Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Altimetry for the future: building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

CFOSAT : A new mission in orbit to observe simultaneously wind and waves at the ocean surface

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New directional wave observations from CFOSAT : impact on ocean/wave coupling in the Southern Ocean

International audienceThe Southern ocean is a complex ocean region with uncertainties related to surface wind forcing and fluxes exchanges at the air/sea interface. The improvement of wind wave generation in this ocean region is crucial for climate studies. With CFOSAT satellite mission, the SWIM instrument provides directional wave spectra for wavelengths from 70 to 500 m, which shed light on the role of correcting the wave direction and peak wave number of dominant wave trains in the wind-waves growth phase. This consequently induced a better energy transfer between waves and a significant bias reduction of wave height in the Southern Ocean (Aouf et al. 2020). The objective of this work is to extend the analysis of the impact of the assimilation of wave number components from SWIM wave partitions on the ocean/wave coupling. To this end, coupled simulations of the wave model MFWAM and the ocean model NEMO are performed during the southern winter period of 2019 (May-July). We have examined the MFWAM/NEMO coupling with and without the assimilation of the SWIM mean wave number components. Several coupling processes related to Stokes drift, momentum flux stress and wave breaking inducing turbulence in the ocean mixing layer have been analyzed. We also compared the coupled runs with a control run without wave forcing in order to evaluate the impact of the assimilation. The results of coupled simulations have been validated with satellite Sea Surface Temperature and available surface currents data over the southern ocean. We also investigated the impact of the assimilation during severe storms with unlimited fetch conditions.Further discussions and conclusions will be commented in the final paper.Aouf L., New directional wave satellite observations : Towards improved wave forecasting and climate description in Southern Ocean, Geophysical Research Letters, DOI: 10.1029/2020GL091187 (in production). What do you want to do ? New mai

CFOSAT Overview

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CFOSAT wave spectra joining the family of L2P-L3 CMEMS Wave products!

International audienceSWIM CFOSAT innovative instrument has already shown its reliability and data quality interest through several publications since its launch in end 2018. Its nadir data are delivered to CMEMS since July 2019 in a L2P/L3. Similarly to other nadir missions AltiKa, Jason3, HY2B, S3…, these easy to use products are based on a selection of valid data from quality criteria, and bias alignment to buoys networks. They are provided in near real time (3h) and with a 1Hz sampling.In 2021, the CFOSAT project team is happy to provide to CMEMS, in addition to the mission full products, a user friendly product, with preselected valid datasets of directional wave spectra and related parameters, and additional information directly derived from the calval expertises upstream. Thanks to it, non expert users should be able to have a simple access to this new product and easy compare it to SAR Wavemode L3 products already in the CMEMS catalogue.This presentation is a user friendly approach to describe the added value, the future improvements planned and the potential of such product for non experts applications

Benefits of the Adaptive algorithm for retracking altimeter nadir echoes: results from simulations and CFOSAT/SWIM observations

International audienceThe accuracy of sea surface parameters retrieved from altimeter missions is predominantly governed by the choice of the so-called "retracking" algorithm, i.e. the model and inversion method implemented to obtain the surface parameters from the backscattered waveform. For continuity reasons, the choice of space agencies is usually to apply the same retracker from one satellite mission to the other to ensure long time homogeneous series. Here, taking the opportunity of a new configuration of the nadir pointing measurements on-board the recently launched CFOSAT satellite with the SWIM (Surface Waves Investigation and Monitoring) instrument (Hauser et al, 2020), the retracking method was upgraded, by implementing a novel algorithm, called "Adaptive" retracker. It combines the improvements brought by Poisson et al (2018) for the estimation of surface parameters from peaked waveforms over sea-ice, improvements in the way the instrumental characteristics are taken into account in the model (mispointing, point target response) and a more accurate consideration of speckle statistics. In this paper, we first show from simulations carried out in the instrumental configuration of SWIM that the Adaptive algorithm has better accuracy and performances than the classical MLE4 algorithm. Then, the geophysical parameters obtained with real data from SWIM are analyzed with comparisons to reference data sets (model and products from altimeters). We show that this new algorithm has several benefits with respect to the classical MLE4 method: no need of look-up tables to correct biases, significant noise reduction on all geophysical variables especially the significant wave height, and performance of inversion over a large set of echo shapes, resulting from standard oceanic scenes as well as highly specular conditions such as over bloom or sea-ice

