A camera system for real-time optical calibration of water-based neutrino telescopes

TL;DR

This paper presents a real-time optical calibration system using CMOS cameras for deep-sea neutrino telescopes, demonstrated in a successful deployment in the Pacific Ocean to measure seawater optical properties.

Contribution

Introduces a novel CMOS camera system with rapid processing algorithms for real-time calibration in large water-based neutrino detectors, validated through a deep-sea deployment.

Findings

Successful deployment at 3420 meters depth in the Pacific Ocean

Captured 3000 images in 30 minutes for calibration

Measured seawater attenuation and absorption lengths at three wavelengths

Abstract

Calibrating the optical properties within the detection medium of a neutrino telescope is crucial for determining its angular resolution and energy scale. For the next generation of neutrino telescopes planned to be constructed in deep water, such as the TRopIcal DEep-sea Neutrino Telescope (TRIDENT), there are additional challenges due to the dynamic nature and potential non-uniformity of the water medium. This necessitates a real-time optical calibration system distributed throughout the large detector array. This study introduces a custom-designed CMOS camera system equipped with rapid image processing algorithms, providing a real-time optical calibration method for TRIDENT and other similar projects worldwide. In September 2021, the TRIDENT Pathfinder experiment (TRIDENT Explorer, T-REX for short) successfully deployed this camera system in the West Pacific Ocean at a depth of 3420 meters. Within 30 minutes, about 3000 images of the T-REX light source were captured, allowing for the in-situ measurement of seawater attenuation and absorption lengths under three wavelengths. This deep-sea experiment for the first time showcased a technical demonstration of a functioning camera calibration system in a dynamic neutrino telescope site, solidifying a substantial part of the calibration strategies for the future TRIDENT project.