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On the relationship between continuous measures of canopy greenness derived using near-surface remote sensing and satellite-derived vegetation products

On the relationship between continuous measures of canopy greenness derived using near-surface remote sensing and satellite-derived vegetation products
On the relationship between continuous measures of canopy greenness derived using near-surface remote sensing and satellite-derived vegetation products
Over the last two decades, satellite-derived estimates of biophysical variables have been increasingly used in operational services, requiring quantification of their accuracy and uncertainty. Evaluating satellite-derived vegetation products is challenging due to their moderate spatial resolution, the heterogeneity of the terrestrial landscape, and difficulties in adequately characterising spatial and temporal vegetation dynamics. In recent years, near-surface remote sensing has emerged as a potential source of data against which satellite-derived vegetation products can be evaluated. Several studies have focussed on the evaluation of satellite-derived phenological transition dates, however in most cases the shape and magnitude of the underlying time-series are neglected. In this paper, we investigated the relationship between the green chromatic coordinate (GCC) derived using near-surface remote sensing and a range of vegetation products derived from the Medium Resolution Imaging Spectrometer (MERIS) throughout the growing season. Moderate to strong relationships between the GCC and vegetation products derived from MERIS were observed at deciduous forest sites. Weak relationships were observed over evergreen forest sites as a result of their subtle seasonality, which is likely masked by atmospheric, bidirectional reflectance distribution function (BRDF), and shadowing effects. Temporal inconsistencies were attributed to the oblique viewing geometry of the digital cameras and differences in the incorporated spectral bands. In addition, the commonly observed summer decline in GCC values was found to be primarily associated with seasonal variations in brown pigment concentration, and to a lesser extent illumination geometry. At deciduous sites, increased sensitivity to initial increases in canopy greenness was demonstrated by the GCC, making it particularly well-suited to identifying the start of season when compared to satellite-derived vegetation products. Nevertheless, in some cases, the relationship between the GCC and vegetation products derived from MERIS was found to saturate asymptotically. This limits the potential of the approach for evaluation of the vegetation products that underlie satellite-derived phenological transition dates, and for the continuous monitoring of vegetation during the growing season, particularly at medium to high biomass study sites.
0168-1923
280-292
Brown, Luke A.
6a693f08-df9e-4494-bb89-8d2897470d4a
Dash, Jadunandan
51468afb-3d56-4d3a-aace-736b63e9fac8
Ogutu, Booker O.
4e36f1d2-f417-4274-8f9c-4470d4808746
Richardson, Andrew D.
adc8a0c3-2169-4342-9fa0-3f9182901c35
Brown, Luke A.
6a693f08-df9e-4494-bb89-8d2897470d4a
Dash, Jadunandan
51468afb-3d56-4d3a-aace-736b63e9fac8
Ogutu, Booker O.
4e36f1d2-f417-4274-8f9c-4470d4808746
Richardson, Andrew D.
adc8a0c3-2169-4342-9fa0-3f9182901c35

Brown, Luke A., Dash, Jadunandan, Ogutu, Booker O. and Richardson, Andrew D. (2017) On the relationship between continuous measures of canopy greenness derived using near-surface remote sensing and satellite-derived vegetation products. Agricultural and Forest Meteorology, 247, 280-292. (doi:10.1016/j.agrformet.2017.08.012).

Record type: Article

Abstract

Over the last two decades, satellite-derived estimates of biophysical variables have been increasingly used in operational services, requiring quantification of their accuracy and uncertainty. Evaluating satellite-derived vegetation products is challenging due to their moderate spatial resolution, the heterogeneity of the terrestrial landscape, and difficulties in adequately characterising spatial and temporal vegetation dynamics. In recent years, near-surface remote sensing has emerged as a potential source of data against which satellite-derived vegetation products can be evaluated. Several studies have focussed on the evaluation of satellite-derived phenological transition dates, however in most cases the shape and magnitude of the underlying time-series are neglected. In this paper, we investigated the relationship between the green chromatic coordinate (GCC) derived using near-surface remote sensing and a range of vegetation products derived from the Medium Resolution Imaging Spectrometer (MERIS) throughout the growing season. Moderate to strong relationships between the GCC and vegetation products derived from MERIS were observed at deciduous forest sites. Weak relationships were observed over evergreen forest sites as a result of their subtle seasonality, which is likely masked by atmospheric, bidirectional reflectance distribution function (BRDF), and shadowing effects. Temporal inconsistencies were attributed to the oblique viewing geometry of the digital cameras and differences in the incorporated spectral bands. In addition, the commonly observed summer decline in GCC values was found to be primarily associated with seasonal variations in brown pigment concentration, and to a lesser extent illumination geometry. At deciduous sites, increased sensitivity to initial increases in canopy greenness was demonstrated by the GCC, making it particularly well-suited to identifying the start of season when compared to satellite-derived vegetation products. Nevertheless, in some cases, the relationship between the GCC and vegetation products derived from MERIS was found to saturate asymptotically. This limits the potential of the approach for evaluation of the vegetation products that underlie satellite-derived phenological transition dates, and for the continuous monitoring of vegetation during the growing season, particularly at medium to high biomass study sites.

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AGRFORMET_Accepted_Manuscript - Accepted Manuscript
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Accepted/In Press date: 10 August 2017
e-pub ahead of print date: 23 August 2017
Published date: 15 December 2017

Identifiers

Local EPrints ID: 413375
URI: https://eprints.soton.ac.uk/id/eprint/413375
ISSN: 0168-1923
PURE UUID: 5834bcd8-3271-4c7e-920e-b445305169f8
ORCID for Luke A. Brown: ORCID iD orcid.org/0000-0003-4807-9056
ORCID for Jadunandan Dash: ORCID iD orcid.org/0000-0002-5444-2109
ORCID for Booker O. Ogutu: ORCID iD orcid.org/0000-0002-1804-6205

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Date deposited: 23 Aug 2017 16:31
Last modified: 15 Aug 2019 04:41

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