Results of Washington D.C. Meeting

1. Results of Washington D.C. Meeting • Science Questions: • Science drives the mission, societal issues are important, but secondary to the science drivers. • The topmost hydrology question is focused on just storage changes, or S and discharge? • The topmost oceanographic question is focused on eddy kinetic energy • In today’s meeting we need to articulate these topmost questions and any necessary additional questions • Risk Reduction Studies: • Needed to keep mission on track for a launch in 2013-2016. • Today, we will discuss needed studies, including those on the mission design, height and slope accuracy required, technology modifications compared to WSOA, WatER • An official SWG report: • We will discuss the timeline for this report toward the end of today’s meeting

2. Actions for Today’s Meeting • Goals of the Meeting: • Facilitate actions toward 2008 funding • Facilitate technology sharing discussions • Conduct the following SWG activities • Key Points for Today: • Science questions worded and prioritized • Define role of coastal, bathymetry, sea ice, etc. • Importance of water vapor, is this a coastal question only? • Define role of nadir altimeter, what is the science it specifically addresses • Risk reduction studies should be identified, prioritized, and assigned to researchers

3. Addressing three issues: (Lee Fu) • (1) Articulate the importance and challenges of measuring the mesoscale and submesoscale processes and explore the options of mission design for making breakthroughs. • A workshop to be held on April 28-30, 2008, at the Scripps Institution of Oceanography • (2) Explore the state of the art of model analysis/prediction of mesoscale water vapor variability, as well as the technologies for direct measurement, and assess options for making wet-tropo corrections. • To be discussed in Coastal Alimtetry Workshop, Feb 5-7, 2008, Silver Springs, MD. • (3) Assess the state of art of coastal tide models around the world and explore the predictability of internal tides. • A workshop to be planned for later this year. Ocean Science Risk Reduction Activities

4. Hydrology and Oceanography Science Questions (1) • Identify science questions: • Is this the list of questions that you think are most appropriate for SWOT? Is the priority ordering correct? Do you suggest modifications?  • Note that we are prioritizing only within the hydrology or only within the oceanography category. • We should have one key, overarching science question for oceanography and similarly one for hydrology.  Hopefully, these questions will be nearly self-evident regarding their importance.  • A goal of today’s meeting is to word-for-word identify the respective key science question. • Because SWOT is a wide-swath altimeter, the questions should focus on the measurements collected from KaRIN.

5. Hydrology and Oceanography Science Questions (2) • Hydrology Science Questions Might Include: • What is the spatial and temporal variability in the world's terrestrial surface water storage and how can we predict these variations more accurately? • How much water is stored on a floodplain and subsequently exchanged with its main channel? • What are the policy implications that freely available water storage data would have for water management? • How much carbon is potentially released from inundated areas? • Can health issues related to waterborne diseases be predicted through better mappings?

6. Hydrology and Oceanography Science Questions (3) • Oceanography Questions Include (Lee Fu) (1) What is the small-scale (1-100 km) variability of ocean surface topography that determines the velocity of ocean currents? How are fronts and eddies formed and evolving? How is oceanic kinetic energy dissipated? (2) What is the synoptic variability of coastal currents? How do the coastal currents interact with the open ocean variability? What are the effects of coastal currents on marine life, ecosystems, waste disposal, and transportation? (3) How does the small-scale ocean variability interact with the atmosphere? Does this interaction provide a mechanism of dissipation of ocean kinetic energy? How does a hurricane interact with the small-scale variability of the upper ocean heat storage? What is the ocean's dynamic response to hurricanes? How is the new knowledge to be used to improve hurricane forecast? (4) How do changes in the global water cycle, both natural and anthropogenic, lead to sea level change? How do variations in continental water discharge contribute to sea level change? What role does the storage of water in artificial reservoirs and lakes play in the sea level change budget? How do variations in coastal sea level change affect predictions of water inundation due to sea level rise and/or storm surge.

