# Correcting for Mobile X-Band Weather Radar Tilt Using Solar Interference
## 3 Solar Interference Assessment Methodology
### Solar Hit Identification  
To determine instances of solar interference within the RAiN-E observations, a combination of open-source radar tools (including the scansun module of BALTRAD's RAVE toolbox and PyART) were used to parse the CfRadial files and identify interference spikes occurring close to the sun's position [20; 21; 22]. The BALTRAD RAVE toolbox implements KNMI's scansun functionality, first described by [PERSON] and [PERSON] [12]. For this work, we use unfiltered horizontal reflectivity as input to the RAVE scansun tool. Within the RAVE toolbox, the following process occurs to identify solar hits for further analysis. Firstly, using the ray timestamps within the radar files, a search radius of five degrees around the sun's known position is calculated and used to find radials that contain a near-continuous (>70%) linear echo (at least 20 km long) at a consistent power level (within 2 dB of a first-estimated mean power value) at high elevations (i.e., higher in altitude than typical weather signals: 8 km for first identification in this case, and 4 km for the second filtered estimation). The RAVE toolbox then converts this power to solar equivalent units (dBsfu) using the radar's calibration constant and fixed parameters (wavelength, antenna gain, etc.), which allows potential monitoring and calibration of the radar receiver in addition to  
\begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt}} \hline \hline
**Date** & **Reason for Site Visit** \\ \hline
30 October 2018 & Deployment of the radar at Sandwith \\
7 November 2018 to 8 November 2018 & Partner site induction and general check \\
13 December 2018 & Site inductions and replacement of satellite dish cable \\
14 February 2019 & Routine site inspection \\
15 April 2019 to 17 April 2019 & Routine site inspection \\
30 April 2019 & Digital receiver fault, removed and sent for repair \\
4 July 2019 & Radar returned to operational mode with new receiver \\
25 September 2019 & Routine site inspection \\
28 October 2019 to 30 October 2019 & Receiver fault investigation and corrosion check \\
05 November 2019 & New receiver board installed \\
25 February 2020 & Project meeting and general-interest site visit \\
14 October 2020 & Scaffold maintenance visit \\
18 December 2020 & No visit, end of campaign radar operations due to fault \\ \hline \hline \end{tabular}
\end{table}
Table 1: List of all site visits during the RAiN-E campaign during which it was possible to undertake level adjustment of the radar. The primary reason for the site visit is stated in the right column.  
providing a basic indication of the radar's pointing accuracy. We then use the pvlib Python package [23] to update the position information from these interference spikes to account for local pressure and temperature information (observed by an automatic weather station deployed with NXPol-1), adjusting the solar position to its apparent position as a result of refraction. These solar identifications (i.e., 'hits') can then be analysed using the methods described in the following sections to better characterise radar positioning offsets.