## 4 Conclusions and Future Work  
The results of this research show that the inexpensive automotive FMCW RADAR (AWR1843-BOOST) is a cost-effective alternative for GPR to assess near-surface water content in the soil (under certain constraints). Such results show that the tested sensor (and its cost-effective working principle) are able to determine soil water content (within certain limitations) in a non-intrusive, proximal sensing manner. \"Direct\" readings are usable for Soil Moisture below 15%. This limitation is severe, but nonetheless, the sensor is very useful for agricultural purposes, for instance to control precision irrigation schedules, leading to cost-efficient management of scarce water resources. Once perfected, this on-the-go sensor will be highly suitable for mapping crop water management in line with precision agriculture. As with many other sensors, it must be recognized that specific readings are likely to be dependent on the soil properties, but simple calibration procedures will avoid that shortcoming.  
Figure 8: RADAR’s readings representation on PondView with nine layers.  
These results were obtained without the real-time data capture adapter DCA1000 EVM of the AWR1843-BOOST. The use of this adapter is likely to improve results (at the cost of slightly more expensive hardware), and this can be done in the future, when the device become available. In addition, additional experiments are needed to ascertain the real precision of the measurements with different soils at higher depths and over increasing depths.  
Non-intrusive SWC assessment is especially interesting in applications such as SWC mapping (where the sensor is transported by any kind of mobile device) or in situations where implementing intrusive sensors is not possible, such as rocky soil or vertical surfaces. The use of non-intrusive sensors in mobile machines or robots is likely to enable the acquisition of ground observations to investigate soil moisture-climate interactions.  
Conceptualization, R.M.C., A.S. and F.S.; Data curation, M.C.; Formal analysis, R.M.C. and M.C.; Funding acquisition, A.S. and F.S.; Investigation, R.M.C.; Methodology, R.M.C. and M.C.; Project administration, A.S., F.S. and M.C.; Software, R.M.C.; Supervision, A.S., F.S. and M.C.; Validation, A.S., F.S. and M.C.; Writing--original draft, R.M.C. and A.S.; Writing--review & editing, R.M.C., A.S., F.S. and M.C. All authors have read and agreed to the published version of the manuscript.  
This work is financed by the ERDF--European Regional Development Fund, through the Operational Programme for Competitiveness and Internationalisation--COMPETE 2020 Programme under the Portugal 2020 Partnership Agreement within project Replant, with reference POCI-01-0247-FEDER-046081.  
Not applicable.  
The DataSets are available publicly [[https://drive.google.com/file/d/1](https://drive.google.com/file/d/1) pEgb5 ckgJb2 jx_aGyM5D0 JYg2 Uj0 TPt/view?usp=sharing]([https://drive.google.com/file/d/1](https://drive.google.com/file/d/1) pEgb5 ckgJb2 jx_aGyM5D0 JYg2 Uj0 TPt/view?usp=sharing), accessed on 8 February 2022.  
The authors declare no conflict of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} USGS & United States Geological Survey \\ WUE & Water Use Efficiency \\ SWC & Surface Water Content \\ RADAR & Radio Detecting And Ranging \\ EME & Electromagnetic Energy \\ FMCW & Frequency Modulated Continuous Wave \\ SM & Soil Moisture \\ EM & Electromagnetic \\ EMI & Electromagnetic Induction \\ GPS-IR & Geographical Positioning System Interferometric Reflectometry \\ GNSS-IR & Global Navigation Satellite System Interferometric Reflectometry \\ RF & Radio Frequency \\ UWB & Ultra-Wideband \\ PC & Personal Computer \\ CNC & Computerized Numerical Control \\ \end{tabular}