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Altimeter mission | Type of product | Source | Availability delay |
Sentinel-6 MF | NTC | EUMETSAT | ~1 month |
Sentinel-3A | NTC | EUMETSAT | ~1 month |
Jason-3 | GDR | CNES/EUMETSAT | Reprocessing only |
OSTM/Jason-2 | GDR | CNES | Reprocessing only |
CryoSat-2 | GDR | ESA | Reprocessing only |
SARAL/AltiKa | GDR | CNES | Reprocessing only |
Topex/Poseidon | GDR | CNES | Reprocessing only |
Jason-1 | GDR | CNES | Reprocessing only |
Envisat | GDR | ESA | Reprocessing only |
ERS-1 | GDR | ESA | Reprocessing only |
ERS-2 | GDR | ESA | Reprocessing only |
The auxiliary products (altimeter standards, geophysical corrections) used in the production are described in Table 2. They are the most up-to-date standards (whose timeliness is compatible with the C3S production planning) and most of them follow the recommendations of the ESA Sea Level CCI project (Quartly et al. 2017; Legeais et al., 2018). More details on the description of these standards can be found in Lievin et al., 2020 and in Kocha et al., 2023 for measurements after 2023/06/08 (in bold in the table).
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Poseidon Topex | Jason-1 | OSTM/Jason-2 | Jason-3 | ERS-1 | ERS-2 | Envisat | Cryosat-2 | SARAL AltiKa | Sentinel-3A | Sentinel-6 MF | |
Orbit | GSFC STD18 | POE-E | POE-F | POE-F | Reaper | POE-E | POE-F | POE-F | POE-F | POE | |
Ionospheric Correction | Filtered dual-frequency altimeter range measurements [Guibbaud et al. 2015]; DORIS on Poseidon | Filtered dual-frequency altimeter range [Guibbaud et al. 2015] (from SSB C-band) | Filtered dual-frequency altimeter from [Guibbaud et al. 2015] & c> 170 from L2 GDRF | Reaper NIC09 model [Scharroo and Smith, 2010] | GIM [Ijima et al., 1999] | Filtered from L2; c>65: GIM [Ijima et al., 1999] corrected for 8mm bias | GIM [Ijima et al., 1999] | Filtered from L2 | L2 Filtered dual frequency | ||
Sea State Bias | Non parametric [Tran et al. 2010] ; BM4 on Poseidon | Non parametric [Tran 2015] | Non parametric [ Tran 2012] | Non parametric from J2 [ Tran 2012] & c>170 from [Tran 2020 report] J3 GDRF | BM3 [Gaspar and Ogor, 1994] | Non parametric [Mertz et al., 2005] | Non parametric [ Tran 2017] | Non parametric [ Tran 2018] Baseline C | Non parametric [ Tran 2018] | Non parametric [ Tran 2012] | Non parametric SSB [Tran 2021] from J3 GDR |
Wet Troposphere | GPD+ [Fernandes and Lazaro, 2015] | JMR (GDRE) radiometer | AMR radiometer | AMR radiometer (c>170 from L2 GDRF) | GPD+ [Fernandes and Lazaro, 2015] | MWR radiometer reprocessed | GPD+ [Fernandes and Lazaro, 2015] | Neural Network (5 entries) V4 | MWR 3 radiometer | MWR radiometer | |
Dry Troposphere | ERA5 (1-hour) model based | ||||||||||
Dynamical Atmospheric Correction | TUGO High frequencies forced with analysed ERA5 pressure and wind field + inverse barometer Low frequencies | TUGO HF forced with analysed ERA 5 pressure an d wind field; and after 02/2016 MOG2D HF forced with analysed ECMWF pressure and wind field + inverse barometer Low Frequencies | MOG2D HF forced with analysed ECM WF pressure and wind [Carrere and Lyard, 2003; operational version 3.2.0] + inverse barometer Low Frequencies | TUGO High frequencies forced with analysed ERA5 pressure and wind field + inverse barometer Low frequencies | TUGO High frequencies forced with analysed ERA5 pressure and wind field; and after 02/2016 MOG2D High frequencies forced with analysed ECMWF pressure and wind field + inverse barometer Low frequencies | TUGO HF forced with analysed ERA5 pressure an d wind field; and after 02/2016 MOG2D HF forced with analysed ECMWF pressure and wind field + inverse barometer Low Frequencies | Before 2023/06/07: MOG2D High frequencies forced with analysed ECMWF pressure and wind field [Carrere and Lyard, 2003; operational version 3.2.0] + inverse barometer Low frequencies After 2023/06/08: TUGO High frequencies forced with analysed ECMWF pressure and wind field + inverse barometer LF | ||||
Ocean Tide | Before 2023/06/07: FES 2014 B [Carrère et al. 2016]; after 2023/06/08: FES22b [Carrère et al., 2023] | ||||||||||
| Internal Tide | Zaron 2019 (HRETv8.1 tidal frequencies: M2, K1, S2, O1) | ||||||||||
| Pole Tide | Desai et al., 2015 ; Mean Pole Location 2017 | ||||||||||
