. ▁Because ▁of ▁the ▁nature ▁of ▁angle ▁measurement , ▁the ▁accuracy ▁d eter ior ates ▁with ▁increasing ▁water ▁depth . ▁Long ▁base ▁line , ▁L BL . ▁This ▁consists ▁of ▁an ▁array ▁of ▁at ▁least ▁three ▁trans pond ers . ▁The ▁initial ▁position ▁of ▁the ▁trans pond ers ▁is ▁determined ▁by ▁USB L ▁and / ▁or ▁by ▁meas uring ▁the ▁bas elines ▁between ▁the ▁trans pond ers . ▁Once ▁that ▁is ▁done , ▁only ▁the ▁ranges ▁to ▁the ▁trans pond ers ▁need ▁to ▁be ▁measured ▁to ▁determine ▁a ▁relative ▁position . ▁The ▁position ▁should ▁theoret ically ▁be ▁located ▁at ▁the ▁intersection ▁of ▁imag inary ▁spher es , ▁one ▁around ▁each ▁trans ponder , ▁with ▁a ▁radius ▁equal ▁to ▁the ▁time ▁between ▁transmission ▁and ▁reception ▁multip lied ▁by ▁the ▁speed ▁of ▁sound ▁through ▁water . ▁Because ▁angle ▁measurement ▁is ▁not ▁necessary , ▁the ▁accuracy ▁in ▁large ▁water ▁depth s ▁is ▁better ▁than ▁USB L . ▁Short ▁bas eline , ▁S BL . ▁This ▁works ▁with ▁an ▁array ▁of ▁trans du cers ▁in ▁the ▁ship ' s ▁h ull . ▁These ▁determine ▁their ▁position ▁to ▁a ▁trans ponder , ▁so ▁a ▁solution ▁is ▁found ▁in ▁the ▁same ▁way ▁as ▁with ▁L BL . ▁As ▁the ▁array ▁is ▁located ▁on ▁the ▁ship , ▁it ▁needs ▁to ▁be ▁corrected ▁for ▁roll ▁and ▁pitch . ▁R iser ▁Ang le ▁Mon itor ing . ▁On ▁dr ill ships , ▁ris er ▁angle ▁monitoring ▁can ▁be ▁fed ▁into ▁the ▁D P ▁system . ▁It ▁may ▁be ▁an ▁elect rical ▁incl