7. Hydrology Virtual Mission Update • The next 8 slides present results of the Hydrologic Virtual Mission • In addition to references, credits also to: • Kostas Andreadis • Mike Durand • Jon Partsch • Tamlin Pavelsky

8. What we know: Global Perspective Present measurements do not provide needed global coverage, but a swath altimeter blankets the globe. • Profiling Altimeter: (16-day repeat) • About half of world’s rivers sampled only once or not at all, no slope thus no river discharge. • Swath Interferometer: (16-day repeat) • Swath provides h, h/x, h/t, and area in one overpass, thus ability to estimate discharge. Alsdorf, D., E. Rodriguez, and D. Lettenmaier, Measuring surface water from space, Reviews of Geophysics, 2007.

9. What we know: Local Scale Water flow across wetlands is far more complex than implied by GRACE, altimetry, in-situ, or any other measurement or model. Flow paths and water sources are not fixed in space and time, rather vary with flood water elevations. Thus, spatial sampling needs to be dense with small pixel sizes and temporally repeated samplings. “If you need more precise measure-ments of natural events on Earth's surface, get into space.” Nature Image shows dh/dt from JERS-1 InSAR, but method works only in flooded forests where the radar pulse has a double-bounce travel path.

10. ( ) 1/2 ¶ h w 5/3 Q = Z n ¶ x What we know: Flow Hydraulics River channel width can be automatically measured in any satellite based image. SRTM DEM Simple equation of water flow demonstrates need to measure width (w), depth (z), slope (dh/dx), and friction coefficient (n). Z and n will come from data assimilation (next slide). Large Width to Depth Rivers Pavelsky & Smith, RivWidth, IEEE GRSL, 2008

11. “RivWidth” of Ohio River Basin Courtesy: J. Partsch

12. How often do these and other rivers and wetlands need to be sampled in order to know the terrestrial surface water portion of the water cycle? What we need to know: Global Perspective Ohio Siberia Amazon Answers are underway via a “Virtual Mission” study. • Virtual Mission Will define: • the required smallest water body needed to be measured • the cost and science trade-offs associated with various orbits and pixel sizes • how to estimate discharge, even where depth cannot be measured • Virtual Mission Uses: • image based classifications to identify present knowledge of water locations • altimetry and GRACE to estimate (crudely) the possible storage variations • data assimilation to estimate errors from various sampling protocols

13. What we need to know: Local Scale What is the spatial and temporal sampling required to estimate discharge in river channels? • Small ~50 km upstream reach of Ohio River • A hydrodynamic model, provides spatial and temporal simulation domain • Are 100 m pixels, with 1 m height accuracies, every 30 days sufficient to accurately reproduce the discharge regime of a given river? • Or, are 10 m pixels, with 10 cm heights, every 3 days required? • What are the cost trade-offs? Data assimilation of synthetic, but realistic, rivers is providing the answers • A water & energy balance model, VIC, provides input for “truth” simulation • Perturbing precipitation with VIC provides input to LISFLOOD for open-loop and filter simulations • KaRIN measurements simulated by corrupting LISFLOOD “truth” water surface heights with expected instrument errors Andreadis et al., GRL, 2007

14. 700 650 600 Discharge (m3/s)‏ 550 500 450 0 10 20 30 40 50 60 Channel Chainage (km)‏ Assimilation Results: Ohio River Channel Discharge Discharge along the channel, April 13, 1995. Data assimilation of the synthetic KaRIN measurements clearly improves the discharge estimate compared to the open loop simulation. 1400 Discharge time series at downstream edge. Discharge errors relative to “truth”: Open Loop = 23.2% 8 day DA = 10.0% 16 day DA = 12.1% 32 day DA = 16.9% 1200 1000 800 Discharge (m3/s)‏ 600 400 200 Andreadis et al., GRL, 2007 Apr 1 Apr 15 May 15 Jun 1 Jun 15 May 1

