Instrumentation for comparing night sky quality and atmospheric conditions of CTA site candidates

TL;DR

This paper introduces ATMOSCOPE, a set of identical, cross-calibrated instruments designed to precisely compare atmospheric and sky conditions at potential CTA sites, enabling better site selection.

Contribution

Development and characterization of ATMOSCOPE, an autonomous multi-purpose weather sensor system for accurate site comparison in the CTA project.

Findings

ATMOSCOPE provides precise atmospheric data for site comparison.

The instruments enable cross-validation of satellite data.

ATMOSCOPE's performance was successfully characterized.

Abstract

Many atmospheric and climatic criteria have to be taken into account for the selection of a suitable site for the next generation of imaging air-shower Cherenkov telescopes, the "Cherenkov Telescope Array" CTA. Such data are not available with sufficient precision, thus a comparison of the proposed sites and final decision based on a comprehensive characterization is impossible. Identical cross-calibrated instruments have been developed which allow for precise comparison between sites, the cross-validation of existing data, and the ground-validation of satellite data. The site characterization work package of the CTA consortium opted to construct and deploy 9 copies of an autonomous multi-purpose weather sensor, incorporating an infrared cloud sensor, a newly developed sensor for measuring the light of the night sky, and an All-Sky-Camera, the whole referred to as Autonomous Tool for Measuring Observatory Site COnditions PrEcisely (ATMOSCOPE). We present here the hardware that was combined into the ATMOSCOPE and characterize its performance.