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NASA Activities in Support of an Advanced Altimeter Mission Tony Freeman

This document outlines the current status, study background, mission objectives, and mission concept for an advanced altimeter mission in support of land and ocean applications. The mission aims to continue sea surface height measurements, study mesoscale phenomena, and enhance understanding of Earth systems. The proposed mission concept includes innovative instruments like a wide-swath radar altimeter and a nadir altimeter, with a budget estimate of around $500 million. The partnership involves NASA, NOAA, and the Navy, with a planned launch date for 2012 to ensure continuity with previous missions. New technology and requirements traceability matrices are highlighted, indicating the mission's alignment with decadal survey results and agency needs.

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NASA Activities in Support of an Advanced Altimeter Mission Tony Freeman

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  1. NASA Activities in Support of an Advanced Altimeter MissionTony Freeman October 2006

  2. Current Status • WSOA was descoped from the OSTM mission in 2005 • In May 2006, the acting division manager for Earth Science at HQ, Bryant Cramer, commissioned a study of a new advanced altimeter mission • Study is the 1st (of several) done in anticipation of decadal survey results • Mission objectives were to include land and ocean applications • Study was completed at the end of summer • Since then, three joint meetings involving NASA, NOAA and the Navy have been held - next meeting in late November • All three agencies need a follow-on altimeter after OSTM, which launches in 2008 and is expected to last 5 years • All 3 agencies require backwards compatibility with the TOPEX/Poseidon/ • Jason-2/OSTM climate data records, i.e. global sea level • An additional driver for NASA is to further our understanding of the Earth system through advances in measurement capability • The advanced altimeter study resulted in a mission concept that can meet the requirements of all three agencies at reasonable cost

  3. Mission Concept • Instruments: • Ka-band wide-swath radar altimeter (1-2 km resolution) • Ku-band nadir altimeter • 3-freq. water vapor radiometer • GPS for POD • Laser retroflector for POD • Orbit: • 993 km altitude, 78 deg inclination • 21-day exact repeat, 10.5 day revisit • Delta II launch • Science Objectives: • Sea surface height measurements (continue the Jason/TOPEX series) • Study mesoscale phenomena • Ocean bathymetry (surface slopes) • Land surface water (hts.+ gradients) • Programmatics: • NASA/NOAA/Navy partnership • Currently no US altimeter planned after Jason-2 • Possible Eumetsat/CNES roles • Launch date 2012 for continuity with Jason-2 • 5-year mission • Mission Cost ~ $500M (FY ‘06) • New technology: • Wide-swath altimeter is a SAR interferometer • Onboard processing

  4. 1- Requirements Traceability • Science requirements are derived from three primary mission concepts submitted to the NRC decadal survey RFI: The WatER mission The Hydrosphere Mapper mission The Bathmetry ABYSS mission Navy and NOAA requirements are derived from: • Navy Altimeter Requirements, Jacobs, G. A. et al, Naval Research Laboratory, NRL/FR/7320--99-9696, Nov. 1999 • NPOESS Integrated Operational Requirements Document-II, January 2002

  5. Apr24_06HM_pollardCharts_2.ppt NASA Requirements: Traceability Matrix(1 of 2) Surface WaTER Sea Surface Topography

  6. Sea Surface Topography Cont. Bathmetry Apr24_06HM_pollardCharts_2.ppt NASA Requirements: Traceability Matrix (2 of 2) References: WatER: The Water Elevation Recovery Satellite Mission, Response to the National Research Council Decadal Survey Request for Information, Doug Alsdorf1, Ernesto Rodriguez2, Dennis Lettenmaier3, and Jay Famiglietti41Ohio State Univ., 2NASA JPL, 3Univ. of Washington, and 4Univ. of California, Irvine The WatER Mission, www.geology.ohio-state.edu/water The Global Hydrosphere Mapper, Response to the National Research Council Decadal Survey Request, L-L. Fu, E. Rodriguez, Jet Propulsion Laboratory, California Institute of Technology ABYSS-Lite: A radar altimeter for bathymetry, geodesy and mesoscale oceanography, Smith et. al. 2005 Altimetric BathmetrY from Surface Slopes, A Proposal in response to NASA AO01-OES-01, July 20, 2001, Principal Investigator: Dr. Walter H. F. Smith

