L2p Upstream data

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.

Altimeter mission Type of product Source Availability delay
Sentinel-3A NRT ESA/EUMETSAT ~3h
STC ~48h
NTC ~1 month
Jason-3 OGDR EUMETSAT/NOAA ~3 to 5h
IGDR CNES ~24h
GDR CNES ~1 to 2 months
Jason-2 OGDR EUMETSAT/NOAA ~3 to 5h
IGDR CNES ~24h
GDR CNES ~1 to 2 months
Cryosat-2 OGDR ESA/CNES Best effort
IGDR ~48h
GDR ESA Best effort
Saral/AltiKa OGDR ISRO/EUMETSAT ~3 to 5h
IGDR CNES ~48h
GDR CNES ~2 months
HY-2A GDR NSOAS Best effort
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
Geosat Follow On GDR NOAA Reprocessing only

Table: Source and delay of availability of the different altimeter data used in input of DUACS system

 

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 data availability Start-End dates
Sentinel-3A 27 ±81.5 770 ~100 Yes Yes Yes 2016/12/13 (cycle 12)

Ongoing

Jason-3 10 ±66 254 ~315 No Yes Yes 2016/02/17 (cycle 1)

Ongoing

Jason-2 10 ±66 254 ~315 No Yes Yes 2008/07/12 (cycle1)

2016/10/02 (cycle 303)

Jason-2 Interleaved 10 ±66 254 ~315 2016/10/13 (cycle 305)

2017/05/17 (cycle 327)

Jason-2 Geodetic tbc tbc tbc tbc 2017/07/11

Ongoing

Cryosat-2 29 (sub cycle) ±88 840 ~98 No No No 2011/01/01 (cycle 13)

Ongoing

Saral/AltiKa 35 ±81.5 1002 ~80 Yes No Yes 2013/03/14 (cycle 1)

2016/07/04 (cycle 35)

SARAL-DP/AltiKa ? ±81.5 ? 2016/07/04 (cycle 100)

Ongoing

HaiYang-2A 14 ±81 386 ~210 Yes Yes Yes 2011/10/01 (cycle 1)

2016/05/03 (cycle 120)

HaiYang-2A geodetic 168 ±81 2016/03/24 (cycle 1)

Ongoing

Topex/Poseidon 10 ±66 254 ~315 No Yes Yes 1992/09/25 (cycle 1)

2002/08/21 (cycle 365)

Topex/Poseidon Interleaved 10 ±66 254 ~315 23/08/2002 (cycle 366)

2005/10/08 (cycle 481)

Jason-1 10 ±66 254 ~315 No Yes Yes 2002/01/15 (cycle 1)

2009/01/26 (cycle 259)

Jason-1 Interleaved 10 ±66 254 ~315 2009/02/10 (cycle 262)

2012/03/03 (cycle 374)

Jason-1 Geodetic 10.91 ±66 280 2012/05/07 (cycle 500)

2013/06/21 (cycle 537)

Envisat 35 ±81.5 1002 ~80 Yes Yes (S-band lost after cycle 65) Yes 2002/04/10 (cycle 5)

2010/10/18 (cycle 93)

Envisat-New 30 ±81.5 862 2010/11/27 (cycle 96)

2012/04/08 (cycle 113)

ERS-1 35 ±81.5 1002 ~80 Yes Yes Yes 1992/10/23 (cycle 15)

1993/12/20 (cycle 27)

And

1995/03/240 (cycle 41)

1996/06/02 (cycle 53)

ERS-1 geodetic 168 ±81.5 04/10/1994 (cycle 30)

03/21/1995 (cycle 40)

ERS-2 35 ±81.5 1002 ~80 Yes Yes Yes 1995/05/15 (cycle 1)

2011/07/04 (cycle 169)

Geosat Follow On 17 ±72 488 ~165 No No Yes 2000/01/07 (cycle 37)

2008/09/07 (cycle 222)

Table : Altimeter missions characteristics and L2p products availability period