The Method of Height Datum Transference Across Sea Based on Trigonometric Levelling

Trigonometric levelling precision is mainly affected by the atmospheric vertical refraction.Laid by quadrilateral,simultaneous and reciprocal observation can eliminate errors caused by atmospheric vertical refraction and improve the precision of the difference of elevation.The robust estimation and least squares adjustment results of the measured data of Huangdao show that for the sea-crossing distance less than 10km,the precision of the normal height transference based on trigonometric levelling which is 2mm/km can fulfill the precision request of second order levelling.Sea-crossing difference of elevation based on trigonometric levelling comparing with the direct observation by geometric levelling and the calculations of EGM08 model,the difference between them is less than 3mm/km,and comparing with the astrogravimetric levelling,the difference is less than 5mm/km.