Since 2009, the Meridional Overturning Circulation (MOC) in the South Atlantic has been observed with an array of in situ moorings on each side of the basin at 34.5°S, the South Atlantic MOC Basin-wide Array (SAMBA). To date, the component of the meridional transport inshore of the shallowest moorings on either side (about 1300 m depth) has been estimated using a time-mean from an ocean model simulation due to lack of better observations. However, because...

The winter conditions of the surface ocean at high latitudes are characterized by stormy seas that pose challenges to coastal communities, fisheries and shipping. Here we investigate conditions in the Bering Sea in winter over the past 20 years using altimeter-derived significant wave height (SWH). Using observations from the Jason-1, -2 and -3 satellites as well as from ERS-2, Envisat, CryoSat-2,SARAL/AltiKa, Sentinel-3A and -3B, we have found that the prevalence of very-high and phenomenal sea...

The Patagonia continental shelf is a vast region within the Southwestern Atlantic Ocean that is known for its high primary production rates and, consequently, for the wide biological diversity present there. To better understand the biological patterns observed, it is necessary to deepen the knowledge of the physical processes that they are exposed to. In this study, we analyze two direct velocity observations of up to 18 months, measured over the South-Patagonia continental shelf, located...

Oceanic equatorial waves play a fundamental role in ocean adjustment in the tropics, and can rapidly transmit forcing over planetary scales. Satellite altimetry data contain a wealth of underexploited information on equatorial inertial gravity waves, down to periods of a few days. The long and relatively continuous altimetry record allows us to achieve a high-resolution view of the zonal-wavenumber frequency spectrum of variability in the equatorial Pacific, providing a depiction of the spectrum of SSH...

Amongst its instruments, the Copernicus Sentinel-3 (S3) missions carry the Synthetic Aperture Radar Altimeter (SRAL) for precise sea surface height (SSH) observations and its companion Microwave Radiometer (MWR) for the retrieval of the path delay in the altimeter range caused by the presence of water vapour and cloud liquid water in the atmosphere. In the scope of an activity sponsored by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT), the University of Porto...

Since the beginning of the precision satellite altimeter era in the early 1990s, efforts have been focused on computing the mean height of the ocean surface for use in various geodetic and oceanographic studies. With 30 years of satellite measurements now available, it is time to rethink the modeling of the mean sea surface (MSS) in the era of climate change. There are linear changes in the height of the ocean surface due to melting...

We present a novel application of satellite altimetry to monitor ocean temperatures on the continental shelf around the Greenland Ice Sheet with the goal of better understanding past and better predicting future sea-level rise. Mass loss from the Greenland Ice Sheet is now responsible for about 20% of the total annual increase in global mean sea-level, a dramatic increase from the 1970’s, 80’s and 90’s when the mass balance of the ice sheet was in...

2022 is a successful time for altimetry, with nine currently flying satellites: CryoSat-2 (2010), Saral/AltiKa (2013), Jason-3 (2016), Sentinel-3A (2016), Sentinel-3B (2018), HY-2B (2018), HY-2C (2020), Sentinel-6 MF (2020), HY-2D (2021), all of them being processed with the same CNES POE-F precise orbit standards. This impressive Low Earth Orbit (LEO) constellation is also planned to be complemented by a tenth altimeter mission, the SWOT next-generation satellite in November 2022. This paper focuses on the two...

Radar altimeters require periodic external calibration to monitor the instrument drifts that are not covered by the internal calibration paths. These activities are normally performed by acquiring data over active transponders and analysing the performances. European radar altimeters such as CryoSat-2, Sentinel-3 A/B and Sentinel-6A rely on transponders on Svalbard and Crete to monitor their stability, while usage of passive reflectors for radar altimeter calibration has been not feasible as the required size for the...

Sentinel-6 is an operational oceanography programme consisting on two satellites that will map the sea surface levels with great precision. Sentinel-6 includes two identical satellites with the first launched on November 21, 2020 (Sentinel-6 Michael Freilich) and the second scheduled for launch in 2025 (satellite B). Following its launch, the Sentinel-6 Validation Team (S6VT) has carried out validation activities with Sentinel-6 Michael Freilich data for more than a year to ensure the best possible outcome...

S6 fully-focused SAR (FF-SAR) waveforms are noticeably narrower than for S6 unfocused SAR (UF-SAR), which produces a significant bias in the geophysical estimates after applying a SAMOSA-based fitting. We demonstrate that a major part of these shape differences can be explained with the shapes of grating lobes and side lobes in the impulse response function (IRF) of FF-SAR and UF-SAR. With this insight, we can compensate for the differences. Note that S6 has been designed...

SWOT mission is expected to be the first satellite to provide high-resolution global surface water elevation maps. These radar interferograms over water surfaces would enable a wide range of research opportunities especially in the field of land hydrology. In this work, satellite observations (river level, width) along with an integrated hydrological modelling scheme is utilized to estimate the river discharge over the Narmada site that we are aiming to establish as a calibration site for...

