Different events can lead to a reduction of data availability. Among these, the most common events are the following:
- A change in the altimeter constellation: either the loss or the introduction of an additional altimeter in the constellation directly impacts the number of altimeter measurements available.
- For a specific platform, a reduction in the number of altimeter measurements available as inputs of the DUACS system processing. This can be linked to an anomaly onboard the platform or on the ground segment, preventing the data reception and impacting the L0 to L2 processing. It can also be induced by an degraded aquisition of the DUACS system that can be induced by missing upstream products and/or auxiliaries (e.g : various geophysical correction specificaly updated at L3)
- An increase of invalid measurements used as inputs of the DUACS system processing. This is usually linked to specific platform events (e.g., manoeuvres), but can also be induced by L0-L2 processing anomalies or specificities. In some rare cases, degraded acquisition by the DUACS system can also lead to an bad data selection.
In December 2023, eight altimeters constitute the altimeter constellation available in NRT 1H:
- Sentinel-6A (S6A) was introduced in the DUACS system in April 2022. It is the reference mission (Jason-3 previously reference mission).
- Jason-3 was temporarily deactivated from the System in Apr 2022 (same orbit than Sentinel6A). It was reactivated on May 2022, once on its new interleaved orbit.
- Sentinel-3A (S3A).
- Sentinel-3B (S3B).
- SARAL-DP/AltiKa (AL). Since February 2019, miss-pointing anomaly leads to a significant reduction of valid measurements. Due to the risk of degradation of the DUACS production, the mission was deactivated from the system starting from 2019/02/04. The mission was reactivated in October 2019 after adding new editing procedures to remove miss-pointing anomalies.
- Cryosat-2 (C2): The last important event occurred during summer 2014, when a processing anomaly induced an important number of L2 missing measurements. These measurements were reprocessed afterward.
- HaiYang-2B (HY-2B).
SWOT-nadir: introduced in the DUACS system in November 2023.
Table : Main events affecting the data availability in NRT conditions.
| Date | Platform | Event |
|---|---|---|
| 2020/01/31-2020/02/13 | J3 | The mission entered in safe hold mode.
The Sentinel-3A mission is used as temporary anchor mission for cross-calibration processing from 2020/02/06 to 2020/03/03 |
| 2020/06/15-2020/06/23 | J3 | The mission entered in safe hold mode |
| 2020/07/07 | HY-2B | HY-2B is introduced in DUACS NRT processing |
| 2020/11/30-2020/12/04 | HY-2B | No upstream measurement available |
| 2021/08/16-2021/08/17 | HY-2B | No upstream measurement available |
| 2020/07/15-2020/10/29 | C2 | The processing of the C2 mission was inhibited, time to manage an orbit change for this mission |
| 2022/04/06 | S6A | Sentinel6A (HR measurement) is introduced in DUACS NRT processing |
| 2022/04/06 – 2022/05/24 | J3 | The processing of the mission was inhibited, time to manage an orbit change for this mission |
| 2022/10/09-2022/10/11 | HY-2B | No upstream measurement available |
| 2022/10/11 | AL | No L3 measurement available |
| 2022/11/17-2022/12/02 | S6A | Various sections of tracks are missing in upstream products. |
| 2022/12/30- 2023/01/08 | AL | |
| 2023/04/30-2023/05/05 | S3A & S3B | Data available with few days delay due to missing L0 inputs from the Marine PDGS (Payload Data Ground Segment) |
| 2023/0731-2023/08/05 | H2B | Data unavailability due to satellite manoeuvre |
| 2023/11/30 | SWON | SWOT-nadir is introduced in DUACS NRT processing |
| 2024/05/11-2024/05/17 | H2B | Data unavailability |