Winter Wheat Nitrogen Status Estimation Using UAV-Based RGB Imagery and Gaussian Processes Regression
Predicting the crop nitrogen (N) nutrition status is critical for optimizing nitrogen fertilizer application. The present study examined the ability of multiple image features derived from unmanned aerial vehicle (UAV) RGB images for winter wheat N status estimation across multiple critical growth s...
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MDPI AG
2020-11-01
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Online Access: | https://www.mdpi.com/2072-4292/12/22/3778 |
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doaj-e06a5cc018e54ea5b6fd88666471c927 |
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record_format |
Article |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Yuanyuan Fu Guijun Yang Zhenhai Li Xiaoyu Song Zhenhong Li Xingang Xu Pei Wang Chunjiang Zhao |
spellingShingle |
Yuanyuan Fu Guijun Yang Zhenhai Li Xiaoyu Song Zhenhong Li Xingang Xu Pei Wang Chunjiang Zhao Winter Wheat Nitrogen Status Estimation Using UAV-Based RGB Imagery and Gaussian Processes Regression Remote Sensing unmanned aerial vehicle winter wheat nitrogen status indicators color space models Gabor-based textures Gaussian processes regression |
author_facet |
Yuanyuan Fu Guijun Yang Zhenhai Li Xiaoyu Song Zhenhong Li Xingang Xu Pei Wang Chunjiang Zhao |
author_sort |
Yuanyuan Fu |
title |
Winter Wheat Nitrogen Status Estimation Using UAV-Based RGB Imagery and Gaussian Processes Regression |
title_short |
Winter Wheat Nitrogen Status Estimation Using UAV-Based RGB Imagery and Gaussian Processes Regression |
title_full |
Winter Wheat Nitrogen Status Estimation Using UAV-Based RGB Imagery and Gaussian Processes Regression |
title_fullStr |
Winter Wheat Nitrogen Status Estimation Using UAV-Based RGB Imagery and Gaussian Processes Regression |
title_full_unstemmed |
Winter Wheat Nitrogen Status Estimation Using UAV-Based RGB Imagery and Gaussian Processes Regression |
title_sort |
winter wheat nitrogen status estimation using uav-based rgb imagery and gaussian processes regression |
publisher |
MDPI AG |
series |
Remote Sensing |
issn |
2072-4292 |
publishDate |
2020-11-01 |
description |
Predicting the crop nitrogen (N) nutrition status is critical for optimizing nitrogen fertilizer application. The present study examined the ability of multiple image features derived from unmanned aerial vehicle (UAV) RGB images for winter wheat N status estimation across multiple critical growth stages. The image features consisted of RGB-based vegetation indices (VIs), color parameters, and textures, which represented image features of different aspects and different types. To determine which N status indicators could be well-estimated, we considered two mass-based N status indicators (i.e., the leaf N concentration (LNC) and plant N concentration (PNC)) and two area-based N status indicators (i.e., the leaf N density (LND) and plant N density (PND)). Sixteen RGB-based VIs associated with crop growth were selected. Five color space models, including RGB, HSV, L*a*b*, L*c*h*, and L*u*v*, were used to quantify the winter wheat canopy color. The combination of Gaussian processes regression (GPR) and Gabor-based textures with four orientations and five scales was proposed to estimate the winter wheat N status. The gray level co-occurrence matrix (GLCM)-based textures with four orientations were extracted for comparison. The heterogeneity in the textures of different orientations was evaluated using the measures of mean and coefficient of variation (CV). The variable importance in projection (VIP) derived from partial least square regression (PLSR) and a band analysis tool based on Gaussian processes regression (GPR-BAT) were used to identify the best performing image features for the N status estimation. The results indicated that (1) the combination of RGB-based VIs or color parameters only could produce reliable estimates of PND and the GPR model based on the combination of color parameters yielded a higher accuracy for the estimation of PND (R<sup>2</sup><sub>val</sub> = 0.571, RMSE<sub>val</sub> = 2.846 g/m<sup>2</sup>, and RPD<sub>val</sub> = 1.532), compared to that based on the combination of RGB-based VIs; (2) there was no significant heterogeneity in the textures of different orientations and the textures of 45 degrees were recommended in the winter wheat N status estimation; (3) compared with the RGB-based VIs and color parameters, the GPR model based on the Gabor-based textures produced a higher accuracy for the estimation of PND (R<sup>2</sup><sub>val</sub> = 0.675, RMSE<sub>val</sub> = 2.493 g/m<sup>2</sup>, and RPD<sub>val</sub> = 1.748) and the PLSR model based on the GLCM-based textures produced a higher accuracy for the estimation of PNC (R<sup>2</sup><sub>val</sub> = 0.612, RMSE<sub>val</sub> = 0.380%, and RPD<sub>val</sub> = 1.601); and (4) the combined use of RGB-based VIs, color parameters, and textures produced comparable estimation results to using textures alone. Both VIP-PLSR and GPR-BAT analyses confirmed that image textures contributed most to the estimation of winter wheat N status. The experimental results reveal the potential of image textures derived from high-definition UAV-based RGB images for the estimation of the winter wheat N status. They also suggest that a conventional low-cost digital camera mounted on a UAV could be well-suited for winter wheat N status monitoring in a fast and non-destructive way. |
topic |
unmanned aerial vehicle winter wheat nitrogen status indicators color space models Gabor-based textures Gaussian processes regression |
url |
https://www.mdpi.com/2072-4292/12/22/3778 |
work_keys_str_mv |
