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| Home > Publications database > Towards consistent assessments of in situ radiometric measurements for the validation of fluorescence satellite missions |
| Journal Article | FZJ-2022-01805 |
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2022
Elsevier Science
Amsterdam [u.a.]
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Please use a persistent id in citations: http://hdl.handle.net/2128/31001 doi:10.1016/j.rse.2022.112984
Abstract: The upcoming Fluorescence Explorer (FLEX) satellite mission aims to provide high quality radiometric measurementsfor subsequent retrieval of sun-induced chlorophyll fluorescence (SIF). The combination of SIF withother observations stemming from the FLEX/Sentinel-3 tandem mission holds the potential to assess complexecosystem processes. The calibration and validation (cal/val) of these radiometric measurements and derivedproducts are central but challenging components of the mission. This contribution outlines strategies for theassessment of in situ radiometric measurements and retrieved SIF. We demonstrate how in situ spectrometermeasurements can be analysed in terms of radiometric, spectral and spatial uncertainties. The analysis of morethan 200 k spectra yields an average bias between two radiometric measurements by two individual spectrometersof 8%, with a larger variability in measurements of downwelling radiance (25%) compared to upwellingradiance (6%). Spectral shifts in the spectrometer relevant for SIF retrievals are consistently below 1spectral pixel (up to 0.75). Found spectral shifts appear to be mostly dependent on temperature (as measured bya temperature probe in the instrument). Retrieved SIF shows a low variability of 1.8% compared with a noisereduced SIF estimate based on APAR. A combination of airborne imaging and in situ non-imaging fluorescencespectroscopy highlights the importance of a homogenous sampling surface and holds the potential to furtheruncover SIF retrieval issues as here shown for early evening acquisitions. Our experiments clearly indicate theneed for careful site selection, measurement protocols, as well as the need for harmonized processing. This workthus contributes to guiding cal/val activities for the upcoming FLEX mission.
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