Abstract
Solar induced fluorescence (SIF) is an ecological variable of interest to remote sensing retrievals, as it is directly related to vegetation composition and condition. FIREFLY (fluorescence imaging of red and far-red light yield) is a high performance spectrometer for estimating SIF. FIREFLY was flown in conjunction with NASA Goddard’s lidar, hyperspectral, and thermal (G-LiHT) instrument package in 2017, as a technology demonstration for airborne retrievals of SIF. Attributes of FIREFLY relevant to SIF retrieval, including detector response and linearity; full-width at half maximum (FWHM); stray light; dark current; and shot noise were characterized with a combination of observations from Goddard’s laser for absolute measurement of radiance calibration facility; an integrating sphere; controlled acquisitions of known targets; in-flight acquisitions; and forward modelling. FWHM, stray light, and dark current were found to be of acceptable magnitude, and characterized to within acceptable limits for SIF retrieval. FIREFLY observations were found to represent oxygen absorption features, along with a large number of solar absorption features. Shot noise was acceptable for direct SIF retrievals at native resolution, but indirect SIF retrievals from absorption features would require spatial aggregation, or repeated observations of targets.
Highlights
The FIREFLY instrument is a high performance spectrometer for estimating solar induced fluorescence (SIF)
SIF is related to photosynthesis, and gross primary productivity (GPP), mediated by the light use efficiency of the plant [3,4]
According to the observations made with Goddard’s laser for absolute measurement of radiance (GLAMR), the full-width at half maximum (FWHM) of FIREFLY spectral channels varied between ~0.12 nm to ~0.2 nm, and a negative relationship was observed between FWHM and wavelength (Figure 4)
Summary
The FIREFLY (fluorescence imaging of red and far-red light yield) instrument is a high performance spectrometer for estimating solar induced fluorescence (SIF). SIF is the re-emittance, at longer wavelengths, of solar energy absorbed by plants. SIF occurs, alongside the production of heat, when absorption of light exceeds the utilization of light by photosynthesis [2]. SIF is related to photosynthesis, and gross primary productivity (GPP), mediated by the light use efficiency of the plant [3,4]. Measuring SIF can provide quantitative insight into GPP [2,5], species composition [3], phenology [6], and the physiological status of plants, including stress [3,6,7], as well as being useful for crop monitoring [8]. The history, theory, methodologies, applications, and current challenges facing the retrieval of SIF via remote sensing were the subject of a recent comprehensive review [9]
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