NOAA's Role in Space-Based Global Precipitation Estimation and Application (2007)

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Co-authored by R. Ferraro, A. Gruber, G. Legg, J. Janowiak, K. Vincent, J. Gurka, B. Martner

The distribution of water and its change over time are two of the most critical issues facing the world’s population. The single most destructive weather-water-climate hazard is flooding, which can result from heavy precipitation from either relatively short-lived “weather” phenomenon (e.g., severe storms, tropical cyclones) to relatively long-lived “climate” events (e.g., El Niño). Because these events occur throughout the world where U.S. interests may be affected, a system to monitor potential flooding hazards is important. NOAA is the sole federal agency that has the responsibility for issuing weather-water-climate warnings for the country. To support this function, NOAA develops and validates algorithms for the retrieval of precipitation rates from remotely sensed data and uses this information for flash flood forecasts, rainfall potential estimates, input into NWP models and climate monitoring. Additionally, NOAA serves the interests of other government agencies here (e.g., the Departments of Defense and State) and abroad by providing assessments of impending hazards

Furthermore accurate and regional precipitation measurements support all of NOAA’s four overarching Strategic Goals:

1. Protect, restore, and manage the use of coastal and ocean resources through ecosystem management approaches.

2. Understand climate variability and change to enhance society’s ability to plan and respond.

3. Serve society’s needs for weather and water information.

4. Support the Nation’s commerce with information for safe and efficient transportation.

NOAA believes that the Global Precipitation Measurement (GPM) Mission is a system that can assist NOAA in meeting its user and mission requirements and fulfilling its strategic goals. The GPM will be a resource that can greatly improve NOAA’s primary mission, which is the protection of life and property by providing timely and accurate information on precipitation events worldwide. This of course is critical for accurate meteorological and hydrologic modeling and assessment. GPM will also serve as a prototype to help NOAA improve its current satellite capabilities and to better define the future operational precipitation measuring system from space. As a testimony to this, the Workshop on NOAA’s Requirements for Global Precipitation Data (November 2001, Report issued May 30, 2002) identifies NOAA’s involvement in GPM as two of its major recommendations. Specifically:

• “NOAA should become an active partner with NASA in the Global Precipitation Measurement Mission. This system will provide the global three hourly precipitation estimates required by the operational modeling centers. Furthermore, significant improvements in precipitation information for nowcasting, extreme precipitation events and flash floods will be achieved when geostationary data, gauges and radars are combined with GPM. Consideration should be given to the establishment of a science team or working group that would define NOAA’s role in and relationship to GPM.”

• “NOAA should sponsor a ground-validation super-site at location that will complement the super-sites that NASA will establish for GPM. These sites would include concentrations of quality precipitation gauges (such as those of NCDC’s Climate Reference Network) and advanced ground-based remote sensors to measure precipitation, clouds, and water vapor independently of the over-flying satellite instruments.”

In addition, NOAA should develop techniques for integrating GPM data into its operational precipitation analysis systems and for assimilating these analyses into weather, water and climate forecast models. These techniques should account for uncertainty in GPM products and for the propagation of this uncertainty by atmospheric and hydrological models.

Testbeds are a new concept in NOAA for accelerating the transfer of research technologies into operational use by the National Weather Service (NWS). The NWS Science and Technology Infusion Plan (STIP) of 2002 calls for the development of a regional and re-locatable Hydrometeorological Testbed (HMT) in which NOAA researchers join forces with NWS weather forecasters and River Forecast Center runoff forecasters to evaluate new precipitation observing and model tools in an operational setting. Once established, such an HMT could also readily serve as a NOAA base for additional GPM ground

validations and would provide a direct link between the new GPM products and operational forecasting.

NOAA has scientific expertise in the retrieval of precipitation from satellites and their utilization for a number of applications, ground monitoring assets, and operational processing capabilities that would make it a unique partner with NASA in the GPM program. NOAA anticipates that the following assets will be available as part of its potential contribution to GPM:

1. Visible, IR, and microwave data from NOAA-operated satellites or satellite data that NOAA anticipates receiving in near real time based on prior data exchange agreements (which will include GOES, POES, DMSP, WindSat, NPOESS Preparatory Mission, and NPOESS).

2. Ongoing cooperative R&D activities with NASA that focus on the areas of precipitation retrieval from satellites and their applications (e.g., Global Precipitation Climatology Project, Joint Center for Satellite Data Assimilation, etc.)

3. GPM Science Team Members (through current/forthcoming NASA Research Opportunities and through a joint agreement with NASA) who possess expertise on:

   1. Rainfall retrieval algorithms (flash flood to climate scale) and associated validation/error modeling

   2. Radiative transfer, in particular, over land surfaces and at millimeter wavelengths

   3. Applications in support of a variety of NOAA missions (i.e., tropical cyclones, climate monitoring, etc.) carried out by centers such as the National Precipitation Prediction Unit (a joint NCEP-NESDIS activity), the Climate Prediction Center, and National Weather Service Forecast Offices and River Forecast Centers

   4. Use of satellite-derived rainfall in NWP models/assimilation techniques

   5. Calibration of satellite sensors

   6. Evaluation of satellite-derived precipitation estimates

4. Field calibration/validation assets:

   1. Climate Reference Network

   2. North American Monsoon Experiment (NAME) rain gauge network

   3. Research and operational radars and profilers, in particular, through the proposed Hydrometeorological Test Bed

   4. Aircraft-borne radiometers to support field campaigns

   5. PACRAIN rain gauge network

5. Hydrological Applications

   1. Multisensor precipitation analysis

   2. Ensemble precipitation analysis

   3. Uncertainty propagation through hydrologic models

   4. Hydrologic data assimilation

   5. Global hydrologic forecast applications

6. Data archival and operational distribution networks

   1. CLASS

   2. EMSNet node

   3. Operational File Server (CEMSCS)

   4. Dedicated networks and circuits for operational distribution to global customers, including all national forecast centers

As a more formal way to become partners on GPM, it is recommended that NOAA and NASA establish a new component to the existing Joint Center for Satellite Data Assimilation that will focus on precipitation measurements and applications. Ultimately, this center will encompass much of NOAA’s precipitation-related activities. Through this center, NOAA will contribute resources to support NOAA Science Team members, a joint Research Announcement, joint field campaigns, and data processing/archival. To accomplish this, NOAA should incorporate the potential benefits of GPM within its ongoing Program Baseline Assessment (PBA) and Gap analysis. For example, a gap was recently identified within the Hydrology Program regarding the insufficient number of global precipitation observations. Clearly, GPM would help NOAA alleviate this gap. Through the PBA process, long-term funding for activities related to GPM can be secured. However, in the short term, NOAA should provide seed funds beginning in FY 04 to formalize its partnering commitment to NASA. Once this has been established, joint, national-based partnering meetings between NASA and NOAA should be held on a regular basis.