Near Real-Time Alongtrack Altimeter Sea Level Anomalies: Options Corinne James and Ted Strub Oregon State University Motivation Modelers want easy access to alongtrack SSHA, SLA or ADT, with enough explanations to understand the uncertainties. Asked C. James to survey what is out there, as a new user. A month later we have 17 pages of notes and growing. This is something the community should do, and update regularly. Non-modelers (and some modelers) are also interested in the gridded SSHA, SLA, ADT data.
Oceanographers are aware of three types of ALT data records, depending on how long it takes to produce them: OGDR, IGDR, GDR RT, NRT, DT 0-7 hr 2-3 d 1-6 mo Data Type Input Data Characteristics of Different Latency Types Alongtrack Single-Mission Alongtrack Multi-Mission RT OGDR <7 hr On Board Delay Orbit Tracking Corrections Input Data Delay Orbit Tracking Corrections OB Model (Pred) OGDR 3-12 hr OB OB Model (Pred) NRT IGDR 2-3 d OB Ground Updated OGDR 3 d OB Ground Updated Historical NRT IGDR 1 MO Ground Ground Updated DT GDR 1-6 mo POD Ground Best DT- Ref GDR 2 mo POD Ground Best DT- Upd GDR 2 mo POD Ground Best Reference = 2 ALT (T/P and ERS Tracks); Updated 4 ALT
Organization Geosat T/P J1 J2 GFO ERS-1 ERS-2 ENVI SAT JPL/PO.DAAC º JPL/Pathfinder º º º º º º? (to mid-2004) NOAA/NESDIS RADS (OGDR,IGDR,GDR) EUMETSAT ESA We can get date from multiple sources or find sources that reliably take responsibility to ensure that the data are consistently processed. AVISO ssalto/duacs (Multisensor) Pistach Sources for Alongtrack Data Sets º º º º º º º º º X CoastALT X CTOH X X X NRL MODAS (RT) º Completed Mission Ongoing Mission X Experimental
Other Variations in the Along-Track Data Alongtrack gridded data: We need to move the data point in the acrossand along-track directions to a standard grid. The Mean Sea Surface (MSS), geoid, and Mean Dynamic Typography all may change over this distance. For exact repeat tracks, we have built up a detailed MSS field from the satellite s wandering ± 1 km over many years. SSH = Altitude range - corrections SSHA = SSH temporal mean, interpolated to data point SLA = SSHA MSS profile inter-mission bias [more detailed cross-over analysis and large-scale regressions remove orbit errors better than a simple inter-mission bias ] ADT = SLA + MDT MDT = MSS geoid X x X Interaction between ALT and Model community would help to clarify which variable is most useful for the modelers.
Jason-1 OSDR: (2-3 hours, for met) OSDR-SSHA (7 hours) IGDR (2-3 days) SSHA GDR (4-6 weeks) SSHA, ATG TOPEX/Poseidon GDR MGDR SSHA, ATG SSHA Example JPL Pathfinder (to mid-2004) Multiple satellites, not updated since 2004. Geosat and GFO
Example NOAA Jason-2 OGDR: (3-5 hours) SSHA: 1Hz and 20Hz IGDR (1-2 days) SSHA: 1Hz and 20Hz S-IGDR (1-2 days) Includes waveform data GDR (60 days) SSHA Example EUMETSAT Jason-2 OGDR: (3-5 hours) SSHA: 1Hz and 20Hz ENVISAT IGDR S-IGDR GDR S-GDR Example ESA
Example RADS (NOAA LSA) ALL ALTIMETERS Alongtrack SLA (not interpolated to a standard grid) Most recent updates: OGDR > IGDR > GDR Multiple choices for correction terms or use of a default NOAA LSA ASCII data in subset regions for the operating satellites Is this the most appropriate type of data for modelers?
Example AVISO Mono-Mission Products Jason-2 IGDR, SSHA, S-IGDR (1-2 days) GDR, GDR-SSHA, S-GDR (60 days) DT CorSSH (fixed grid) (Altitude Range Corrections) (90 days) DT SLA (SSH MSS Mean Profile Inter-Mission Bias) (90 days) PISTACH experimental ocean or land (25 km overlap) ENVISAT DT CorSSH (90 days) DT SLA (90 days) Jason-1 IGDR, S-IGDR (2-3 days) GDR, S-GDR (4-6 weeks) DT CorSSH (90 days) DT SLA (90 days) ERS-1, ERS-2, GFO, T/P: DT CorSSH, DT SLA (T/P: MGDR, WVFDR, WWV)
Example AVISO (Ssalto/Duacs) Multi-Mission Alongtrack Products Daily cross-over analyses, OI long-wavelength error, fixed alongtrack grid Jason-1, Jason-2, Envisat (presently operating) RT-SLA (OGDR SSH MSS Mean Profile Inter-Ocean Bias, fixed grid) RT-ADT (SLA + MDT) (3-12 hours) NRT-SLA, NRT-ADT OGDR (3 days) NRT-SLA, NRT-ADT historical IGDR (1 month) DT-SLA, DT-ADT: Reference (2 satellites) (2 months) DT-SLA, DT-ADT: Updated (all satellites) (2 months) Regional (Med Sea and Black Sea) Extended (NE Atlantic, Gulf of Mexico) T/P, ERS-1, ERS-2, GFO DT-SLA, DT-ADT, Ref and Upd (2 months) Multi-Mission MAPPED Products MSLA and MADT Similar versiona to Alongtrack data 1/3º, 1/4º, 1º RT (OGDR, 0 days), NRT (OGDR, 0-6 days), historical NRT (IGDR, 1 month), DT Reference and Upd (2 months) Monthly mean climatology SLA
Other Issues Wet Tropo Tracking Tides SSB? Use of tide gauges to fill in Smoothing and other techniques to use the noisier RT and NRT data. How to approximate the CTOH quality? Detailed editing and smoothing of individual corrections? Or just edit and smooth the final SLA? Recommend? RADS for Alongtrack Data, AVISO for mapped data. Edit and smooth final SLA
Near Reducing Noise: If modelers want to use the RT or NRT data, what editing and Smoothing is needed? Editing and smoothing final SLA works as well as editing and smoothing all of the corrections.