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Jason-Continuity of Service

Jason-Continuity of Service. Meeting: Science requirements for the Jason-CS orbit Different orbit after Jason-3? Two studies. Main question to be addressed. Is it possible to consider a lower altitude orbit for the Jason-CS series without detrimental

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Jason-Continuity of Service

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  1. Jason-Continuity of Service • Meeting: • Science requirements for the Jason-CS orbit • Different orbit after Jason-3? • Two studies

  2. Main question to be addressed • Is it possible to consider a lower altitude orbit • for the Jason-CS series without detrimental • effects on the key applications that are • dependent on the series [Jason] of missions? • EUMETSAT commissioned two studies.

  3. Study commissioning: Constraints • General: • Emphasis on continuity of Mean Sea Level Rise Record • Contributing to observing of the mesoscale variability • Technical: • Exact repeat • Avoidance of tidal aliasing • Avoidance of climate signal aliasing • Optimisation in a constellation of nadir altimeter • Only Non-Sun-synchronous Orbits • However, question old strategies and define best choices for future missions

  4. Recently completed studies (CLS, Hamburg) • CollecteLocalisation Satellite (CLS) group (PM: Joel Dorandeu) • Assessment of tidal aliasing • Down-selection of few orbit candidates allowing for low orbits • Assessment of spatial and temporal sampling in relation to key applications • Consideration of reference altimetry system, as part of a 2 or 3 satellite constellation • Universität Hamburg (UHH) group (PM: Detlef Stammer) • Building on initial results from CLS study (few orbit candidates) • Focus on mean SSH changes and tides • Consideration of reference altimetry system, as part of a 2 or 3 satellite constellation

  5. CLS Study: Pre-selection of orbit candidates Global recommendations from analysis of past and planned altimeter missions - Optimisation of orbitgeometry Altitude between 800 and 1400 km (Berthias, 2008) Repeat cycle between 10 and 35 days High inclination to cover polar oceans Non sun-synchronousorbits => 22000 potential orbits! Tidal aliasing criteria were applied to filter out unsuitable orbits

  6. CLS Study: Orbit candidates, after drastic selection

  7. Impact of orbit candidates on MSL trend estimation – A samplingeffect! cm • SLA mapsinterpolatedunder satellites groundtracksthen global and regional estimations of MSL trends: • Global MSL trend: • -No impact of the orbit configuration on global MSL trend • Regional MSL trends: • Differences in West Indian Ocean, the North sea, the Baltic sea, the North Pacific Ocean • - upto ~ 2 mm/y differences • - Differences not visible between J1 and A878 which have a similar cycle (10 days)

  8. Evolution of the cross-track distance as a function of observing duration • J1+TPN best for 7-12 days • A926 and A923 can resolve smaller scales for 1-3 days time scales • A926, A801 and A1104 can resolve smaller scales for longer period >12-13 days (= mesoscale observation) • A1104 is bad for periods below 11 days • A878 is good for 9-10 days periods

  9. CLS Reconstruction error on SSH and currents • Mono-satellite: • Jason has the worst performances • GFO has the smallesterrors • A878 (c10) isbetterthan Jason (lower alt.) • A926 (c13) is best option - similar to GFO • Multi-satellites constellations: • 4-sat. configuration is the best configuration • 2 sat. : • The optimized J2-J1N is the best option by far • Very few differencesbetweenother configurations • Proposedorbit candidates have slightlysmallererrors: A926 (c13) the best • Results are consistentswithotherstudiesalthoughconsideringdifferent model and regions

  10. CLS Study: Orbit Candidate Shortlist • A878_i66_c10: basically equivalent to a Jason orbit, but in a 850-900 km range (139 revolutions per cycle vs 127  10% denser sampling than Jason), sub-cycle duration is different : 1 day vs 3 days, scanning over 3000 km (with a resolution of 300km) without any interlacing • A926_i67_c13: A GFO-like repeat cycle and a T/P-like inclination, Sub-cycle duration is 4 days, interlaced scans of 3000km at a resolution of 750km, every 4 days. • A801_i71_c22: a longer repeat cycle of 22 days and a 7 day sub-cycle 3 interlaced eastward propagating scans performed within a given cycle spatial resolution of these sub-cycle scans is roughly equal to 430km. Synthesis of the interest of the orbit candidates as far as applications are concerned. 1 is for best suitability; 2 medium; 3 for least favourable case; score 0 or grey columns correspond to the case when the orbit is not optimised for the application.

