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.