The WISDOM Project
A strong population increase and the climate change have caused severe changes in the Mekong Delta, source of natural resources for several million inhabitants. Extreme flood events occur more frequently, drinking water availability is decreasing, soils show indications of salinization or acidification . Therefore, an optimized resource management is needed. The goal of the Vietnamese-German WISDOM (The Water-related Information System for the Sustainable Development Of the Mekong Delta) research project is to build an information system for the Mekong Delta containing all important hydrologic, ecologic data to support and assist the decision of planners and local authorities .
One of WISDOM’s tasks is to verify the potential of GNSS-Reflectometry (GNSS-R) for precise water level monitoring of the Mekong Delta as a possible complement for already existing monitoring instruments (satellite and ground based altimetry). This work is realized at the GFZ Section 1.1 in collaboration with Section 5.4 (Hydrology).
GNSS Reflectometry measurements in Vietnam
Two GNSS-R measurement campaigns have been performed in February 2012 and March 2013 at Can Tho city (9.99°N, 105.74°E) (see Figure 1). For each campaign, two measurement series with different antenna heights were recorded. The first series on the terrace of the Hotel with an approximate height of 10 m and the second on the Hotel roof with an approximate height of 20 m above the reflecting surface.
To get approximate measurements of water level changes due to tides, a leveling staff was installed during the first measurement campaign. A staff reading was made every 30 minutes. Because of the floating vegetation, passing ships and darkness in the evening an accurate and continuous reading was not possible. In the second measurement campaign a gauge instrument was installed. The carrier phase based GNSS-R altimetry was applied  with the GORS-receiver.
A model of the phase observations is computed. The best fit between model and observations is searched using a least squares method. As outliers and cycle slips will falsify the results, a preprocessing of the data is necessary. With these pre-processed data, a mean height for the observed time interval is computed. Figure 2 shows that the derived mean height agree at the decimeter level with the measurements of a tide gauge instrument 6 km away from the measurement place [1, 2].