# Weather Radar in Complex Orography
## 4 Solutions and Results
### Calibration, Monitoring and Control
Overall, the Swiss radar sites each send more than 370 monitoring parameters to the central processing server for every elevation sweep, that is, every 10 to 20 s. These include parameters of all the hardware components (antenna control unit, transmitter, receiver), the temperature and humidity in various locations (outside, inside the radome, in the technical room, inside the receiver box), and the building infrastructure (heating, ventilation, climate, uninterrupted power supply, electric consumption, door lock). The strategy behind this is to monitor a large number of parameters at a high temporal resolution, which are automatically analysed for suspicious trends, discontinuities and other anomalies. All the monitoring parameters are archived and can be accessed manually via an interactive online platform that was designed for system diagnostics and troubleshooting, both remotely and on site, by the maintenance personnel. Figure 17 shows the degradation of an ageing TR-limiter. The red and green curves show the signals detected by the receiver in silent gates when the noise source was injected in front of the TR-limiter of the horizontal and vertical polarisation channels, respectively. The temporal variation of the red and green curves exhibits the dependence of the receiver channels on temperature. When calculating the difference between the two, a continuous degradation of the horizontal channel was revealed, which, over the course of six months, reached a value of minus 0.3 dB. This degradation is confirmed by the online samples of Sun's signals and is related to the ageing of a defective TR-limiter. Interestingly, this degradation was not confirmed, to the same extent, by the measurements of repeated _manually_ triggered slow scans of the Sun performed offline at three different stages during the same period (not shown in Figure 17). The manually triggered offline measurements of the Sun revealed a degradation of only minus 0.05 dB, the reason for which was not clear. This illustrates the importance of using different sources of information in parallel for one and the same aspect being tested. A bias in the reflectivity measurements of the order of 0.3 dB is not critical for single-polarisation algorithms, but it can lead to significant errors in products that rely on dual-polarisation data. Figure 16: The antenna radiation pattern of the Plaine Morte radar, measured under real conditions, with the radome, at the site at 2937 m above sea level, after commissioning in 2014. The parabolic antenna has a diameter of 4.2 m and a gain of 45 dB. The measurements were made by an external receiver located on a nearby mountain. In another case, the combination of different information sources was the key to locating the cause of an error. During the acceptance tests of the new dual-polarisation radar on Lema, differential reflectivity Z\({}_{DR}\) was monitored by means of measurements of the Sun, drizzle, an external transponder and an external receiver. The measurements of the Z\({}_{DR}\) bias from the Sun (+0.8 \(\pm\) 0.1 dB ), drizzle (+0.8 \(\pm\) 0.2 dB ) and the external transponder (+0.6 dB ) all revealed a bias with the same sign and of the same order of magnitude. However, the test with the external receiver, which is the only one that does not include the receiving path of the weather radar, revealed a small bias, in the opposite direction, of \(-\)0.1 dB. These test results correctly pointed out an error in the receiving path, and the issue was solved by replacing the Rx calibration unit of the Lema radar.