Friday, 7 June 2002
A new smart sun-tracking and sky-scanning platform for radiometric instruments
A new sun-tracking platform has been developed for angular positioning of instruments such as direct-beam sunphotometers, normal-incidence pyrheliometers, and shaded pyranometers. Movement is controlled by embedded solar ephemeris calculations (predictive tracking) and/or by feedback from a quadrant detector (active tracking), whichever is appropriate for prevailing conditions. The integration of both tracking mechanisms allows the platform to correct for reasonable misalignments which occur during setup or afterward; an optional embedded GPS receiver further automates this process.
In addition to sun-tracking, the platform can be programmed to scan the sky, moving to user-selectable or pre-determined positions, either relative to the sun or absolute. When optimized for smaller payloads, the movement can be much faster than that of previous trackers, making measurement of sky radiance distribution feasible.
We present an overview of the tracker's design, and analysis and simulation of its performance in a wide range of atmospheric conditions. We also show results obtained from operating it with a Yankee Environmental Systems SPUV-10 as the payload, and comparison with corresponding results from other trackers.