1 July 20, 2000 Geosat Follow-On An examination from an operational point of view Impact on operational products Overall system performance (from sensor to product) At the present level, would the data be useful to operational products? What areas would lead to the most significant data improvement?

2 July 20, 2000 System, from Sensor to Product Altimeter InstrumentGeorge Hayne, Dave Hancock(GSFC) Water Vapor RadiometerChris Ruf(Univ. Mich.) Satellite Timing InfluenceJohn Lillibridge, Robert Cheney(NOAA) Ionosphere CorrectionToni Mannucci(JPL) Dry TroposphereNOGAPS Satellite Orbit PositionSteve Klosko, Frank Lemoine(GSFC) Cross-ComparisonsC.K. Shum(Ohio St. Univ.) NAVO ProcessingGregg Jacobs, Kirk Whitmer(NRL)

3 July 20, 2000 Are the Data Good Enough? This is a misleading question Data is never good enough QC and error reduction are the make-or-break component of environmental prediction systems We must always strive to improve system accuracy, reduce data errors, and improve data QC Range Measurement Satellite Range Height above Ellipsoid Sea Level Non-tidal Sea Level Ocean Surface Pressure Temperature and Salinity Structure Radar Path Delays Orbit Solutions Geoid / Mean Ocean Height Tide Model Inverse Barometer (Atmospheric Load) MODAS Synthetics We must consider the entire system

4 July 20, 2000 Are the Data of Sufficient Quality to Include in Operation Products? Would operational products (MODAS, NLOM) benefit from this data as it is now? Yes Points that must be examined to demonstrate this: How does NAVO deal with errors inherent in the present GFO data? To what level are the errors reduced? How do we know products would benefit? What is the product improvement from this data?

5 July 20, 2000 Doppler Orbit Solution Errors GFO SSH using doppler orbits Doppler-based orbit errors are on the order of a 2 meters The oceanographic signal is lost

6 July 20, 2000 Laser Orbit Solution Errors Medium precision laser orbits errors are on the order of 10 cm Some of the larger scale ocean circulation begins to become apparent as individual track errors average out GFO SSH using medium precision orbits

7 July 20, 2000 TOPEX Orbit Solution Errors TOPEX GPS orbits have errors of a few cm Large scale ocean circulation as well as eddy features are visible Some ground tracks are obvious outliers due to orbit errors TOPEX SSH using GPS orbits

8 July 20, 2000 Orbit Error Corrections We want to minimize orbit errors A majority of orbit error is concentrated at long wavelengths Taking advantage of this, we estimate and remove the orbit error from all data streams May 1, 2000July 20, 2000 Estimated Orbit Error Amplitude

9 July 20, 2000 Doppler Vs. Laser Orbits after Correction We correct ALL altimeter data sets for orbit errors The post-correction difference is usually less than 1 cm SSH based on Laser Orbits minus SSH based on Doppler Orbits

10 July 20, 2000 Data Quality Control TOPEXGFO All altimeter data streams pass through a series of quality control filters to detect and remove anomalous data Data removed by QC procedures is flagged and tracked daily QC removes any tracks in which data is found to be anomalous compared to historical data (orange), or in which orbit errors are not correctable (red)

11 July 20, 2000 Global60S to 60N GFO65%81% TOPEX85%95% What Portion of the Data are of Use? TOPEX and GFO processed by the NAVO operational software, ALPS Data from May 1 through July 5 This analysis does not include ALL possible data, but all GDR data from NAVO Events such as the loss of data from being out of ERO are not included Percent of data usable for each day during May and June Most data above 60 N is lost (ERS-2 QC analysis)

12 July 20, 2000 What are the Causes of Data Loss? Doppler orbit splicing appears to be the major contributor to data loss The tracks removed by the QC algorithms from December 1999 indicate laser-based SSH minus doppler-based SSH to have discontinuities

13 July 20, 2000 What is the Data Accuracy? SSH Anomaly difference at points where satellite ground tracks cross one another indicate measurement errors (though actual oceanographic variations will affect the difference) RMS crossover differences of a satellite with itself are a measure of consistency and noise within the individual measurement system, while crossover differences with other satellites are a measure of consistencies between measurement systems SSH difference RMS Crossover differences (cm) between 55S and 55N

14 July 20, 2000 SSH Anomaly Offline T/P and GFO output from ALPS GFO TOPEX

15 July 20, 2000 SSH Anomaly Offline T/P and GFO output from ALPS GFO TOPEX

16 July 20, 2000 SSH Anomaly Offline T/P and GFO output from MODAS 2-D (analysis for June 15, 2000) GFOTOPEX GFO + TOPEX

17 July 20, 2000 Suppose There is an SSH Error, What are the MODAS Temperature Errors? Assume a 5 cm sea surface height error, what are the errors induced in MODAS synthetics?

18 July 20, 2000 Expected SSH Errors Offline T/P and GFO output from MODAS 2-D (analysis for June 15, 2000) GFOTOPEX GFO + TOPEX Missing DataBetween tracks

19 July 20, 2000 Models The NLOM system is presently assimilating TOPEX and ERS-2 NLOM SSH NAVO BOGUS positions based on MCSST

20 July 20, 2000 Model Assimilation Errors Based on twin model experiments Errors are dependent on ground track coverage and quantity of data Increased data quantity improves model results

21 July 20, 2000 A substantial portion (81%) of GFO data is presently useful in operational products Operational products will benefit from this data Data improvement efforts would continue to increase the data return and accuracy GFO