Paper Info
Title
Off-Nadir Hyperspectral Sensing for Estimation of Vertical Profile of Leaf Chlorophyll Content within Wheat Canopies.
Abstract
Monitoring the vertical profile of leaf chlorophyll (Chl) content within winter wheat canopies is of significant importance for revealing the real nutritional status of the crop. Information on the vertical profile of Chl content is not accessible to nadir-viewing remote or proximal sensing. Off-nadir or multi-angle sensing would provide effective means to detect leaf Chl content in different vertical layers. However, adequate information on the selection of sensitive spectral bands and spectral index formulas for vertical leaf Chl content estimation is not yet available. In this study, all possible two-band and three-band combinations over spectral bands in normalized difference vegetation index (NDVI)-, simple ratio (SR)- and chlorophyll index (CI)-like types of indices at different viewing angles were calculated and assessed for their capability of estimating leaf Chl for three vertical layers of wheat canopies. The vertical profiles of Chl showed top-down declining trends and the patterns of band combinations sensitive to leaf Chl content varied among different vertical layers. Results indicated that the combinations of green band (520 nm) with NIR bands were efficient in estimating upper leaf Chl content, whereas the red edge (695 nm) paired with NIR bands were dominant in quantifying leaf Chl in the lower layers. Correlations between published spectral indices and all NDVI-, SR- and CI-like types of indices and vertical distribution of Chl content showed that reflectance measured from 50 degrees, 30 degrees and 20 degrees backscattering viewing angles were the most promising to obtain information on leaf Chl in the upper-, middle-, and bottom-layer, respectively. Three types of optimized spectral indices improved the accuracy for vertical leaf Chl content estimation. The optimized three-band CI-like index performed the best in the estimation of vertical distribution of leaf Chl content, with R-2 of 0.84-0.69, and RMSE of 5.37-5.56 mu g/cm(2) from the top to the bottom layers, while the optimized SR-like index was recommended for the bottom Chl estimation due to its simple and universal form. We suggest that it is necessary to take into account the penetration characteristic of the light inside the canopy for different Chl absorption regions of the spectrum and the formula used to derive spectral index when estimating the vertical profile of leaf Chl content using off-nadir hyperspectral data.
Year
DOI
Venue
2017
10.3390/s17122711
SENSORS
Keywords
Field
DocType
off-nadir spectral reflectance,vertical profile,leaf chlorophyll content,optimized spectral indices,winter wheat
Nadir,Spectral index,Remote sensing,Hyperspectral imaging,Normalized Difference Vegetation Index,Engineering,Spectral bands,Chlorophyll,Red edge,Canopy
Journal
Volume
Issue
ISSN
17
12
1424-8220
Citations 
PageRank 
References 
1
0.35
2
Authors
6
Name
Order
Citations
PageRank
Weiping Kong122.14
Wenjiang Huang217951.84
Raffaele Casa36511.75
Xian-Feng Zhou4549.35
Huichun Ye5139.18
Yingying Dong61811.41