As there was no dive on April 22, the 2023 Shakedown + EXPRESS: West Coast Exploration expedition took the opportunity to conduct mapping and other operations. This video provides a top-down look as the team launches the CTD (conductivity, temperature, and depth) instrument prior to conducting a "patch test" to calibrate the mapping sonars on NOAA Ship Okeanos Explorer. CTD data allow scientists to detect how the conductivity and temperature of water changes relative to depth. This information is important in acquiring sound velocity profiles of the water column to apply to multibeam sonar or other sonar data for accuracy of bathymetry measurements.