Prepared by

Seth I. Gutman

Chief, GPS-Met Observing Systems Branch

NOAA Forecast Systems Laboratory Demonstration Division

April 19, 2002

CORS Contributions to

Weather Forecasting

Topics

• Introduction:

How CORS data provides important new

information for weather forecasting.

• Implementation:

How the NOAA Forecast Systems

Laboratory is using CORS data to improve

weather forecast accuracy.

• A Look Toward the Future:

How NOAA might use the growing

CORS infrastructure to improve

operational weather forecasting in 2010.

Introduction

• Improved short-term weather forecasts, especially of

severe weather and precipitation, is an important goal

for NOAA, the National Oceanic and Atmospheric

Administration.

• Our ability to do so, however, is currently limited by

the lack of timely and accurate observations of water

vapor in the atmosphere.

• Water vapor is one of the most important components

of the Earth’s atmosphere. It is the source of clouds

and precipitation, and an ingredient in most major

weather events.

• Water vapor varies greatly in time and space, making

it difficult to monitor with conventional observing

systems, such as weather balloons, surface

observations, and satellites.

• Water vapor variability is also largely responsible for

time-dependant errors in GPS positioning, especially

in the measurement of the vertical coordinate.

• To mitigate this problem, methods have been

developed to treat the signal delays caused by the

neutral atmosphere as a nuisance parameter and

remove them to improve survey accuracy.

• Verification of the accuracy of these signal delay

estimation techniques has led to the development of a

new atmospheric remote sensing tool called GPS

Meteorology or GPS-Met for short.

• In GPS-Met, we use data from a network of CORS

sites, in conjunction with improved GPS satellite

orbits, to estimate the total excess signal path length

caused by refractivity in the troposphere.

Introduction

• The total tropospheric signal delay has a

wet and dry component.

• The dry delay is caused by the mass of the

atmosphere, and can be estimated with high

accuracy from a collocated surface pressure

measurement.

• The wet delay is simply the difference

between the total delay and the dry delay.

• The ratio of the wet delay to the dry delay is

the integrated mixing ratio.

• Finally, the wet delay is nearly proportional

to the total quantity of precipitable water

vapor in the atmosphere directly above a

CORS site.

IONOSPHERIC

DELAY

TOTAL

ATMOSPHERIC

DELAY

TROPOSPHERIC

DELAY

HYDROSTATIC

DELAY

WET

DELAY

GPS Signal Delay Structure

Introduction

Implementation

PCCBoulder, CO

-

Processing

FTS-2000

CommsSystem

NGSSilver Spring

-

CORSArchive

FTS-2000CommsSystem

GPSConstellation

SOPACLa Jolla, CA

-Rapid Orbits

FTP

FTP

IGSGlobal Sites

-

GPS Obs

Impact onForecastsZTD

IPW

DataDistribution

ResearchersDOE

NESDISWSFO'sOthers

Hourly RINEXFiles

FRD

NCEP

Hourly RINEXFiles

30 min TrimbleR00 Files

Continuous AshtechZ-12 Files

NOAA Sites

with GPS and

Sfc. Met Sensors

DOT (USCG &

FHWA) NDGPS

Sites with Sfc.

Met Sensors

Other Sites with

GPS and Sfc.

Met Sensors Internet

Hourly Orbits

• The GPS-Met Demonstration Network consists of two

types of sites: Backbone and In-fill:

- Backbone sites belong to NOAA or other federal,

state and local government agencies. They have

collocated surface met sensors and are maintained

as operational systems and as such are considered

to be trusted public resources.

- In-fill sites belong to government agencies,

universities, or other organizations for educational,

research, or proprietary applications. They are not

necessarily maintained as operational systems and

the owners are not obligated to do so.

• The network will expand by acquiring data from both

types of sites. In the near term, most will be backbone

sites belonging to agencies like NOAA, FHWA and

USCG.

Implementation

Implementation

115 CORS GPS-Met Sites + 58 waiting for positions and Sfc. Met.

Implementation

NDGPS Site at Appleton, WA

OAR - Tsfc

, Psfc

, RH, IPWV,

NOS - Tsfc

, Psfc

, RH, Twater

, V, IPWV

OSU - Tsfc

, Psfc

, RH, Twater

, V, IPWV

USCG - Tsfc

, Psfc

, RH, IPWV

MDOT - Tsfc

, Psfc

, RH, IPWV

V PRECIP,

Perry

CCV3

MCD1

KYW1

MAI1

MOB1

TallahasseeJacksonville

TampaMelbourne

Miami

Key West

EXISTING USCG DGPS SITE

POTENTIAL FDOT DGPS SITE

FDOT DGPS SITE at NOAA/NWS WFO

0 50 100 km

Great Lakes CO-OPS Project & MDOTFlorida DOT

Ohio DOT

Mesa County, CO

Implementation

Long-Term Comparisonof GPS and Rawinsondes

Sonde - GPS IPW

Comparisons ARM

SGP CART Site

Jan 1996 - Sep 1999

1996

N = 1382

Mean Dif. = 0.0346 cm

Std. Dev. = 0.1977 cm

Corr. = 0.9886

1997

N = 813

Mean Dif. = 0.0501 cm

Std. Dev. = 0.1965 cm

Corr. = 0.9874

1998

N = 771

Mean Dif. = -0.0431 cm

Std. Dev. = 0.2308 cm

Corr. = 0.9817

1999

N = 551

Mean Dif. = -0.0460 cm

Std. Dev. = 0.2070 cm

Corr. = 0.9851

1996 - 1999

N = 3600

Mean Dif. = 0.0080 cm

Std. Dev. = 0.2102 cm

Corr. = 0.9854

Equation of best fit line

Y = 0.9876125443 * X + 0.01837114798

0 1 2 3 4 5 6

Sonde IPW (cm)