| Solid Tide | Elastic response to tidal potential [Cartwright and Tayler, 1971; Cartwright and Edden, 1973] | ||||||||||
| Mean Sea Surface | Before 2023/06/07: Hybrid (SIO,CNES/CLS15,DTU15) [Sandwell et al.,2017 ; Ole et al.; Pujol et al.,2018]; after 2023/06/08: Hybrid MSS (SIO22; CNES/CLS22, DTU21) [Laloue et al., 2024] | ||||||||||
| Mean Dynamic Topography | CNES_CLS18 (Mulet et al, 2021) combined with CMEMS_2020 | ||||||||||
| Glacial Isostatic Adjustment (GIA) | The DUACS L4 products are not corrected from GIA effects | ||||||||||
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Between 1993 and 1998, the retrievals of global mean sea level (MSL) have been known to be affected by an instrumental drift in the TOPEX-A measurements, which has been quantified by several studies as discussed in the C3S Product Quality Assessment Report ([C3S_PQAR], section 3.2) and in Legeais et al. (2020). The altimeter sea level community agrees that it is necessary to correct the TOPEX-A record for the instrumental drift to improve the accuracy and the uncertainty of the total sea level record. An empirical correction of this drift based on a global comparison between altimetry and _in situ_ tide gauge measurements (WCRP sea level budget group, 2018) has been proposed in the data files. The correction value included in the dedicated variable can be added to the gridded SLA, to correct for the observed instrumental drift during the lifetime of the TOPEX-A mission (the correction is null after this period). This is a global correction to be added a posteriori (and not before) to the global mean sea level estimate derived from the gridded sea level data. It can be applied at regional or local scales as a best estimate (better than no correction, since the regional variation of the instrumental drift is unknown). However, even if the corrections proposed by the different studies available lead to similar global MSL trends and accelerations (in agreement with climate models), there is not yet a consensus on the best approach to estimate the drift correction at global and regional scales. The recommendation of the Ocean Surface Topography Science Team (OSTST) is to wait for the future release of a reprocessed TOPEX dataset. Therefore, the TOPEX-A correction has been proposed as a separate variable within the C3S sea level data files vDT2021 (and not directly included in the SLA estimate). See the sea level Product Quality Assessment Report [C3S_PQAR] for further details. |
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Altimeter mission | Cycle duration (days) | Latitude range (°N) | Number of tracks in the cycle | Inter-track distance at equator (km) | Sun- synchron ous | Dual- frequency Altimeter | Radiometer on board | Temporal period processed by DUACS system for C3S product | |
Begin date | End date | ||||||||
Topex/Poseidon | 10 | ±66 | 254 | ~315 | No | Yes | Yes | 1992/11/20 | 2002/04/24 |
Jason-1 | 10 | ±66 | 254 | ~315 | No | Yes | Yes | 2002/04/24 | 2008/10/19 |
OSTM/Jason-2 | 10 | ±66 | 254 | ~315 | No | Yes | Yes | 2008/10/19 | 2016/05/26 |
Jason-3 | 10 | ±66 | 254 | ~315 | No | Yes | Yes | 2016/05/26 | 2022/02/10 |
ERS-1 | 35 | ±81.5 | 1002 | ~80 | Yes | Yes | Yes | 1992/11/20* | 1995/05/15 |
ERS-1 Geodetic | 168 | - | 1994/04/10 | 1995/03/21 | |||||
ERS-2 | 35 | ±81.5 | 1002 | ~80 | Yes | Yes | Yes | 1995/05/15 | 2002/05/14 |
Envisat | 35 | ±81.5 | 1002 | ~80 | Yes (S-band | 2002/05/14 | 2010/10/18 | ||
Envisat-New Orbit | 30 | ±81.5 | 862 | - | Yes | lost after cycle 65) | Yes | 2010/10/26 | 2012/04/08 |
Cryosat-2 | 29 (sub cycle) | ±88 | 840 | ~98 | No | No | No | 2012/04/08 | 2013/03/14 |
SARAL/AltiKa | 35 | ±81.5 | 1002 | ~80 | Yes | No | Yes | 2013/03/14 | 2016/03/20 |
Sentinel-3A | 27 | ±81.5 | 770 | ~100 | Yes | Yes | Yes | 2016/03/20 | On-going |
Sentinel-6 MF | 10 | ±66 | 254 | ~315 | No | Yes | Yes | 2022/02/10 | On-going |
The user and service requirements related to the sea level ECV product are described in detail in [C3S_TRD]. The characteristics (spatial and temporal coverage) listed in the above table are in agreement with these target requirements. The [C3S_TRD] document also includes a gap analysis, describing what could be achieved to better answer the user's needs so that the sea level product remains relevant and up-to-date.
