Empirical assessment of possible X-band radar installation sites, based on on-site clutter tests

In a research project of the Hydraulics Laboratory of the Katholieke Universiteit Leuven (K.U.Leuven) for the water company Aquafin, a small, short range, high resolution X-band weather radar, called Local Area Weather Radar - City Radar (LAWR-CR, DHI), is being used for investigation of the spatial rainfall accuracy improvement in urban drainage models. The system is based on standard X-band marine radar technology, making it cost-effective in comparison to other systems. Since marine radars are manufactured for naval navigation purposes rather than meteorological measurements, their transmitted electromagnetic beam tends to have a large vertical opening angle, making them more sensitive to direct ground clutter when installed on the mainland. With a vertical opening angle of 20 degrees, the LAWR-CR suffers from this disadvantage as well. Furthermore, the limited range of 15 km for quantitative precipitation estimation of the radar restricts the number of suitable installation sites, since they all have to be near the study area. Therefore, finding the appropriate location is a critical step in the installation of the system. The paper describes an empirical approach, based on on-site clutter tests, to assess the suitability of a particular site for radar installation. Four locations were regarded as appropriate for testing. This preselection was based on criteria such as permission of the property owners, minimal beam blockage and accessibility to power supply and data transmission. The clutter tests consisted of dry weather measurements using the Micro Radar, a compact X-band radar. The small size of the Micro Radar makes fast assembly and disassembly of the test set-up possible. Although ground reflections are less intense for the Micro Radar, due to lower output power, to some extent the larger vertical opening angle of 25 degrees compensates for this. Taking these contrasting features into account, the results of the performed clutter tests were considered representative for the expected clutter. None of the investigated locations produced entirely clutter free radar images. Consequently, a further investigation of the clutter above the area of interest was required. After excluding the locations with unacceptable clutter in the study area, the remaining sites were carefully checked for clutter-free images above the rain gauges that will be used in the radar-gauge comparison. Finally, from the two remaining sites considered suitable for installation, the one closest to the study area was chosen.status: publishe