The Global Mean Sea Level (GMSL) climate data record is monitored since 1992 thanks to the reference altimetry missions TopEx/Poseïdon, Jason-1/-2 /-3 and now Sentinel-6A MF. The first and historical mission TopEx/Poseïdon has been shown to be affected by an instrumental degradation of its side-A altimeter (Beckley et aL, 2018) from the middle of 1995 until the change to the side-B in February 1999. The instrumental degradation strongly affects the GMSL long-term stability (Watson et...

The integral length scale of a turbulent velocity is treated as the characteristic scale of the largest scale of motions in the turbulent flow. It is a key parameter in turbulent theory and numerical simulations. The ocean surface waves show complex turbulence-like dynamics. In this work, the integral length scale of ocean surface waves provided by the China France Oceanography Satellite (CFOSAT) is examined. The results show that the integral length scales possess evident spatial...

Since the launch of TOPEX/Poseidon and ERS-1 in the early 90’s more than 10 other Altimetry missions were launched and operated by different agencies. The level 2 data (destinated to expert users) are distributed using different file formats (binary, netcdf) and contain different geophysical standards used to compute the sea level anomaly. Some datasets evolve rapidly and are regularly reprocessed, whereas other datasets, especially from finished missions are seldom reprocessed or not at all (and...

The Copernicus Sentinel-6A mission was successfully launched on the 21st November 2020. This mission is taking the responsibility to extend the global sea level record on the reference low inclination orbit started in 1992 with TOPEX/Poseidon mission and continued by the Jason series. This new Copernicus constellation (Sentinel-6B launch expected in 2026) will ensure the continuity of this unique high-precision coverage of altimetry data in support to climate change monitoring, research, and forecasting, as well...

Sentinel-6 mission has been launched in November 2020. It is the first altimetry mission with explicit requirements for the accuracy of Global Mean Sea Level drift. In support of this goal, JPL has developed a transponder that allows for an accurate monitoring of the altimeter. This transponder is the first instrument of its kind to operate in both the Ku and C bands. It will therefore allow for a full calibration of range and power...

Consistent calibration and monitoring is a basic prerequisite for providing reliable time series of global and regional sea level variations from altimetry. The precision of sea level measurements and regional biases for eight altimeter missions (Jason-1/2/3, Sentinel-6MF, Envisat, Saral, Sentinel-3A/B) is assessed at eleven GNSS-controlled tide gauge stations in the German Bight (SE North Sea) for the period 2002 to 2021. The gauges are operated operationally by the German Waterway and Shipping Administration (WSV) and...

Over the ocean, an altimeter's sigma0 values are interpreted as a measure of local wind speed due to its effect on surface roughness. However, for climatological studies of possible changes in wind climate it is essential to have confidence in the stability of the calibration of a sensor and also in the relative calibrations of different sensors. Here I review the application of dual-frequency monitoring techniques applied to the Sentinel-3A and 3B altimeters and also...

In the framework of the European Long Term Data Preservation Program (LTDP+), which aims at generating innovative Earth system data records named Fundamental Data Records (FDR) and Thematic Data Records (TDP), similar to level 2+ geophysical products, ESA/ESRIN has launched two years ago a reprocessing activity of the ERS-1, ERS-2 and ENVISAT altimeter and radiometer dataset. A large consortium of thematic experts has been formed to perform these activities which are 1) to define new...

CryoSat-2 was launched twelve years ago and was the first European mission dedicated to the cryosphere, with the objectives to monitor precise changes in the thickness of polar ice sheets and floating sea ice. For that, the satellite carries the first Synthetic Aperture Interferometric Altimeter (SIRAL) which still remains one of the most innovative altimeters in space although newer versions are boarded on different satellite missions. Going beyond its ice monitoring objectives, CryoSat-2 has also...

In this study, we demonstrate that remote internal waves are important for the local energetics in regional ocean circulation models. In addition to mesoscale forcing, we force 4-km Regional Ocean Modelling System (ROMS) simulations of the U.S. West Coast with surface tides and internal waves from an 8-km Hybrid Coordinate Ocean Model (HYCOM) simulation. We evaluate the regional model’s boundary conditions for reflections, we validate our simulations with observations, and we study internal wave energetics...

As part of the assessment of Sentinel-6 high-rate (20 Hz) high-resolution data and in preparation for the future swath data from SWOT, various improvements to in situ instrumentation at the Bass Strait validation facility have been explored. An array of six new GNSS/INS equipped Mk-VI buoys have been developed and deployed for an 8-day trial deployment along Sentinel-6 pass 088. Five deployment locations with up to 10 km spacing were used, centred on the historical...

We use three years of Sea Surface Height (SSH) observations over the World Ocean to analyze its spectral characteristics: spectral slope and noise levels. Our analyses are based on previous works that focused on the spectral slope characterization through a linear regression over a geographically dependent wavelength range, corresponding to the mesoscale wavelength range. In our current analysis, we adopt a methodology that allows for the characterization of the spectral slope by optimal fit of...

The energy radiated by the Earth toward space does not compensate the incoming radiation from the Sun leading to a small positive energy imbalance at the top of the atmosphere (0.4–1 Wm–2). This imbalance is coined Earth’s Energy Imbalance (EEI). At decadal time scales, it is mostly caused by anthropogenic greenhouse gas emissions and it is driving the current warming of the planet. Combined with surface temperature measurements the EEI measurement informs on the sensitivity...