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Area | Latitude coverage | Longitude coverage |
Global Ocean | 90°S/90°N | 0°/360° |
| Note |
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Note that the latitudinal coverage of the maps depends on the ice coverage and nominally reaches 82° of latitude (except for data from CryoSat-2) because of the orbital inclination of the satellites. When no measurement is available (at higher latitudes or over the continents), the grid is filled with the default '_FillValue'. |
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Type | Name | Content | Unit | Scale Factor |
float | time(time) | Time of measurement | days since 1950-01-01 | none |
float | latitude(latitude) | Latitude of measurement | degrees_north | none |
float | longitude(longitude) | Longitude of measurement | degrees_east | none |
float | lat_bnds (latitude,nv) | latitude values at the north and south bounds of each pixel. | degrees_north | none |
float | lon_bnds(longitude,nv) | longitude values at the west and east bounds of each pixel. | degrees_east | none |
int | nv(nv) | Useful for grid definition | none | none |
int | crs | Describes the grid_mapping used by the data in this file. This variable does not contain any data; only information about the geographic coordinates system. | none | none |
int | sla(time,latitude,longitude) | Sea level Anomaly | meters | 10-4 |
int | err_sla(time,latitude,longitude) | Formal mapping error | meters | 10-4 |
int | ugosa(time,latitude,longitude) | Geostrophic velocity anomalies: eastward zonal component | m/s | 10-4 |
int | vgosa(time,latitude,longitude) | Geostrophic velocity anomalies: northward meridian component | m/s | 10-4 |
int | err_ugosa(time,latitude,longitude) | Formal mapping error on zonal velocity anomalies | m/s | 10-4 |
int | err_vgosa(time,latitude,longitude) | Formal mapping error on meridional velocity anomalies | m/s | 10-4 |
int | adt(time,latitude,longitude) | Absolute dynamic topography | meters | 10-4 |
int | ugos(time,latitude,longitude) | Absolute geostrophic velocity: eastward zonal component | m/s | 10-4 |
int | vgos(time,latitude,longitude) | Absolute geostrophic velocity: northward meridian component | m/s | 10-4 |
int | tpa_correction | TOPEX-A instrumental drift correction derived from altimetry and tide gauges global comparisons | m | 10-4 |
int | flag_ice | Ice Flag based on CDR OSI-SAF products until 2016 (OSI-450), Interim products from 2016 (OSI- 430-b) | - | 10-4 |
Monthly sea level product
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Type | Name | Content | Unit | Scale Factor |
float | time(time) | Time of measurement | days since 1950-01-01 | none |
float | latitude(latitude) | Latitude of measurement | degrees_north | none |
float | longitude(longitude) | Longitude of measurement | degrees_east | none |
float | lat_bnds (latitude,nv) | latitude values at the north and south bounds of each pixel. | degrees_north | none |
float | lon_bnds(longitude,nv) | longitude values at the west and east bounds of each pixel. | degrees_east | none |
| float | climatology_bnds(time,nv) | Useful for grid definition | meters | |
int | nv(nv) | Useful for grid definition | none | none |
int | crs | Describes the grid_mapping used by the data in this file. This variable does not contain any data; only information about the geographic coordinates system. | none | none |
int | sla(time,latitude,longitude) | Sea level Anomaly | meters | 10-4 |
| int | eke(time,latitude,longitude) | Eddy Kinetic Energy | cm2/s2 | 10-4 |
Appendix A - Specifications of the daily sea level product
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Copernicus Climate Change Service
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This document has been produced in the context of the Copernicus Climate Change Service (C3S). The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreement signed on 11/11/2014). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium - Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view. |
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