Combining C-band and X-band weather radars for accurate precipitation measurements over urban areas

Over approximately the last decade there has been a growing interest for using quantitative precipitation estimates measured by weather radars in urban hydrological applications. This activity, development and research has led to the consideration, that weather radar measurements today are an important supplement to the traditional tipping bucket rain gauges in urban hydrology. Currently, the weather radar is perceived as a valuable tool to enlighten the dynamic effects in the drainage system caused by the time and spacial distributed progressions in the rainfall event. In the same way, the weather radar is considered as an indispensable tool for accurate short-time precipitation forecast, which in the near future facilitates intelligent and active adapting drainage systems with the potential consequences of a more efficient wastewater transport and treatment.

An important prerequisite for this wide application of weather radar precipitation data in the field of urban drainage is, however, that the volume integration, which the radar conducts of the precipitation in the atmosphere, is representative of the actual precipitation hitting the ground surface and affecting the urban drainage system. If this transformation is incorrect or insufficient described it may cause significant errors in the radar based rainfall measurements, reducing the overall data quality and its applicability for e.g. urban drainage modelling or precipitation forecasts.

Different types of weather radars ranging from massive long-range S- and C-band radars to small cost-efficient X-band radars are in operation today. In Denmark it is quite common with dual coverage from both C- and X-band radars. The radars are operating with different configurations regarding: antenna design, wavelength, scanning strategy etc, which results in different properties for the measurement. Shorter wavelength results in a higher resolution and thereby a more detailed description of the precipitation and its propagation, while longer wavelengths are less sensitive to the atmospheric attenuation. Depending on antenna design and the scanning strategy, the volumetric integration of the atmosphere is different regarding e.g. the vertical opening angle of the antenna, which means that some radar types scan the whole cloud formation while others scan a part of it.

The basic concept behind the PhD project is its possibility to reduce the weaknesses and inaccuracies of one radar type by utilising the strength from another and vice versa. The overall aim for the PhD project is to investigate, how this combination is possible and furthermore, to develop the necessary intercalibration and data assimilation tools to produce a merged measurement. The expected outcome of the project is that it will facilitate methods for data fusion of different types of weather radar data in radar networks that produces a single combined precipitation image which outperforms the individual radars. This will increase the overall quality, value and the future applicability of weather radar based precipitation measurements in the field of urban drainage.