole.
Other unique features of this work are as follows:
(1) It uses the Earthâ€™s spherically symmetric atmospheric model, instead of the often-used simplistic plane-parallel model, enabling the determination of the CASD using Almucantar scan radiance for all sun zenith angles.
(2) It is independent of the sensor (camera or imager) altitude; thus, it can be used from aboard ground-based, air-borne, and space-borne platforms.
(3) It can be used for accurately determining the non-terrestrial aerosol properties such as on the Moon, Mars, Asteroids, and other planetary bodies.
(4) Its double scattering calculations are an example of calculating higher orders of scattering to study the multiple scattering effects, that prevail when the atmospheric aerosol medium optical depth is greater than 0.3.
(5) Its retrieval of the CASD is independent of the aerosol complex refractive index.
(6) Finally, even though presently doable, this work leaves for the future the computation of polarization effects of radiation scattered by the aerosols to determine the shape of the particles.
Click to view the Table of Contents