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The Mission Performance Working Group is a body composed of experts from EUMETSAT, NASA, ESA, NOAA and CNES. The group meets on a regular basis, and it is aiming at monitoring the Sentinel-6MF overall altimetry mission performance. The group assesses on mission and payload performance budgets, data products quality, algorithm development, new processor verification and validation performance, calibration and validation planning, as well as provides scientific support to the reprocessing calibration and validation, key mission instrument meetings and mission performance meetings. The MPWG activities are similar to those done by the MSEs as per previous Jason mission. In this presentation, the MPWG will share with the OSTST the latest calibration and validation findings including any mission scientific challenges. Moreover, we will present the scientific plans for Sentinel-6MF evolutions, and provide an estimated timeline for these evolutions to be available to the Sentinel-6MF user community.

A microwave range transponder has been operating at the CDN1 Cal/Val site on the mountains of Crete for about 6 years to calibrate international satellite radar altimeters at the Ku-band. This CDN1 transponder is part of the European Space Agency Permanent Facility for Altimetry Calibration (PFAC), and has been producing continuously as of 2015 a time series of range biases for Sentinel-3A, Sentinel-3B, Sentinel-6A, Jason-2, Jason-3 and CryoSat-2. A second range and sigma-0 transponder at a crossover location of Sentinel-6 “Michael Freilich” on the island of Gavdos is also operational as of 11-Oct-2021. This work presents a thorough examination of the transponder Cal/Val responses in an effort to understand and determine which factors are responsible for the observed changes in the Cal/Val results. Fourteen uncontrolled and three controlled sources of variations have been investigated. The latest calibration results for the Jason-3, the Copernicus Sentinel-3A and -3B, Sentinel-6A and the HY-2B radar altimeters will be described based on four sea-surface and two transponder Cal/Val sites of the PFAC in west Crete, Greece. Absolute biases for Jason-3, Sentinel-6A, Sentinel-3A, Sentinel-3B and HY-2B will be given using various techniques, infrastructure and settings.

The altimetry data record (1993-2022) has enabled the global mean sea level (GMSL) rise to be quantified. Not only is the sea level rising, but it is accelerating (Dieng et al., 2017; Nerem et al., 2018; Ablain et al. 2019) and understanding this acceleration is necessary both to support society’s response to climate change and to inform climate research on the sea level budget, greenhouse gas forcing and the Earth energy imbalance. Here we describe work on quantifying the uncertainty on the sea level climate data record, and identifying the uncertainty needed to provide new answers to the climate research questions. Work by Ablain et al. (2019) and updated in Guérou et al. (2022) at a global scale, has quantified GMSL rise as +3.3 mm/yr (90% confidence uncertainties 0.3 mm/yr) over 1993-2021. Its acceleration has been quantified at 0.12 ± 0.05 mm/yr². At local scales, (Prandi et al. 2021), the sea level is rising almost everywhere over the globe, at rates ranging between 0 and 6 mm/yr, with uncertainties ranging from 0.8 to 1.2 mm/yr depending on the location. The local sea level accelerations are ranging between -1 mm/yr² and +1 mm/yr² with uncertainties between 0.057 and 0.12 mm/yr² (Prandi et al., 2021). Here we present more recent work refining these uncertainty estimates through a metrological approach that propagates uncertainties, and error covariance structures, through the full processing chain of the altimeter measurement from the raw waveform to GMSL, using methods described in Mittaz et al. (2019). We review the assumptions in the derivation of the retracking model from the radar equation, consider error correlation structures in the corrections, and provide fresh consideration of the error covariance matrix, building on the earlier research. The work was developed in the ASELSU project funded by ESA. The project has also reviewed the climate science research questions to understand the need for improved altimeter observations. There are three major science questions that require accuracies greater than those currently achieved. These questions are the closure of the sea level budget, the detection and attribution of the signal in sea level that is forced by greenhouse gas emissions (GHG) and the estimate of the Earth energy imbalance (EEI). Dieng et al. 2017: https://doi.org/10.1002/joc.4996. Nerem et al. 2018: https://doi.org/10.1073/pnas.1717312115 Ablain et al 2019: https://doi.org/10.5194/essd-2019-10 Guérou et al. 2022: https://doi.org/10.5194/egusphere-2022-330 Prandi et al. 2021: https://doi.org/10.1038/s41597-020-00786-7 Mittaz et al. 2019: https://doi.org/10.1088/1681-7575/ab1705