  7. Navy Requirements • Sea Surface height, atmospheric correction parameters, and orbit solutions are required within 48hours. Wave heights are required within 3 hours. • The required instrument white noise level must be below 3 cm rms. • The required total range error must be under 5 cm (peak error) after all atmospheric corrections are applied. • Required real time orbit solutions must contain under 1 m error at 1 cycle per satellite orbit revolution (cpr) and less than 2 cm integrated errors at higher frequencies. • An exact repeat orbit must be required, and the satellite must be held to within a 1 km swath of a predefined ground track. • The required repeat period must not be less than 20 days* • A minimum of one instrument is required. With only one instrument, this data must be used in conjunction with systems such as MODAS and NRL Layered Ocean Model (NLOM). • Two altimeter are recommended on the NPOESS Polar-Orbiting Operational Environmental Satellite System (NPOESS) for error reduction and redundancy. • Major tidal constituents should not be aliased to frequencies that contain significant ocean variability. These frequencies include the annual, semi-annual, and mean. Source: Navy Altimeter Requirements, Jacobs, G. A. et al, Naval Research Laboratory, NRL/FR/7320--99-9696, Nov. 1999. * "The NPOESS IORD-II contains approved/validated altimeter requirements that adequately define the Navy's needs; however, recent studies show that Navy would consider an Exact Repeat Period threshold of slightly greater than the currently cited 20 days." Cmdr. Mark Gunzelman, personal communication, Aug 2006

  8. NPOESS Requirements Source: NPOESS Integrated Operational Requirements Document-II, January 2002

  9. NPOESS Requirements Source: NPOESS Integrated Operational Requirements Document-II, January 2002

  10. 5- Mission Concept- Orbit Parameters • 78 degrees inclination. • Exact repeating groundtrack after ~21 days (286 orbits at 993km). • This leaves ~17x100km diamond-shaped areas (see graphic) not covered (~1% of area on earth in +-30deg lat; ~0.5% +-78deg Lat.) • Orbit will be shifted in longitude after 1.5 years to fill gaps for bathymetry science coverage. • 993 km altitude was chosen to provide an even distribution of coverage during cycle completion. Range of altitude explored: 800 to 1000km. Ref: Francois Rogez (JPL) this study may 2003

  11. 5- Mission Concept: Orbit Parameters:Coverage map after 21 days • After 21 days, 286 swaths are uniformly distributed in longitude, leaving gaps of 17 km between swaths at the equator. • Adding up the coverage from ascending and descending passes leaves diamond shaped gaps with a cumulative area measuring about 800k m^2 at the equator. • The gaps disappear above • 30 deg latitude. • All coverage Gaps are • filled when the orbit • is shifted at 1.5 yr • Intervals over • mission life Maps near the equator showing the 120km swath and the ~17 km gaps. A 1 degree lat/lon grid is shown with dotted red lines. Ref: Francois Rogez (JPL) this study

  12. 10- Key Instrument Performance Parameters: Ka-Band Interferometer Performance Summary 4/18/06 Ref: Louise Veilleux Advanced Altimeter Mission Study, (JPL) April 2006

  13. 10- Key Instrument Performance Parameters: Ku & C-Band Altimeter & Radiometer Summary 4/18/06 Ref: Louise Veilleux Advanced Altimeter Mission Study, (JPL) April 2006

  14. Science Measurement Requirements • Continues the TOPEX/Jason/OSTM record while adding new capabilities

  15. Summary • Study Conclusions: • Trade study examined many options • An advanced altimeter mission can meet the diverse requirements of NASA, the Navy and NOAA • Estimated cost to each agency is less than a stand-alone conventional altimeter mission • International partnering arrangement with CNES/Eumetsat in the mode of Jason-1 is feasible • For a late 2011 launch and overlap with OSTM (Jason-2), need a Phase A start in 2007 ==> Decision point shortly after release of decadal survey

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