Inaugural Meeting of the WATER HM Science Working Group

Inaugural Meeting of the WATER HM Science Working Group

October 29th and 30th, 2007 in Washington D.C.

Meeting Contacts:

Doug Alsdorf

Lee-Lueng Fu

Nelly Mognard

Yves Menard

Scroll down for list of meeting attendees and SWG members and important hotel information

Goal of the SWG

The overall goal of the SWG is to conduct a mission definition study leading to an optimal preliminary design of the mission given science requirements and technology and cost constraints.

Overall Meeting Goal

To make decisions and initiate actions that will eventually complete the overall goal of the SWG as noted above. By the end of the meeting, October 30th, decisions will be made on the issues described after the agenda.

Daily Agenda

(printable version click here)

Monday October 29th All Day

The Morning Session Focuses on Science Drivers

8:30 to 8:40: Introduction, Accomplishments of WATER HM this past year: Doug Alsdorf

8:40 to 8:50: SWG charge: Lee-Lueng Fu

8:50 to 9:15: Reports from NASA and CNES HQ regarding WATER HM: Eric Lindstrom, Eric Thouvenot, Herve Jeanjean, Jared Entin, Mike Freilich

9:15 to 9:30: Review of Hydrology Science Questions: Dennis Lettenmaier

9:30 to 9:45: Review of Oceanography Science Questions: Lee-Lueng Fu

9:45 to 11:15: Break-out Session: Prioritization of Science Questions: Two individual groups will form with one prioritizing hydrology questions and the other oceanography questions. These questions are not expected to be cross-cutting or conflicting. Rather, we seek the topmost questions for hydrology and topmost for oceanography. Hydrology session will be moderated by Doug Alsdorf and Nelly Mognard. Oceanography session will be moderated by Lee Fu and Yves Menard.

11:15 to 11:30: Coffee Break

11:30 to 12:30: Entire Group, Report of Break-Out Session Findings, Discussion and Finalize Decisions 1 and 2. Questions will be individually prioritized for hydrology and oceanography. We will not prioritize an oceanography or hydrology question above the other. Moderated by Doug Alsdorf, Lee-Lueng Fu, Nelly Mognard, Yves Menard

12:30 to 1:30: Lunch

The Afternoon Session Focuses on Science Linkages to Mission Design & Technology

1:30 to 1:40: Introduction to Risk Reduction Issues: Doug Alsdorf, Issues include (1) spacecraft power and orbit, (2) hydrology virtual missions identifying needed spatial and temporal resolutions, (3) radiometer accuracies over coastal and land surfaces and alternative strategies, (4) field results of Ka-band radar over rivers, (5) mitigation of rain rates, and (6) any others

1:40 to 2:10: Hydrology virtual mission: Dennis Lettenmaier

2:10 to 3:45: Spacecraft Power and Orbit, 15 minute presentations by

Tidal aliasing issues: Richard Ray

Tidal aliasing issues: Florent Lyard

Current orbit design: Steve Nerem

Spacecraft and associated key points: Bruno Lazard

JPL studies: Ernesto Rodriguez

3:45 to 4:00: Coffee Break

4:00 to 5:00: Water vapor corrections and radiometer issues: 15 minute presentations by

Issues with coastal zones: Ted Strub

Options with various radiometers: Shannon Brown

CLS perspective on radiometers: Estelle Obligis

5:00 to 5:15: First day meeting wrap-up: Doug Alsdorf

Tuesday October 30th Morning Only

8:30 to 8:50: Field results of Ka-band radar over rivers: Delwyn Moller

8:50 to 9:15: Ka-band radar studies, CNES Pre-Phase A work: Bruno Cugny

9:15 to 10:15: Entire Group, Discussion and Finalize Decisions 3 and 4: issues of rain rates and Ka-band vs. Ku-band will be raised. Moderated by Doug Alsdorf, Lee-Lueng Fu, Nelly Mognard, Yves Menard

10:15 to 10:30: Coffee Break

Remainder of the Morning Session Focuses on Naming Team Leaders and Action Items

10:30 to 11:00: Timeline for completion of SWG Goal and related report: Lee-Lueng Fu, Discussion will focus on report content, assignments, and schedules.Decision 5 will be finalized.

11:00 to 11:30: Mission timelines and funding availability: Eric Lindstrom, Eric Thouvenot, Herve Jeanjean, Jared Entin, Discussion will focus on a potential schedule that includes submission of SWG report in 2008, pre-project planning in 2009, and project start in 2010. NASA HQ and CNES will need to comment on the reality of this scenario and corresponding funding issues. Decision 6 will be finalized.