15. Virtual Mission: Bathymetric Slope Sensitivity: • SWOT can measure inundated area and total storage on floodplains. • Knowing these through time, allows selection of correct channel bathymetric slope. • Errors are being assessed through data assimilation. Slide: Mike Durand

16. Wording & Prioritization of the Science Questions (1) • Identify science questions and prioritize them: • Potential other science targets (bathymetry, land topography, etc.) should be identified, but only those that avoid science, technology, and cost creep. • e.g., sea-ice could be a target but probably should not drive the orbit selection. • The science drivers should be prioritized in terms of ″critical and must have″ to those of less importance but still valuable. This prioritization should focus the mission and prohibit creep. • e.g., measuring surface water storage changes is critical whereas measuring sea ice freeboard is not. • Questions need careful articulation and accuracy in their wording. • e.g., “how much surface water” vs. “what is the spatial and temporal variability in surface water”

17. Wording & Prioritization of the Science Questions (2) • Technology and Mission Considerations: • Mission lifetime is 3 to 5 years, with increasing costs for longer times. Science questions should be answerable with data collected during mission timeframe. • Questions should be answerable by the accuracy and resolutions provided by KaRIN. • Additional Considerations: • Modeling is increasingly important for understanding the global water cycle and oceanic circulation issues. What do models require?

18. Wording & Prioritization of the Science Questions (3) • A suggested wording and prioritization for hydrology: • What is the spatial and temporal variability in the world's terrestrial surface water storage and discharge? How can we predict these variations more accurately? • How much water is stored on a floodplain and subsequently exchanged with its main channel? • What are the policy implications that freely available water storage and discharge data would have for water management? • Related, but not purely hydrologic questions: • How much carbon is potentially released from inundated areas? • Can health issues related to waterborne diseases be predicted through better mappings?

19. Wording & Prioritization of the Science Questions (4) • Suggested wording and prioritization for oceanography (Lee Fu) (1) What is the small-scale (1-100 km) variability of ocean surface topography that determines the velocity of ocean currents? How are fronts and eddies formed and evolving? How is oceanic kinetic energy dissipated? (2) What is the synoptic variability of coastal currents? How do the coastal currents interact with the open ocean variability? What are the effects of coastal currents on marine life, ecosystems, waste disposal, and transportation? (3) How does the small-scale ocean variability interact with the atmosphere? Does this interaction provide a mechanism of dissipation of ocean kinetic energy? How does a hurricane interact with the small-scale variability of the upper ocean heat storage? What is the ocean's dynamic response to hurricanes? How is the new knowledge to be used to improve hurricane forecast? (4) How do changes in the global water cycle, both natural and anthropogenic, lead to sea level change? How do variations in continental water discharge contribute to sea level change? What role does the storage of water in artificial reservoirs and lakes play in the sea level change budget? How do variations in coastal sea level change affect predictions of water inundation due to sea level rise and/or storm surge.

20. Miscellaneous: • Mission Name: • Should now use “SWOT” instead of “WATER HM” for consistency with Decadal Survey, U.S. Congressional actions, and CNES. • Note usage of SWOT in new graphic, above. • SWOT “Booklet” • At least one other Decadal Survey mission has an 8-page “booklet” • Ocean Sciences ASLO Meeting: • Wide-swath session is Wednesday, March 5, from 13:30 to 17:30 • Future “Townhall” meetings: • When, where, and should we have these? Presumably with large, international meetings? • Mission Web pages: • Are largely hydrologic in orientation, we need more oceanographic details. Your contributions are welcomed. • Do we need a “forum” section for on-going discussions outside of email?

21. Key Points for Today: • Science questions worded and prioritized • Define role of coastal, bathymetry, sea ice, etc. • Importance of water vapor, is this a coastal question only? • Define role of nadir altimeter, what is the science it specifically addresses • Risk reduction studies should be identified, prioritized, and assigned to researchers