AT yuanyuanfu winterwheatnitrogenstatusestimationusinguavbasedrgbimageryandgaussianprocessesregression AT guijunyang winterwheatnitrogenstatusestimationusinguavbasedrgbimageryandgaussianprocessesregression AT zhenhaili winterwheatnitrogenstatusestimationusinguavbasedrgbimageryandgaussianprocessesregression AT xiaoyusong winterwheatnitrogenstatusestimationusinguavbasedrgbimageryandgaussianprocessesregression AT zhenhongli winterwheatnitrogenstatusestimationusinguavbasedrgbimageryandgaussianprocessesregression AT xingangxu winterwheatnitrogenstatusestimationusinguavbasedrgbimageryandgaussianprocessesregression AT peiwang winterwheatnitrogenstatusestimationusinguavbasedrgbimageryandgaussianprocessesregression AT chunjiangzhao winterwheatnitrogenstatusestimationusinguavbasedrgbimageryandgaussianprocessesregression |
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1724432273345871872 |
spelling |
doaj-e06a5cc018e54ea5b6fd88666471c9272020-11-25T04:06:08ZengMDPI AGRemote Sensing2072-42922020-11-01123778377810.3390/rs12223778Winter Wheat Nitrogen Status Estimation Using UAV-Based RGB Imagery and Gaussian Processes RegressionYuanyuan Fu0Guijun Yang1Zhenhai Li2Xiaoyu Song3Zhenhong Li4Xingang Xu5Pei Wang6Chunjiang Zhao7Key Laboratory of Quantitative Remote Sensing in Agriculture of Ministry of Agriculture, Beijing Research Center for Information Technology in Agriculture, Beijing 100097, ChinaKey Laboratory of Quantitative Remote Sensing in Agriculture of Ministry of Agriculture, Beijing Research Center for Information Technology in Agriculture, Beijing 100097, ChinaKey Laboratory of Quantitative Remote Sensing in Agriculture of Ministry of Agriculture, Beijing Research Center for Information Technology in Agriculture, Beijing 100097, ChinaKey Laboratory of Quantitative Remote Sensing in Agriculture of Ministry of Agriculture, Beijing Research Center for Information Technology in Agriculture, Beijing 100097, ChinaKey Laboratory of Quantitative Remote Sensing in Agriculture of Ministry of Agriculture, Beijing Research Center for Information Technology in Agriculture, Beijing 100097, ChinaKey Laboratory of Quantitative Remote Sensing in Agriculture of Ministry of Agriculture, Beijing Research Center for Information Technology in Agriculture, Beijing 100097, ChinaKey Laboratory of Quantitative Remote Sensing in Agriculture of Ministry of Agriculture, Beijing Research Center for Information Technology in Agriculture, Beijing 100097, ChinaKey Laboratory of Quantitative Remote Sensing in Agriculture of Ministry of Agriculture, Beijing Research Center for Information Technology in Agriculture, Beijing 100097, ChinaPredicting the crop nitrogen (N) nutrition status is critical for optimizing nitrogen fertilizer application. The present study examined the ability of multiple image features derived from unmanned aerial vehicle (UAV) RGB images for winter wheat N status estimation across multiple critical growth stages. The image features consisted of RGB-based vegetation indices (VIs), color parameters, and textures, which represented image features of different aspects and different types. To determine which N status indicators could be well-estimated, we considered two mass-based N status indicators (i.e., the leaf N concentration (LNC) and plant N concentration (PNC)) and two area-based N status indicators (i.e., the leaf N density (LND) and plant N density (PND)). Sixteen RGB-based VIs associated with crop growth were selected. Five color space models, including RGB, HSV, L*a*b*, L*c*h*, and L*u*v*, were used to quantify the winter wheat canopy color. The combination of Gaussian processes regression (GPR) and Gabor-based textures with four orientations and five scales was proposed to estimate the winter wheat N status. The gray level co-occurrence matrix (GLCM)-based textures with four orientations were extracted for comparison. The heterogeneity in the textures of different orientations was evaluated using the measures of mean and coefficient of variation (CV). The variable importance in projection (VIP) derived from partial least square regression (PLSR) and a band analysis tool based on Gaussian processes regression (GPR-BAT) were used to identify the best performing image features for the N status estimation. The results indicated that (1) the combination of RGB-based VIs or color parameters only could produce reliable estimates of PND and the GPR model based on the combination of color parameters yielded a higher accuracy for the estimation of PND (R<sup>2</sup><sub>val</sub> = 0.571, RMSE<sub>val</sub> = 2.846 g/m<sup>2</sup>, and RPD<sub>val</sub> = 1.532), compared to that based on the combination of RGB-based VIs; (2) there was no significant heterogeneity in the textures of different orientations and the textures of 45 degrees were recommended in the winter wheat N status estimation; (3) compared with the RGB-based VIs and color parameters, the GPR model based on the Gabor-based textures produced a higher accuracy for the estimation of PND (R<sup>2</sup><sub>val</sub> = 0.675, RMSE<sub>val</sub> = 2.493 g/m<sup>2</sup>, and RPD<sub>val</sub> = 1.748) and the PLSR model based on the GLCM-based textures produced a higher accuracy for the estimation of PNC (R<sup>2</sup><sub>val</sub> = 0.612, RMSE<sub>val</sub> = 0.380%, and RPD<sub>val</sub> = 1.601); and (4) the combined use of RGB-based VIs, color parameters, and textures produced comparable estimation results to using textures alone. Both VIP-PLSR and GPR-BAT analyses confirmed that image textures contributed most to the estimation of winter wheat N status. The experimental results reveal the potential of image textures derived from high-definition UAV-based RGB images for the estimation of the winter wheat N status. They also suggest that a conventional low-cost digital camera mounted on a UAV could be well-suited for winter wheat N status monitoring in a fast and non-destructive way.https://www.mdpi.com/2072-4292/12/22/3778unmanned aerial vehiclewinter wheatnitrogen status indicatorscolor space modelsGabor-based texturesGaussian processes regression |