11:30 to 12:00: Open Forum: What are the issues on the horizon? How will we handle the massive data volume from WATER HM? To what degree and how should the SWG connect with society and policy? Should we engage international agencies? To what degree and how should the SWG connect with operational applications/operational agencies? Moderated by: Doug Alsdorf, Lee-Lueng Fu, Nelly Mognard, Yves Menard

12:00 to 12:15: Meeting wrap-up: Doug Alsdorf

Decisions to be Made During Meeting

Decision 1: Define the science questions

The overall science agenda for WATER HM includes physical oceanography and hydrology. We need to ensure that our science goals can be answered by the spatial and temporal resolutions and the height and slope accuracies of the KaRIN instrument. Specific science questions tied with the technology studies (below) need to be finalized. Potential other science targets (bathymetry, land topography, etc.) should be identified, but only those that avoid science and technology creep.

Decision 2: Prioritize the science questions

The science drivers should be prioritized in terms of ″critical and must have″ (e.g., determination of storage changes in lakes and reservoirs) to those of less importance but still valuable (e.g., land surface topography). This prioritization should focus the mission and prohibit science, technology, and cost creeps.

Decision 3: Identify linkages between science and technology issues

Our science questions need to drive the technology. For example, oceanographic science questions define the need for certain orbits whereas hydrologic science requires high-spatial resolutions to sample rivers with smaller widths (less than 100m). This sampling may require a certain amount of power to ensure a signal-to-noise ratio capable of supplying the needed height accuracies. Power requirements are a function of the orbit.

CNES developed initial studies necessary for submitting the WatER proposal to ESA whereas JPL has a large investment in WSOA related studies. The SWG needs to update these previous studies by ensuring that the hydrology and oceanographic science drivers are within a reasonable budget (i.e., develop cost trade-offs). Some studies have already been conducted or are in progress. For example, field experiments showing Ka-band radar returns from rivers, data assimilation to determine river discharge, and assessments of SRTM for estimating discharge have already been conducted. A hydrology virtual mission study is now fully funded by NASA and will provide trade-offs between various sampling strategies and the derived discharge and storage changes.

Decision 4: Prioritize risk reduction studies

Various studies have been discussed such as a need to update the CNES WatER power consumption study which focused on sun-synchronous orbits with stationary solar panels instead of a non-sun-synchronous orbit with solar panels rotating once per orbit (or other configurations). Such studies recognize that the oceanographic community at the Hobart OST meeting endorsed non-sun-synchronous orbits. Additional needed studies will include the usage of DEMs to mitigate spacecraft roll errors and to correct errors from atmospheric water vapor; determining the power necessary to meet the required height accuracies; the degree to which rain rates are mitigated; height accuracy over small rivers; etc. Prioritizing the needed studies and securing their funding are functions of the SWG.

Decision 5: Name individuals to lead tasks and resolve related issues

People in the SWG were selected for their expertise related to the issues outlines in Decisions 1-4 and detailed below. We expect that individuals from the SWG will lead the risk reduction studies and provide final reports upon conclusion of the studies. A key aspect of leading a risk-reduction team is to ensure that the optimal number of researchers are immediately available to conduct the work.

Decision 6: Timeline

A timeline is needed to ensure that the mission makes steady forward progress and so that CNES and NASA can make plans for funding key activities. A job of the SWG is to ensure timely funding for these trade-off studies.

Action Item 1: Ensure funding sources

Post-meeting actions will immediately focus on securing funds for the highest priority risk-reduction studies. NASA, JPL, and CNES have all indicated willingness to engage in funding key studies.

Action Item 2: Communicate with team leaders

We need to develop a routine of regular interaction with risk-reduction teams. Telecoms will be used as well as the WATER HM web page ( for archiving preliminary and final study results, providing links to risk-reduction models,

Action Item 3: Continue to develop the joint-science community

A key aspect of the SWG is to ensure that the global community of oceanographers and hydrologists recognize the importance of bringing together our two communities. This will likely require regular WATER HM presentations at international and specialized meetings, occasional open meetings hosted by the SWG, publication of results, and interactions with key leaders at CNES and NASA HQ (and perhaps other Federal and National agencies?).