0

1

2

3

4

5

6

GP

S I

PW

(cm

)

1996

1997

1998

1999

WVIOP 2000 PWV (Clear Sky) Data Comparisons

Referenced to Spare MWR

Recent Comparisons

Observations

GOES-8 WV

GOES-8 IR

Analysis & Forecast

WIAP 13km PWV Analysis w/GPS-Met

NCEP Instantaneous Precip Product

, NC

• Assessments of the impact of ground-based GPS-Met

on weather forecast accuracy have been carried out at

FSL since 1997.

• They utilize a research version of the RUC-20 NWP

model with a 1-hour data assimilation cycle over a

region in the central U.S. approximately 700 km x 900

km.

• Each cycle uses all available observations including

rawinsonde, surface, aircraft, wind profiler, and GOES

satellite TPW.

• The only difference is that a second (parallel) run

includes ground-based GPS-Met observations.

• Evaluation is based on Equitable Threat Score (EQT),

Probability of Detection (POD), and Bias.

Implementation

Wx Forecast Improvement

24-h Accumulated Precipitation (inches)

0

5

10

15

20

25

30

35

40

45

50

55

Nu

mb

er

of C

ase

s in

20

01

24-Hour Precipitation Verification

Equitable Threat Score

Better with GPS

Worse with GPS

No Change

1 2 3 4 5 6

24-h Accumulated Precipitation (inches)

0

5

10

15

20

25

30

35

40

Nu

mb

er

of C

ase

s

24-Hour Precipitation Verification

Probability of Detection

Better with GPS

Worse with GPS

No Change

0.01" 0.10" 0.25" 0.50" 1.00" 1.50"1 2 3 4 5 6

24-h Accumulated Precipitation (inches)

0

5

10

15

20

25

30

35

40

45

Nu

mb

er

of C

ase

s

24-Hour Precipitation Verification

Bias

Less with GPS

More with GPS

No Change

0.01" 0.10" 0.25" 0.50" 1.00" 1.50"1 2 3 4 5 6

24-h Accumulated Precipitation (inches)

0

5

10

15

20

25

30

35

40

45

50

55

Nu

mb

er

of C

ase

s

24-Hour Precipitation V erification

Equitable Threat Score

Better with GPS

Worse with GPS

No Change

0.01" 0.10" 0.25" 0.50" 1.00" 1.50"

24-h Accumulated Precipitation (inches)

0

5

10

15

20

25

30

35

40

45

Nu

mb

er

of C

ase

s in

20

01

24-Hour Precipitation Verification

Probabi l ity of Detection

Better with GPS

Worse with GPS

No Change

0.01” 0.10” 0.25” 0.50” 1.10” 1.50” 2.00”0.01” 0.10” 0.25” 0.50” 1.10” 1.50” 2.00”

2000

2000

2000

24-h Accumulated Precipitation (inches)

0

5

10

15

20

25

30

35

40

45

Nu

mb

er

of C

ase

s in

20

01

24-Hour Pre c ipitation Verification

Bias

Less with GPS

More with GPS

No Change

0.01” 0.10” 0.25” 0.50” 1.10” 1.50” 2.00”

EQTS 2000 POD 2000 Bias 2000

EQTS 2001 POD 2001 Bias 2001

A Look Toward the Future

It’s April 19, 2010.

• The GPS Block IIF satellites are being replaced by the

new Block III spacecraft.

• The EC Galileo constellation has been fully

operational for about one year.

• There are 15-20 Global Navigation Satellites in view

at all times over North America.

• The NOAA GPS-Met Demonstration Network

transitioned from research to operations within the

National Weather Service back in 2008.

• The Operational GPS-Met Network consists of about

400 backbone sites and 600 in-fill sites throughout

North America.

• The GPS-Met Network continues to grow as new

CORS sites are brought on line for real-time

operations.

• The network delivers absolute tropospheric delays,

delay gradients and IPWV every 15 minutes. Relative

delays and IPWV are calculated every epoch in areas

of very dense coverage under special conditions (e.g.

severe weather).

• Data from the IGS Global Tracking Network are used

routinely for environmental satellite calibration and

validation, seamlessly tying together the observations

from hundreds of platforms and sensors in space and

time.

GPS-Met in 2010

• Differential correctors are provided by NGS for real-

time high accuracy (~ 20 cm) GPS positioning and

navigation.

• The correctors are calculated from data provided by

NOAA high resolution space and tropospheric weather

models that continuously assimilate data from all

available environmental observing systems, including

CORS and space-based GPS receivers.

• This leads to private/commercial hands-off or robotic

land, sea, and air transportation systems.

• For National Defense, re-locatable windows can be

quickly established anywhere on the planet that

produce very high accuracy correctors for unmanned

or tele-operated military operations.

GPS-Met in 2010