Abstract
Traditionally, sea level is observed at tide gauge stations, which usually also serve as height reference stations for national leveling networks and therefore define a height system of a country. One of the main deficiencies to use tide gauge data for geodetic sea level research and height systems unification is that only a few stations are connected to the geometric network of a country by operating permanent GNSS receivers next to the tide gauge. As a new observation technique, absolute positioning by SAR using active transponders on ground can fill this gap by systematically observing time series of geometric heights at tide gauge stations. By additionally knowing the tide gauge geoid heights in a global height reference frame, one can finally obtain absolute sea level heights at each tide gauge. With this information the impact of climate change on the sea level can be quantified in an absolute manner and height systems can be connected across the oceans. First results from applying this technique at selected tide gauges at the Baltic coasts are promising but also exhibit some problems related to the new technique. The paper presents the concept of using the new observation type in an integrated sea level observing system and provides some early results for SAR positioning in the Baltic sea area.
Highlights
Sea level is observed at tide gauge stations, which usually serve as height reference stations for national leveling networks and define a height system of a country
In order to investigate the feasibility of using active SAR transponders for geometric positioning and to use these observations for height system unification and absolute sea level determination, some tide gauge stations in the Baltic Sea area located in different countries were selected as test cases
These transponders often to five pass geometries and two satellites (Sentinel-1A and Sentinel-1B), depending on the acquisition are called Electronic Corner Reflectors (ECR) in order to distinguish them from passive corner reflectors plan [26]
Summary
Over the open sea oceans, altimetry is the main source instantaneous providing the sea absolute sea. Sea level is usually observed with tide gauges delivering instantaneous sea surface heights relative to a zero marker of the tide gauge station [5,6]. For a long-term analysis and for the determination of absolute height changes with respect to a reference height, one needs to know if the zero marker of the station is stable or undergoes changes. It becomes obvious that for fully consistent and absolute sea level observations at the coasts, several quantities determined by different means need to be combined in a consistent reference system [11] These quantities are the tide gauge observations relative to a zero marker, the ellipsoidal heights with respect to a geometric reference system, and the physical heights referring to a physical reference system
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