The CLEO spectrometer system: first results

We present first results from the newly developed remote sensing instrument CLEO (CLear Sky Observatory). CLEO consists of a commercially available CCD miniature spectrometer (Hamamatsu C10082CAH) and foreoptics to measure the global and diffuse solar irradiance. The irradiance is measured through a teflon diffuser. The diffuse irradiance is obtained moving a 180° metal band in the optical path to block the solar direct beam. CLEO measures simultaneously UV and Visible radiation from 163nm to 845nm, in steps of 0.3nm with a resolution of 1nm. The spectrometer is temperature controlled to 10°C to stabilize its optical properties. The dark count is frequently measured using a motorized four positions filterwheel with an opaque disc at one position that acts as a shutter used to block the light input. The system automatically adjusts the integration time to optimize the signal-to-noise. Another difference to previous shadowband instruments is that CLEO moves the shadowband over the whole hemisphere instead of just a few positions in and around the sun's direction. This has the advantage of simplifying the installation procedure and solves the problem with the shadow only partially covering the diffuser due to instrument misalignment.