Polarimetric GNSS RO aboard the PAZ satellite: status of the ROHP-PAZ experiment
Presenter:
Estel Cardellach
Institut de Ciencies de l'Espai (ICE-CSIC) Institut d'Estudis Espacials de Catalunya (IEEC)
¹ Institute of Space Studies (ICE, CSIC), Barcelona, Spain ² Institute for Space Studies of Catalonia (IEEC), Barcelona, Spain ³ Jet Propulsion Laboratory, California Institute of Technology (JPL), Pasadena CA, U.S.A. ⁴ University Corporation for Atmospheric Research (UCAR), Boulder CO, U.S.A. ⁵ National Oceanic and Atmospheric Administration (NOAA), Silver Spring MD, U.S.A. ⁶ Hisdesat, Madrid, Spain
Invited talk
The Spanish satellite PAZ, in orbit since February 2018, carries an innovative GNSS Radio Occultation (RO) payload called the “Radio-Occultation and Heavy Precipitation” experiment (ROHP-PAZ). The novelty of this experiment is its ability to acquire the GNSS signals at two linear polarizations to detect precipitation. The measurement principle is based on the polarimetric phase shift between H- and V-polarized signals, received after forward scattering off rain droplets, acting as a ‘radar of opportunity’. This is done through a dual-polarization RO antenna pointing to the limb of the Earth in the anti-velocity direction of PAZ for capturing setting occultations, and a modified GNSS RO receiver to track the signals of the horizontal (H) and vertical (V) antenna ports in an independent yet synchronous way. The hypothesis of the experiment is that it is possible to detect and quantify heavy rain from the differences between the phase-delays of GNSS signals propagating through large rain droplets in their vertical and horizontal components. The results from the first five months of data, published on January 2019, confirm this hypothesis.
Although both H and V polarizations are independent, they can still be processed to provide the ‘traditional’ RO observables and thus retrieve vertical atmospheric profiles of thermodynamic parameters. Therefore, this technology represents the first sensor with capabilities to resolve coincident thermodynamic and precipitation profiles in extreme rain events, with potential for improving our understanding of these type of phenomena.
The RO data acquisition was switched on in May 10, 2018. As part of the commissioning phase and cal/val activities, extensive co-locations are being searched between ROHP-PAZ profiles, data from the Global Precipitation Measurement (GPM) mission and other precipitation and cloud sensors. The studies are intended to refine the retrieval algorithms as well as to assess the complementarity between these type of measurements (including the thermodynamic profiling) and dedicated precipitation radars. An overall description of the mission experiment will be presented, together with its current status, advances and results.
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