identify the baseline/be baseline node in identify the reference/be the reference node in defined for/utilize be a property of/have a property of have the time of/be the time for be a property of/have a property of identify the observing/be observing facility in be a property of/have a property of be part of/be assembly of facility reference point observation definition position sensor facility positioning measurement activity pty event observation pty sensor calibration pty source start time pty transient property seismic facility node seismic geometry set earth surface point