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Article

Compensation of Oxygen Transmittance Effects for Proximal Sensing Retrieval of Canopy–Leaving Sun–Induced Chlorophyll Fluorescence

1
Image Processing Laboratory (IPL), Parc Científic, Universitat de València, 46980 Paterna, València, Spain
2
NASA, Goddard Space Flight Centre (GSFC), Greenbelt, MD 20771, USA
3
Optics of Photosynthesis Laboratory, Institute for Atmospheric and Earth System Research (INAR/Forest Sciences), Department of Forest Sciences, University of Helsinki, P.O. Box 27, 00014 Helsinki, Finland
*
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(10), 1551; https://doi.org/10.3390/rs10101551
Received: 15 August 2018 / Revised: 20 September 2018 / Accepted: 25 September 2018 / Published: 26 September 2018
Estimates of Sun–Induced vegetation chlorophyll Fluorescence (SIF) using remote sensing techniques are commonly determined by exploiting solar and/or telluric absorption features. When SIF is retrieved in the strong oxygen (O 2 ) absorption features, atmospheric effects must always be compensated. Whereas correction of atmospheric effects is a standard airborne or satellite data processing step, there is no consensus regarding whether it is required for SIF proximal–sensing measurements nor what is the best strategy to be followed. Thus, by using simulated data, this work provides a comprehensive analysis about how atmospheric effects impact SIF estimations on proximal sensing, regarding: (1) the sensor height above the vegetated canopy; (2) the SIF retrieval technique used, e.g., Fraunhofer Line Discriminator (FLD) family or Spectral Fitting Methods (SFM); and (3) the instrument’s spectral resolution. We demonstrate that for proximal–sensing scenarios compensating for atmospheric effects by simply introducing the O 2 transmittance function into the FLD or SFM formulations improves SIF estimations. However, these simplistic corrections still lead to inaccurate SIF estimations due to the multiplication of spectrally convolved atmospheric transfer functions with absorption features. Consequently, a more rigorous oxygen compensation strategy is proposed and assessed by following a classic airborne atmospheric correction scheme adapted to proximal sensing. This approach allows compensating for the O 2 absorption effects and, at the same time, convolving the high spectral resolution data according to the corresponding Instrumental Spectral Response Function (ISRF) through the use of an atmospheric radiative transfer model. Finally, due to the key role of O 2 absorption on the evaluated proximal–sensing SIF retrieval strategies, its dependency on surface pressure (p) and air temperature (T) was also assessed. As an example, we combined simulated spectral data with p and T measurements obtained for a one–year period in the Hyytiälä Forestry Field Station in Finland. Of importance hereby is that seasonal dynamics in terms of T and p, if not appropriately considered as part of the retrieval strategy, can result in erroneous SIF seasonal trends that mimic those of known dynamics for temperature–dependent physiological responses of vegetation. View Full-Text
Keywords: sun–induced chlorophyll fluorescence (SIF); proximal sensing; O2 transmittance; fraunhofer line discriminator (FLD); spectral fitting method (SFM); air temperature; atmospheric pressure sun–induced chlorophyll fluorescence (SIF); proximal sensing; O2 transmittance; fraunhofer line discriminator (FLD); spectral fitting method (SFM); air temperature; atmospheric pressure
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MDPI and ACS Style

Sabater, N.; Vicent, J.; Alonso, L.; Verrelst, J.; Middleton, E.M.; Porcar-Castell, A.; Moreno, J. Compensation of Oxygen Transmittance Effects for Proximal Sensing Retrieval of Canopy–Leaving Sun–Induced Chlorophyll Fluorescence. Remote Sens. 2018, 10, 1551. https://doi.org/10.3390/rs10101551

AMA Style

Sabater N, Vicent J, Alonso L, Verrelst J, Middleton EM, Porcar-Castell A, Moreno J. Compensation of Oxygen Transmittance Effects for Proximal Sensing Retrieval of Canopy–Leaving Sun–Induced Chlorophyll Fluorescence. Remote Sensing. 2018; 10(10):1551. https://doi.org/10.3390/rs10101551

Chicago/Turabian Style

Sabater, Neus, Jorge Vicent, Luis Alonso, Jochem Verrelst, Elizabeth M. Middleton, Albert Porcar-Castell, and José Moreno. 2018. "Compensation of Oxygen Transmittance Effects for Proximal Sensing Retrieval of Canopy–Leaving Sun–Induced Chlorophyll Fluorescence" Remote Sensing 10, no. 10: 1551. https://doi.org/10.3390/rs10101551

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