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NWS OPS Committee September 19, 2007. NWS Geospatial Accuracy Issues. Richard Koehler, PhD Forecast Decision Training Branch Boulder, CO. [email protected] 303-497-8369. Quick bio. Current – OCWWS, Training Division

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Nws geospatial accuracy issues

NWS OPS Committee September 19, 2007

NWS Geospatial Accuracy Issues

Richard Koehler, PhD

Forecast Decision Training Branch

Boulder, CO

[email protected]


Quick bio
Quick bio

  • Current – OCWWS, Training Division

  • FDTB in Boulder, CO (co-located with COMET), hydrologist

  • Education

  • Univ. of Ariz., Tucson, AZ PhD Hydrology and remote sensing

  • NPS, Monterey, CA MS Mapping, charting, and geodesy

  • Univ. of Ariz., Tucson, AZ BS, MS Watershed management

  • Other NOAA positions (~ 20 years with NOAA)

  • Retired NOAA Corps – several NOS, NWS assignments


    • DOC Pioneer Grant recipient, “Integrating GIS into River Forecast Operations”, 1993

  • NOS - Hydrographic survey ships RAINIER and WHITING

  • Lead NOS Hydrographic Sciences/Marine Charting instructor

  • Coming soon already here
    Coming soon! Already here!

    2 miles

    or is it really

    2 miles, ± 2.5 mile?


    Some questions to consider

    Current example of an NWS geospatial product

    Quick geospatial lessons

    NWS data references and accuracy

    NWS elevation data

    WSR-88D database comparison

    Estimated location accuracy

    Summary situation

    Proposed solutions

    Key issues and questions
    Key issues and questions

    (June 2004 report)

    NWS Digital Services

    1 - Very high temporal and spatial detail used to populate the NDFD

    2 - Provide data with spatial and temporal consistency

    3 - More detailed forecasts/warnings use higher spatial/temporal resolution data

    Increased access to, and use of this detailed, accurate, and consistent source of weather information will help decision makers in all sectors of society.

    Are NWS geospatial data….

    Detailed? Standardized?

    Accurate? Reliable?

    Consistent? Defendable?

    If “No” or “I don’t know” to any of these, is someone’s life endangered?

    Some answers

    The following caveats apply:

    3) Accuracy of these data is not guaranteed.

    GIS Applications in Climate and Meteorology

    Shipley, Graffman, and Ingram


    16th Internat. Conf. on IIPS for Met., Oceano., and Hydro.

    Position errors of ~ 2 km between the NAD27 and NAD83 ellipsoids

    Significant errors (~ 20 km) when data from spherical Earth is placed the NAD83 ellipsoid.


    3rd Nat. Heavy Precip Workshop

    Some answers?

    OST/SEC GIS Map Group



    Spatial geographic information issued by the National Weather Service (NWS) for use by the user community.

    Data consist of a variety of official NWS forecast zones and county designations used by be NWS.

    The Importance of Correctly Identifying

    Sensor Locations in the Modernized NWS

    Koehler and Tuell (Grady, not Jason)

    Nws geospatial data current example2
    NWS geospatial data – current example



    4.1 km, 2.5 mi

    IE 7

    3.9 km, 2.4 mi

    1.6 mi



    Quick lesson 1 not all lat long are the same1

    2 mi2

    1000 m radius

    Foothills Lab FlagpoleNAD83

    500 m radius

    Quick lesson 1 – Not all lat/long are the same

    Locations from different “map datums”

    Some GPS units provide 70 different datums

    Quick lesson 1 – Not all lat/long are the same

    Why so many different datums?

    To match the Earth’s shape in different places.

    Earth shape is the gravity-based geoid

    Geoid is “bumpy”

    Reference ellipsoid is “smooth”

    A datum links an ellipsoid to the geoid

    Quick lesson 2 nsrs

    National Spatial Reference System (NSRS)

    Accurate, stable and consistent survey network, datums, map projections, GPS, detailed data -

    NAD83, NAVD88

    Quick lesson 2 - NSRS






    Urban zones




    Fed govt standard

    What about NWS products?

    Entrusted to NOAA

    Quick lesson 2 nsrs1
    Quick lesson 2 - NSRS

    NOAA's National Geodetic Survey (NGS) defines and manages a national coordinate system.

    National Spatial Reference System (NSRS), provides the foundation for transportation and communication; mapping and charting; and a multitude of scientific and engineering applications.

    geospatial information


    “It is possible that the adoption of the term ‘NDFD Spatial Reference System’ may cause some serious confusion with the general public, considering it comes from the same NOAA that gives them the NSRS or National Spatial Reference System.” 

    Dru A. Smith, Ph.D., Chief Geodesist , NGS

    Quick lesson 3 datum elements and gis

    Lat/Long NAD83

    Datum NAD83

    Survey Observations

    (ground points)

    Geospatial parameters

    Accurate geospatial data

    Unknown geospatial accuracy, datum, or source,…

    Reference Ellipsoid

    GIS, AWIPS, etc

    GRS 80

    Accurate, useful products

    Questionable products

    (Shape of Earth)

    Quick lesson 3 – Datum elements and GIS

    No GIS or software can make inaccurate geospatial data more accurate. Quality must begin at the start of a project.

