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

Gruber, Thomas; Ågren, Jonas; Angermann, D; Ellmann, Artu; Engfeldt, Andreas; Gisinger, Christoph; Jaworski, Leszek; Marila, Simo; Nastula, Jolanta; Nilfouroushan, Faramarz; Oikonomidou, Xanthi; Poutanen, Markku; Saari, Timo; Schlaak, Marius; Swiatek, Anna; Varbla, Sander; Zdunek, Ryszard

doi:10.3390/rs12223747

Cited by 7 publications

(16 citation statements)

References 46 publications

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“…We also observe an apparent shift between ascending (negative ∆α) and descending (positive ∆α) tracks, which is highest for transponder 141 (>0.5 m) and smallest for transponder 148 (<0.1 m). Although [1] report an incidence angle dependence of the transponder's internal range delay, our results could not confirm this. It is interesting to note the completely different range delay behavior between units 141 and 148, despite that these are separated only 46.5 m. For standard deviations of the range coordinate differences, even if the uncertainties of GNSS measurements, orbit state vectors, and atmospheric signal delay corrections are considered, we still reach at least a factor 2 worse results.…”

Section: Absolute Positioningcontrasting

confidence: 98%

“…R ADAR transponders are active electronic devices that receive a radar signal, amplify it, and transmit it back to its source, such as a satellite carrying a Synthetic Aperture Radar (SAR) antenna. They can serve as a compact alternative to corner reflectors (CR) for precise SAR positioning [1], [2], SAR interferometry (InSAR), deformation monitoring over areas with few natural coherent scatterers [3], InSAR datum connection, and geodetic data integration to provide an absolute reference to the inherently relative InSAR measurements [4].…”

Section: Introductionmentioning

confidence: 99%

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On the Efficacy of Compact Radar Transponders for InSAR Geodesy: Results of Multiyear Field Tests

Czikhardt

Marel²,

Papčo

et al. 2022

IEEE Trans. Geosci. Remote Sensing

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Compact and low-cost radar transponders are an attractive alternative to corner reflectors (CR) for SAR interferometric (InSAR) deformation monitoring, datum connection, and geodetic data integration. Recently, such transponders have become commercially available for C-band sensors, which poses relevant questions on their characteristics in terms of radiometric, geometric, and phase stability. Especially for extended time series and for high-precision geodetic applications, the impact of secular or seasonal effects, such as variations in temperature and humidity, has yet to be proven. Here we address these challenges using a multitude of short baseline experiments with four transponders and six corner reflectors deployed at test sites in the Netherlands and Slovakia. Combined together, we analyzed 980 transponder measurements in Sentinel-1 time series to a maximum extent of 21 months. We find an average Radar Cross Section (RCS) of over 42 dBm 2 within a range of up to 15 degrees of elevation misalignment, which is comparable to a triangular trihedral corner reflector with a leg length of 2.0 m. Its RCS shows temporal variations of 0.3-0.7 dBm 2 (standard deviation) which is partially correlated with surface temperature changes. The precision of the InSAR phase double-differences over short baselines between a transponder and a stable reference corner reflectors is found to be 0.5-1.2 mm (one sigma). We observe a correlation with surface temperature, leading to seasonal variations of up to ±3 mm, which should be modeled and corrected for in high precision InSAR applications. For precise SAR positioning, we observe antenna-specific constant internal electronic delays of 1.2-2.1 m in slant-range, i.e., within the range resolution of the Sentinel-1 IW product, with a temporal variability of less than 20 cm. Comparing similar transponders from the same series, we observe distinct differences in performance. Our main conclusion is that these characteristics are favorable for a wide range of geodetic applications. For particular demanding applications, individual calibration of single devices is strongly recommended.

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Section: Absolute Positioningcontrasting

confidence: 98%

Section: Introductionmentioning

confidence: 99%

On the Efficacy of Compact Radar Transponders for InSAR Geodesy: Results of Multiyear Field Tests

Czikhardt

Marel²,

Papčo

et al. 2022

IEEE Trans. Geosci. Remote Sensing

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“…Conversely, inconsistent use of reference epoch (e.g., terms DT RSL (ϕ, λ, t, t 0 ) and VLM leveled (ϕ, λ)•(t − t A ) are employed together) would produce absolute mean DT estimates that do not refer to the same equipotential reference surface, potentially ensuing in misinterpretation of the results. In case a common reference epoch does not exist, it should be established, but similar use of TG data in a common system also requires that zero values of TGs refer to the same equipotential surface at an established reference epoch (e.g., see [59] for a potential method to connect TG stations to a common system). On the other hand, if the objective is to study sea level trends, adopting a common system may not be beneficial (i.e., consistent use of reference epoch is not mandatory).…”

