The Jason-2 Mission Geodetic Phase

Alejandro Egido (NOAA - Laboratory for Satellite Altiemtry, United States)

CoAuthors

Nicolas Picot (CNES, France); Cristina Martin-Puig (EUMETSAT, Germany); Shailen Desai (NASA/JPL, USA); Eric Leuliette (NOAA - LSA, USA); Remko Scharoo (EUMETSAT, Germany)

Event: 2017 Ocean Surface Topography Science Team Meeting

Session: The Geoid, Mean Sea Surfaces and Mean Dynamic Topography

Presentation type: Type Oral

On June 20th, 2017 the four partners Jason-2 Joint Steering Group decided to move the Jason-2 satellite to its geodetic phase. On July 8th, 2017 Jason-2 reached its final long repeat orbit (LRO), approximately 27 km below the historical T/P reference orbit, and on July 11th the onboard instruments resumed nominal operations. The operational geodetic data records (O-GDRs) were analyzed by the four partners before releasing again the products to users.

The Jason-2 LRO is approximately 27 km below the historical T/P orbit still used by Jason-3. It has the following sub-cycles (near repeat) and cycle (exact repeat):

• Sub-cycle: 4 nodal days - 3.97 days - 51 revolutions
• Sub-cycle: 17 nodal days - 16.86 days - 217 revolutions (434 passes)
• Sub-cycle: 81 nodal days - 80.31 days - 1034 revolutions
• Sub-cycle: 145 nodal days - 143.77 days - 1851 revolutions
• Cycle: 371 nodal days - 367.84 days - 4736 revolutions

The first two sub-cycles are beneficial for sea-state and mesoscale operational applications respectively: they guarantee a nearly geographically homogeneous sampling for the temporal scales of interest (e.g. for operational model assimilation). The very long repeat cycle yields a fine grid of approximately 8-km: it is beneficial for marine geodesy (e.g. improvement of bathymetry and mean sea surface models). The 145-day sub-cycle is also a "fallback geodetic sub-cycle”. This sub-cycle was selected as a "coarse geodetic grid", i.e. as a safety net if full geodetic cycles cannot be completed. The strategy is inherited from Jason-1 EoL where we tried to optimize all sub-cycles (shorter ones for sea-state and mesoscale, and longer ones for geodesy). The LRO orbit maximizes the geodetic sampling both at a yearly scale (nominal grid) and for shorter periods of approximately 5 months (fallback grid). To illustrate, assuming Jason-2 dies after 5-6 months of long repeat orbit, at least one “fallback sub-cycle” will be collected. If Jason-2 lives longer than this, multiple coarse resolution grids will be collected. If Jason-2 LRO outlives its first geodetic cycle, it could be possible to let the ground track drift in longitude and to acquire a geodetic dataset with an unprecedented resolution of 4 km or less.

To improve the sea surface height anomaly (SSHA) data quality in the Jason-2 LRO data products an updated mean sea surface (MSS) model has been adopted. The new MSS model is the latest CNES/CLS MSS 2015 solution (https://www.aviso.altimetry.fr/en/data/products/auxiliary-products/mss.html ), which is referenced to the 20-year period spanning 1993-2012. The MSS model provided on the prior data products (version “d” products during the 10-day exact repeat phase) was the 2011 solution, referenced to the 7-year period spanning 1993-1999 and has a lower quality on LRO ground track. The global bias between these two MSS models is approximately 2.5 cm, due to their different reference periods.

In this presentation, we provide specific technical details on the Jason-2 mission geodetic phase, concentrating on the long repeat orbit characteristics and on the quality of the Jason-2 data products after the LRO was attained.
 

Oral presentation show times:

RoomStart DateEnd Date
Symphony II Thu, Oct 26 2017,09:00 Thu, Oct 26 2017,09:15
Alejandro Egido
NOAA - Laboratory for Satellite Altiemtry
United States
alejandro.egido@noaa.gov