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Remote Sensing and Machine Learning in Vegetation Biophysical Parameters Estimation (Second Edition)

A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Remote Sensing in Agriculture and Vegetation".

Deadline for manuscript submissions: 30 April 2025 | Viewed by 4970

Special Issue Editors


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Guest Editor
Chinese Academy of Sciences, Beijing, China
Interests: egetation; chlorophyll content; remote sensing; forest health
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Guest Editor
School of Engineering, University of Western Australia, Crawley, Australia
Interests: vegetation parameter retrieval; vegetation phenology; vegetation monitoring; climate variability; ecosystem resilience
Special Issues, Collections and Topics in MDPI journals
School of Geography and Planning, and Guangdong Key Laboratory for Urbanization and Geo-simulation, Sun Yat-sen University, Guangzhou, China
Interests: solar‐induced chlorophyll fluorescence; terrestrial carbon cycle; remote sensing of vegetation
Special Issues, Collections and Topics in MDPI journals
Department of Remote Sensing, Nanjing University of Information Science & Technology, Nanjing 210044, China
Interests: vegetation parameters estimation; hyperspectral remote sensing; agricultral & ecological remote sensing
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Vegetation biophysical parameters are important indicators when characterizing the canopy density and structure of vegetation, such as the leaf area index (LAI), fractional vegetation coverage (FVC), biomass, leaf angle distribution (LAD), clumping index (CI), canopy height, etc. The vegetation biophysical parameters estimated through remote-sensing approaches support numerous applications in agriculture, forestry and other vegetation ecosystems.

The current algorithms employed to estimate biophysical parameters of vegetation include statistical regression, radiative transfer models, machine learning and deep learning techniques. Regression models based on a single vegetation spectral index or another spectral feature are simple and easy to use, with relatively stable accuracy; they are therefore the most widely utilized models. In contrast, machine learning has the ability to nonlinearly model the relationships between the biophysical parameters of vegetation and a satellite-derived spectrum. Deep learning, a new machine learning method, was initially used for target recognition and classification, and has gradually become a popular approach for the estimation of the biophysical parameters of vegetation.

Various types of remote sensing data (optical, LiDAR, SAR, etc.) have different advantages for extracting different vegetation biophysical parameters. The synthesis of different remote-sensing data is also important for estimation of certain vegetation parameters. Additionally, the estimation algorithm is closely related to the spatial and temporal resolution of those remote-sensing data.

Due to the complexity of land-surface vegetation, challenges regarding the estimation of vegetation parameters remain in terms of algorithm performance and applications. Advanced remote-sensing techniques and machine learning provide unprecedented opportunities to tackle these challenges. For example, the spectral responses region of different vegetation physical parameters (including biochemical parameters) may overlap, whereby the integration of multi-source remote sensing data offers significant potential in this regard.

This Special Issue aims to address advances and challenges in the remote-sensing estimation of vegetation biophysical variables using various algorithms and satellite data, and to enhance and promote the application of the estimated parameters. Original research articles and reviews are welcome. Research topics may include (but are not limited to) the following:

(1) The applicability of vegetation parameter estimation algorithms (regression, machine learning, deep learning) in various scenarios (regions, vegetation types, etc.);

(2) New methods such as a vegetation spectral index for vegetation biophysical parameter estimation;

(3) The integration and assimilation of multi-source remote sensing data and other data for vegetation biophysical parameter estimation;

(4) A case study of the applications of estimated vegetation parameters in ecosystems such as agriculture, forest and grassland areas (remote sensing of crop growth, vegetation phenology, vegetation degradation and recovery, etc.).

Dr. Quanjun Jiao
Prof. Dr. Wei Su
Dr. Qiaoyun Xie
Dr. Xing Li
Dr. Bo Liu
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • vegetation biophysical parameter estimation
  • vegetation spectral indices
  • multispectral/hyperspectral/LiDAR/SAR
  • satellite/airborne/UAV/tower-based/ground observation
  • regression/RTM/machine learning/deep learning
  • agriculture
  • forest
  • grassland
  • vegetation dynamics monitoring

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Related Special Issue

Published Papers (5 papers)