    Nws geospatial data how accurate
    NWS geospatial data – how accurate?

    *conversion equation available to address this

    Nws geospatial data how accurate1
    NWS geospatial data – how accurate?

    Implied NWS product geospatial accuracy






    Number of products














    Estimated accuracy (distance in km)

    Nws elevation data
    NWS elevation data

    NWS Standards for SLOSH Basin Databases (Draft standards, 8/29/06)

    Depths and land elevations must all be referenced to the same common datum (traceable to NAVD-1988).

    All elevation and bathymetric data used will be made available to the NWS, allowing the NWS to do checks and comparisons. (i.e. verification)

    Source documentation will accompany these data, including a determination of the accuracy of these data.

    POC: Wilson A. Shaffer

    Nws wsr 88d database comparison
    NWS WSR-88D database comparison

    Recent item:

    One RFC found an 88-d site with a 680 meter position difference between Integrated Hydrologic Forecast System (IHFS) and NCDC lat/long.

    Estimated location accuracy
    Estimated location accuracy

    Weather “event”, “point” data, warning area vertex

    Datum uncertainty (100 m)

    Radar site uncertainty (100 to 700 m)

    Map background uncertainty (1 km)

    Radar plot (or model) uncertainty (1.5 km)

    Other possible uncertainty? (4 km)

    Gridded data basis

    Point location could have an uncertainty of ~ ± 2 km RSS

    Same as an area of 3,100 acres

    ~ 5 mi2


    Document and create a “data pedigree”

    Reference datum for all products

    Projections used in all files

    Data source

    Data accuracy


    Proper display of NWS data in GIS software

    Consistent quality for any end users

    Both vertical and horizontal datums – i.e. where things are located

    Current situation synopsis
    Current situation synopsis

    Future Goal - NWS Digital Services

    Requires accurate, consistent, and detailed geospatial data

    Reality check

    Web maps don’t match ground coordinates (4 km error), points = ± 2 km uncertainty

    WGS84, NAD27, NCEP Sphere, “NULL”, NGVD29, MSL, NAD83, NAVD88

    Multiple datums = end user confusion

    Little documentation or metadata (one office = 99% locations “NULL” datum)

    Politically embarrassing to NWS, NOS/NGS, and especially NOAA

    Geospatial data with poor or unknown accuracy effects

    Will frustrate Digital Services efforts

    Will mean any high resolution product will have suspect quality (such as NDFD)

    Will cause questionable verification

    Will cause loss of confidence in NWS by emergency managers & partners

    Worst case – poor/misused products may endanger lives

    Little training provided

    Untrained staff are creating geospatial products

    Vertical Datum training unfunded for FY08 ($5K)

    Proposed solutions
    Proposed solutions

    Work with NOS/NGS

    NGS Director & chief geodesist willing to help NWS (building next door)

    NGS has world-class expertise in all things geospatial

    In best interest of NOAA, NWS, and NOS/NGS

    Establish an NWS geospatial policy which includes:

    NWS conforming to established national standards

    Assessing, adopting and put into practice geospatial QA/QC

    Ensuring complete metadata (data pedigree including location accuracy)

    A “Geospatial Information Officer” (GIO) under the CIO

    Similar to USGS, EPA, Homeland Security, multiple states, others agencies

    Single NWS ‘go to’ person to coordinate geospatial topics

    Provide adequate training for everyone (mgmt and field)

    Proposed solutions1
    Proposed solutions

    Developing a white paper for management review

    “Proposed Steps to Address NWS Geospatial Issues”

    • What are the geospatial accuracy needs of NWS?

    • What level of accuracy are current NWS geospatial data and products?

    • What level of geospatial QA/QC is needed?

    • How much training will be required?

    Proposed solutions2
    Proposed solutions

    Developing a white paper for management review

    “Proposed Steps to Address NWS Geospatial Issues”

    A. Background summary of geospatial fundamentals

    B. Major issue is broken down into the following subsection:


    Actions required

    Support information

    Potential solution

    Estimated timeframe

    Estimated costs

    Proposed solutions3
    Proposed solutions

    Existing white paper available for review

    Draft“Geospatial Policy for NOAA’s National Weather Service”

    The following four key points form the basis of a geospatial policy for NOAA/NWS:

    1) Ensure all NWS geospatial data conform to the NSRS.

    2) Partner with NOS/NGS on all geospatial related activities.

    3) Ensure all geospatial and georeference data have a reference datum listed with the data. The preferred horizontal datum is NAD83 and the preferred vertical datum is NAVD88. If any other datum is used, that information shall be provided with the product.

    4) Use the GRS80 reference ellipsoid as the shape of the Earth when geodetic calculations are needed.

    Define the geospatial accuracy needed to create NWS products

    List the geospatial accuracy for all NWS products

    Proposed solutions4
    Proposed solutions

    Training material under development

    Preparing e-learning module for NOAA LMS

    Mapping datums and geospatial issues:

    The science of location and the keys to an accurate GIS

    Intra-NOAA cooperative project

    NWS/OCWWS: Rick Koehler, FDTB hydrologist

    NOS/NGS: David Zilkoski , NGS Director

    NESDIS/NGDC: Anna Milan, associate scientist

    Thanks to Jim Hoke, Leroy Spayd, and Tony Mostek