Advanced Altimeter Mission

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					NASA Activities in Support
of an Advanced Altimeter

      Tony Freeman
        October 2006
                         Advanced Altimeter Mission
                          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
                            Advanced Altimeter Mission
                           Mission Concept
                                             • 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
                                            • 993 km altitude, 78 deg inclination
                                            • 21-day exact repeat, 10.5 day revisit
                                            • Delta II launch
Science Objectives:
  • Sea surface height measurements        Programmatics:
    (continue the Jason/TOPEX series)       • NASA/NOAA/Navy partnership
  • Study mesoscale phenomena               • Currently no US altimeter planned
  • Ocean bathymetry (surface slopes)         after Jason-2
  • Land surface water (hts.+ gradients)    • Possible Eumetsat/CNES roles
 New technology:                            • Launch date 2012 for continuity with
   • Wide-swath altimeter is a SAR            Jason-2
     interferometer                         • 5-year mission
   • Onboard processing                     • Mission Cost ~ $500M (FY ‘06)
                   Advanced Altimeter Mission

         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
                                 NASA Requirements: Traceability Matrix
                                            Advanced Altimeter Mission
                                                                                                                      (1 of 2)
CategoryScience Objectives                                                                                                              Mission Functional Requirementsevel 2 Data Products
                                                                       Scientific Measurement RequirementsInstrument Functional Requirements                          L
                                                                       Global monitoring of storage change by
      Surface WaTER

                                                                                                                                                        Orbit /repeat (14 days in the       Global maps of water surface
                                                                       measuring changes in water body
                                                                                                                    Ka-band Interferometer              tropics, less than 7 days in the    elevations and area are expected
                                 WatER Science Objectives:             height and spatial extent with time.
                                                                                                                    Requirements: Height accuracy       Arctic). Exact repeat is not        after every period of global
                                 Determine surface water storage       Derivation of river discharge from
                                                                                                                                                                                            coverage (e.g., ~weekly).
          Surface Water

                                                                                                                    5cm. Slope accuracy 10urad          required, rather samples
                                 change and discharge to predict       measurements of slope and spatial
                                                                                                                    (1cm/km). Spatial resolution        anywhere within the swath are       Individual swaths will be useful for
                                 the land surface branch of the        extent within a hydrodynamic model
                                                                                                                    finer than a 100 m posting. 120     sufficient for describing water     local water managers.
                                 global hydrologic cycle; Measure      assimilation. Revisit time ~2 weeks in
                                                                                                                    km total swath.                     height. Precise orbit               Hydrologists need derived
                                 flood hydraulics; assess the role     the tropics and less than 1 week in the
                                                                                                                                                        determination required.             products that are global maps of
                                 of fresh water storage as a           Arctic.
                                                                                                                                                                                            water storage change and
                                 regulator of biogeochemical cycles
                                                                                                                                                        Minimum 1 year, with a 3 year       discharge. Hydraulic engineers
                                 such as carbon and nutrients. [A]     3 year baseline operation, with a 5 year     3 year reliability, with a 5 year
                                                                                                                                                        baseline mission, with a 5 year     will need maps of h, dh/dt, dh/dx
                                                                       goal.                                        goal.                                                                   and area.

                                                                       Monitor global mesoscale activity
                                                                       through the measurement of sea
                                                                       surface height (SSH) with a spatial
                                                                       resolution of 1 km x 1 km with random
                                                                       noise no greater than 1.5 cm.

                                                                       In the open ocean 30 km away from the                                            Orbit repeat periods shall be
                                                                                                                    Ka-band Interferometer:             between 10-25 days.
                                                                       coast, the SSH accuracy shall be less
                                                                                                                    1.5 cm precision with 2 km x 2
                                                                                                                    km resolution.                      Non-sun-synchronous orbit is
                                                                       4.6 cm (1) at wavelengths shorter than                                                                               Fully calibrated, validated science
                                                                                                                    Nadir Radiometer:                   required.
                                                                       500 km; the total SSH accuracy (all                                                                                  data: Geolocated, calibrated
                                                                                                                    Resolve tropospheric correction
                                                                       scales included) shall be less than 5.1                                                                              interferometer strip data of sea
                                                                                                                    with 1.2 cm accuracy.               Exact repeat ground tracks with
                                 Hydrosphere Mapper Science            cm (2) .                                                                                                             surface height on a per orbit basis
        Sea Surface Topography

