## 3 Currently Operational UAS Systems for SIF Retrieval
### \"Piccolo-Doppio\"--A Dual-Field of View (FOV) Dual Spectrometer System
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Platform** & **Spectoraliometer** & & **Additional Components** & **Unmanned Aerial System (UAS)** & **Highlights** \\ \hline  & Dimensions & \(182\times 110\times 47\) mm & Radio control for data & & & Can be used with two \\  & Dimensions & \(182\times 110\times 47\) mm & transferring & Custom & Tarot T910 frame KDE 4213 & Spectroradometers \\ \cline{2-6}  & Spectral range (nm) & 650-800 & Battery Lithium Polymer & hexacopter & motors pikhank autopilot & Two independent channels \\ \cline{2-6}  & Approximate & & Originally arasberry F & T-motor U8 100 kr motors & & Dual FOV for NIR reflectance \\  & spectral interval (nm) & 0.15 & Model A. Currently & Quadcopter & Based on a crypphon & and SIF \\  & (mm) & & updated to P3 & dynamics frame & (D\({}_{2}\)-A/O\({}_{2}\)-B) \\ \cline{2-6}  & QEPro (Ocan & & & & \\ Optics, Inc., USA) & & & & & \\  & FWHM (nm) & 0.31 5 \% optical & & & \\  & FWHM (nm) & & & & \\  & & optical slit) & & & \\ \cline{2-6}  & Digital range & & & & \\  & (analogogue to digital & 18 & & & \\  & converter; bit) & & & & \\ \cline{2-6}  & SNR & 1000:1 & 600 A3 Pro & & & \\ \cline{2-6}  & Dynamic range & \(8.5\times 10^{4}\):1 & & & \\ \cline{2-6}  & Integration time & up to 60 min & & & \\ \cline{2-6}  & Hiss been & & NRQoSAT, QEPro, Flame, HR4000 & & & \\  & tested with: & & & & \\ \hline  & & & & & \\ \cline{2-6}  & Dimensions & \(182\times 110\times 47\) mm & Dual GNSS antenna & Dimensions: \(1.67\times 1.52\) 0.75 & & \\ \cline{2-6}  & & Spectral range (nm) & & & & \\ \cline{2-6}  & QEPro (Ocan & & & & \\ Optics, Inc., USA) & & & & & \\  & spectral interval (nm) & 0.37 & Grasshopper 3 machine & 600 & & \\  & (mm) & & & & \\ \cline{2-6}  & FWHM (nm) & 0.80 & RTK correction & & & \\ \cline{2-6}  & Digital range (bit) & 18 & & & \\ \cline{2-6}  & SNR & 1000:1 & & & \\ \cline{2-6}  & Dynamic range & \(8.5\times 10^{4}\):1 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the main characteristics of the spectroradiometer and UAS utilized for each project. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Platform** & **Spectroadiometer** & **Additional Components** & **Unmanned Aerial System (UAS)** & **Highlights** \\ \hline \multirow{6}{*}{**AirHeAV** **FionPlane**} & Dimensions & \(182\times 110\times 47\) mm & Data acquisition module & Wingpoura 4.40 m & \\ \cline{2-5}  & Spectral range (nm) & 650-800 & & Length 3.32 m & \\ \cline{2-5}  & Approximate & & Independent battery & take-off weight 24 kg & The GPrpo is integrated with a large but light UAS capable to elevate several kilometers with one spectrometer coupled \\ \cline{2-5}  & QPerro (Ocean) & interval (mm) & & FloxPlane & take-off weight 24 kg & the GPrpo is integrated with a large but light UAS capable to elevate several kilometers with one spectrometer coupled \\ \  
Figure 1 summarizes the main steps to process Piccolo-Doppio data, from the extraction of JavaScript Object Notation (JSON) files into MATLAB(r) (Mathworks, Field Spectroscopy Facility Post Processing Toolbox) [43] to the multiplication of the radiance (or irradiance) by the non-linearity corrected, the normalized, and the dark current corrected values per pixel for each spectroradiometer and optical direction. Currently, the data processing workflow and codes are updated to Python3. Alongside the software solutions, the authors worked on hardware developments, e.g., the design of the fore optic and fiber optic assembly in order to maximize the light transmission, thus achieving integration times of 50-75 ms at VNIR, and 500-1500 ms at SIF wavelengths under clear-sky conditions in northern Europe (when the spectroradiometer's maximum dynamic range is utilized). Nonetheless, the QEPro is prone to the etaloning effect caused by the interference of the light reflected in the boundaries of its thinned back-illuminated charge coupled device [42] detector, consequently producing wavy-aspect outputs.