GPS-based Ocean Altimetry Mission Concept for a Tsunami Early Warning System

In this presentation we describe a mission concept for rapid ocean altimetry measurements based on GPS reflections under the assumption that real-time ocean surface heights, when combined with other observations, can be used to confirm, model and predict the effects of tsunamis as part of a tsunami early warning system. Our goal is to provide this global capability within 30 minutes of tsunami generation as indicated from seismic and buoy networks. Ocean surface heights are assumed to be required on a 4x4 degree (400x400km) ocean grid to 50 cm every 30 minutes. These measurements would then be assimilated into tsunami propagation models for updated hazards assessments. The concept mission consists of a constellation of 6 low-Earth orbit satellites distributed in 6 evenly spaced planes at 40 deg. inclination and 800 km altitude tracking GPS and Galileo, collectively referred to as GNSS. Each satellite would be equipped with multiple antennas pointed in such a way to provide a full view of the ocean and at all viewing angles with 20 db gain. The basic measurements are phase delay of the civil L2 and L5 GPS signals anticipated to become available in the near future and their counter part in the Galileo system. Each satellite of the monitoring constellation would provide on average of ~20 simultaneous GNSS reflection measurements with surface height precision of about 10 cm for each 1-sec measurement. The probability of having no reflection measurements in a 4x4 degree area and missing a significant tsunami signal anywhere on the world's oceans below 60 degree latitudes would be less than 16% in a half-hour, less than 5% in 1-hour and less than 0.5% in 2-hour after of the start of a tsunami.