Effects of crop leaf angle on LAI-sensitive narrow-band vegetation indices derived from imaging spectroscopy

Xiaochen Zou, Iina Haikarainen, Iikka P. Haikarainen, Pirjo Mäkelä, Matti Mõttus, Petri Pellikka (Corresponding Author)

Research output: Contribution to journalArticleScientificpeer-review

3 Citations (Scopus)

Abstract

Leaf area index (LAI) is an important biophysical variable for understanding the radiation use efficiency of field crops and their potential yield. On a large scale, LAI can be estimated with the help of imaging spectroscopy. However, recent studies have revealed that the leaf angle greatly affects the spectral reflectance of the canopy and hence imaging spectroscopy data. To investigate the effects of the leaf angle on LAI-sensitive narrowband vegetation indices, we used both empirical measurements from field crops and model-simulated data generated by the PROSAIL canopy reflectance model. We found the relationship between vegetation indices and LAI to be notably affected, especially when the leaf mean tilt angle (MTA) exceeded 70 degrees. Of the indices used in the study, the modified soil-adjusted vegetation index (MSAVI) was most strongly affected by leaf angles, while the blue normalized difference vegetation index (BNDVI), the green normalized difference vegetation index (GNDVI), the modified simple ratio using the wavelength of 705 nm (MSR705), the normalized difference vegetation index (NDVI), and the soil-adjusted vegetation index (SAVI) were only affected for sparse canopies (LAI < 3) and MTA exceeding 60°. Generally, the effect of MTA on the vegetation indices increased as a function of decreasing LAI. The leaf chlorophyll content did not affect the relationship between BNDVI, MSAVI, NDVI, and LAI, while the green atmospherically resistant index (GARI), GNDVI, and MSR705 were the most strongly affected indices. While the relationship between SR and LAI was somewhat affected by both MTA and the leaf chlorophyll content, the simple ratio (SR) displayed only slight saturation with LAI, regardless of MTA and the chlorophyll content. The best index found in the study for LAI estimation was BNDVI, although it performed robustly only for LAI > 3 and showed considerable nonlinearity. Thus, none of the studied indices were well suited for across-species LAI estimation: information on the leaf angle would be required for remote LAI measurement, especially at low LAI values. Nevertheless, narrowband indices can be used to monitor the LAI of crops with a constant leaf angle distribution.

Original languageEnglish
Article number1435
JournalApplied Sciences
Volume8
Issue number9
DOIs
Publication statusPublished - 22 Aug 2018
MoE publication typeNot Eligible

Fingerprint

leaf area index
crops
vegetation
leaves
Crops
narrowband
Spectroscopy
Imaging techniques
spectroscopy
normalized difference vegetation index
canopies
Soils
soils
spectral reflectance
Radiation
Wavelength
nonlinearity
reflectance

Keywords

  • Field crops
  • Imaging spectroscopy
  • LAI
  • Leaf inclination angle
  • Vegetation indices

Cite this

Zou, Xiaochen ; Haikarainen, Iina ; Haikarainen, Iikka P. ; Mäkelä, Pirjo ; Mõttus, Matti ; Pellikka, Petri. / Effects of crop leaf angle on LAI-sensitive narrow-band vegetation indices derived from imaging spectroscopy. In: Applied Sciences. 2018 ; Vol. 8, No. 9.
@article{8e1397b89e194b4d8380125dcfd36480,
title = "Effects of crop leaf angle on LAI-sensitive narrow-band vegetation indices derived from imaging spectroscopy",
abstract = "Leaf area index (LAI) is an important biophysical variable for understanding the radiation use efficiency of field crops and their potential yield. On a large scale, LAI can be estimated with the help of imaging spectroscopy. However, recent studies have revealed that the leaf angle greatly affects the spectral reflectance of the canopy and hence imaging spectroscopy data. To investigate the effects of the leaf angle on LAI-sensitive narrowband vegetation indices, we used both empirical measurements from field crops and model-simulated data generated by the PROSAIL canopy reflectance model. We found the relationship between vegetation indices and LAI to be notably affected, especially when the leaf mean tilt angle (MTA) exceeded 70 degrees. Of the indices used in the study, the modified soil-adjusted vegetation index (MSAVI) was most strongly affected by leaf angles, while the blue normalized difference vegetation index (BNDVI), the green normalized difference vegetation index (GNDVI), the modified simple ratio using the wavelength of 705 nm (MSR705), the normalized difference vegetation index (NDVI), and the soil-adjusted vegetation index (SAVI) were only affected for sparse canopies (LAI < 3) and MTA exceeding 60°. Generally, the effect of MTA on the vegetation indices increased as a function of decreasing LAI. The leaf chlorophyll content did not affect the relationship between BNDVI, MSAVI, NDVI, and LAI, while the green atmospherically resistant index (GARI), GNDVI, and MSR705 were the most strongly affected indices. While the relationship between SR and LAI was somewhat affected by both MTA and the leaf chlorophyll content, the simple ratio (SR) displayed only slight saturation with LAI, regardless of MTA and the chlorophyll content. The best index found in the study for LAI estimation was BNDVI, although it performed robustly only for LAI > 3 and showed considerable nonlinearity. Thus, none of the studied indices were well suited for across-species LAI estimation: information on the leaf angle would be required for remote LAI measurement, especially at low LAI values. Nevertheless, narrowband indices can be used to monitor the LAI of crops with a constant leaf angle distribution.",
keywords = "Field crops, Imaging spectroscopy, LAI, Leaf inclination angle, Vegetation indices",
author = "Xiaochen Zou and Iina Haikarainen and Haikarainen, {Iikka P.} and Pirjo M{\"a}kel{\"a} and Matti M{\~o}ttus and Petri Pellikka",
note = "ISSN tarkistettu 26.9.18",
year = "2018",
month = "8",
day = "22",
doi = "10.3390/app8091435",
language = "English",
volume = "8",
journal = "Applied Sciences",
issn = "2076-3417",
publisher = "MDPI",
number = "9",

}

Effects of crop leaf angle on LAI-sensitive narrow-band vegetation indices derived from imaging spectroscopy. / Zou, Xiaochen; Haikarainen, Iina; Haikarainen, Iikka P.; Mäkelä, Pirjo; Mõttus, Matti; Pellikka, Petri (Corresponding Author).

