The Role of GPS Radio Occultation Observations in the Global Observing System

for Weather, Water and Climate

NOAA BriefingApril 1, 2005

Rick Anthes and Chris RockenUniversity Corporation for Atmospheric Research

Boulder, Colorado, USAhttp://www.cosmic.ucar.edu

Thanks to NSF and NOAA for their support of GPS RO!

Purpose of Meeting

• Update on GPS Radio Occultation results and COSMIC

• Build NOAA Stakeholder Support for transitioning research into operations– Continue COSMIC for FY08-FY11– Develop plans for an operational RO

constellation following COSMIC

GPS RO-Research to Ops• GPS radio occultation is a promising atmospheric

observing system for both weather and climate:– Temperature, water vapor, electron density information– High vertical resolution– High accuracy (<1K)– Unaffected by clouds– Self calibrating, no instrument drift or satellite-to-satellite bias

(important for climate detection)• GPS RO data will be valuable to:

– Weather prediction– Climate monitoring and analysis

• World’s most accurate atmospheric thermometer!– ionospheric research and space weather forecasting– Calibrate/complement/enhance other satellite observing systems

• Need plan for transition from research into operations

National and International Priorities• U.S. 2003 Climate Change Science Program

(CCSP)• Global Earth Observing System of Systems

(GEOSS)• New Priorities for the 21st Century: NOAA’s

Strategic Plan Updated for FY2005-FY2010• World Meteorological Organization

– GCOS-92, WMO/TD No. 1219, October 2004– WMO/CBS/OPAG IOS ET-ODRRGOS Final Report, 6-10 Sept.

2004, Annex VI

Earth Observation Summit IWashington, DC, July 31, 2003

Summit represented a high level governmental/political commitment to move toward a comprehensive, coordinated, global network:

• Issued declaration to support this concept

• Launched development of 10-year implementation plan

• Established the Group on Earth Observations with US Co-Chair

34 Nations

20 International Organizations

Group on Earth bservations

GCOS Implementation Plan for the Global Observing System for Climate

October 2004

Action A20 (AF13): GPS RO measurements shouldbe made available in real time, incorporated intooperational data streams, and sustained over thelong-term.

GCOS-92, WMO/TD No. 1219, October 2004

GOS Implementation Plan Draft

Rec S12: The opportunities for a constellation of ROsounders should be explored and operationalimplementation planned. There has been goodprogress in planning for NRT distribution of METOP/GRAS and COSMIC data.Action: WMO Space Programme to discuss with spaceagencies (1) proposal to develop a shared groundnetwork system and (2) operational constellations followingCOSMIC.

WMO/CBS/OPAG IOS ET-ODRRGOS Final Report, 6-10 Sept. 2004, Annex VI

New Priorities for the 21st CenturyNOAA’s Strategic Plan

Updated for FY2005-FY2010

Understand Climate Variability and ChangeImprove the quality and quantity of climate observations

Serve Societies Needs for Weather and Water InformationWeatherSpace WeatherWater

“Develop and infuse research results and new technologies more efficiently to improve products and services. Streamline dissemination, and communicate vital information more effectively.”

“Increase quantity, quality, and accuracy of satellite data that are processed and distributed within target time.”

GPS RO and COSMIC Update and Recent Results

Chris RockenCOSMIC Chief Scientist

GPS Satellite

LEO Satellite

Radio Signal

LEO Orbit

Atmosphere

GPS Radio Occultation (RO)Deduce atmospheric refractivity based on precise measurement of phase delay and amplitude.

Signals Abundant

GPS GlonassGalileo

60–90Sourcesin space

T. Yunck, JPL

1. High accuracy: (equivalent to <1 K from 5-25 km)

Unique Attractions of GPS Radio Occultation

2. Limb sounding geometry complementary to ground and space nadir viewing instruments

3. High vertical resolution (100m near surface - 1km tropopause)

4. All weather-minimally affected by aerosols, clouds or precipitation

5. Independent height and pressure6. Requires no first guess sounding7. Independent of radiosonde calibration8. No instrument drift9. No satellite-to-satellite bias10. Profiles ionosphere, stratosphere, troposphere11. Inexpensive

T. Yunck, JPL

Atmospheric Refractivity N

€

N = 77.6 PT

+ 3.73 ×10−5 Pw

T 2 − 4.03×107 ne

f 2

N: pressure (P)temperature (T)water vapor pressure (PW)electron density (ne)GPS frequency (f)

Observed Atmospheric Volume

L~300 kmZ~1 km

Issues with GPS RO• Representativeness: Horizontal “average” ~300

km Fundamental to measurement• Penetration to lower troposphere

– GPS/MET median penetration ~500mbCHAMP soundings penetration improvedFinal resolution of issue requires improved GPS receiver

• Negative N bias in lower troposphere, tropical regionsCauses understood, partially resolved, final resolution requires improved GPS receiver (currently undergoing testing at JPL)

QuickTime™ and a decompressor

are needed to see this picture.Note:

Wave structure above tropopause (gravity waves)

Details at Tropopause

Temperature inversions near surface

In preparation for COSMIC GPS/MET, CHAMP, SAC-C mission data are analyzed and compared to NCEP. ECMWF, and radiosondes

Extensive comparisons between analysis centers are conducted

RO Validation

latestprevious

rmsbias

Continued improvements in retrieval

(previous and latest iono. correction)

Figure also shows (for Aug. 2002):

