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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 Orbit.

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Radio Occultation

From GPS/MET to COSMIC


Background global positioning system gps satellites low earth orbit leo satellites
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 Orbit

Atmosphere

Radio Signal

LEO Satellite


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

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 set behind Earth limb while the signal slices through the atmosphere

GPS

Glonass

Galileo

---------------

60–90

sources

in space

T. Yunck, JPL


Unique Attractions of GPS Radio Occultation set behind Earth limb while the signal slices through the atmosphere

1. High accuracy: Averaged profiles to < 0.1 K

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 overview

JPL + Stanford set behind Earth limb while the signal slices through the atmosphere

Use Radio

Occultation (RO) to

Explore planetary

atmospheres

Radio Occultation Mission Overview

COSMIC

Operational Demonstration

2006-2011

METOP

(COSMIC II)

Operations RO Missions

UCAR manages GPS-MET

RO Mission - Proof of Concept

1995 - 1997

CHAMP and SAC-C Missions

Improved Proof of Concept

2000 - 2005


Cosmic at a glance

  • C set behind Earth limb while the signal slices through the atmosphereonstellation 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 at a Glance


COSMIC Status set behind Earth limb while the signal slices through the atmosphere


Payloads
Payloads set behind Earth limb while the signal slices through the atmosphere

GPS Occultation receiver

  • 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

  • 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)

  • 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


Cosmic system

6 Satellite COSMIC Microsat Constellation set behind Earth limb while the signal slices through the atmosphere

GPS s/c

Taiwan OPS

R.O. RT

Data E/S(Fairbanks)

R.O. RT

Data E/S(Kiruna)

RT Fiducal

Network

TT&C

NSPO

MOC, MCC, SCC, FDF

TT&C

Real Time CDAAC (Boulder)

C W B

TACC

vBNSSTARTAPTanet, I2

U.S. Universities & Mission

Teams

NESDIS

Other

Users

Other Customers

University

Science

Centers

Operational Centers

COSMIC System

S band

S band

S band

L band

T1

T1

Payload Commands and All Real-Time Data Products

LAN

S/C Telemetry

T1

Internet


Getting COSMIC Results to Weather Centers set behind Earth limb while the signal slices through the atmosphere

NCEP

Input

Data

NESDIS

CDAAC

ECMWF

CWB

GTS

UKMO

BUFR Files

WMO standard

1 file / sounding

JMA

Canada Met.

This system is currently under development by UCAR, NESDIS, + UKMO

Data available to weather centers within < 180 minutes of on-orbit collection


Summary

Summary set behind Earth limb while the signal slices through the atmosphere

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


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