Ideas on a

Network Evaluation and Design System

Prepared for EPA OAQPS

Richard Scheffe

by

Rudolf B. Husar and Stefan R. FalkeCenter for Air Pollution Impact and Trend Analysis, CAPITA

Washington University, St. Louis

Draft, December 18, 2000

Network Modification: The Design Paradox

The optimal design of a monitoring network runs into the ‘network design paradox’:

To place the monitors at the ‘right’ place one would need to know the concentrations everywhere.

If one knew the concentration everywhere, there would be no need for a network.

For brand new network, this is a major problem, since one has very little knowledge of the real concentrations. However, the performance of existing network can be can be improved with high level of confidence since one knows the features of the concentration field.

The geographic layout of a network can be modified by moving existing stations to a ‘better place’, adding new stations where the information value is high, or eliminating stations that have low value. Ideally, these operations should be aided by suitable tools rather then by ‘eyeballing’ or trial-and-error.

A Web-Based Approach to Evaluate Existing Networks

AIRS DataHourly Concentr.

PopulationCensus Tract

Single MeasuresDaily Max Concentration

Number of Exceedances

Deviation from NAAQS

Estimation Uncertainty

Area of Sampling zone

Popul. in Sampling Zone

Combined Meas.Health Risk (Pop*Conc)

Deviation/Uncertainty

GeospatialAreas, Roads, Sources

Web Browser -

User Interface

An existing network could be dynamically evaluated using web-based data (AIRS, population and geo-spatial).

User could examine the network performance by

selecting any of the single or combined measures

varying the time window of evaluation

selecting specific sub-regions

Measures Times

Network Modification Tool: Proposed Design

The role of a network modification tool is to allow changes to be conducted in a ‘virtual environment’ so that a designer can evaluate different network layout scenarios while seeking the ‘optimal layout’.

Computationally, the evaluation of a modified network would be performed the same way as for the unmodified network described previously. The only difference is that for the ‘virtual’ (changed) stations, all concentration-related values would be estimated based on the existing unmodifiedstation values.

Specifically, the tool should :

Evaluate the current network performance

Allow making changes in the layout (add, eliminate, move station)

Display the consequences of network layout change on the multiple performance measures

The above sequence of operations should be performed in an interactive graphic environment, using simple cut, paste and move (drag) operations on a Web browser.

All the concentration input data needed for the Network Modification (NetMod) tool should be available from a web server dedicated for that purpose. The geospatial data (discussed next) are now largely available from reliable public sources (servers).

Network Modification Tool: Geographic Context

Network design/modification demands additional consideration of many factors that can not be expressed algorithmically ( e.g. cost of change, co-location with other samplers, station history, etc.)

A separate class of factors that influence station placement is the geographic ‘neighborhood‘ of a station location. The NetMod tool should provide a rich geographic context for any prospective (or for that matter existing) monitoring site.

Fortunately, web-based Geographic Information Systems (GIS) are currently revolutionizing the access, display and manipulation of geo-spatial data.

The next pages illustrate some of current the possibilities.

Confluence of Major GIS Programs

• Digital Earth: Digital Earth will be a virtual representation of our planet that enables a person to explore and interact with the vast amounts of natural and cultural information gathered about the Earth. (Consensus definition). The Digital Earth Initiative (DEI) is an ad hoc inter-agency working group to define the US federal participation in DE.

• Federal Geographic Data Committee (FGDC): FGDC coordinates the development of the National Spatial Data Infrastructure (NSDI) i.e. the policies, standards, and procedures for cooperatively produce and share geographic data between 17 federal agencies, state, local and tribal governments, the academic community, and the private sector.

• Open GIS Consortium (OGC): The vision of OGC is ‘The complete integration of geospatial data and geoprocessing resources into mainstream computing’ through (1) Consensus Interface Specification (2) Enable Industry to Build Plug-and-Play Components (3) Testbed Approach and Specification Development

Spatial Context Examples

• SOx emission density by county and point source emissions by plant.

• Spatial context to monitoring: SOx emission density by county.

Map Zoom: From National to Street Level

Example Map User Interface

National Geographic MapMachine.

Map Layer Examples

• Topographic map

• Toxic Waster Sites