Data quality monitoring in the presence of aerosols and other adverse atmospheric conditions with H.E.S.S

TL;DR

This paper introduces the Cherenkov transparency coefficient, a new atmospheric monitoring metric for H.E.S.S. that detects long-term atmospheric transparency changes using Cherenkov data, improving data quality assessment under adverse conditions.

Contribution

The paper presents the Cherenkov transparency coefficient, a novel, hardware-independent atmospheric monitoring tool derived from Cherenkov data, correlated with satellite measurements for better atmospheric condition assessment.

Findings

Cherenkov transparency coefficient effectively measures atmospheric transparency changes.

It shows positive correlation with MISR satellite measurements.

The method enhances data quality control in Cherenkov telescope observations.

Abstract

Cherenkov telescope experiments, such as H.E.S.S., have been very successful in astronomical observations in the very-high-energy (VHE; E $>$ 100 GeV) regime. As an integral part of the detector, such experiments use Earth's atmosphere as a calorimeter. For the calibration and energy determination, a standard model atmosphere is assumed. Deviations of the real atmosphere from the model may therefore lead to an energy misreconstruction of primary gamma rays. To guarantee satisfactory data quality with respect to difficult atmospheric conditions, several atmospheric data quality criteria are implemented in the H.E.S.S. software. These quantities are sensitive to clouds and aerosols. Here, the Cherenkov transparency coefficient will be presented. It is a new monitoring quantity that is able to measure long-term changes in the atmospheric transparency. The Cherenkov transparency coefficient derives exclusively from Cherenkov data and is quite hardware-independent. Furthermore, its positive correlation with independent satellite measurements, performed by the Multi-angle Imaging SpectroRadiometer (MISR), will be presented.