WISDOM: GNSS-R based flood monitoring

In the last years, due to climate changing conditions severe changes in the Mekong delta in Vietnam have been recorded. The goal of the German Vietnamese WISDOM project is to build an information system for an optimized resource management. One of WISDOM's tasks, is the flood monitoring of the Mekong delta. Since earth-reflected L-band signals from the Global Navigation Satellite System (GNSS) show a high reflectivity on water and ice surfaces or wet soil, GNSS-Reflectometry (GNSS-R) could contribute to monitor the water level on the Mekong delta and be used as a complement to already existing monitoring instruments. With the aim to obtain precise phase observations, a new generation of GORS (GNSS Occultation, Reflectometry and Scatterometry) JAVAD GNSS receiver has been developed. In a two week lasting campaign, the receiver has been tested and several traces have been recorded using two antennas. To derive an average height of the water level, a phase model has been computed. combined with the coherent observations, the minimum slope has been extracted based on the Least-Squares method. As cycle slip and outliers distort the results, a preprocessing of the data has been made. A cycle slip detection strategy that allows for their detection,identification and correction is proposed. To identify outliers, the data snooping method developed by Baarda is used. Issues Related related to the stochastic modelling of GPS observations are addressed and a first model is proposed. First results of water level derivation at decimetre level are presented. These results could then be used as an approximation for the next computation step: the ambiguities fixing.