  11. Hamburg Study: POP model versus altimetry POP (daily maps) Eddy resolving 10 years data Merged Altimeter (TPO/ERS or JS-1/Env, AVISO weekly maps)

  12. Global mean error spectrum: mono-satellite missions 1 cpy < f ≤ 12 cpy f ≤ 1 cpy error variance [cm2] error variance [cm2] cm² cm² • Spatial errors decrease with increasing ERP • Temporal error increases with increasing ERP • Optimum: ERP ≈ 20 days (annual – interannual SSH) • ERP ≈ 15 days (monthly – intra-annual SSH)

  13. Global mean error spectrum: orbit constellations cm² cm² f ≤ 1 cpy 1 cpy < f ≤ 12 cpy • Three- and four-satellite constellations have similar performance, especially for annual mean SSH and spatial errors • 22 days ERP orbit has large temporal error, better combination with S-3A,B constellations is ERP=13.5 days

  14. SSH error depending on orbit inclination:global ocean Error strongly dependent on inclination: 1.2 mm (i=65°)  0.5 mm (i=76°)  0.3 mm (i=81°) for ERP/1 month 0.3 mm(i=65°)  <0.2 mm (i=76°)  <0.1 mm (i=81°) for annual mean SSH Error cm [cm] inclination [°] Inclination Reference numbers: Annual cycle: ~ 4 mm, Trend: ~ 3 mm/year Larger error results from not sampling the high-latitude oceans

  15. Global ocean: variability • Mono-satellite missions: strong dependence on inclination, as already discussed • No strong deviations from earlier finding • Only small difference among the constellations (A801-i71-c22 is best) error variance [cm2]

  16. Global ocean: Trend • Best candidate mission is mono-satellite mission with highest inclination (76°) • All constellations have only slightly larger error • Worst case error (0.063 mm/a) only 2% of expected trend (3mm/a) trend error [cm/a]

  17. Hamburg Study: Conclusions and Orbits • The detailed choice of orbits of future single- or constellation satellite missions will not fundamentally impact the estimates of large-scale and global SSH time series • Other important conclusion were that • A larger error does result from not sampling the global ocean. For global ocean and large regions on high latitudes (Nordic Seas, Arctic Ocean) SSH error depends strongly on inclination. • Based on simulated SSH observations, constellations lead to slightly better results, however, the improvement is marginal. • Proposed Orbits: (in addition to CLS study recall T/P orbit and SWOT orbit suggestions)

  18. Combined Study conclusions • It is possible to fly in a lower altitude orbit for the Jason series without detrimental effects on the key applications depending on the series of missions, including the sea level rise monitoring. • Proposing a final preference is difficult. Given the climate objective of the Jason-series, missions with a higher inclination could be preferred. • Further consideration should be given to an orbit with a even a higher inclination (>=78 degrees), to fully cover the global ocean and to broaden the scientific return over land. • Although not addressed in detail in these studies in detail: Special care should be taken to cal/val issues related to a change in orbit.

  19. The agencies would like: • a clear scientific recommendation : • On acceptance of a change of orbit to meet the definition of a reference climate mission • and a ranking of preference for the proposed orbits. • Or the justification for keeping the Jason orbit

  20. End of Presentation • End of Presentation.

  21. Rationale for a lower/different orbit • Extendedexpectedlifetime – reducedexposure to radiation • Better de-orbitingpossibilities - Bigreduction in neededpropellant. • Optimisation of spatial temporal sampling - In a constellation contextdifferentchoicescanbe made. • Higher inclination to get more polar ocean observations -potentialalignmentwith SWOT. • Reducedlaunchcosts - (likelyminor)

  22. Rationale for remaining in current orbit • Guaranteedcontinuity of climate data record – primary objective of Jason-CS • Jason-CS will have a new altimeter, new bus, & possibly new radiometer – hence, greatneed for cross-calibration. • 10-day orbit provides simultaneous collinear cross-calibration in 'formation-flight' phase. (New orbit will only provide non-simultaneous crossover calibration.) • Orbital debris at 1336-km much less than at lower orbits, greatly reducing need for avoidance maneuvers and risk of mission loss • High latitude & meso-scale will be covered concurrently by at least 2 Sentinel altimeters. • What defines a reference mission if not the present 10-day orbit?

  23. Methodology gridding espat observation SSHPOP daily, 10‘ reality etemp Orbit track for one ERP etotal observation gridding negligible

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