Automated Sun Photometer Measurements

As part of a new effort we are now working on an automated sun tracking sun photometer. The system locates the sun in an image and controls two stepper motors to point a spectrometer at the sun. The figure below shows some recent Langley plot calibration measurements at the Mauna Loa observatory. Usually Langley plots are only carried out to air mass 5. In this case measurements were made from air mass 20 (near sunrise). The non-linear features are due to the earth's curvature and refraction. As a test of a new Monte Carlo radiation model we are working on, the sun photometer measurements were modeled. Aerosol layers were placed at 15-30 km height and also at 4-5 km height. Better agreement occurs when the aerosols are placed at lower altitudes. A new paper on the Monte Carlo model has been submitted for publication.