NWS Geospatial Accuracy Issues
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Transcript of NWS Geospatial Accuracy Issues
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NWS Geospatial Accuracy Issues
NWS OPS Committee September 19, 2007
Richard Koehler, PhD
Forecast Decision Training Branch
Boulder, [email protected]
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?