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NASA Activities in Support
of an Advanced Altimeter
Mission
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
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 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
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
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.
goal.
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
than
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
Topography
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.
Apr24_06HM_pollardCharts_2.ppt
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
Bathmetry
gravity field & global bathymetry radian over scales of 6-8 km. contribution smaller than 1 micro- mission lifetime.
at (1) scales sufficient to resolve
Bathymetry
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.
Apr24_06HM_pollardCharts_2.ppt
References:
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,
Irvine
2. The WatER Mission, www.geology.ohio-state.edu/water
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.
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
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:
10-
Ka-Band Interferometer Performance Summary
4/18/06
Ref: Louise Veilleux Advanced Altimeter Mission Study, (JPL) April 2006
Advanced Altimeter Mission
Key Instrument Performance Parameters:
10-
Ku & C-Band Altimeter & Radiometer Summary
4/18/06
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.
Oceanography
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
Bathymetry
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
Cryosphere
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
Ecology
Carbon fluxes at air-water boundaries Yes
Advanced Altimeter Mission
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
