Computation of a new Mean Dynamic Topography for the Mediterranean Sea from model outputs, altimeter measurements and oceanographic in-situ data

Rio, Marie Hélène; Pascual, Ananda; Poulain, Pierre‐Marie; Menna, Milena; Barceló-Llull, Bàrbara; Tintoré, Joaquı́n

doi:10.5194/osd-11-655-2014

Cited by 28 publications

(25 citation statements)

References 19 publications

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“…Before the current computation, the SLA data are filtered in the along-track direction by applying a Loess 30-km low-pass filter. A synthetic mean dynamic topography-the regional MDT (Rio et al 2014)-is added to the altimetric SLA to derive an estimation of the absolute surface velocities. Results are represented in Figure 8 Observation of the Coastal Ocean Variability 323 above, only the data within 80 km of the coast and the 10 cycles of Jason-2 closest in time with SRL data are considered.…”

Section: Application To the Regional Coastal Circulationmentioning

confidence: 99%

Ku– and Ka-band Altimeter Data in the Northwestern Mediterranean Sea: Impact on the Observation of the Coastal Ocean Variability

Birol

Niño

2015

Marine Geodesy

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The strong increase in altimeter measurement errors near land surfaces is a limiting factor for coastal applications. We analyze the performance of the new Ka-band SARAL/AltiKa (SRL) mission in the northwestern Mediterranean Sea. SRL sea surface height (SSH) measurements are compared with those from the Jason-2 Ku-band satellite mission. The results show a significant increase in both quantity and quality of SSH data available near coastlines when using SRL data. Available edited data are 95.1% of SRL compared with 88.6% for Jason-2. Closer than 10 km to the coastline, available SRL data are still about 60% and only about 31% for Jason-2. Comparisons of the altimeter sea level variations are made with available coastal tide gauge data. The differences obtained between altimeter and tide gauge SLA time series are reduced for SRL (3.3 cm in average) compared with Jason-2 (4.2 cm in average), especially closer than 30 km to the land. It results in higher correlations (by 30%) obtained with SRL data. The coastal circulation derived from altimetry using SRL data shows an offshore meandering, which is more stable in time and with larger velocities close to the coast than that derived from Jason-2 observations.

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Section: Application To the Regional Coastal Circulationmentioning

confidence: 99%

Ku– and Ka-band Altimeter Data in the Northwestern Mediterranean Sea: Impact on the Observation of the Coastal Ocean Variability

Birol

Niño

2015

Marine Geodesy

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“…The same processing as in [13] is applied for HF radar and as well as for both SARAL/AltiKa and Jason-2 missions. Surface geostrophic velocities from altimetry are computed by finite differences applied to the Absolute Dynamic Topography (ADT), which is obtained by adding SLA and the SMDT-MED2014 Mean Dynamic Topography [14]). …”

Section: Saral-altika Capabilities To Detect Coastal Currents: Comparmentioning

confidence: 99%

The Benefits of the Ka-Band as Evidenced from the SARAL/AltiKa Altimetric Mission: Scientific Applications

et al. 2018

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Abstract:The India-France SARAL/AltiKa mission is the first Ka-band altimetric mission dedicated primarily to oceanography. The mission objectives were firstly the observation of the oceanic mesoscales but also global and regional sea level monitoring, including the coastal zone, data assimilation, and operational oceanography. SARAL/AltiKa proved also to be a great opportunity for inland waters applications, for observing ice sheet or icebergs, as well as for geodetic investigations. The mission ended its nominal phase after three years in orbit and began a new phase (drifting orbit) in July 2016. The objective of this paper is to highlight some of the most remarkable achievements of the SARAL/AltiKa mission in terms of scientific applications. Compared to the standard Ku-band altimetry measurements, the Ka-band provides substantial improvements in terms of spatial resolution and data accuracy. We show here that this leads to remarkable advances in terms of observation of the mesoscale and coastal ocean, waves, river water levels, ice sheets, icebergs, fine scale bathymetry features as well as for the many related applications.

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“…In addition, the altimetric SLAs have the mean ocean circulation removed, whereas the gliders provide the total upper ocean baroclinic flow. For consistency, the mean dynamic topography and mean geostrophic velocities derived from Rio et al (2014) are added to the altimetric data for this comparison. The third main difference is the time taken to make a section over 100 to 300 km.…”

Section: Co-located Altimeter and Glider Observationsmentioning

confidence: 99%

Observability of fine-scale ocean dynamics in the northwestern Mediterranean Sea

et al. 2017

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Abstract. Technological advances in the recent satellite altimeter missions of Jason-2, SARAL/AltiKa and CryoSat-2 have improved their signal-to-noise ratio, allowing us to observe finer-scale ocean processes with along-track data. Here, we analyse the noise levels and observable ocean scales in the northwestern Mediterranean Sea, using spectral analyses of along-track sea surface height from the three missions. Jason-2 has a higher mean noise level with strong seasonal variations, with higher noise in winter due to the rougher sea state. SARAL/AltiKa has the lowest noise, again with strong seasonal variations. CryoSat-2 is in synthetic aperture radar (SAR) mode in the Mediterranean Sea but with lower-resolution ocean corrections; its statistical noise level is moderate with little seasonal variation. These noise levels impact on the ocean scales we can observe. In winter, when the mixed layers are deepest and the submesoscale is energetic, all of the altimeter missions can observe wavelengths down to 40-50 km (individual feature diameters of 20-25 km). In summer when the submesoscales are weaker, SARAL can detect ocean scales down to 35 km wavelength, whereas the higher noise from Jason-2 and CryoSat-2 blocks the observation of scales less than 50-55 km wavelength.This statistical analysis is completed by individual case studies, where filtered along-track altimeter data are compared with co-located glider and high-frequency (HF) radar data. The glider comparisons work well for larger ocean structures, but observations of the smaller, rapidly moving dynamics are difficult to co-locate in space and time (gliders cover 200 km in a few days, altimetry in 30 s). HF radar surface currents at Toulon measure the meandering Northern Current, and their good temporal sampling shows promising results in comparison to co-located SARAL altimetric currents. Techniques to separate the geostrophic component from the wind-driven ageostrophic flow need further development in this coastal band.

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Computation of a new Mean Dynamic Topography for the Mediterranean Sea from model outputs, altimeter measurements and oceanographic in-situ data

Cited by 28 publications

References 19 publications

Ku– and Ka-band Altimeter Data in the Northwestern Mediterranean Sea: Impact on the Observation of the Coastal Ocean Variability

Ku– and Ka-band Altimeter Data in the Northwestern Mediterranean Sea: Impact on the Observation of the Coastal Ocean Variability

The Benefits of the Ka-Band as Evidenced from the SARAL/AltiKa Altimetric Mission: Scientific Applications

Observability of fine-scale ocean dynamics in the northwestern Mediterranean Sea

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