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NWS Geospatial Accuracy Issues

NWS OPS Committee September 19, 2007

Richard Koehler, PhD

Forecast Decision Training Branch

Boulder, COrichard.koehler@noaa.gov

303-497-8369

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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

NWS - CBRFC and NWRFC

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

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2 miles or is it really

2 miles, ± 2.5 mile?

Coming soon! Already here!

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Outline

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

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Key issues and questions

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?

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.

(June 2004 report)

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Some answers?

Purpose: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.

GIS Applications in Climate and MeteorologyShipley, Graffman, and Ingram

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.

OST/SEC GIS Map Group

The Importance of Correctly Identifying Sensor Locations in the Modernized NWSKoehler and Tuell (Grady, not Jason)

19923rd Nat. Heavy Precip Workshop

200016th Internat. Conf. on IIPS for Met., Oceano., and Hydro.

The following caveats apply: 3) Accuracy of these data is not guaranteed.

http://www.weather.gov/geodata/cat_descrip.html

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NWS geospatial data – current example

?

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NWS geospatial data – current example

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NWS geospatial data – current example

PA

MD

DE

FireFox4.1 km, 2.5 mi

IE 73.9 km, 2.4 mi

1.6 mi

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

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Foothills Lab Flagpole

NAD83

1000 m radius

500 m radius

2 mi2

Locations from different “map datums”

Some GPS units provide 70 different datums

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

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Why so many different datums?

To match the Earth’s shape in different places.

Earth shape is the gravity-based geoid

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

Geoid is “bumpy”Reference ellipsoid is “smooth”A datum links an ellipsoid to the geoid

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Topography

Shoreline

Boundaries

Urban zones

Roads

Streams

Vegetation

Longitude

LatitudeNational Spatial Reference System (NSRS)

Accurate, stable and consistent survey network, datums, map projections, GPS, detailed data -NAD83, NAVD88

Quick lesson 2 - NSRS

Entrusted to NOAAWhat about NWS products?

Fed govt standard

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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

metadata

“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

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Geospatial parameters

Datum NAD83

GIS, AWIPS,

etc

Quick lesson 3 – Datum elements and GIS

Reference Ellipsoid

GRS 80

(Shape of Earth)

Survey Observations Lat/Long NAD83

(ground points)

Accurate geospatial data

Accurate, useful products

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

Unknown geospatial accuracy, datum,

or source,…

Questionable products

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NWS geospatial data – what system is used?

Product or database Datum Earth shape Note

TOR, FFW, SVR, SMW

watches and warnings

WGS84 WGS84 Dept of Defense system (not the fed govt standard)

NDFD WGS84 WGS84 Also listed as NCEP Sphere

NWS GIS data

- Rivers and streams

NAD27 Clarke 1866 Obsolete datum, Error if assumed to be NAD83

NWS GIS data

- Cities and towns

NAD83 Clarke 1866 ambiguous, datum and spheroid do not match

RFC “location table” unknown unknown “NULL” datum for 98.7% of locations at one office

AWIPS NAD83 GRS80 Consistent with NSRS

NOAA/NOS/ National Geodetic Survey (NGS)

NAD83 GRS80 Basis of NSRS

“Gold Standard”

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NWS geospatial data – how accurate?

Product Geospatial Data Source

Estimated Location Accuracy

AWIPS background maps 1:2,000,000 maps ± 1 km or greater (NMAS)

Listed to 0.1 m precision

Watches and warning areas AWIPS display unknown, precision is ~1 km

NDFD unknown Unknown, spacing ~ 5 km, precision is 0.1 m

Radar tornado signatures (2006 study)

AWIPS display ± 1.4 km mean error

(12 km max error )

NCEP global model Multiple sources – no conversions to common system

Unknown datum, ± 1 km

Spherical to geographic coord

w/o conversion, ± 20 to 30 km *NOS/NGS survey marks

Basis of NSRS

geodetic level survey methods

± 1 to 2 mm

“Gold standard”

* conversion equation available to address this

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Implied NWS product geospatial accuracy

NWS geospatial data – how accurate?

0

5

10

20

25

30

35

40

0.001 0.03 1 2 4 5 10 100 unknown

Estimated accuracy (distance in km)

Nu

mb

er

of

pro

du

cts

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NWS elevation data

Item Reference Note

AHPS gage elevations NGVD 29 and NAVD88 NGVD 29 is obsolete

NDFD WGS 84 geoid Potential two meters elevation difference

Some hydro products “Mean Sea Level” ambiguous

NGS benchmarks NAVD 88 “Gold standard”

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

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NWS WSR-88D database comparison

Statistic NCDC vs OSTNo. WSR-88D pairs compared 159

No. pairs with exact same lat/long 0 (None)

Max difference 5,500 m (5.5 km)

Avg difference 85 m

# pairs diff by 100+ m ~ 10%

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.

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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)

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

Same as an area of 3,100 acres

Gridded data basis

~ 5 mi2

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Metadata

Document and create a “data pedigree”

Reference datum for all products

Projections used in all files

Data source

Data accuracy

Ensure

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

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Current situation synopsisFuture 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 providedUntrained staff are creating geospatial products

Vertical Datum training unfunded for FY08 ($5K)

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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)

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Proposed solutions

Developing a white paper for management review

“Proposed Steps to Address NWS Geospatial Issues”

1. What are the geospatial accuracy needs of NWS?

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

3. What level of geospatial QA/QC is needed?

4. How much training will be required?

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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:

Issue

Actions required

Support information

Potential solution

Estimated timeframe

Estimated costs

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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

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Training material under developmentPreparing 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

Proposed solutions

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Questions?