Development of method for adjusting the national I and II orders vertical network based on the local geoid Hon Dau

he paper concentrates on researching results in building of method and software VNAOLG-VIGAC (Vertical Network Adjustment On Local Geoid - Vietnam Institute of Geodesy And Cartography) for adjustment of national first, second orders vertical network bassed on local geoid Hon Dau. Main results consist of researching method for conversion of a measured geometric height differences from mean tide system to zero tide sysstem; construction of method of transformation of the measured geometric height differences into a geopotential differences; method of calculation of weights of the geopotential differences on first, second orders levelling lines; method of detection of outlier levelling lines and methods of correction of results of the national first, second orders vertical network adjustment on case of change of observables (adding of some new levelling lines, restoring of some lost benchmarks) by principle: Based on present results of the national first, second orders vertical network adjustment without readjustment of the whole network. The experiment results of software VNAOLG-VIGAC for the national first, second orders vertical network adjustment on the Vietnam Northern region with 143 first, second orders benchmarks, 17 first order levelling lines, 5 second order levelling lines showed that RMS unit weight is equal to ± 1.185 kGal.mm/1km, maximal RMS of adjusted geopotential reaches ± 0,021 kGal.m. Adjustment of the national first, second orders vertical network adjustment on the Vietnam Northern region in zero tide system leads to maximal offset of normal heights at level of ± 7 cm in comparison with those of in mean tide system.