                                                                                                                    GPS:                                cross-track separation less than
                                 Objectives : Measure mesoscale                                                                                                                             on a 2 km grid near coastlines.
                                                                                                                    Determine orbit with radial         +/- 1 km.
                                 activity, including fronts, eddies,   Within 30 km from the coast, the SSH                                                                                 Wind speed strip data on a similar
                                                                                                                    accuracy of 2 cm.
                                 and boundary currents; eddy           accuracy at wavelengths shorter than                                                                                 grid. Both products with less than
                                 mean-flow interactions, eddy          500 km shall be less than 4.9 cm (3)                                             The attitude of the Ka-band         30 day latency.
                                 transports, and the role of eddies    and the total SSH accuracy shall be less                                         interferometer shall be maintained
                                 in climate; physical-biological       than 5.3 cm (4) .                                                                steady (no yaw-steering)           Quick look data : Geolocated,
                                 interactions and the role of eddies                                                                                                                       partially calibrated interferometer
                                 in the carbon cycle; coastal tides    Wind speed measurement shall have an                                             Fully calibrated and validated     strip data of sea surface height on
                                 and open ocean internal tides;        accuracy of 2 m/s.                                                               science data are required within   a per orbit basis on a 2 km grid
                                 and coastal currents [B]                                                                                               30 days. Quick-look data with      near coastlines. Wind speed strip
                                                                                                                                                        less quality are required within 1 data on a similar grid. Both
                                                                       Global coverage of sea surface height
                                                                                                                                                        day for coastal and other          products with less than 1 day
                                                                       measurements for ice free oceans with
                                                                                                                                                        operational applications.          latency.
                                                                       a repeat cycle less than 25 days.
 Sea Surface

                                                                                                                    Ka-band Interferometer : provide
                                                                       Aliased periods of the eight leading tidal
                                                                                                                    above measurement accuracy
                                                                       components (M2, S2, K1, K2, P1, Q1,
                                                                                                                    over a total swath of [120] km.
                                                                       N2, O1) shall be separated from one
                                                                       another with maximum period less than
                                                                       one year.

                                                                       3 year baseline operation, with a 5 year     3 year reliability, with a 5 year   3 year baseline mission, with a 5
                                                                       goal.                                        goal.                               year goal.
                                                                                         Advanced Altimeter Mission
                                NASA Requirements: Traceability Matrix
                                                                                                                  (2 of 2)
CategoryScience Objectives                                                                                                            Mission Functional Requirementsevel 2 Data Products
                                                                     Scientific Measurement RequirementsInstrument Functional Requirements                          L
Sea Surface Topography

                                                                     Measure ocean surface topography
Cont. Sea Surface Topography

                                                                     covering at least -66 to +66 degrees in
                                                                     latitude, with 3.4 cm accuracy at 6.2                                                                                  Geolocated, calibrated strip height
                                                                                                             Nadir Altimeter (Ku and C band):
                                                                     km along-track resolution, with                                                                                        data on a per orbit basis on a 6.2
                                                                                                             2.6 cm height accuracy (1.6 cm
                                                                     measurement drift less than 1mm/year.                                      Exact repeat ground tracks with             km grid. Wind speed strip data
                                                                                                             Ku noise, 2 cm sea-state bias, 0.5
                                                                                                                                                cross-track separation less than            on a similar grid.
                               Nadir Altimeter Science                                                       cm ionospheric error) with along-
                                                                     Measurement products to continue the                                       +/- 1 km
                               Objectives : Basin-scale ocean                                                track resolution of 6-7 km.
                                                                     TOPEX/Poseidon, Jason, and                                                                                             Products to have less than a 30
                               circulation, heat transport, El
                                                                     OSTM/Jason-2 time series, although                                                                                     day latency.
                               Nino/La Nina, sea level rise.
                                                                     different orbit inclinations and ground
                                                                     tracks are acceptable.                                                                                                 Data to be cross-calibrated versus
                                                                                                                                                                                            OSTM nadir altimeter at
                                                                                                                                                                                            associated crossover points.
                                                                     3 year baseline operation, with a 5 year 3 year reliability, with a 5 year      3 year baseline mission, with a 5
                                                                     goal.                                    goal.                                  year goal.

