Radio occultation (RO) is aremote sensing technique used for measuring the physical properties of a planetaryatmosphere orring system. Satellites carrying onboard GNSS-Radio occultation instruments includeCHAMP,GRACE and GRACE-FO,MetOp and the recently launchedCOSMIC-2.[1]
Atmospheric radio occultation
editAtmospheric 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 isocculted by the atmosphere. Whenelectromagnetic radiation passes through the atmosphere, it is refracted (or bent). The magnitude of therefraction depends 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 shift of the signal given the geometry of the emitter and receiver. The amount of bending can be related to the refractive index by using anAbel transform on the formula relating bending angle to refractivity. In the case of the neutral atmosphere (below the ionosphere), information on the atmosphere'stemperature,pressure and water vapor content can be derived, thus giving radio occultation data applications inmeteorology.[1]
GNSS radio occultation
editGNSS radio occultation (GNSS-RO), historically also known asGPS radio occultation (GPS-RO orGPSRO), 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 forecasting tool, and could also be harnessed in monitoringclimate change. The technique involves alow-Earth-orbit satellite receiving a signal from aGNSS satellite. The signal has to pass through the atmosphere and getsrefracted along 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 the GNSS satellite and thelow-Earth-orbit satellite changes over time, allowing for a vertical scanning of successive layers of the atmosphere.[5]
GNSS-RO observations can also be conducted from aircraft[6] or on high mountaintops.[7]
Planetary satellite missions
editCurrent missions includeREX onNew Horizons.[8]
Satellite missions
edit- CLARREO
- Microlab 1
- FORMOSAT-3/COSMIC
- FORMOSAT-7/COSMIC-2
- CHAMP
- GRACE
- Oceansat
- RO instrument onboardSentinel-6 Michael Freilich
- GRAS instrument onboardMetOp satellites
- Spire LEMUR cubesats
- Yunyao 1
See also
editReferences
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.S2CID 251652497.
- ^Melbourne, W. G.; Davis, E. S.; Duncan, C. B.; Hajj, G. A.; Hardy, K. R.; Kursinski, E. R.; Meehan, T. K.; Young, L. E.; Yunck, T. P. (1994).The application of spaceborne GPS to atmospheric limb sounding and global change monitoring (Report). Jet Propulsion Laboratory. NASA-CR-199799, JPL-PUBL-94-18.
- ^Kursinski, E. R.; Hajj, G. A.; Schofield, J. T.; Linfield, R. P.; Hardy, K. R. (1997)."Observing Earth's atmosphere with radio occultation measurements using the Global Positioning System".Journal of Geophysical Research: Atmospheres.102 (D19):23429–23465.Bibcode:1997JGR...10223429K.doi:10.1029/97JD01569.ISSN 0148-0227.
- ^"GPS 'thermometer' could flag up climate change". Retrieved2008-02-16.
- ^"GPS Space-Based & GPS Radio occultation". Archived fromthe original on 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.S2CID 23345728.
- ^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.
