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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 4 | Copyright

Special issue: Observing Atmosphere and Climate with Occultation Techniques...

Atmos. Meas. Tech., 11, 1883-1900, 2018
https://doi.org/10.5194/amt-11-1883-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Apr 2018

Research article | 05 Apr 2018

Information content in reflected signals during GPS Radio Occultation observations

Josep M. Aparicio1,3, Estel Cardellach2,3, and Hilda Rodríguez2,3 Josep M. Aparicio et al.
  • 1Meteorological Research Division, Environment and Climate Change Canada (ECCC), 2121 Transcanada Hwy, Dorval, QC, Canada
  • 2Institut de Ciències de l'Espai (ICE), Consejo Superior de Investigaciones Científicas (CSIC), Cerdanyola del Vallès, Spain
  • 3Institut d'Estudis Espacials de Catalunya (IEEC), Cerdanyola del Vallès, Spain

Abstract. The possibility of extracting useful information about the state of the lower troposphere from the surface reflections that are often detected during GPS radio occultations (GPSRO) is explored. The clarity of the reflection is quantified, and can be related to properties of the surface and the low troposphere. The reflected signal is often clear enough to show good phase coherence, and can be tracked and processed as an extension of direct non-reflected GPSRO atmospheric profiles. A profile of bending angle vs. impact parameter can be obtained for these reflected signals, characterized by impact parameters that are below the apparent horizon, and that is a continuation at low altitude of the standard non-reflected bending angle profile. If there were no reflection, these would correspond to tangent altitudes below the local surface, and in particular below the local mean sea level. A forward operator is presented, for the evaluation of the bending angle of reflected GPSRO signals, given atmospheric properties as described by a numerical weather prediction system. The operator is an extension, at lower impact parameters, of standard bending angle operators, and reproduces both the direct and reflected sections of the measured profile. It can be applied to the assimilation of the reflected section of the profile as supplementary data to the direct section. Although the principle is also applicable over land, this paper is focused on ocean cases, where the topographic height of the reflecting surface, the sea level, is better known a priori.

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It is shown that during a satellite-to-satellite radio transmission, over the Earth's limb, the signal bounced off the ocean contains information of the low atmosphere as shown with radio occultations. This bounced signal is particularly clear over colder oceans but less clear over the tropics. This information is indicative of the properties of the low troposphere and can be used as a remote sensing measurement for weather.
It is shown that during a satellite-to-satellite radio transmission, over the Earth's limb, the...
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