FLORIS: phase A status of the fluorescence imaging spectrometer of the Earth Explorer mission candidate FLEX

Abstract

The Fluorescence Explorer (FLEX) mission is currently subject to feasibility (Phase A) study as one of the two candidates of ESA's 8th Earth Explorer opportunity mission. The FLuORescence Imaging Spectrometer (FLORIS) will be an imaging grating spectrometer onboard of a medium sized satellite flying in tandem with Sentinel-3 in a Sun synchronous orbit at a height of about 815 km. FLORIS will observe vegetation fluorescence and reflectance within a spectral range between 500 nm and 780 nm. It will thereby cover the photochemical reflection features between 500 nm and 600 nm, the Chlorophyll absorption band between 600 and 677 nm, and the red-edge in the region from 697 nm to 755 nm being located between the Oxygen A and B absorption bands.By this measurement approach, it is expected that the full spectrum and amount of the vegetation fluorescence radiance can be retrieved, and that atmospheric corrections can efficiently be applied. FLORIS will measure Earth reflected spectral radiance at a relatively high spectral resolution of ~0.3 nm around the Oxygen absorption bands. Other spectral band areas with less pronounced absorption features will be measured at medium spectral resolution between 0.5 and 2 nm. FLORIS will provide imagery at 300 m resolution on ground with a swath width of 150 km. This will allow achieving global revisit times of less than one month so as to monitor seasonal variations of the vegetation cycles. The mission life time is expected to be at least 4 years. The fluorescence retrieval will make use of information coming from OLCI and SLSTR, which are onboard of Sentinel-3, to monitor temperature, to detect thin clouds and to derive vegetation reflectance and information on the aerosol content also outside the FLORIS spectral range.In order to mitigate the technological and programmatic risk of this Explorer mission candidate, ESA has initiated two comprehensive bread-boarding activities, in which the most critical technologies and instrument performance shall be investigated and demonstrated. The breadboards will include representative optics and dispersive elements in a configuration, which is expected to be very close to the instrument flight configuration. This approach follows the guideline to reach, before it goes into the implementation phase, a technology readiness level of at least 5. It thereby requires a demonstration of predicted performance in a configuration, where the basic technological components are integrated with reasonably realistic supporting elements such that it can be tested in a simulated environment.We will report, within the limits of the competitive nature of the industrial studies, on the currently running or planned preparatory activities. We will present the mission configuration, the imposed instrument requirements and the identified instrument concepts as derived by the Phase A studies.

Combining Sun-Induced Chlorophyll Fluorescence and Photochemical Reflectance Index Improves Diurnal Modeling of Gross Primary Productivity

“…New model formulations and developments are, however, needed to fully exploit the information content inherent in the fluorescence signal (i.e., full emission shape, peak emissions at 687 nm and 740 nm). Such information will soon become frequently available from future satellite sensors (e.g., ESA's TROPOMI onboard Sentinel-5 [51], FLORIS onboard FLEX [52]). …”

Parallel Seasonal Patterns of Photosynthesis, Fluorescence, and Reflectance Indices in Boreal Trees

“…Further understanding of the mechanisms underlying reflectance indices and fluorescence in different vegetation types and natural environments is essential to the proposed FLuorescence EXplorer (FLEX) mission, which will enable both reflectance indices and SIF to assess photosynthetic phenology from satellites [35]. This mission will provide insight into ecosystem phenology and productivity beyond that of satellite missions providing reflectance (MODIS) or SIF (e.g., Orbiting Carbon Observatory-2: OCO-2) by allowing concurrent measurements of reflectance indices and SIF at finer scales.…”

Radiometric assessment method for diffraction effects in hyperspectral imagers applied to the earth explorer #8 mission candidate flex

“…Entrance pupil diameter 80 mm The basic geometrical and optical properties [6,7], which are considered for the assessment of the diffraction limitations of FLORIS, are summarized in Tab. 1.…”

“…It allows for a simplified assessment of hyperspectral imaging systems and provides an estimate of the expected radiometric accuracy limitations. By applying the model to investigate diffraction effects of FLORIS, the optical payload of the Earth Explorer #8 Mission Candidate FLEX [6,7], we show that an analysis based on the diffraction limited PSF significantly overestimates the corresponding stray light error.…”

“…Particular missions currently operating include EO-1/Hyperion, PROBA/CHRIS and HICO [1][2][3][4]. In addition, several candidates such as EnMAP, PRISMA, and FLORIS/FLEX are currently under development or in planning stage [1,[5][6][7]. The corresponding optical instruments are based on pushbroom type configuration, which enable extended acquisition of spatial as well as spectral information.…”