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Unidata Real-time Weather Data, Use Cases, and International Standards

This page is a workspace for people to contribute to background information that might be of interest to GIS practitioners wanting to work with atmospheric and related data.   Please keep in mind that it's not a formal document but a place where people can make their own additions for others to make use of.

Types of real-time weather data served by Unidata

Unidata provides access to a wide range of real-time weather data via the push technology of the Internet Data Distribution (IDD) system and via THREDDS Data Servers (TDS) such as the motherlode TDS maintained by Unidata.   The main categories of data are described on the 
Unidata Data Page: 
The links in the above list provide much more detailed information about sub-categories and the data and access methods.

Use Cases

A couple very general use cases that illustrate the challenges of accessing working with such a wide range of data in an interoperable and integrated GIS environment are:

1. Airport Storm Use Case: 

This use case shows the challenges of accessing and integrating in a coherent fashion all the observational weather data along with the forecasts for the area around an aiport as a storm approaches.

2. Physics-based Interpolation (aka upscaling and downscaling of datasets).  

The challenge in this case is estimating the value of certain atmospheric parameters (e.g. temperature, pressure, wind speed) at points between the actual measured or forecast points. The NCAR Daymet site provides access to such services.

International standards related to netCDF and CF Conventions

An overview of the plan for establishing netCDF and the related Climate and Forecast (CF) conventions as OpenGeospatial Consortium (OGC) standard is provided in the OGC CF-netCDF Primer.  In April last year, the OGC offficially adopted  the netCDF classic core and binary encoding.  The next steps already underway are:
  • CF extension to the netCDF core standard (in draft specification form)
  • CF-netCDF extension to the WCS core standard (in draft specification form)
  • Enhanced Data Model extension to the netCDF core standard (in draft specification form)
  • Uncertainty model for netCDF-CF (in discussion paper form)
There have been important recent transitions that will impact closely related standards:
  • OPeNDAP has become a voting member of the OGC Technical Committee
  • The TC chair has given the go ahead to begin work on using the existing NASA standard for the binary encoding of the netCDF enhanced data model in a subset of HDF5.
These transitions are important to the CF-netCDF initiative because they provide mechanisms for OGC standardization of closely related specs that are the responsibility of other organizations (OPeNDAP and HDF) that previously were not actively involved in the OGC standards process.

Note that the CF-netCDF work is being done in close collaboration with the University of Florence / Italian CNR Earth and Space Science Laboratory group.  There are a couple additional areas that need to be addressed as this work progresses.
  • Register a formal mime type for netCDF with IANA.
  • Provide coherence to the numerous related core and extension standards.   Primers (such as the one cited above) with an overall overview are a help but not a solution. Perhaps a three-tier brokering approach to web services will provide a practical mechanism for tying the various components together.