Calibration and Validation of the Polarimetric Radio Occultation and Heavy Precipitation onboard PAZ experiment and potential scientific applications
Presenter:
Ramon Padullés
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
(1): Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA; (2): Scripps Institution of Oceanography, La Jolla, San Diego, CA; (3): Institut de Ciències de l’Espai, Consejo Superior de Investigaciones Científicas, Institut d’Estudis Espacials de Catalunya
Talk
The Radio Occultations and Heavy Precipitation experiment on board the Spanish satellite PAZ measuring since May 10th 2018 was launched to prove the Polarimetric Radio Occultation (PRO) concept ability to detect precipitation. Soon after the activation of the experiment it became clear that the signals exhibited signatures of precipitation structures, therefore confirming the hypothesis and its main science goal.
The technique consists in measuring the phase difference between the horizontal (H) and vertical (V) components of the electromagnetic field coming from the Global Positioning System (GPS) satellites in an occulting geometry. H and V components are measured independently, yet synchronously, with a dual linear polarized antenna placed on a Low Earth Orbiter and pointing towards the limb of the Earth in the satellite’s anti-velocity direction. In the presence of asymmetric hydrometeors (flattened during their fall by air drag), the phase delay in the H component is larger than for the V component. PAZ data confirm that this phase delay difference can be measured.
In this presentation we will discuss the on-orbit calibration and correction of the effects that can have an impact in the PRO observables other than hydrometeors, such as the effect of metallic structures near the antenna, Faraday Rotation at the ionosphere, signal impurities in the transmission, altered cross polarization isolation, etc. This calibration is performed with an extensive dataset consisting on one year of observations co-located with independent information about precipitation and ionospheric activity. The calibrated observables are validated against the Global Precipitation Mission (GPM) precipitation products (mostly 2-Dimensional but also 3-D). The validation shows how the calibrated products can be used as a proxy for precipitation, with almost no false positive nor false negative detections. The signals also exhibit signatures well above the freezing level, possibly indicating sensitivity to frozen hydrometeors and cloud structures.
Such products, together with the standard Radio Occultation thermodynamic retrievals (vertical profiles of temperature, pressure and water vapor), represent the first products that provide coincident vertical precipitation and thermodynamic information obtained with the same sensor, and that can be obtained globally, regardless of cloud conditions, seamlessly across ocean/land boundaries and with high vertical resolution. The characteristics of these products enable exploring many open science questions that could not be addressed until now, some of them are illustrated here.
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