In: Applied Sciences, Vol. 8, No. 9, 1435, 22.08.2018.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Effects of crop leaf angle on LAI-sensitive narrow-band vegetation indices derived from imaging spectroscopy

AU - Zou, Xiaochen

AU - Haikarainen, Iina

AU - Haikarainen, Iikka P.

AU - Mäkelä, Pirjo

AU - Mõttus, Matti

AU - Pellikka, Petri

N1 - ISSN tarkistettu 26.9.18

PY - 2018/8/22

Y1 - 2018/8/22

N2 - Leaf area index (LAI) is an important biophysical variable for understanding the radiation use efficiency of field crops and their potential yield. On a large scale, LAI can be estimated with the help of imaging spectroscopy. However, recent studies have revealed that the leaf angle greatly affects the spectral reflectance of the canopy and hence imaging spectroscopy data. To investigate the effects of the leaf angle on LAI-sensitive narrowband vegetation indices, we used both empirical measurements from field crops and model-simulated data generated by the PROSAIL canopy reflectance model. We found the relationship between vegetation indices and LAI to be notably affected, especially when the leaf mean tilt angle (MTA) exceeded 70 degrees. Of the indices used in the study, the modified soil-adjusted vegetation index (MSAVI) was most strongly affected by leaf angles, while the blue normalized difference vegetation index (BNDVI), the green normalized difference vegetation index (GNDVI), the modified simple ratio using the wavelength of 705 nm (MSR705), the normalized difference vegetation index (NDVI), and the soil-adjusted vegetation index (SAVI) were only affected for sparse canopies (LAI < 3) and MTA exceeding 60°. Generally, the effect of MTA on the vegetation indices increased as a function of decreasing LAI. The leaf chlorophyll content did not affect the relationship between BNDVI, MSAVI, NDVI, and LAI, while the green atmospherically resistant index (GARI), GNDVI, and MSR705 were the most strongly affected indices. While the relationship between SR and LAI was somewhat affected by both MTA and the leaf chlorophyll content, the simple ratio (SR) displayed only slight saturation with LAI, regardless of MTA and the chlorophyll content. The best index found in the study for LAI estimation was BNDVI, although it performed robustly only for LAI > 3 and showed considerable nonlinearity. Thus, none of the studied indices were well suited for across-species LAI estimation: information on the leaf angle would be required for remote LAI measurement, especially at low LAI values. Nevertheless, narrowband indices can be used to monitor the LAI of crops with a constant leaf angle distribution.

AB - Leaf area index (LAI) is an important biophysical variable for understanding the radiation use efficiency of field crops and their potential yield. On a large scale, LAI can be estimated with the help of imaging spectroscopy. However, recent studies have revealed that the leaf angle greatly affects the spectral reflectance of the canopy and hence imaging spectroscopy data. To investigate the effects of the leaf angle on LAI-sensitive narrowband vegetation indices, we used both empirical measurements from field crops and model-simulated data generated by the PROSAIL canopy reflectance model. We found the relationship between vegetation indices and LAI to be notably affected, especially when the leaf mean tilt angle (MTA) exceeded 70 degrees. Of the indices used in the study, the modified soil-adjusted vegetation index (MSAVI) was most strongly affected by leaf angles, while the blue normalized difference vegetation index (BNDVI), the green normalized difference vegetation index (GNDVI), the modified simple ratio using the wavelength of 705 nm (MSR705), the normalized difference vegetation index (NDVI), and the soil-adjusted vegetation index (SAVI) were only affected for sparse canopies (LAI < 3) and MTA exceeding 60°. Generally, the effect of MTA on the vegetation indices increased as a function of decreasing LAI. The leaf chlorophyll content did not affect the relationship between BNDVI, MSAVI, NDVI, and LAI, while the green atmospherically resistant index (GARI), GNDVI, and MSR705 were the most strongly affected indices. While the relationship between SR and LAI was somewhat affected by both MTA and the leaf chlorophyll content, the simple ratio (SR) displayed only slight saturation with LAI, regardless of MTA and the chlorophyll content. The best index found in the study for LAI estimation was BNDVI, although it performed robustly only for LAI > 3 and showed considerable nonlinearity. Thus, none of the studied indices were well suited for across-species LAI estimation: information on the leaf angle would be required for remote LAI measurement, especially at low LAI values. Nevertheless, narrowband indices can be used to monitor the LAI of crops with a constant leaf angle distribution.

KW - Field crops

KW - Imaging spectroscopy

KW - LAI

KW - Leaf inclination angle

KW - Vegetation indices

UR - http://www.scopus.com/inward/record.url?scp=85052516691&partnerID=8YFLogxK

U2 - 10.3390/app8091435

DO - 10.3390/app8091435

M3 - Article

VL - 8

JO - Applied Sciences

JF - Applied Sciences

SN - 2076-3417

IS - 9

M1 - 1435

ER -