## 5 Conclusions and Further Work  
This study demonstrated that the methods used by laboratory-scale active thermography can be evaluated on solar loading thermograms. Depending on location conditions, such as weather and cloud coverage, both strong and weak resemblances to different testing methodologies, such as lock-in or step-heating thermography, can be observed. In general, signal-to-noise ratio is satisfactory in a solar loaded context, but the erratic excitation conditions, such as fluctuating irradiation and changing wind speeds, hamper the accuracy of the previously established assumptions made by the evaluation algorithms. It was found that ideally, the experimental setup should record the region of interest perpendicularly in the first place. As this is not feasible in every experiment, separating ROIs from the whole image and correcting the perspective error can improve the apparent contrast and enhance visual clarity on the images. Further work should evaluate how to take into account the given environmental conditions to better fit a specific test cast. For example, manual shading of a particular ROI may generate a step-heating scenario in strong sunlit conditions without the need for specific cloud coverage. Wind speed and ambient temperature could also be measured and evaluated to calculate the heat flow of the specific structures at all points in the experiment. However, specific algorithms and methods must be devised to correct the influences of these unpredictable factors. Conceptualization, S.K. and H.-G.H. ; methodology, S.K. ; software, S.K. and T.H. ; validation, S.K. and H.-G.H. ; writing--original draft preparation, S.K. ; writing--review and editing, S.K., T.H. and H.-G.H. ; visualization, S.K. ; supervision, H.-G.H. ; project administration, H.-G.H. ; funding acquisition, H.-G.H. All authors have read and agreed to the published version of the manuscript. Figure 12: Perspective- and albedo-corrected surface heat capacity images. Funding: The European Regional Development Fund (ERDF), especially grant number 14.2.1.4-2016-1, funded this research. Furthermore, we acknowledge support of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) and Saarland University within the funding program Open Access Publishing. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Acknowledgments: Gratitude goes to [PERSON] and [PERSON] for excellent practice in scientific exchange. Furthermore, the authors thank [PERSON] for her help with experimental setup and conduction. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results. References  
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