# New developments in aerosol measurements using stellar photometry

## TL;DR

This paper presents advanced methods for high-precision aerosol optical depth measurements using stellar photometry, leveraging data from the FRAM telescope and laboratory calibration to improve accuracy beyond 0.01.

## Contribution

It introduces novel calibration and analysis techniques that enhance the precision of aerosol measurements via stellar photometry in high-energy astrophysics.

## Key findings

- Achieved VAOD measurement precision approaching 0.01
- Developed calibration methods accounting for CCD non-linearity
- Demonstrated applicability with data from Pierre Auger and CTA sites

## Abstract

The idea of using stellar photometry for atmospheric monitoring for optical experiments in high-energy astrophysics is seemingly straightforward, but reaching high precision of the order of 0.01 in the determination of the vertical aerosol optical depth (VAOD) has proven difficult. Wide-field photometry over a large span of altitudes allows a fast determination of VAOD independently of the absolute calibration of the system, while providing this calibration as a useful by-product. Using several years of data taken by the FRAM (F/(Ph)otometric Robotic Atmospheric Monitor) telescope at the Pierre Auger Observatory in Argentina and about a year of data taken by a similar instrument deployed at the planned future Southern site of the Cherenkov Telescope Array in Chile, we have developed methods to improve the precision of this measurement technique towards and possibly beyond the 0.01 mark. Detailed laboratory measurements of the response of the whole system to both the spectrum and intensity of incoming light have proven indispensable in this analysis as the usual assumption of linearity of the CCD detectors is not valid anymore for the conditions of the observations.