## 6 Conclusions  
Substantial progress has been made in the last 10 years in the passive measurement of F data. Besides the remarkable advancements in technology, more sophisticated measurement setups and protocols have also been defined and implemented, while standardization has mainly evolved as a result of standardized systems, such as the FluoWat, FloX, and Piccolo. Future steps should aim to incorporate atmospheric correction as well as implement standardized quality checks and flags in the data by default. This also involves tracking metadata and ancillary data to improve the interpretation and further use of F data. Besides instrumental and data science, more research is also needed on the comparability and transferability of results from different experiments across spatial and temporal scales. Such research needs can be supported by combining observational results with virtual ecosystems obtained from computer models. The scenarios should include the effects of diversity in plant functional traits across vegetation types and should be able to describe heterogeneous landscapes. All of these steps are necessary to facilitate the synthesis of activities and to move beyond single sites and single campaigns. Since these topics are too complex to be addressed by individual researchers, we hope that the promising collaborations between researchers will continue and allow the community to identify and implement solutions to these challenges. The following are available online at: [[http://www.mdpi.com/2072-4292/11/8/927/s1](http://www.mdpi.com/2072-4292/11/8/927/s1)]([http://www.mdpi.com/2072-4292/11/8/927/s1](http://www.mdpi.com/2072-4292/11/8/927/s1)); Figure S1: Diurnal photosynthetic photon flux density (PPFD; red line) and relative standard deviation of fluorescence at 760 nm (F\({}_{760}\); black cycles) for a sunny day with few clouds (A) and a cloudy day with strong cloud cover (B). Measurements were taken with a QE Pro over sugar beet on 20.08.2015 (A) and 30.07.2015 (B), Merzenhausen, Germany. The spectroradiometer system has a spectral resolution of 1 nm FWHM (full-width at half maximum), a spectral sampling interval (SI) of 0.3 nm, and a signal-to-noise ratio (SNR) of 1000:1 in a spectral range from 300 to 1000 nm. Measurements were taken every 6-8 seconds; Figure S2: Diurnal photosynthetic photon flux density (PPFD; red line) and relative standard deviation of fluorescence at 760 nm (F\({}_{760}\); black cycles)for a sunny day with few clouds (A) and a cloudy day with strong cloud cover (B) after using a 1% illumination filter. Measurements were taken with a QE Pro over sugar beet on 20.08.2015 (A) and 30.07.2015 (B), Merzenhausen, Germany. The spectroradiometer system has a spectral resolution of 1 nm FWHM (full-width at half maximum), a spectral sampling interval (SI) of 0.3 nm, and a signal-to-noise ratio (SNR) of 1000:1 in a spectral range from 300 to 1000 nm. Measurements were taken every 6-8 seconds, Figure S3: Boxplot of the relative standard deviation (RSD) of fluorescence at 760 and 687 nm (7\({}_{\rm 760}\) and F\({}_{\rm 870}\)) for four different illumination quality filters. The dataset was measured over 65 days from June to August 2015 within a sugar beet field in Merzenhausen, Germany. The quality filter labeled \"none\" does not consider illumination changes between two measurement cycles (6-8 s), the quality filters 10%, 1%, and 0.1% discard samples that show an illumination change of 10, 1, 0.1% between two measurement cycles, respectively. The green bar in the Boxplot shows the median value, the whiskers show the minimum and maximum RSD, the lower box border shows the first quartile, and the upper box border the third quartile, Table S1: Proposed metadata attributes for spectroradiometric data for F retrieval grouped by metadata categories, with core attributes shaded in gray and justification for their inclusion in the F metadata set.