Analysis of the Geopotential Anomalous Component at Brazilian Vertical Datum Region Based on the Imarui Lagoon System

Abstract

The region contiguous to the Brazilian Vertical Datum (BVD) lacks of observations and data required for realizing its connection with other vertical networks in the world as required for a Global Vertical Reference System (GVRS). A consistent positional and gravity data base in the region is a fundamental condition for realizing the future Vertical Datum SIRGAS (Sistema de Referencia Geocentrico para as Americas) – DVSIRGAS (Drewes et al., Vertical Reference System, IAG Symposia Series, Springer, Berlin. vol. 124, pp. 297–301, 2002). In the BVD region, placed in the Imbituba harbor, South Brazil, several benchmarks (BM’s) have been lost. In order to improve the distribution of data in this region, we conducted a study on the behavior of the system of three linked lagoons under influence of the ocean dynamics in the region. They cover about 20 × 30 km with a 140 km perimeter in the contiguous region of the BVD. The purpose was to use its mean level as an indicator of a natural equipotential surface close to the geoid (or quasi-geoid). A local geodetic network with about 200 points was established. In this network gravity and precise position with Global Positioning System (GPS) were observed. Some of these points are existing BM’s connected to the BVD. Three tide gauges that recorded the heights of the water level in the lagoons over a period of approximately 3 months were also employed. In this lagoon system, it was possible to determine an approximate equipotential surface from the mean lagoon level (MLL). Then, we determined the shift between the geopotential in the BVD and the lagoon system. Estimations coming from a global geopotential model allowed determination of a provisional value for the Sea Surface Topography (SST) in the BVD.