After successfully designing, building, testing and deploying the first pathfinder STRAW (STRings for Absorption length in Water) for a neutrino telescope in the northern Pacific Ocean, the first results of the ongoing measurements of the optical properties of the deep sea are encouraging. To complete the assessment of the site and experiment with a longer mooring line, STRAW-b, a second pathfinder experiment has been conceived. STRAW-b is composed of ten modules distributed over a 500 meter vertical electrical-optical cable and will host two spectrophotometers to study the emission spectrum of the ambient light, a lidar to investigate the scattering effect in water, a muon chamber and a set of cameras.
Construction of STRAW-b was finalized at the TUM physics department in winter 2020. After shipping the entire hardware to Vancouver island, the mounted line was tested in the surface pool of ONC. The deployment of STRAW-b in the Cascadia basin close to the location of STRAW was completed in September 2020.