Long Term Geodetic Monitoring Using Active C-Band Radar Transponders And Sentinel-1 - First Results

Reliable and accurate long term geodetic monitoring with SAR requires the installation of either passive corner reflectors or, alternatively smaller active devices. We report our first results using novel off-the-shelf transponders or electronic corner reflectors (ECRs) for geodetic measurements with Sentinel-1 C-band Synthetic Aperture Radar (SAR) data. For this purpose we set up a triangular arrangement consisting of one trihedral corner reflector and two active ECRs at the campus of German Aerospace Center (DLR) in Oberpfaffenhofen, Germany. We describe the practical aspects of such ECRs as well as first radiometric characteristics. Moreover, we present geometric accuracy numbers derived from imaging geodesy, i.e. absolute radargrammetric positioning, as well as from interferometric phase measurements

Geodetic SAR for Height System Unification and Sea Level Research—Observation Concept and Preliminary Results in the Baltic Sea

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

Signal-in-Space Range Analysis for Navigation Satellite Systems

The signal-in-space range error (SISRE) constitutes a key performance indicator for all navigation satellite systems. Within the scope of this thesis, specific aspects of SISRE monitoring are addressed. The implications of inconsistencies and errors affecting the broadcast ephemeris data of the International GNSS Service (IGS) are discussed, and solutions to identified receiver-specific problems are suggested. The impact of systematic clock biases observed between the broadcast and precise clock solutions of GLONASS is examined next and satellite-specific clock corrections are derived with the objective of improving the overall GLONASS SISRE budget. Clock offsets up to 2.8 m are demonstrated, with a 0.60 m uncertainty introduced by inconsistencies between the precise clock solutions of the IGS analysis centers. An application for the estimation of observed range deviations (ORDs) in a multi-GNSS framework is finally developed, and the derived ORDs are compared against representative SISRE values from comparisons between broadcast and precise ephemerides. Overall, the compatibility of the results provides evidence of the importance of the ORDs in SISRE monitoring

First Experiences with Active C-Band Radar Reflectors and SENTINEL-1

We report our first results with Sentinel-1 Interferometric Wide Swath (IW) data using novel off-the-shelf electronic corner reflectors (ECRs) for geometric measurements with C-band Synthetic Aperture Radar (SAR). At the German Aerospace Center (DLR) campus in Oberpfaffenhofen, we set up an arrangement consisting of two trihedral corner reflector and two active ECRs. We describe the practical aspects of such ECRs as well as first radiometric characteristics. Moreover, we present geometric accuracy as derived from imaging geodesy, i.e. absolute radargrammetric positioning in 2D and 3D, as well as interferometric phase measurement