Details of Agenda:

I. Decisions 1 and 2 focus on science questions:

The suggested top priority hydrology question is focused on the terrestrial surface water contribution to the global water cycle. The suggested top priority oceanography question is focused on the dynamics of kinetic energy in ocean currents. The prioritization of all WATER HM science questions is a task for the entire SWG. Additional hydrology science questions under consideration include those related to flood hazards, water resource management, carbon evasion, and health issues. Additional oceanographic science questions include those related to coastal zones, contributions to climate data records, improving hurricane forecasts, and operational needs like those related to transportation, pollution, and wasted disposal.

These questions need careful articulation. For example, saying that WATER HM will answer the question of ″how much surface water is on the Earth″ is not exactly true. Rather, WATER HM will address the question of ″what is the spatial and temporal variability of terrestrial surface waters around the globe″. Questions related to sea level also need clarification because WATER HM may not be explicitly designed to address the question of ″what is the rate of sea level rise″. Rather, WATER HM will make high-resolution measurements of ocean surface topography and issues related to the mean sea surface. Oceanographic questions will need to carefully consider internal tides, which operate at ~100 km spatial scales and external tides, which are ~1000 km scales. Internal tides are a function of the thermocline and operate on spatial scales similar to meso-scale currents, thus they can be a source of error. Both internal and external tides are a source of error via aliasing.

All questions need to be refined so that the height and spatial accuracies required for answering the question are cost effective (see next section). For example, hydrology is proceeding with a NASA funded study, the Virtual Mission, which will define the accuracy trade-offs associated with coarse vs. fine samplings and how effective these are for constraining the global terrestrial water cycle, improving flood hydraulics, and the other hydrology questions. A key consideration for all questions is the design lifetime of the satellite mission. Costs increase markedly for longer mission lifecycles, e.g., 3 years compared to 5 years. Thus questions should be focused on those that can be answered in a minimal amount of time.

There is a certain degree of ″excitement″ that needs to be enveloped by the science questions. For example, measuring vector winds does not engage the general public, whereas the entire world is keenly interested in hurricanes. Similarly, floods have a tremendous economic impact, especially in developing countries. While WATER HM is not a flood chasing satellite, it should provide new insights toward understanding how floods evolve. Applications of WATER HM measurements are important, but we should view WATER HM as a demonstrator of science. Essentially, the science questions will need to have some degree of direct applicability while focusing on unanswered science questions of great impact.

We also welcome other science questions, particularly those related to ocean bathymetry and sea ice. Synergies with these questions need to be developed so that new science questions do not lead to costly technology creep. For example, if the optimal WATER HM orbit configuration does not extend well into Arctic ocean, then is the additional cost to cover the ice pack too prohibitive?

Modeling is increasingly important for understanding the global water cycle and oceanic circulation issues. Satellite measurements are never sufficiently frequent enough to measure the full dynamics of water movement (e.g., every second), however the spatial density of wide-swath samples allows a high-resolution and broad-scale application in modeling. We need to determine the requirements of models and ensure that our colleagues from the various hydrologic, ocean circulation and climate modeling communities are involved in WATER HM planning and its eventual measurements.

In summary, hydrology science questions to be directly addressed by WATER HM are at the zero-order level, i.e., highly important and with immediate impact. The great achievements resulting from Topex/Poseidon and its successors allow oceanography to ask higher-order questions on the kinetic energy of the ocean that is of great importance to both climate science and practical applications.

II. Decisions 3 and 4 focus on trade studies

Discussions will focus on the various activities that are designed to address the trade-offs between science questions, technology required to address the questions, and the involved costs.

Hydrology is conducting a series of ″Virtual Mission″ (VM) studies which include data assimilation. A VM consists of a water balance model which supplies rainfall generated runoff at a coarse grid scale (e.g., 0.5 degree) to a fine-scale (~100 m) hydrodynamic model which routes water through a channel and across a floodplain. The routing results in water surfaces which are then sampled with an instrument simulator designed with various error characteristics (e.g., layover, thermal noise, etc.). These measurements represent the KaRIN instrument and are subsequently used in a data assimilation scheme designed to assess the importance of the errors in constraining discharge estimates and storage change measurements. Published first-results are promising and represent a new avenue for working with spaceborne surface water measurements.

Hydrology is also using SRTM elevation measurements as a proxy for KaRIN. Although SRTM is at least an order of magnitude lower in accuracy than the design of KaRIN, published first-results using a simple Mannings n approach suggest that SRTM is capable of supplying discharge estimates from large rivers such as the Amazon, Ohio, and Missouri.