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NWS OPS Committee September 19, 2007. NWS Geospatial Accuracy Issues. Richard Koehler, PhD Forecast Decision Training Branch Boulder, CO. richard.koehler@noaa.gov 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



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?




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 -


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


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