Animprovedabsolutecalibrationtechnologybasedonindirectmeasurementswasdevelopedthroughtwoprobativeexperiments,theperformanceofwhichwasevaluatedbyapplyingtheapproachtoinsituseasurfaceheight(SSH)attheTianhengIsland(tidalgauge)andthesatellitenadir(GPSbuoy).UsingGeoid/MSS(meanseasurface)data,whichaccountedforaconstantoffsetbetweennadirandonshoretidalgaugewaterlevels,andTMD(tidalmodeldriver),whichcanceledoutthetime-varyingoffsets,nadirSSH(seasurfaceheight)couldbeindirectlyacquiredatanonshoretidalgaugeinsteadoffromdirectoffshoreobservation.TheapproachextrapolatedtheonshoreSSHouttotheoffshorenadirwithanaccuracyof(1.88±0.20)cmandastandarddeviationof3.3cm,whichsuggestedthattheapproachpresentedwasfeasibleinabsolutealtimetercalibration/validation(Cal/Val),andtheapproachenormouslyfacilitatedtheobtainingSSHfromtheoffshorenadir.
