Altimeter upstream data description
DUACS system takes in input Level 2 Plus (L2P) altimeter products and processes a cross-calibration and merging processing in order to generate and deliver Level 3 (L3) and Level 4 (L4) products. L2P products generation is under the responsibility of different space agencies. Contrary to L2 products, L2P products include the update of geophysical standards to calculate sea level anomalies (i.e. instrumental, geophysical, environmental corrections; MSS) (see table for the list of the different corrections applied) and a validity flag that is used to remove spurious measurements. The L2P measurement from different altimeters is not cross-calibrated; this means that some global and regional biases can be observed between measurement from two different altimeters.
The L2P altimeter measurements used as input in the DUACS system consist in products from different missions, that are available under three forms, with different delays of availability:
- Fast delivery or Near Real Time products (OGDR or NRT). These products do not always benefit from precise orbit determination, nor from some external model-based corrections (Dynamic Atmospheric Correction (DAC), Global Ionospheric Maps (GIM)).
- The Intermediate or Short Time Critical products (IGDR or STC) that are the latest high-quality altimeter data produced in near-real-time
- Delayed Time or Non Time Critical product (GDR or NTC)
Details of the different L2p altimeter products sources and delay of availability are given in the following tables.
OGDR/NRT and IGDR/STC are both used in operational system while GDR/STC are involved in delayed time processing.
Table: Source and delay of availability of the different altimeter data used in input of DUACS system
| Altimeter mission | Type of product | Source | Availability delay |
|---|---|---|---|
| Sentinel-3A | NRT | ESA/EUMETSAT | ~3 h |
| STC | ~48 h | ||
| NTC | ~1 month | ||
| Sentinel-3B | NRT | ESA/EUMETSAT | ~3 h |
| STC | ~48 h | ||
| NTC | ~1 month | ||
| Sentinel-6A | NRT | ESA/EUMETSAT | ~3 h |
| STC | ~48 h | ||
| NTC | ~1 month | ||
| Jason-3 | OGDR | EUMETSAT/NOAA | ~3 to 5 h |
| IGDR | CNES | ~24h | |
| GDR | CNES | ~3 months | |
| Cryosat-2 | NOP | ESA/CNES | ~7 h |
| IOP | ~48 h | ||
| GOP | ESA | ~3 month | |
| Saral/AltiKa | OGDR | ISRO/EUMETSAT | ~3 to 5 h |
| IGDR | CNES | ~48 h | |
| GDR | CNES | ~2 months | |
| SWOT-nadir | OGDR | CNES | ~3 to 5 h |
| IGDR | CNES | ~48 h | |
| HaiYang-2C | IGDR | NSOAS | ~48h |
| HaiYang-2B | IGDR | NSOAS | ~48 h |
| GDR | NSOAS | Best effort | |
| HaiYang-2A | GDR | NSOAS | Best effort |
| Topex/Poseidon | GDR | CNES | Reprocessing only |
| Jason-1 | GDR | CNES | Reprocessing only |
| Jason-2 | GDR | CNES | Reprocessing only |
| Envisat | GDR | ESA | Reprocessing only |
| ERS-1 | GDR | ESA | Reprocessing only |
| ERS-2 | GDR | ESA | Reprocessing only |
| Geosat Follow On | GDR | NOAA | Reprocessing only |
Table : Altimeter missions characteristics and L2p products availability period
| Altimeter mission | Cycle duration (days) | Latitude range (°N) | Number of track in the cycle | Inter-track distance at equator (km) | Sun-synchronous | Dual-frequency Altimeter | Radiometer on board | Input (L2p) data availability Start-End dates |
|---|---|---|---|---|---|---|---|---|
| Sentinel-3A | 27 | ±81.5 | 770 | ~100 | Yes | Yes | Yes | 2016/03/01 (cycle 1) |
| Ongoing | ||||||||
| Sentinel-3B | 27 | ±81.5 | 770 | ~100 | Yes | Yes | Yes | 2018/11/23 (cycle 19; interleaved orbit) Ongoing |
| Sentinel-6A | 10 | ±66.0 | 254 | ~315 | No | Yes | Yes | 2020/11/30 (cycle 1) |
| Ongoing | ||||||||
| SWOT-nadir (Calval phase) | 1 | ±77.6 | 28 | ~1500 | No | Yes | Yes | 2023/01/17 (cycle 403) |
| 2023/07/20 (cycle 588) | ||||||||
| SWOT-nadir (science phase) | 21 | ±77.5 | 584 | ~140 | No | Yes | Yes | 2023/07/21 (cycle 1) |
| Ongoing | ||||||||
| Jason-3 | 10 | ±66.0 | 254 | ~315 | No | Yes | Yes | 2016/02/12 (cycle 1) |
| 2022/04/07 (cycle 226) | ||||||||
| Jason-3 Interleaved | 10 | ±66.0 | 254 | ~315 | No | Yes | Yes | 2022/04/25 (cycle 300) |
| Ongoing | ||||||||
| Jason-2 | 10 | ±66.0 | 254 | ~315 | No | Yes | Yes | 2008/07/12 (cycle1) |
| 2016/10/02 (cycle 303) | ||||||||
| Jason-2 Interleaved | 10 | ±66.0 | 254 | ~315 | No | Yes | Yes | 2016/10/13 (cycle 305) |
| 2017/05/17 (cycle 327) | ||||||||
| Jason-2 | 9.86 | ±66.0 | 254 | – | No | Yes | Yes | 2017/07/11 (cycle 500) |
| Long Repeat Orbit | 2018/11/13 (cycle 612) | |||||||
| Cryosat-2 | 29 (sub cycle) | ±88.0 | 840 | ~98 | No | No | No | 2010/07/16 (cycle 7) |
| 2020/07/31 (cycle133) | ||||||||
| Cryosat-2 New Orbit | 25 (sub-cycle) | ±88.0 | 724 | ~98 | No | No | No | 2020/08/01 (cycle 200) Ongoing |
| Saral/AltiKa | 35 | ±81.5 | 1002 | ~80 | Yes | No | Yes | 2013/03/14 (cycle 1) |
| 2015/03/31 (cycle 24) | ||||||||
| SARAL-DP/AltiKa | 35 | ±81.5 | 1002 | – | Yes | No | Yes | 2015/03/31 (cycle 24) |
| Ongoing | ||||||||
| HaiYang-2A | 14 | ±81.0 | 386 | ~210 | Yes | Yes | Yes | 2014/04/12 (cycle 67) |
| 2016/03/15 (cycle 117) | ||||||||
| HaiYang-2A geodetic | 9 (sub cycle) | ±81.0 | 248 | – | Yes | Yes | Yes | 2016/03/30 (cycle 118) |
| 2020/06/09 (cycle 289) | ||||||||
| HaiYang-2B | 14 | ±81.0 | 386 | ~210 | Yes | Yes | Yes | 2019/11/15 (cycle 27) |
| Ongoing | ||||||||
| Topex/Poseidon | 10 | ±66.0 | 254 | ~315 | No | Yes | Yes | 1992/09/25 (cycle 1) |
| 2002/04/23 (cycle 353) |