## 5 Conclusions  
In this study, the results of an intensive characterization effort for a high performance spectrometer, FIREFLY (Fluorescence imaging of red and far-red light yield) were presented. To evaluate the instrument for its potential to retrieve solar induced fluorescence (SIF) by various methods, the quantitative characterizations included shot noise, full-width at half maximum (FWHM), response, linearity, band wavelength, stray light, and dark current. The results confirmed FIREFLY as a high-specification instrument for SIF retrieval by contemporary standards. Through forward modelling of simulated FIREFLY spectra and simulated SIF signals, it was determined that a high degree of precision and certainty in the characterizations was essential, since SIF signals are expected to comprise such a low proportion of radiance. The uncertainties remaining in the characterizations were propagated into potential SIF retrieval error, revealing several promising avenues for further study. In particular, it would be of value to have coincident ground control observations of leaf and canopy SIF for airborne data product validation purposes. FIREFLY was found to be suitable for direct SIF retrievals in terms of noise and other instrument attributes, but to further reduce SIF uncertainty would require enhanced strategies to account for the influence of irradiance, atmosphere, and target reflectivity. Other studies have suggested the efficacy of various spectral fitting methods (SFM) for this purpose, and these methods will likely be the focus of efforts to produce an operational SIF product from FIREFLY. For indirect retrievals from absorption features, including the oxygen features, it was concluded that the effects of noise would have to be mitigated, with spatial aggregation a viable option for SIF retrievals intended for comparison to coarser resolution satellite observations of SIF. Repeated observations were identified as another alternative to mitigate noise in SIF retrievals, and could be achieved by mounting FIREFLY on alternative platforms such as towers or UAVs. The interpretation of SIF observations can benefit from the contextualizing information provided by the coincident data from other instruments included in NASA Goddard's lidar, hyperspectral, and thermal (G-LiHT) instrument package. The potential of the lidar, hyperspectral, and high resolution RGB imagery should be considered in the context of designing synthesized SIF data products. Overall, the challenges of accurately retrieving SIF can only be met with a well-characterized instrument. This study represents substantial progress towards the appropriate level of characterization for FIREFLY to retrieve a competent SIF product. Several aspects of this study should be of benefit to efforts to characterize similar instruments, including the analytical tools, the forward modelling tools, and the investigative approaches employed. Code and data are available at [[https://glihtdata.gsfc.nasa.gov/files/FIREFLY/](https://glihtdata.gsfc.nasa.gov/files/FIREFLY/)]([https://glihtdata.gsfc.nasa.gov/files/FIREFLY/](https://glihtdata.gsfc.nasa.gov/files/FIREFLY/)). Conceptualization, B.C., L.C., and I.P. ; methodology, B.C., L.C., J.N., and I.P. ; software, B.C., L.C., J.N., and I.P. ; validation B.C., L.C., J.N., I.P., and J.M. ; formal analysis, B.C., L.C., J.N., and I.P. ; investigation, B.C., L.C., J.N., and I.P. ; resources, B.C., L.C., and J.M. ; data curation, B.C., L.C., and J.N. ; writing--original draft preparation, B.C., L.C., J.N., and I.P. ; writing--review and editing, B.C., L.C., J.N., J.M., and I.P. ; visualization, J.N., and I.P. ; supervision, B.C. ; project administration, B.C. ; and funding acquisition, B.C. and L.C. All authors have read and agreed to the published version of the manuscript. This research was funded by the NASA Earth Science Division (ESD) in support of the \"Fluorescence Airborne Research Experiment (FLARE)\". Headwall Photonics for instrument design and assembly. GLAMR facility staff for support with calibration activities.