# Correcting for Mobile X-Band Weather Radar Tilt Using Solar Interference
## 2 Weather Radar Deployment and Data  
NXPol-1 is a dual-polarisation mobile X-band research radar that undertakes short (one month) to medium (two year) duration deployments [17]. NXPol-1 is a single-axle trailer-mounted system built by Leonardo Germany GmbH and is capable of operating independently using only the trailer. NXPol-1 is, however, typically deployed on top of two 20-foot (6.06 m) shipping containers, which house radar control computers and additional field campaign supplies while elevating the radar above the surrounding environment (Figure 1). The radar is manually levelled on top of the platform using the trailer's three adjustable legs: two at the rear and one centred at the front. A dual-axis bubble level provides 0.05\({}^{\circ}\) precision per graduation for this process and is mounted on the radar trailer. The focus of this paper is NXPol-1's deployment for the Radar Applications in Northern England (RAiN-E) campaign [18]. The radar was deployed from October 2018 to December 2020 at the United Utilities reservoir near Sandwith in Cumbria (54.517\({}^{\circ}\)N, 3.615\({}^{\circ}\)W). Given the radar's location, site visits were limited by travel time and typically occurred bi-monthly during the first year of the project. However, following the onset of the COVID-19 pandemic, visits were restricted to emergency situations only for the majority of 2020 (all visits are shown in Table 1). These site visits were primarily to check on site safety or to address minor non-radar issues. During this deployment, the two shipping containers were placed on a scaffold subframe supported on multiple legs with wooden bases constructed over a grassed (soft surface) area (Figure 1). As a result, the radar was routinely re-levelled on its container platform to account for potential settling of the scaffold frame on site. During the entire deployment, NXPol-1 scanned a volume coverage pattern of 10 elevations from 0.5\({}^{\circ}\) to 20\({}^{\circ}\) (at 0.5, 1, 1.5, 2, 3, 4.5, 6, 7.5, 10 and 20 degrees) followed by a 90\({}^{\circ}\) elevation rotation and a semi-hemispheric (180\({}^{\circ}\)) range-height indicator (RHI) scan along a fixed azimuth (90\({}^{\circ}\) to 270\({}^{\circ}\)), with the whole sequence repeating roughly every 6 min. The radar collected dual-polarimetric moments including reflectivity in both horizontal and vertical channels, differential reflectivity, cross-polar correlation coefficient and differential phase shift, along with the signal-to-noise ratios in both channels. A complete set of the radar moments stored can be found in the open-access radar data archive [18]. While NXPol-1's control software (RAVIS\({}^{\circledR}\), Leonardo Germany GmbH, Neuss, Germany) allows offline solar raster scans, they cannot be scheduled to occur at regular intervals; instead, they require manual intervention. These were, therefore, only used during the radar's initial deployment (to align the azimuth angles to north and check the elevation) and following intervention with the radar system. For a period of four days in September 2020, multiple raster scans were undertaken to provide an additional assessment of the preliminary results that led to this study. The results from these scans cannot be automatically saved for further analysis. In this case, the elevation, azimuth and receiver  
Figure 1: NXPol-1 deployed in Sandwith, Cumbria for the RAiN-E project. The two shipping containers are installed on a scaffolding frame over an uneven grassed surface. The scaffolding extends to form an access staircase and safety railings for working on NXPol-1 during the deployment. (Rx) offsets were manually recorded along with the time of the scan. These results can be found in Table 1 in Appendix A. To further support the analysis presented here, observations made by NXPol-1 at the Chilbolton Observatory (51.145\({}^{\circ}\)N, 1.439\({}^{\circ}\)W) have also been utilised [19].