Section: Tide Gauge Time Series In Relation To the Baltic Sea Chart D...mentioning

confidence: 99%

Treatment of Tide Gauge Time Series and Marine GNSS Measurements for Vertical Land Motion with Relevance to the Implementation of the Baltic Sea Chart Datum 2000

et al. 2022

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Tide gauge (TG) time series and GNSS measurements have become standard datasets for various scientific and practical applications. However, the TG and geodetic networks in the Baltic Sea region are deforming due to vertical land motion (VLM), the primary cause of which is the glacial isostatic adjustment. Consequently, a correction for VLM, either obtained from a suitable VLM model or by utilizing space-geodetic techniques, must be applied to ensure compatibility of various data sources. It is common to consider the VLM rate relative to an arbitrary reference epoch, but this also yields that the resulting datasets may not be directly comparable. The common height reference, Baltic Sea Chart Datum 2000 (BSCD2000), has been initiated to facilitate the effective use of GNSS methods for accurate navigation and offshore surveying. The BSCD2000 agrees with the current national height realizations of the Baltic Sea countries. As TGs managed by national authorities are rigorously connected to the national height systems, the TG data can also be used in a common system. Hence, this contribution aims to review the treatment of TG time series for VLM and outline potential error sources for utilizing TG data relative to a common reference. Similar consideration is given for marine GNSS measurements that likewise require VLM correction for some marine applications (such as validating marine geoid models). The described principles are illustrated by analyzing and discussing numerical examples. These include investigations of TG time series and validation of shipborne GNSS determined sea surface heights. The latter employs a high-resolution geoid model and hydrodynamic model-based dynamic topography, which is linked to the height reference using VLM corrected TG data. Validation of the presented VLM corrected marine GNSS measurements yields a 1.7 cm standard deviation and –2.7 cm mean residual. The estimates are 1.9 cm and –10.2 cm, respectively, by neglecting VLM correction. The inclusion of VLM correction thus demonstrates significant improvement toward data consistency. Although the focus is on the Baltic Sea region, the principles described here are also applicable elsewhere.

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“…If all this is considered carefully, one could connect tide gauges across oceans for unifying height systems and for observing the sea level in an absolute sense with respect to a global equipotential surface. A detailed description of the components of the observing system, the scientific challenges to be addressed for combining the various observations and references to related literature is provided in our first related paper [1] and is not repeated here.…”

Section: Introductionmentioning

confidence: 99%

“…These ECRs are capable to amplify C-Band SAR signals received from the Sentinel-1 satellites and therefore are well-defined persistent scatters to be used for geodetic positioning. All details about the individual stations and the conducted experiments are described in [1]. 4.…”

Section: Introductionmentioning

confidence: 99%

Geodetic SAR for Height System Unification and Sea Level Research—Results in the Baltic Sea Test Network

et al. 2022

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Coastal sea level is observed at tide gauge stations, which usually also serve as height reference stations for national networks. One of the main issues with using tide gauge data for sea level research is that only a few stations are connected to permanent GNSS stations needed to correct for vertical land motion. As a new observation technique, absolute positioning by SAR using off the shelf active radar transponders can be installed instead. SAR data for the year 2020 are collected at 12 stations in the Baltic Sea area, which are co-located to tide gauges or permanent GNSS stations. From the SAR data, 3D coordinates are estimated and jointly analyzed with GNSS data, tide gauge records and regional geoid height estimates. The obtained results are promising but also exhibit some problems related to the electronic transponders and their performance. At co-located GNSS stations, the estimated ellipsoidal heights agree in a range between about 2 and 50 cm for both observation systems. From the results, it can be identified that, most likely, variable systematic electronic instrument delays are the main reason, and that each transponder instrument needs to be calibrated individually. Nevertheless, the project provides a valuable data set, which offers the possibility of enhancing methods and procedures in order to develop a geodetic SAR positioning technique towards operability.

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

Cited by 7 publications

References 46 publications

On the Efficacy of Compact Radar Transponders for InSAR Geodesy: Results of Multiyear Field Tests

On the Efficacy of Compact Radar Transponders for InSAR Geodesy: Results of Multiyear Field Tests

Treatment of Tide Gauge Time Series and Marine GNSS Measurements for Vertical Land Motion with Relevance to the Implementation of the Baltic Sea Chart Datum 2000

Geodetic SAR for Height System Unification and Sea Level Research—Results in the Baltic Sea Test Network

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