Fraction of clear skies above astronomical sites: a new analysis from the GOES12 satellite

TL;DR

This paper introduces a new homogeneous satellite-based methodology to quantify clear and stable nights at various astronomical sites, providing consistent and comparable data for observational planning.

Contribution

It presents a novel approach using GOES12 satellite infrared data with enhanced analysis techniques for assessing clear nights across different sites.

Findings

High percentage of clear nights at Paranal (88%) and Tolonchar (86.5%)

Stable nights are fewer than clear nights by 2% to 20% depending on the site

Methodology reduces noise and distinguishes clear from stable nights effectively

Abstract

Comparing the number of clear nights (cloud free) available for astronomical observations is a critical task because it should be based on homogeneous methodologies. Current data are mainly based on different judgements based on observer logbooks or on different instruments. In this paper we present a new homogeneous methodology on very different astronomical sites for modern optical astronomy, in order to quantify the available night time fraction. The data are extracted from night time GOES12 satellite infrared images and compared with ground based conditions when available. In this analysis we introduce a wider average matrix and 3-Bands correlation in order to reduce the noise and to distinguish between clear and stable nights. Temporal data are used for the classification. In the time interval 2007-2008 we found that the percentage of the satellite clear nights is 88% at Paranal, 76% at La Silla, 72.5% at La Palma, 59% at Mt. Graham and 86.5% at Tolonchar. The correlation analysis of the three GOES12 infrared bands B3, B4 and B6 indicates that the fraction of the stable nights is lower by 2% to 20% depending on the site.