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An assessment of photosynthetic light use efficiency from space: modeling the atmospheric and directional impacts on PRI reflectance

An assessment of photosynthetic light use efficiency from space: modeling the atmospheric and directional impacts on PRI reflectance
An assessment of photosynthetic light use efficiency from space: modeling the atmospheric and directional impacts on PRI reflectance
Estimation of photosynthetic light use efficiency (?) from satellite observations is an important component of climate change research. The photochemical reflectance index, a narrow waveband index based on the reflectance at 531 and 570 nm, allows sampling of the photosynthetic activity of leaves; upscaling of these measurements to landscape and global scales, however, remains challenging. Only a few studies have used spaceborne observations of PRI so far, and research has largely focused on the MODIS sensor. Its daily global coverage and the capacity to detect a narrow reflectance band at 531 nm make it the best available choice for sensing ? from space. Previous results however, have identified a number of key issues with MODIS-based observations of PRI. First, the differences between the footprint of eddy covariance (EC) measurements and the MODIS footprint, which is determined by the sensor's observation geometry make a direct comparison between both data sources challenging and second, the PRI reflectance bands are affected by atmospheric scattering effects confounding the existing physiological signal. In this study we introduce a new approach for upscaling EC based ? measurements to MODIS. First, EC-measured ? values were “translated” into a tower-level optical PRI signal using AMSPEC, an automated multi-angular, tower-based spectroradiometer instrument. AMSPEC enabled us to adjust tower-measured PRI values to the individual viewing geometry of each MODIS overpass. Second, MODIS data were atmospherically corrected using a Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm, which uses a time series approach and an image-based rather than pixel-based processing for simultaneous retrievals of atmospheric aerosol and surface bidirectional reflectance (BRDF). Using this approach, we found a strong relationship between tower-based and spaceborne reflectance measurements (r2 = 0.74, p < 0.01) throughout the vegetation period of 2006. Swath (non-gridded) observations yielded stronger correlations than gridded data (r2 = 0.58, p < 0.01) both of which included forward and backscatter observations. Spaceborne PRI values were strongly related to canopy shadow fractions and varied with different levels of ?. We conclude that MAIAC-corrected MODIS observations were able to track the site-level physiological changes from space throughout the observation period.
photosynthesis, carbon cycling, pri, remote sensing, maiac, 6s, atmospheric correction, multi-angular, brdf, eddy covariance, modis, upscaling, photochemical reflectance index, amspec, lidar, hyperspectral, spectroradiometer, flux tower, global carbon cycle, douglas fir
0034-4257
2463-2475
Hilker, Thomas
c7fb75b8-320d-49df-84ba-96c9ee523d40
Lyapustin, Alexei
49921e95-158c-446e-bddc-e49a17320c27
Hall, Forrest G.
19da6ee8-b54b-4eee-b5b6-e8e3a92f6bcf
Wang, Yujie
6915380d-4c23-4fef-a172-6880ddeff699
Coops, Nicholas C.
5511e778-fec2-4f54-8708-de65ba5a0992
Drolet, Guillaume
8f2be437-10e0-4a38-aef0-b3cc5f26c5d4
Black, T. Andrew
f6187e30-d043-4094-b5ef-372c60de403b
Hilker, Thomas
c7fb75b8-320d-49df-84ba-96c9ee523d40
Lyapustin, Alexei
49921e95-158c-446e-bddc-e49a17320c27
Hall, Forrest G.
19da6ee8-b54b-4eee-b5b6-e8e3a92f6bcf
Wang, Yujie
6915380d-4c23-4fef-a172-6880ddeff699
Coops, Nicholas C.
5511e778-fec2-4f54-8708-de65ba5a0992
Drolet, Guillaume
8f2be437-10e0-4a38-aef0-b3cc5f26c5d4
Black, T. Andrew
f6187e30-d043-4094-b5ef-372c60de403b

Hilker, Thomas, Lyapustin, Alexei, Hall, Forrest G., Wang, Yujie, Coops, Nicholas C., Drolet, Guillaume and Black, T. Andrew (2009) An assessment of photosynthetic light use efficiency from space: modeling the atmospheric and directional impacts on PRI reflectance. Remote Sensing of Environment, 113 (11), 2463-2475. (doi:10.1016/j.rse.2009.07.012).

Record type: Article

Abstract

Estimation of photosynthetic light use efficiency (?) from satellite observations is an important component of climate change research. The photochemical reflectance index, a narrow waveband index based on the reflectance at 531 and 570 nm, allows sampling of the photosynthetic activity of leaves; upscaling of these measurements to landscape and global scales, however, remains challenging. Only a few studies have used spaceborne observations of PRI so far, and research has largely focused on the MODIS sensor. Its daily global coverage and the capacity to detect a narrow reflectance band at 531 nm make it the best available choice for sensing ? from space. Previous results however, have identified a number of key issues with MODIS-based observations of PRI. First, the differences between the footprint of eddy covariance (EC) measurements and the MODIS footprint, which is determined by the sensor's observation geometry make a direct comparison between both data sources challenging and second, the PRI reflectance bands are affected by atmospheric scattering effects confounding the existing physiological signal. In this study we introduce a new approach for upscaling EC based ? measurements to MODIS. First, EC-measured ? values were “translated” into a tower-level optical PRI signal using AMSPEC, an automated multi-angular, tower-based spectroradiometer instrument. AMSPEC enabled us to adjust tower-measured PRI values to the individual viewing geometry of each MODIS overpass. Second, MODIS data were atmospherically corrected using a Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm, which uses a time series approach and an image-based rather than pixel-based processing for simultaneous retrievals of atmospheric aerosol and surface bidirectional reflectance (BRDF). Using this approach, we found a strong relationship between tower-based and spaceborne reflectance measurements (r2 = 0.74, p < 0.01) throughout the vegetation period of 2006. Swath (non-gridded) observations yielded stronger correlations than gridded data (r2 = 0.58, p < 0.01) both of which included forward and backscatter observations. Spaceborne PRI values were strongly related to canopy shadow fractions and varied with different levels of ?. We conclude that MAIAC-corrected MODIS observations were able to track the site-level physiological changes from space throughout the observation period.

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More information

Accepted/In Press date: 18 July 2009
e-pub ahead of print date: 14 August 2009
Published date: 16 November 2009
Keywords: photosynthesis, carbon cycling, pri, remote sensing, maiac, 6s, atmospheric correction, multi-angular, brdf, eddy covariance, modis, upscaling, photochemical reflectance index, amspec, lidar, hyperspectral, spectroradiometer, flux tower, global carbon cycle, douglas fir
Organisations: Global Env Change & Earth Observation

Identifiers

Local EPrints ID: 384690
URI: http://eprints.soton.ac.uk/id/eprint/384690
ISSN: 0034-4257
PURE UUID: 44ce2d51-d833-4feb-910f-1d36b886fe06

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Date deposited: 27 Jan 2016 12:43
Last modified: 14 Mar 2024 22:03

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Contributors

Author: Thomas Hilker
Author: Alexei Lyapustin
Author: Forrest G. Hall
Author: Yujie Wang
Author: Nicholas C. Coops
Author: Guillaume Drolet
Author: T. Andrew Black

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