CFOSAT (China France Oceanography SATellite): an innovative satellite for ocean wave studies

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First results on wave spectral properties from the CFOSAT satellite

International audienceCFOSAT is an innovative satellite mission to be launched on October 29th, 2018. It is presently in the final stage of preparation thanks to a fruitfull Chinese-French cooperation started in 2006. CFOSAT will provide for the first time colocated observations on wind vector, wave spectral parameters (wave spectra and associated parameters) from a combination of two radar instruments (SWIM and SCAT) working in altimeter and wave spectrometer modes (SWIM) and wind scatterometer mode (SCAT). The observation products will offer the opportunity to develop new studies from global observations, as joint analysis of space evolution of wind and waves, detailed analysis of the spectral properties of the wave field (in particular its directionality) and relationship between long waves (measured by SWIM) and short wave properties (indirect information from the normalized radar cross-section). The data will also be used in combination with wave and atmospheric numerical models (through assimilation) in order to improve wave and atmospheric forecast. The information on peak wavenumber, wave direction, directional spread for several wave spectrum partitions, will also be of great interest to study wave/current interactions.During these last years, the algorithms for wind and wave inversion have been prepared in France and China by expert laboratories and space agencies. They are under implementation in mission centers and will be ready to provide products a couple of weeks after the satellite launch. During the conference we will show the very first data sets obtained from SWIM as well as the first validation analysis of wave products. This will include comparisons to wave parameters from model outputs, in situ data and other satellite data (altimeter, SAR) at cross-over points. The focus will be put on the main parameters of the wave spectra (significant wave height, peak direction, peak wavelength)

Swim now in orbit: a new horizon for wave observation

International audienceThe CFOSAT (China France Oceanography SATellite) mission is a CNES-CNSA space mission for ocean surface wind and wave observation. The satellite has been successfully launched on October, 29th, 2018 from China. The satellite behaves perfectly well until now with nice scientific acquisitions. For the very first time, wind and waves are observed at the same time and place. These simultaneous observations open new research fields on climate monitoring, sea-air interactions understanding and sea state forecasting.CFOSAT embarks two payloads: a wave scatterometer, SWIM (French contribution) and a wind scatterometer, SCAT (Chinese contribution). Both are Ku-band real aperture radar taking advantage of different backscattering properties. At high incidence angles (SCAT), the radar signal is sensitive to Bragg scattering, i.e. small surface roughness induced by the wind. At low incidence angles (SWIM), the radar backscattering depends only on large slopes, i.e. the waves.In this paper, we will present the status on the SWIM instrument and the SWIM products produced by the French ground segment. This status will be provided after 7 months in orbit, at the end of the commissioning phase. At the time of the writing of the abstract (few days after the launch), we are just checking the health of the satellite and the instruments as well as the generation of the first products. We are not thus able to provide quantitative results to the reviewers at this stage. During the commissioning phase, the internal calibration modes of SWIM are tested (internal impulse response, antenna calibration law, reception noise level). The different acquisition modes are also tested (sequence of the six beams and on-board processing options).The CFOSAT system is composed of the satellite with SWIM and SCAT on-board and two ground segments, one in China (CHOGS) and one in France (FROGS). Both mission centers process all the SWIM and the SCAT data. This paper is relative to the processing performed at FROGS for SWIM only. The CFOSAT data are processed in near real time in the French mission center up to level 2 (CNES) and in differed time from level 2 to level 4 (IFREMER). The products are available on-line on the AVISO+ website.The main scientific products of SWIM are the 2D wave spectrum at a spatial scale of 70x90 km², the backscattering coefficient profiles per 0.5° step in incidence and 15° step in azimuth and the significant wave height and wind speed from the nadir beam.The paper will detail the performance of the instrument relative to SNR and backscattering coefficient accuracy, pointing knowledge accuracy. The overall availability of the data will also be discussed (coverage over ocean, distance to coasts, coverage of the continents and ice sheets).We will also present the results on level 2 products