                                                                                                               Ka-band Interferometer:
                                                                                                               Height precision (uncorrelated        The mission orbit design should
                               Bathymetry Science Objectives :       Measurement of East-West & North-         random error) at 1km postings of      include all orbit shifts required to
                               Improve understanding of marine       South sea surface slope to 1 micro-       1.5 cm. Systematic error              get full ocean coverage over the

                               gravity field & global bathymetry     radian over scales of 6-8 km.             contribution smaller than 1 micro-    mission lifetime.
                               at (1) scales sufficient to resolve

                                                                                                               radian over scales of 6-8 km
                               roughness that drives ocean                                                     (residual slopes after calibration)                                          Global gravity & bathymetry maps
                               mixing, internal wave generation,
                                                                                                                                                     Global coverage between +/- 66         at 6-8 km resolution.
                               and tidal generation; and (2) to
                                                                                                               Averaging of mesoscales signals       degrees latitude with no spatial
                               determine the heights of
                                                                     Measurement of sea surface slope with     requires at least 1 year data         gaps.
                               seamounts accurately enough for
                               navigation and habitat                100% coverage between +/- 66              collection for each point. Full
                               considerations [C].                   degrees latitude.                         coverage requires instrument          A mission lifetime of at least 2
                                                                                                               lifetime of at least two years.       years is required to average ocean
                                                                                                                                                     mesoscale signal contamination.

                  1. 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 Famiglietti4 1Ohio State Univ., 2NASA JPL, 3Univ. of Washington, and 4Univ. of California,
                  2. The WatER Mission,
                  3. 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
                  4. ABYSS-Lite: A radar altimeter for bathymetry, geodesy and mesoscale oceanography, Smith et. al. 2005
                  5. Altimetric BathmetrY from Surface Slopes, A Proposal in response to NASA AO01-OES-01, July 20, 2001, Principal Investigator: Dr. Walter H. F. Smith
                                      Advanced Altimeter Mission

                                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.

* "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
                                    Advanced Altimeter Mission
                          NPOESS Requirements

Source: NPOESS Integrated Operational Requirements Document-II, January 2002
                                    Advanced Altimeter Mission
                          NPOESS Requirements

Source: NPOESS Integrated Operational Requirements Document-II, January 2002
                                           Advanced Altimeter Mission

            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
                                         Advanced Altimeter Mission
               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                      Maps near the
  30 deg latitude.                              equator showing
                                                the 120km
• All coverage Gaps are                         swath and the
  filled when the orbit                         ~17 km gaps.
  is shifted at 1.5 yr                          A 1 degree
  Intervals over                                lat/lon grid is
  mission life                                  shown with
                                                dotted red lines.

  Ref: Francois Rogez (JPL) this study
                                              Advanced Altimeter Mission
             Key Instrument Performance Parameters:

         Ka-Band Interferometer Performance Summary

Ref: Louise Veilleux Advanced Altimeter Mission Study, (JPL) April 2006
                                              Advanced Altimeter Mission
    Key Instrument Performance Parameters:

Ku & C-Band Altimeter & Radiometer Summary

Ref: Louise Veilleux Advanced Altimeter Mission Study, (JPL) April 2006
                                          Advanced Altimeter Mission
       Science Measurement Requirements
• Continues the TOPEX/Jason/OSTM record while adding new capabilities
  Measurement                                                                    OSTM                     Adv. Alt.
  Measure ocean surface topography between +/- 66 deg lat., with 3.4 cm
  accuracy, 6.2 km resolution, drift < 1 mm/yr.                                    Yes                       Yes
  Continue TOPEX/Poseidon, Jason and OSTM time series                              Yes                       Yes
  3 year mission lifetime, with 5-year goal                                        Yes                       Yes
  Avoid tidal aliasing                                                             Yes                       Yes
  Monitor global mesoscale activity with 1x1 km spatial resolution                                           Yes
  Within 30 km of coast, measure SSH with 5 cm accuracy                                                      Yes
  Global coverage of SSH for ice-free oceans at intervals < 25 days                                          Yes
  Measurement of E-W and N-S sea surface slopes to 1 micro-radian over 6-
  8 km                                                                                                  Yes, in 3 years
  Measurement of sea surface slope with 100% coverage between +/- 66
  deg lat.                                                                                              Yes, in 3 years
  Centimeter accuracy topographic measurements                                     Yes                        Yes
                                                                                                      Yes, except for the
                                                                                                     northernmost part of
                                                                                                  Greenland and the Antarctic
  Adequate spatial sampling                                                                                 interior
  Surface Water Hydrology
                                                                            Only largest rivers
  Global monitoring of water storage changes                                    and lakes                      Yes
  River discharge rates                                                                                        Yes
  Local River Slope                                                                                            Yes
  Adequate spatial sampling                                                                                    Yes
  Adequate temporal sampling                                                                                   Yes
  Floodplain topography                                                                            For low relief topography
  Carbon fluxes at air-water boundaries                                                                      Yes
                  Advanced Altimeter Mission

• 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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