Status of GNSS reflectometry related receiver developments and feasibility studies in the frame of the German Indonesian Tsunami Early Warning System

Kurzfassung

In the frame of the German Indonesian Tsunami Early Warning System (GITEWS) project a multi-frequency Global Navigation Satellite System (GNSS) Occultation, Reflectometry and Scatterometry (GORS) space receiver is developed. It is based on commercial off-the-shelf (COTS) GNSS receiver technology, as the core instrument for a future tsunami detection constellation of small Low Earth Orbit (LEO) satellites. For use in reflectometry, scatterometry and radio-occultation measurements as well as high-precision navigation applications, specific adaptations of the GNSS receiver firmware are desirable, which require a close interaction between scientists and the receiver manufacturer. Within the GITEWS project GFZ has set up a team consisting of GFZ, DLR and JAVAD GNSS (JAVAD) to adapt and extend their new generation GNSS receivers for advanced scientific space applications. Specific adaptations address the improvement of the cold start time-to-first-fix, the selection of optimal tracking loop parameters and channel slaving for monitoring of reflected signals. Besides pseudorange, phase and signal-to-noise measurements, the modified receiver allows output of In-Phase (I) and Quadrature-Phase (Q) accumulations at 5msec intervals (200Hz). As a major step forward compared to current space receivers, the new receiver supports tracking of the civil L2C signal of the GPS constellation. An overview of the current status is given and first results are discussed. Within GITEWS the feasibility of a tsunami detection mission is studied, including the constellation mission design, the options for operating the system and the ways to develop an end-toend system for the quick response to tsunami events. In parallel simulation studies of the GNSS signals reflected to a LEO satellite are carried out. This will be realised by a Zavorotny and Voronovich scattering model with a two-scale model approach using an Elfouhaily sea wave spectrum. An overview of the current activities is given and first results are discussed.