STRAW (STRings for Absorption length in Water): pathfinder for a neutrino telescope in the deep Pacific Ocean

We report about the design and the initial performances of the pathfinder mission for a possible large scale neutrino telescope named STRings for Absorption length in Water (STRAW). In June 2018 STRAW has been deployed at the Cascadia Basin site operated by Ocean Network Canada and has been collecting data since then. At a depth of about 2600 meters, the two STRAW 120 meters tall mooring lines are instrumented by three Precision Optical Calibration Modules (POCAM) and five Digital Optical Sensors (sDOM). We describe the instrumentation deployed and first light in the Pacific Ocean.