Radio occultation
Radio occultation(RO) is aremote sensingtechnique used for measuring the physical properties of a planetaryatmosphereorring system.Other satellite carriers onboard GNSS-Radio occultation includeCHAMP (satellite),GRACE and GRACE-FO,MetOpand the recently launchedCOSMIC-2.[1]
Atmospheric radio occultation[edit]
Atmospheric radio occultation relies on the detection of a change in a radio signal as it passes through a planet's atmosphere, i.e. as it isoccultedby the atmosphere. Whenelectromagnetic radiationpasses through the atmosphere, it is refracted (or bent). The magnitude of therefractiondepends on the gradient of refractivity normal to the path, which in turn depends on the density gradient. The effect is most pronounced when the radiation traverses a long atmospheric limb path. At radio frequencies the amount of bending cannot be measured directly; instead, the bending can be calculated using theDoppler shiftof the signal given the geometry of the emitter and receiver. The amount of bending can be related to the refractive index by using anAbel transformon the formula relating bending angle to refractivity. In the case of the neutral atmosphere (below the ionosphere) information on the atmosphere'stemperature,pressureand water vapor content can be derived by giving radio occultation data applications inmeteorology.[1]
GNSS radio occultation[edit]
GNSS radio occultation(GNSS-RO), historically also known asGPS radio occultation(GPS-ROorGPSRO), is a type of radio occultation that relies on radio transmissions from GPS (Global Positioning System), or more generally from GNSS (Global Navigation Satellite System), satellites.[2][3]This is a relatively new technique (first applied in 1995) for performing atmospheric measurements. It is used as aweather forecastingtool, and could also be harnessed in monitoringclimate change.The technique involves alow-Earth-orbitsatellite receiving a signal from aGPSsatellite. The signal has to pass through the atmosphere and getsrefractedalong the way. The magnitude of the refraction depends on the temperature and water vapor concentration in the atmosphere.[4]
GNSS radio occultation amounts to an almost instantaneous depiction of the atmospheric state. The relative position between theGPSsatellite and thelow-Earth-orbitsatellite changes over time, allowing for a vertical scanning of successive layers of the atmosphere.[5]
GPSRO observations can also be conducted from aircraft[6]or on high mountaintops.[7]
Planetary satellite missions[edit]
Current missions includeREXonNew Horizons.[8]
Satellite missions[edit]
- CLARREO
- Microlab 1
- FORMOSAT-3/COSMIC
- FORMOSAT-7/COSMIC-2
- CHAMP
- GRACE
- Oceansat
- Sentinel-6 Michael Freilich
- GRAS sensor onboardMetOpsatellite
- SpireLEMUR cubesats
- Yunyao 1
See also[edit]
References[edit]
- ^abDing, Tong; Awange, Joseph L.; Scherllin‐Pirscher, Barbara; Kuhn, Michael; Anyah, Richard; Zerihun, Ayalsew; Bui, Luyen K. (16 September 2022)."GNSS Radio Occultation Infilling of the African Radiosonde Data Gaps Reveals Drivers of Tropopause Climate Variability".Journal of Geophysical Research: Atmospheres.127(17).Bibcode:2022JGRD..12736648D.doi:10.1029/2022JD036648.hdl:20.500.11937/91903.S2CID251652497.
- ^Melbourne et al. 1994.The application of spacebourne GPS to atmospheric limb sounding and global change monitoring.Publication 94-18, Jet Propulsion Laboratory
- ^Kursinski et al. 1997.Observing the Earth's atmosphere with radio occultation measurements using the Global Positioning System.J. Geophys. Res.102:23.429-23.465.
- ^"GPS 'thermometer' could flag up climate change".Retrieved2008-02-16.
- ^"GPS Space-Based & GPS Radio occultation".Archived fromthe originalon 2009-05-15.Retrieved2008-02-16.
- ^Xie, F.; Haase, J. S.; Syndergaard, S. (2008). "Profiling the atmosphere using the airborne GPS occultation technique: A sensitivity study".IEEE Transactions on Geoscience and Remote Sensing.46(11).doi:10.1109/TGRS.2008.2004713.S2CID23345728.
- ^Zuffada, C.; Hajj, G. A.; Kursinski, E. R. (1999)."A novel approach to atmospheric profiling with a mountain-based or airborne GPS receiver"(PDF).Journal of Geophysical Research.104(D20): 24435–24447.Bibcode:1999JGR...10424435Z.doi:10.1029/1999JD900766.
- ^"Payload Technical Specifications".Pluto.jhuapl.edu.Retrieved2023-01-27.
9. Alexander, P., A. de la Torre, and P. Llamedo (2008), Interpretation of gravity wave signatures in GPS radio occultations, J. Geophys. Res., 113, D16117, doi:10.1029/2007JD009390.
