# Weather Radar in Complex Orography
## 4 Solutions and Results
### Siting  
The choice of a suitable site is obviously a critical step. Many studies have been presented in the literature to simulate ground clutter and shielding of a radar using digital terrain information and a beam propagation model, see, for instance, [19; 113; 114; 116; 130]. Siting in a mountainous region is always a compromise between a high site on a peak in the centre of the mountain range with limited shielding and the possibility of long-range surveillance (we call this type \"peak\"), a mountain site at an intermediate height on a crest somewhat offset from the main mountain range with the highest peaks (\"offseta\" type), or a site lower down in a valley that allows the precipitating cloud to be observed at low heights (\"valley\" type), see Figure 11. In addition, there is also the \"plain\" type, which corresponds to a radar sited on a tower or a hill that is far away from the nearest mountain range and can overlook a plain with few or no obstacles. This subdivision is oversimplified, but it illustrates the main options for siting a radar to oversee precipitation over complex orography. All four types have pros and cons, and none is ideal. A combination is likely to give the best results. For the \"peak\" type, it is tempting to chose one of the highest peaks of the mountain range. However, this is probably not the best option. Moving away from the ridge with the highest peaks, it is often possible to find a considerably lower site with limited shielding, better access, easier conditions for construction work and the possibility of seeing the precipitating cloud at lower heights. The latter is an important aspect, as the number of hydrometeors and the chances of obtaining a sufficient number of good measurements, which would allow meteorological variables to be derived, decreases rapidly with height, see Section 3. A radar of the \"peak\" type can not see down into narrow valleys, but it is the only site in complex orography that allows precipitating clouds to be sampled close to the terrain and with a narrow beam over a large area. The beams of the radars of the \"offseta\" and \"plain\" types over the mountain range are high above the terrain and broad, due to the long distances. A site of the \"valley\" type can see falling hydrometeors down in the valley, but its range is seriously limited by the surrounding slopes and crests. Figure 11: Four different types of radar sites used to monitor precipitating clouds over complex orography. The rays and the grey shading indicate the part of the atmosphere that can be seen by the “plain”, “peak” and “offseta” radars. The range of visibility of the “valley” type is limited to the visible cone above that valley, which is not shown in the figure. The Swiss radar sites on Monte Lema and La Dole belong to the \"offside\" type, whereas the two Alpine sites on Plaine Morte and Weissfulhappifel, which were added in 2014 and 2016, are of the \"peak\" type (Figure 1). Another example of the \"peak\" type is the Austrian radar on the Valluga mountain. The site of the polarimetric Doppler X-band radar, operated by the University of Grenoble, see, for instance, [131], is an important example of the \"valley\" type with ideal visibility over the target area, that is the city of Grenoble. The sites in deep Alpine valleys of the mobile polarimetric X-band radars operated by EPFL and MeteoSwiss also belong to the \"valley\" type, see, for instance, [132]. The radars on Albis near Zurich and Bric della Croce near Turin (Italy) are examples of the \"plain\" type. Figure 12 illustrates the contribution of different types of sites to the observation of precipitating clouds over and near a mountain range. It shows precipitation accumulated over one year (2016) along a vertical north-south cross section that crosses the central European Alps. However, there is no single ideal site. Only a combination of different types of sites in complex orography will provide good data quality in all regions. Data quality decreases as the range and level of shielding increase.