Radio Occultation From GPS/MET to COSMIC

Background: Global Positioning System (GPS) Satellites

Low-Earth Orbit (LEO) Satellites• A GPS receiver in LEO can track GPS radio signals

that are refracted in the atmosphere

GPS Satellite

LEO Satellite

Radio Signal

LEO Orbit

Atmosphere

Occultation Geometry

• During an GPS occultation a LEO ‘sees’ the GPS rise or set behind Earth limb while the signal slices through the atmosphere

Occultation geometry

• The GPS receiver on the LEO observes the change in the delay of the signal path between the GPS SV and LEO

• This change in the delay includes the effect of the atmosphere which delays and bends the signal

Signals Abundant

GPS GlonassGalileo

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60–90sourcesin space

T. Yunck, JPL

1. High accuracy: Averaged profiles to < 0.1 K

Unique Attractions of GPS Radio Occultation

2. Assured long-term stability

3. All-weather operation

4. Global 3D coverage: stratopause to surface

5. Vertical resolution: ~100 m in lower trop

6. Independent height & pressure/temp data

7. Compact, low-power, low-cost sensor

T. Yunck, JPL

Radio Occultation Mission OverviewJPL + StanfordUse RadioOccultation (RO) to Explore planetary atmospheres

CHAMP and SAC-C MissionsImproved Proof of Concept2000 - 2005

UCAR manages GPS-MET RO Mission - Proof of Concept1995 - 1997

COSMIC Operational Demonstration

2006-2011

METOP(COSMIC II)

Operations RO Missions

COSMIC at a Glance Constellation Observing System for Meteorology Ionosphere

and Climate (ROCSAT-3) 6 Satellites launched in late 2005 Orbits: alt=800km, Inc=72deg, ecc=0 Weather + Space Weather data Global observations of:

● Pressure, Temperature, Humidity● Refractivity● TEC, Ionospheric Electron Density

● Ionospheric Scintillation

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

Climate Monitoring Geodetic Research

COSMIC Status

Payloads•High-resolution (1 Hz) absolute total electron content (TEC) to all GPS satellites in view at all times (useful for global ionospheric tomography and assimilation into space weather models)

•Occultation TEC and derived electron density profiles (1 Hz below the satellite altitude and 50 Hz below ~140 km), in-situ electron density

•Scintillation parameters for the GPS transmitter–LEO receiver links

•Data products available within 15 - 120 minutes of on-orbit collection

Tri-band Beacon (TBB)•Phase and amplitude of radio signals at 150, 400, and 1067 MHz transmitted from the COSMIC satellites and received by chains of ground receivers.•TEC between transmitter and receivers•Scintillation parameters for LEO transmitter - receiver links

Tiny Ionosphere Photometer (TIP)•Nadir intensity on the night-side (along the sub-satellite track) from radiative recombination emission at 1356 Å•Derived F layer peak density•Location and intensity of ionospheric anomalies (Auroral Oval)

GPS Occultation receiver

COSMIC System

6 Satellite COSMIC Microsat Constellation

C W B

TT&C NSPOMOC, MCC, SCC, FDF

UniversityScienceCenters

R.O. RTData E/S

(Fairbanks)

R.O. RTData E/S(Kiruna)

Real Time CDAAC (Boulder)

U.S. Universities & Mission

Teams

NESDIS

RT FiducalNetwork

OtherUsers

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T1

Internet

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Payload Commands and All Real-Time Data Products

S/C Telemetry

vBNSSTARTAPTanet, I2

Taiwan OPS

T1

Other Customers

TT&C

GPS s/c

TACCT1

LAN

Operational Centers

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Input

Data

CDAAC

NESDIS

GTS

NCEP

ECMWF

CWB

UKMO

Canada Met.

JMA

BUFR FilesWMO standard1 file / sounding

Getting COSMIC Results to Weather Centers

This system is currently under development by UCAR, NESDIS, + UKMOData available to weather centers within < 180 minutes of on-orbit collection

Summary•Radio occultation is a new and promising remote sensing technique

•Technique was demonstrated and now COSMIC aims to:–Improve data quality in lower troposphere - new technology–Increase number of soundings –Show impact in operational models - work at NCEP, UKMO, ECMF

•COSMIC launch is on schedule for December of 2005

•COSMIC “operational demonstration” - should be followed by continuous operational missions