Seismic Marine Positioning Equipment posEquipType extPosEquipType refinedPosEquipType refinedExtPosEquipType POSC 1.0 tail buoy A buoy with a radar reflector or other locator device that shows the position of the end of the streamer. vessel antenna The antenna on the seismic vessel, used as a reference point. depth controller A device on the streamer that insures proper towing depth. time break sensor A sensor which records the first arrival of a seismic wave that has travelled through the water. uphole sensor A receiver placed near the surface shot hole location, whose purpose is to record the first time arrival of the seismic source.