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Within the German Indonesian tsunami early warning system (GITEWS) project, the GeoForschungsZentrum Potsdam (GFZ) has set up a team consisting of the GFZ, the German Aerospace Center (DLR) and JAVAD GNSS to adapt and extend their new generation GNSS receivers for advanced scientific space applications on small low Earth orbit (LEO) satellites. The GNSS occultation, reflectometry and scatterometry (GORS) space receiver prototype consists of a commercial off-the-shelf JAVAD GNSS GeNeSiS-112 72 channel receiver board with raw data and position solution output. As major step forward compared to current space receivers, the new GORS receiver prototype supports tracking of the civil L2C signal of the GPS constellation. This will enable loss-less dual frequency tracking of occultation events down to very low altitudes. Signal simulator tests show that the prototype provides proper GPS measurements for orbit determination and scientific applications under the signal dynamics of a user satellite in LEO. More than 65% of the time the number of tracked GPS satellites comprises between 9 and 11 with a minimum of 7 all the time. The raw measurement noise analysis indicates reasonable agreement with theoretical models for the CA code noise and LA carrier phase noise. In particular, noise values of 0.25 m (C/A), 0.15 m (P1 and P2), 0.6 mm (LA) and 0.4 mm (L1 and L2) are obtained at 45 dB-Hz.

Within the development of the German Indonesian Tsunami Early Warning System (GITEWS) project, concept studies for space-based warning systems were initiated. Related activities to develop new and appropriate remote sensing technologies like space-based GNSS reflectometry and scatterometry were started in 2006. The intention behind these studies is to apply multi-frequency GNSS receivers aboard of independently planned Earth observation or dedicated multi-satellite missions to monitor sea surface heights with decimeter precision for tsunami detection. Simulation studies within GITEWS indicated that a large number of LEO satellites is required to monitor the ocean with the appropriate resolution in space and time in order to detect a tsunami wave signature. For example, a GNSS reflectometry/scatterometry LEO constellation of 48 satellites would have needed 10 minutes to detect the Sumatra tsunami with 96% probability. Such a constellation could be realized by a set of small and affordable satellites which are equipped with appropriate GNSS instrumentation based on commercial off-the-shelf (COTS) receivers rather than dedicated expensive space receivers. GFZ has set up and leads a team complemented by the German Aerospace Center (DLR) and JAVAD GNSS to adapt and extend the new generation JAVAD GNSS receivers for advanced scientific space applications on small LEO satellites. The GNSS occultation, reflectometry and scatterometry (GORS) space receiver prototype consists of a COTS JAVAD GNSS GeNeSiS-112 72 channel receiver board. As major step forward compared to current space receivers the new GORS receiver prototype supports tracking of the civil L2C signal emitted from modernized GPS satellites (GPS-M). Signal simulator tests show that this prototype provides proper GPS measurements for orbit determination and scientific applications under the signal dynamics of a simulated LEO satellite. The receiver firmware is modified to allow for two-frequency 200 Hz in-phase and quad-phase data output and open-loop tracking of reflected GPS signals. Ground-based water level observations at Lake Walchen were conducted in the Bavarian Alps on July 17-19, 2007. On Mount Fahren (11.315°E, 47.607°N, 1673.5m) a single right-hand circular polarized GPS L1/L2 patch antenna was positioned and tilted by 45° from zenith direction to allow direct and reflected GPS signal reception in parallel from Lake Walchen water surface 824.6m below. Carrier phase observations of coherent reflected signals could be recorded successfully and height profiles of the lake surface could be obtained from both GPS L1 C/A and L2C signal observations within cm-level accuracy. These results show good agreement with water level observations from a conventional tide gauge sensor. Furthermore, it is possible to record the reflected signal waveform in order to derive surface roughness, wave height and wind speed information. The current activities are focused on the next generation GORS2 receiver prototype which is based on the JAVAD GNSS TRIUMPH COTS receiver platform. The TRIUMPH chip has 216 channels for tracking all types of GNSS signals including GPS, GLONASS, Galileo, QZSS, WAAS, EGNOS, and Compass/Beidou. Beside of the high number of available channels and GNSS signals the TRIUMPH receiver family can provide 1-4 RF antenna frontends and external frequency in/output. Within GITEWS signal simulation, performance analyses and environmental tests will be conducted with a set of 1-RF TRIUMPH TR-G3T boards. Additionally, further receiver software modifications will be made together with the manufacturer and ground-based and airborne campaigns are planned with a multi-frontend GORS2 prototype.

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. These 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.