  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.
