Utilizing ocean reflected GPS L1 C/A and the new GPS L2C signals for Tsunami Detection from space: Possible small satellite constellations and the GORS instrument

Abstract

Within the German Indonesian Tsunami Early Warning System (GITEWS) project concept studies and new technology developments using Global Navigation Satellite System (GNSS) reflectometry and scatterometry have been initiated. Thes techniques use ocean reflected GNSS signals for tsunami detection from space. With modified multi-frequency GNSS receivers onboard a satellite densely spaced grids of sea surface heights with decimeter accuracy could be established fairly rapidly. Simulation studies analyze various scenarios of low earth orbit (LEO) satellite constellations with respect to tsunami detection time and show that only a large number of LEO satellites can monitor the sea surface with sufficient high resolution in space and time. The studies assume optimum signal reception. Such a LEO constellation could be realized by small and affordable satellites, equipped with GNSS instrumentation based on the use of commercial off-the-shelf (COTS) rather than dedicated expensive space receivers. Within GITEWS the new generation JAVAD GNSS receivers are adapted and extended for such advanced space applications. The GNSS occultation, reflectometry and scatterometry (GORS) space receiver prototype uses a modified firmware that allows for open-loop tracking of reflected GPS signals. As major step forward compared to current space receivers GORS supports tracking of the civil GPS L2C signal. Signal simulator tests show that the prototype provides proper GPS measurements for orbit determination and scientific applications under LEO signal dynamics. A ground-based experiment evaluates the extended functionality of the GORS receiver and illustrates the proof-of-concept of a GPS reflectometry measurement for two frequencies. Water level observations of Lake Walchen could be remotely obtained by carrier-phase delay with cm-level accuracy. Furthermore, the receiver is able to record reflected GPS signal waveforms.