Water level monitoring of the Mekong Delta using GNSS reflectometry technique

In the last years extreme flood events occur more frequently in Vietnam. Conventional satellite altimeters offer high altimetric accuracy but with insufficient spatial and temporal resolution. Ground based instrumentation enables a high altimetric accuracy with high temporal resolution, but for a point location only. GNSS-Reflectometry (GNSS-R) reveals new perspectives for water level monitoring. To test the possibility of using this innovative technique as a gauge instrument, a two weeks lasting measurement campaign was conducted in Vietnam, in February 2012. The data analysis showed the presence of multipath effects other than the water level in the direct and the reflected signals that deteriorate the results. Using the Empirical Mode Decomposition method (EMD), the water reflections are isolated from further multipath. With a model of these reflections, a correlation of 0.84 instead of 0.67 between the GNSS-R calculated water level changes and the recorded water level changes from a gauge instrument could be reached. Furthermore, applying EMD improves the standard deviation of the determined water heights from 12cm to 5cm.