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Excess Path Model for Space-based GNSS Reflectometry: A PRETTY mission concept study

Semmling, Maximilian and Moreno Bulla, Mario Andres and Hoque, Mohammed Mainul and Zus, Florian and Wickert, Jens (2022) Excess Path Model for Space-based GNSS Reflectometry: A PRETTY mission concept study. International Workshop on GNSS Ionosphere IWGI 2022, 26.-28. Sep. 2022, Neustrelitz, Germany.

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Signals of Global Navigation Satellite Systems (GNSS) became an important source for remote sensing over the last decades. Signal delays introduced either by atmospheric refraction or by Earth surface reflection are used to monitor the Earth system. Neutral gas properties and electron density in the atmosphere are retrieved, for example, by radio occultation techniques. Sea surface altimetry and ocean wind retrievals can be based on respective reflectometry techniques. The GNSS signals experience an excess path delay when propagating in atmospheric media (neutral and electron gases) relative to propagation delay in vacuum. It is an essential observable for atmospheric sounding and a major bias for sea surface altimetry. The ESA satellite mission PRETTY (Passive REflecTo- and dosimeTrY) shall be launched end of 2022. The three-unit cubesat is equipped with a designated GNSS reflectometry receiver for altimetry and dosimeters for space weather monitoring. In a current study the scientific opportunities of the reflectometry payload are investigated. The excess path model contributes to the altimetric mission goal by providing corrections for the space-based scenario. The model has two major parts. The first part is a purely geometric model to determine the specular point of the Earth's surface reflection (Sp) and the three distance vectors connecting Sp with the receiver (Rx) and with the transmitter (Tx), as well as, the vector connecting Tx and Rx, directly. The second part involves the atmospheric correction. Neutral gas and ionospheric refractivity profiles are derived along the three vectors (between Sp, Rx and Tx). Dedicated atmospheric input data are obtained from: ERA5 (Reanalysis products of the European Centre of Medium-Range Weather Forecast) and NEDM (Neustrelitz electron density model of the German Aerospace Center). Spatial and temporal variability of refractivity is resolved down to 30 km horizontally in 1h intervals (neutral gas by ERA5) and down to about 250 km horizontally in the ionosphere with semi-diurnal scale and longer. In a final step the excess phase path (delay in neutral gas and advance in ionosphere) is computed using the refractivity profiles. It is achieved either by slant path integration (disregarding bending effects) or by ray tracing calculations (considering ray bending). First tests of the model were performed for mountain-based observation scenarios (receiver height at 1430 m above Mediterranean Sea). In this scenario the excess path delay of direct signals in grazing angle geometry (5° elevation) varies between 14 and 16 m depending on atmospheric conditions. The relative excess path (of the reflected signal relative to the direct one) lies between 8 and 10 m under the same conditions. The excess path variability of up to 20% (2 m) indicates the necessity of a precise model considering spatial and temporal variations in refractivity, especially as variability in the space-based scenario will still increase.

Item URL in elib:https://elib.dlr.de/193357/
Document Type:Conference or Workshop Item (Speech)
Title:Excess Path Model for Space-based GNSS Reflectometry: A PRETTY mission concept study
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Semmling, MaximilianUNSPECIFIEDhttps://orcid.org/0000-0002-5228-8072UNSPECIFIED
Hoque, Mohammed MainulUNSPECIFIEDhttps://orcid.org/0000-0001-5134-4901UNSPECIFIED
Zus, FlorianHelmholtz Centre Potsdam, GFZ German Re search Centre for Geosciences, Potsdam, GermanyUNSPECIFIEDUNSPECIFIED
Wickert, JensGeoForschungsZentrum Potsdamhttps://orcid.org/0000-0002-7379-5276UNSPECIFIED
Refereed publication:No
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Keywords:GNSS reflectometry, PRETTY mission, Ionospheric delay
Event Title:International Workshop on GNSS Ionosphere IWGI 2022
Event Location:Neustrelitz, Germany
Event Type:Workshop
Event Dates:26.-28. Sep. 2022
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Solar-Terrestrial Physics SO
Location: Neustrelitz
Institutes and Institutions:Institute for Solar-Terrestrial Physics > Space Weather Observation
Deposited By: Semmling, Dr. Maximilian
Deposited On:23 Mar 2023 07:41
Last Modified:23 Mar 2023 07:41

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