1. ECMWF model in southern hemisphere is worse > 20 km than in northern hemisphere (climatology may also be worse)

2. Positive bias at tropical tropopause (due to higher resolution of RO)

3. Negative N-bias most pronounced in tropics

Newest RO - ECMWF Refractivity Comparisons

GPS radio occultation missionsMission Launch-Duration # Soundings/day RemarksGPS-MET 4/1995 2+ ~125 Proof of Concept

CHAMP 11/2000 ~5 ~250 Improved receiver, tracking

SAC-C 11/2000 ~3 ~300 Improved receiver, open loop tracking test

GRACE 5/2002 ~5 ~500 RO data not yet available

COSMIC 12/2005 ~5 ~2500 Real time-ops

TerraSAR-X 7/2005 ~5 ~400 COSMIC RX & Antennas

EQUARS 7/2006 ~3 ~400 COSMIC RX & CHAMP antennas

METOP 4/2006 ~5 ~500 Real time - ops

COSMIC II ? 3/2009 ~5 ~5000 Real time-ops

Observations should cooperate, not compete!

Combined Soundings at CIMSS

• RMS and bias of temperature profile retrievals from ATOVS alone (blue) and ATOVS plus CHAMP (red) with respect to radiosonde measurements for the months of October 2001, January 2002, April 2002, and July 2002.

• (Borbas et al, CIMSS)

Information content from1D-Var studiesIASI (Infrared Atmospheric Sounding Interferometer)

RO (Radio Occultation)

(Collard+Healy, QJRMS,2003)

Randel et al., 2003

DeseasonalizedT anomalies.4S-4N.Downward proppatterns assocwith QBO.

Contours 0.5 K

QBO over Equator

UK Met Office Study (Healy et al. 2004)

• Forecast impact experiment run for 16 days of CHAMP dataMay/June 2001

• ~160 CHAMP profiles/day (0.35% of total data)

• All other available obs assimilated (ATOVS, sfc,aircraft,radiosondeSat winds, SSMI winds)-~47,450 total

• N assimilated for 4<Z<30 km only

Healy, Jupp and Marquardt, Geophys.Res.Lett, 2004

RMS temperaturedifferences at 250 mband 50 mb betweenControl and GPS ROanalyses.

(Healy et al., 2004)

250 hPa SH (lat<-20º) 50 hPa NH (lat>20º)

Mean and RMS fit to radiosonde T observations for control(red) and GPS RO (blue, dashed) experiments.

COSMIC (Constellation Observing System for Meteorology, Ionosphere

and Climate) 6 Satellites launched in late 2005 Three instruments:

GPS receiver, TIP, Tri-band beacon Weather + Space Weather data Global observations of:

Pressure, Temperature, HumidityRefractivityIonospheric Electron DensityIonospheric Scintillation

Demonstrate quasi-operational GPS limb sounding with global coverage in near-real time

Improved retrievals over GPS/MET, CHAMP

COSMIC Program Status

o: EQUARSo: COSMIC

Distribution of GPS Occultation events in 24 hrs with EQUARS (2006, inclination angle<20o) and

COSMIC (2005, 6 LEO satellites at 72o)

EQUARS

Dense data rate in equatorial region

COSMIC

Global coverage, but less data at low latitudes

+

Concluding Remarks• GPS radio occultation technique is a very promising

atmospheric observing system for both weather and climate:– High vertical resolution– High accuracy– All weather– No instrument drift (important for climate detection)

• GPS RO data will be valuable to:– climate change analysis, validating of climate simulations– operational weather prediction– ionospheric research and space weather forecasting– calibrate other observing systems (e.g., radiosonde and other satellite

obs.)• GPS RO technique is here to stay (COSMIC is coming, and

more missions are being planned)

Summary and Look Ahead• Proof of concept of the potential value of GPS

RO observations has been demonstrated (weather, climate, space weather)

• Operational GPS RO observations called for by WMO studies

• Augment present and planned satellite remote sensing at a reasonable cost– Support US CCSP, GEOSS, NOAA Strategic Plan

• Transition COSMIC constellation into full operations beginning in ~2009-2010

• Plan for success!

COSMIC-II (C2)

•~2500 (5000) high-quality, independent soundings to complement and improve infrared and microwave soundings

•Risk reduction

•Affordable (<$15M/year ongoing costs-total)

•Launch in 2009 would overlap COSMIC by one year, allowing tests of value of 5000 (7500) vs. 2500 soundings

•Major new contribution to GEOSS

[Higher number of soundings in ( ) if Galileo included]

C2 baseline concept spacecraftin flight Total Mass Estimate: 24 Kg.Total Orbit Average Power: 29 wattsStowed Size: 50 cm x 40 cm x 10 cm

Improved occultation receiverReduced latency (<25 min)GPS and Galileo tracking

Activity Name Start Date Finish Date 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Launch of COSMIC 10/4/05

Operation of COSMIC 10/18/05 10/17/10

Planning for COSMIC II 10/1/04 9/30/06

Development of COSMIC II 10/1/06 10/18/09

Launch of COSMIC II 10/18/09

Operation of COSMIC II 10/18/09 10/17/14

Planning for COSMIC III 10/1/09 9/30/10

Development of COSMIC III 10/1/10 10/17/13

Launch of COSMIC III 10/18/13

Operation of COSMIC III 10/18/13 10/17/18

COSMIC II-Summary• Transition research into operations-

maintain a constellation of small satellites in low Earth orbit producing RO observations to help meet the weather, climate and space weather operational requirements as part of the GEOSS.