A New Method for Aerosol Measurement using Wide-field Photometry

TL;DR

This paper introduces a novel wide-field photometry method for measuring vertical aerosol optical depth during clear nights, achieving high precision without light pollution, suitable for astronomical sites.

Contribution

The paper presents a new, precise, and light-pollution-free method for aerosol measurement using a CCD camera and wide-field imaging, applicable at astronomical sites.

Findings

Achieves VAOD measurement precision better than 0.008 optical depths.

Demonstrates good agreement with Sun/Moon Photometer measurements.

Suitable for use at sites with existing astronomical instruments.

Abstract

We present a new method to measure the vertical aerosol optical depth (VAOD) during clear nights using a wide-field imager - a CCD camera with a photographic lens on an equatorial mount. A series of 30-second exposures taken at different altitudes above the horizon can be used to measure the VAOD with a precision better than 0.008 optical depths within a few minutes. Such a measurement does not produce any light and is thus suitable for use at sites where other astronomical instruments are located. The precision of the VAOD measurement depends on laboratory calibration of spectral properties of the system and of the response of the camera electronics to varying illumination levels, as well as careful considerations of details of stellar photometry and modelling of the dependence of measured stellar fluxes star color and position within the field of view. The results obtained with robotic setups at the future sites of the Cherenkov Telescope Array show good internal consistency and agreement with the simultaneous measurements from a Sun/Moon Photometer located at the same site.