The Copernicus Sentinel-6 mission: Enhanced continuity of satellite sea level measurements from space

Donlon, Craig; Cullen, R.; Giulicchi, Luisella; Vuilleumier, Pierrik; Francis, C. R.; Kuschnerus, Mieke; Simpson, William M.; Bouridah, Abderrazak; Caleno, M.; Bertoni, Roberta; Rancaño, J.; Pourier, Eric; Hyslop, Andrew; Mulcahy, James; Knockaert, Robert; Hunter, C.A.; Webb, Alan; Fornari, Marco; Vaze, Parag; Brown, Shannon; Willis, J. K.; Desai, S. D.; Desjonquères, Jean-Damien; Scharroo, Remko; Martín-Puig, Cristina; Leuliette, E. W.; Egido, Alejandro; Smith, Walter H. F.; Bonnefond, Pascal; Gac, Sophie Le; Picot, Nicolas; Tavernier, G.

doi:10.1016/j.rse.2021.112395

Cited by 95 publications

(52 citation statements)

References 114 publications

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“…Sentinel-6 is a multi-national satellite mission aiming to provide continuity of service for sea surface altimetry in the third decade of the current century (Scharroo et al 2016;Donlon et al 2021). It builds on the legacy of the TO-PEX/Poseidon and Jason-1/-2/-3 missions, and is therefore also known as Jason Continuity of Service (CS) mission.…”

Section: Introductionmentioning

confidence: 99%

“…It builds on the legacy of the TO-PEX/Poseidon and Jason-1/-2/-3 missions, and is therefore also known as Jason Continuity of Service (CS) mission. The prime instrument is a Poseidon-4 Ku/C-band altimeter (Cullen and Francis 2014;Donlon et al 2021), which offers both low-and high-resolution modes and represents a major evolution over the Poseidon-3 instruments of Jason-2 and -3. Using two frequencies, ionospheric path delays in the altimeter measurements can be compensated and the total electron content below the spacecraft can be measured.…”

Section: Introductionmentioning

confidence: 99%

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Sentinel-6A precise orbit determination using a combined GPS/Galileo receiver

Montenbruck

Hackel

Wermuth

et al. 2021

J Geod

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The Sentinel-6 (or Jason-CS) altimetry mission provides a long-term extension of the Topex and Jason-1/2/3 missions for ocean surface topography monitoring. Analysis of altimeter data relies on highly-accurate knowledge of the orbital position and requires radial RMS orbit errors of less than 1.5 cm. For precise orbit determination (POD), the Sentinel-6A spacecraft is equipped with a dual-constellation GNSS receiver. We present the results of Sentinel-6A POD solutions for the first 6 months since launch and demonstrate a 1-cm consistency of ambiguity-fixed GPS-only and Galileo-only solutions with the dual-constellation product. A similar performance (1.3 cm 3D RMS) is achieved in the comparison of kinematic and reduced-dynamic orbits. While Galileo measurements exhibit 30–50% smaller RMS errors than those of GPS, the POD benefits most from the availability of an increased number of satellites in the combined dual-frequency solution. Considering obvious uncertainties in the pre-mission calibration of the GNSS receiver antenna, an independent inflight calibration of the phase centers for GPS and Galileo signal frequencies is required. As such, Galileo observations cannot provide independent scale information and the estimated orbital height is ultimately driven by the employed forces models and knowledge of the center-of-mass location within the spacecraft. Using satellite laser ranging (SLR) from selected high-performance stations, a better than 1 cm RMS consistency of SLR normal points with the GNSS-based orbits is obtained, which further improves to 6 mm RMS when adjusting site-specific corrections to station positions and ranging biases. For the radial orbit component, a bias of less than 1 mm is found from the SLR analysis relative to the mean height of 13 high-performance SLR stations. Overall, the reduced-dynamic orbit determination based on GPS and Galileo tracking is considered to readily meet the altimetry-related Sentinel-6 mission needs for RMS height errors of less than 1.5 cm.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sentinel-6A precise orbit determination using a combined GPS/Galileo receiver

Montenbruck

Hackel

Wermuth

et al. 2021

J Geod

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“…For the analysis performed in this paper, the only consequence of this feature is implicitly found in the waveforms computed over an ocean, which necessarily include contributions from these nearby replicas. Such a feature is minimized in Sentinel-6 since its radar altimeter operates in interleaved mode and the only replicas are due to the fact that after every 64-pulse burst of Ku-band pulses, there is a 1 calibration pulse followed by a 1 C-band pulse for ionospheric corrections [7], inducing minor replicas spaced by roughly 300 m in the along-track direction.…”

