ESDS Program

Bridging the Digital Divide between Discrete and Continuous Space-Time Array Data to Enhance the Accessibility to and Usability of NASA Earth Sciences Data for the Hydrological Community

Principal Investigator (PI): William Teng, Wyle Information Systems, LLC

A longstanding and significant "Digital Divide" in data representation exists between hydrology and climatology and meteorology. Typically, in hydrology, earth surface features are expressed as discrete spatial objects such as watersheds, river reaches, and point observation sites; and time varying data are contained in time series associated with these spatial objects. Long-time histories of data may be associated with a single point or feature in space. In meteorology and climatology, remotely sensed observations and weather and climate model information are expressed as continuous spatial fields, with data sequenced in time from one data file to the next. Hydrology tends to be narrow in space and deep in time, while meteorology and climatology are broad in space and narrow in time.

This Divide has been an obstacle, specifically, between the hydrological community, as represented by the Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI) and relevant data sets at NASA's Goddard Earth Sciences Data and Information Services Center (GES DISC). CUAHSI has developed the Hydrologic Information System, which is built on international geospatial standards, with one of its aims to bridge the Divide. GES DISC has a long history of supporting energy and water cycle data sets, represented by two of its discipline-oriented entities, Precipitation DISC (PDISC) and Hydrology DISC (HDISC). The opportunity costs of the Divide are high. It has largely prevented the routine access and use of NASA Earth science data by the hydrological and, more generally, geospatial community.

There have been a number of preliminary efforts, over the past several years, to explore ways to bridge the Divide. One specific example is an HIS Web service providing access to selected Moderate Resolution Imaging Spectroradiometer (MODIS) data, via the NASA Giovanni visualization and analysis system. A more recent effort by GES DISC and US Environmental Protection Agency Better Assessment Science Integrating point and Nonpoint Sources resulted in a customized service enabling the access to 30-year time series of a single parameter of the North American Land Data Assimilation System (NLDAS) data set, based on a reorganization of the archived data and the GrADS Data Server. An ongoing prototype effort by CUAHSI, GES DISC, and NASA's Goddard Space Flight Center Hydrological Sciences Branch is aimed at demonstrating the feasibility of accessing selected NLDAS parameters, via WaterML-compliant Web services and GDS, by HIS users from within a client such as HydroDesktop. All of these prototype efforts have shown the potential for bridging the Divide. Significant impediments remain, however, including the scaling from a few test parameters to a vastly greater number of parameters.

The overall approach of the proposed project comprises the following:

  1. Incorporate NASA data into the HIS ontology; integrate NASA data into the HIS OpenGIS Catalogue Service for the Web (CS-W) specification.
  2. Develop WaterML Web services for NASA data; reorganize NASA data for optimal access and use.
  3. Enhance the CUAHSI HydroDesktop system to (1) access NASA’s continuous array data and summarize them over discrete spatial objects, such as watersheds and (2) enable comparison of time series of point observations from monitoring site locations with those of remotely sensed data measured over the same locations.
  4. Develop hydrological use cases to guide the implementation, and serve as the metric for the usefulness, of the project technologies.

This project would represent a significant advance in extending NASA Earth science data to a large hydrological user community that has, heretofore, mostly unable to easily access and use NASA data.

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