## 5 Discussion  
The design of the UAV calibration procedure and the field campaign were designed to be able to evaluate the estimated range limit and range resolution. The field campaign was designed to evaluate the feasibility of using the radar as a portable instrument. The UAV calibration procedure and field campaign showed that this radar design was able to retain the advantages envisioned in the original design presented by [13], but overcoming the problems found in that attempt. Now, the unambiguous range is increased to 500 m and the resolution improved to 20 m, which gives over 45 points along the profile. Although the found resolution of the radar (\(\sim\)20 m), which was estimated by the calibration procedure, is higher than the theoretically estimated resolution of 15 m, it is known that certain non-ideal factors can degrade the range resolution of FMCW radars. Non-ideal factors may include the reduced effective modulation bandwidth due to time-of-flight delays, the increased main-lobe null-to-null bandwidth when FFT windows are applied, a reduced receiver frequency resolution due to a reduction in the pulse processing time, and nonlinearity of frequency sweeps [15; 16]. This issue highlights the need of the external calibration method for range. During the day of the campaign, a large stratocumulus cloud deck covered the Chilean coast intercepting the topography as seen in the MODIS images (Data available in [[https://worldview.earthdata.nasa.gov/?v=-97.28884731789906_,-50.34962354523486_,-48.564583224612235_,-25.759096510654174&t=2019-01-20-T15%3A19%3A46Z&l=Reference_Labels](https://worldview.earthdata.nasa.gov/?v=-97.28884731789906_,-50.34962354523486_,-48.564583224612235_,-25.759096510654174&t=2019-01-20-T15%3A19%3A46Z&l=Reference_Labels)]([https://worldview.earthdata.nasa.gov/?v=-97.28884731789906_,-50.34962354523486_,-48.564583224612235_,-25.759096510654174&t=2019-01-20-T15%3A19%3A46Z&l=Reference_Labels](https://worldview.earthdata.nasa.gov/?v=-97.28884731789906_,-50.34962354523486_,-48.564583224612235_,-25.759096510654174&t=2019-01-20-T15%3A19%3A46Z&l=Reference_Labels))(hidden),Reference_Features(hidden),Coastlines, MODIS_Terra_Cloud_Top_Height_Day(palette=rainbow_2),VIIRS_NOAA20_CorrectedReflectance_TrueColor(hidden),VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor) (Figure 9). From the nearby Santo Domingo upper air sounding station (approx. 120 km south of Papudo also at the coast), at 12:00 UTC (i.e., about 2 h before the measurements presented) the cloud layer was identified from about 310 to 663 m a.m.s.l. (Data available in [[https://climatologia.meteochile.gob.cl/application/index/productos/RE5014](https://climatologia.meteochile.gob.cl/application/index/productos/RE5014)]([https://climatologia.meteochile.gob.cl/application/index/productos/RE5014](https://climatologia.meteochile.gob.cl/application/index/productos/RE5014)) by using the Santo Domingo station code of 330030 with the time of 12:00 p.m.) (see Figure 10). One could reasonably expect a relatively homogeneous cloud top height near the coast even for the relatively large extension between Santo Domingo and Papudo as seen in the MODIS cloud top temperature image (Figure 9). Cloud top temperatures are within 283 to 285 K (10 to 12 C) over a large region off the coast of Chile, including Santo Domingo and Papudo. The sounding from Santo Domingo confirms that this cloud top temperature corresponds to the temperature at the base of the temperature inversion layer that  
Figure 8: **(a)** radar reflectivity retrieval, calculated using the internal calibration and the UAV based distance calibration presented in Section 3. It also shows the time averaged reflectivity profile; (**b**) shows the Uncalibrated Doppler Velocity retrievals. Positive values indicate movement towards the radar.