Section: Resultsmentioning

confidence: 99%

“…From the European side, isardSAT has addressed mainly the objective (O2.5) by developing and implementing a Fully-Focussed SAR processor in the time domain [10] and adapting it to two radar altimeters: Sentinel-3 [6] and Sentinel-6 [7]. The fact that, in Sentinel-3, the range compression is performed through deramp on-receive while in Sentinel-6 it is performed via matched filtering requires some tuning when adapting the processors: indeed, the Residual Video Phase correction [10] is only required for Sentinel-3 and must be avoided for Sentinel-6.…”

Section: Research Approachmentioning

confidence: 99%

“…The European group has focussed on the implementation of new SAR altimetry processing techniques. As of today, data from European radar altimeters such as CryoSat-2 [5], Sentinel-3 [6] and Sentinel-6 [7] are operationally processed by means of SAR-based Delay-Doppler (DD) processing techniques [8], which present a limited along-track resolution to around 300 m due to the fact that they do not perform a full coherent combination of echoes. Indeed, in DD processing, the received echoes are only recombined coherently within a pulse burst, while the combination of echoes from all the bursts within the synthetic aperture is performed incoherently [8,9].…”

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confidence: 99%

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Results of the Dragon 4 Project on New Ocean Remote Sensing Data for Operational Applications

et al. 2021

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This paper provides an overview of the Dragon 4 project dealing with operational monitoring of sea ice and sea surface salinity (SSS) and new product developments for altimetry data. To improve sea ice thickness retrieval, a new method was developed to match the Cryosat-2 radar waveform. Additionally, an automated sea ice drift detection scheme was developed and tested on Sentinel-1 data, and the sea ice drifty capability of Gaofen-4 geostationary optical data was evaluated. A second topic included implementation and validation of a prototype of a Fully-Focussed SAR processor adapted for Sentinel-3 and Sentinel-6 altimeters and evaluation of its performance with Sentinel-3 data over the Yellow Sea; the assessment of sea surface height (SSH), significant wave height (SWH), and wind speed measurements using different altimeters and CFOSAT SWIM; and the fusion of SSH measurements in mapping sea level anomaly (SLA) data to detect mesoscale eddies. Thirdly, the investigations on the retrieval of SSS include simulations to analyse the performances of the Chinese payload configurations of the Interferometric Microwave Radiometer and the Microwave Imager Combined Active and Passive, SSS retrieval under rain conditions, and the combination of active and passive microwave to study extreme winds.

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Benefits of Fully Focused SAR Altimetry to Coastal Wave Height Estimates: A Case Study in the North Sea

Schlembach

Ehlers²,

Kleinherenbrink³

et al. 2023

Preprint

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Estimating the three geophysical variables significant wave height (SWH), sea surface height, and wind speed from satellite altimetry continues to be challenging in the coastal zone because the received radar echoes exhibit significant interference from strongly reflective targets such as mud banks, sheltered bays, ships etc. Fully focused SAR (FF-SAR) processing exhibits a theoretical along-track resolution of up to less than half a metre. This suggests that the application of FF-SAR altimetry might give potential gains over unfocused SAR (UF-SAR) altimetry to resolve and mitigate small-scale interferers in the along-track direction to improve the accuracy and precision of the geophysical estimates. The objective of this study is to assess the applicability of FF-SAR-processed Sentinel-6 Michael Freilich (S6-MF) coastal altimetry data to obtain SWH estimates as close as possible to the coast. We have developed a multi-mission FF-SAR processor and applied the coastal retracking algorithm CORALv2 to estimate SWH. We assess different FF-SAR and UF-SAR processing configurations, as well as the baseline Level-2 product from EUMETSAT, by comparison with the coastal, high-resolution SWAN-Kuststrook wave model from the Deltares RWsOS North Sea operational forecasting system. This includes the evaluation of the correlation, the median offset, and the percentage of cycles with high correlation as a function of distance to the nearest coastline. Moreover, we analyse the number of valid records and the L2 noise of the records. The case study comprises five coastal crossings of S6-MF that are located along the Dutch coast and the German coast along the East Frisian Islands in the North Sea. We find that the FF-SAR-processed dataset with a Level-1b posting rate of 140 Hz shows the greatest similarity with the wave model. We achieve a correlation of ~0.8 at 80% of valid records and a gain in precision of up to 29% of FF-SAR vs UF-SAR for 1-3 km from the coast. FF-SAR shows, for all cycles, a high correlation of greater than or equal to 0.8 for 1-3 km from the coast. We estimate the decay of SWH from offshore at 30 km to up to 1 km from the coast to amount to 26.4% +- 3.1%.

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The Copernicus Sentinel-6 mission: Enhanced continuity of satellite sea level measurements from space

Cited by 95 publications

References 114 publications

Sentinel-6A precise orbit determination using a combined GPS/Galileo receiver

Sentinel-6A precise orbit determination using a combined GPS/Galileo receiver

Results of the Dragon 4 Project on New Ocean Remote Sensing Data for Operational Applications

Benefits of Fully Focused SAR Altimetry to Coastal Wave Height Estimates: A Case Study in the North Sea

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