The main payload of Sentinel-6 Michael Freilich is a dual-band (Ku and C) pulse-width limited radar altimeter, called Poseidon-4, that transmits pulses at a high pulse repetition frequency thus making the received echoes phase coherent and suitable for azimuth processing. Among the different unique characteristic of Poseidon-4, it is worth recalling that digital pulse range compression is performed on-board to transform the received chirp using a matched filter. Thus, a proper calibration approach has been developed, including both an internal and external calibration. In particular, this abstract presents the long-term monitoring of the internal calibration data for chirp replica and for attenuator that are processed on ground by ad-hoc tools provisioned by Aresys to ESA: • CAL1 INSTR: This mode measures the internal instrument transfer function in Ku band and in C band. The results of these measures can be taken into account at Digital compression level in the chirp replica(f) to optimize the impulse response of the instrument. • CAL ATT: Since amplification gain control knowledge directly impacts the σ0 measurements, an attenuation calibration is included in the design. This measures the top of the range impulse response within the full attenuation dynamic range that is then matched to a corresponding value on ground. The performance of Poseidon-4 altimeter is here presented by analysis of the long-term monitoring of the on-ground processed data from CAL1 INSTR and CAL ATT calibration sequences commanded on board. The analysis of such calibration data allows to verify that the instrument has reached the requirements and that it is maintaining the key performance over its life. Moreover, in-depth analysis of the calibration data revealed how the instrument depends on its temperature and on the orbit of the satellite.

The Sentinel. 6 satellite has a new platform, with a very different geometry from the preceding missions like Jason 1,2,3. The main difference is that the solar array panel is now fixed on the satellite body, and the satellite has a fixed attitude in the local orbital frame (with small rotations for geodetical pointing and ground velocity alignment). As a consequence the sun direction relative to the panels has important variations along one orbit. On Jason 3 the illumination of the solar array panels is always close to the normal direction : as a consequence the solar radiation pressure force produced by the panels has a well defined direction independent of the material coefficients. Also, the amplitude does not depend on the balance between the electrical energy production of the array and the material thermally absorbed part. This thermally absorbed part has no impact on the global force, due to a similar re-radiation on both surfaces of the panels. On Sentinel 6, this property does not hold anymore, and the standard modeling of the panel surfaces (with absorbed, diffuse and specular parts), with correction for the re-radiated part, does not lead to satisfactory results. Here, we analyze the solar array thermal behavior thanks to in flight information (temperatures variations along the orbit, for different sun orbital angle cases, and energy production of the array). A thermal model is constructed using thermal coefficients adjusted on these flight data (thermal capacity of the panels). An updated solar radiation pressure model is then constructed.

A technique is presented for the development of a high precision and resolution Mean Sea Surface (MSS) model. The model utilises Radar altimetric sea surface heights extracted from the geodetic phase of the ESA ERS-1 mission. The methodology uses a modified Le Traon et al. (1995) cubic-spline fit of dual ERS-1 and TOPEX/Poseidon crossovers for the minimisation of radial orbit error. The procedure then uses Fourier domain processing techniques for spectral optimal interpolation of the mean sea surface in order to reduce residual errors within the model. Additionally, a multi-satellite mean sea surface integration technique is investigated to supplement the first model with additional enhanced data from the GEOSAT geodetic mission.The methodology employs a novel technique that combines the Stokes' and Vening-Meinsz' transformations, again in the spectral domain. This allows the presentation of a new enhanced GEOSAT gravity anomaly field.

The small satellite industry faces a special challenge when it comes to the selection of a launch vehicle. Given the limited number of dedicated lifters and a disadvantageous payload weight/cost ratio, the launch planner must often compromise satellite system performance to remain within the profiles of throw weight, altitude, inclination, and cost associated with the obvious choices of launch vehicles. This paper provides a detailed look at the world's inventory of launch vehicles, particularly those that are appropriate for use as dedicated lifters of small satellites and those that can accommodate small satellites as non-primary payloads. The term small satellite includes spacecraft up to 500 kg in weight. The descriptions of the vehicles provided herein include representative examples of each type, highlighting the characteristics that are most important to launch planners. The purpose of the paper is to permit the program planner to recognize those vehicles which fit the mission profile for cost and orbital performance. Sufficient information will be provided in this paper and in the oral presentation at the conference to reveal some less obvious options for both dedicated and piggy-back missions. Emphasis is placed on the needs of the small satellite community, particularly on the cost performance trades that have great leverage on the capitalization and the on-orbit capabilities of small-scale systems. The material is derived from open sources including industry publications and vendor literature, and is supplemented by interviews with suppliers and users of launch services.