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Research

27 pages, 7620 KiB  
Article
Maturity Prediction in Soybean Breeding Using Aerial Images and the Random Forest Machine Learning Algorithm
by Osvaldo Pérez, Brian Diers and Nicolas Martin
Remote Sens. 2024, 16(23), 4343; https://doi.org/10.3390/rs16234343 - 21 Nov 2024
Viewed by 258
Abstract
Several studies have used aerial images to predict physiological maturity (R8 stage) in soybeans (Glycine max (L.) Merr.). However, information for making predictions in the current growing season using models fitted in previous years is still necessary. Using the Random Forest machine [...] Read more.
Several studies have used aerial images to predict physiological maturity (R8 stage) in soybeans (Glycine max (L.) Merr.). However, information for making predictions in the current growing season using models fitted in previous years is still necessary. Using the Random Forest machine learning algorithm and time series of RGB (red, green, blue) and multispectral images taken from a drone, this work aimed to study, in three breeding experiments of plant rows, how maturity predictions are impacted by a number of factors. These include the type of camera used, the number and time between flights, and whether models fitted with data obtained in one or more environments can be used to make accurate predictions in an independent environment. Applying principal component analysis (PCA), it was found that compared to the full set of 8–10 flights (R2 = 0.91–0.94; RMSE = 1.8–1.3 days), using data from three to five fights before harvest had almost no effect on the prediction error (RMSE increase ~0.1 days). Similar prediction accuracy was achieved using either a multispectral or an affordable RGB camera, and the excess green index (ExG) was found to be the important feature in making predictions. Using a model trained with data from two previous years and using fielding notes from check cultivars planted in the test season, the R8 stage was predicted, in 2020, with an error of 2.1 days. Periodically adjusted models could help soybean breeding programs save time when characterizing the cycle length of thousands of plant rows each season. Full article
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19 pages, 5207 KiB  
Article
Enhancing the Precision of Forest Growing Stock Volume in the Estonian National Forest Inventory with Different Predictive Techniques and Remote Sensing Data
by Temitope Olaoluwa Omoniyi and Allan Sims
Remote Sens. 2024, 16(20), 3794; https://doi.org/10.3390/rs16203794 - 12 Oct 2024
Viewed by 674
Abstract
Estimating forest growing stock volume (GSV) is crucial for forest growth and resource management, as it reflects forest productivity. National measurements are laborious and costly; however, integrating satellite data such as optical, Synthetic Aperture Radar (SAR), and airborne laser scanning (ALS) with National [...] Read more.
Estimating forest growing stock volume (GSV) is crucial for forest growth and resource management, as it reflects forest productivity. National measurements are laborious and costly; however, integrating satellite data such as optical, Synthetic Aperture Radar (SAR), and airborne laser scanning (ALS) with National Forest Inventory (NFI) data and machine learning (ML) methods has transformed forest management. In this study, random forest (RF), support vector regression (SVR), and Extreme Gradient Boosting (XGBoost) were used to predict GSV using Estonian NFI data, Sentinel-2 imagery, and ALS point cloud data. Four variable combinations were tested: CO1 (vegetation indices and LiDAR), CO2 (vegetation indices and individual band reflectance), CO3 (LiDAR and individual band reflectance), and CO4 (a combination of vegetation indices, individual band reflectance, and LiDAR). Across Estonia’s geographical regions, RF consistently delivered the best performance. In the northwest (NW), the RF model achieved the best performance with the CO3 combination, having an R2 of 0.63 and an RMSE of 125.39 m3/plot. In the southwest (SW), the RF model also performed exceptionally well, achieving an R2 of 0.73 and an RMSE of 128.86 m3/plot with the CO4 variable combination. In the northeast (NE), the RF model outperformed other ML models, achieving an R2 of 0.64 and an RMSE of 133.77 m3/plot under the CO4 combination. Finally, in the southeast (SE) region, the best performance was achieved with the CO4 combination, yielding an R2 of 0.70 and an RMSE of 21,120.72 m3/plot. These results underscore RF’s precision in predicting GSV across diverse environments, though refining variable selection and improving tree species data could further enhance accuracy. Full article
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24 pages, 11990 KiB  
Article
Plant Species Classification and Biodiversity Estimation from UAV Images with Deep Learning
by Marco Conciatori, Nhung Thi Cam Tran, Yago Diez, Alessandro Valletta, Andrea Segalini and Maximo Larry Lopez Caceres
Remote Sens. 2024, 16(19), 3654; https://doi.org/10.3390/rs16193654 - 30 Sep 2024
Viewed by 1189
Abstract
Biodiversity is a characteristic of ecosystems that plays a crucial role in the study of their evolution, and to estimate it, the species of all plants need to be determined. In this study, we used Unmanned Aerial Vehicles to gather RGB images of [...] Read more.
Biodiversity is a characteristic of ecosystems that plays a crucial role in the study of their evolution, and to estimate it, the species of all plants need to be determined. In this study, we used Unmanned Aerial Vehicles to gather RGB images of mid-to-high-altitude ecosystems in the Zao mountains (Japan). All the data-collection missions took place in autumn so the plants present distinctive seasonal coloration. Patches from single trees and bushes were manually extracted from the collected orthomosaics. Subsequently, Deep Learning image-classification networks were used to automatically determine the species of each tree or bush and estimate biodiversity. Both Convolutional Neural Networks (CNNs) and Transformer-based models were considered (ResNet, RegNet, ConvNeXt, and SwinTransformer). To measure and estimate biodiversity, we relied on the Gini–Simpson Index, the Shannon–Wiener Index, and Species Richness. We present two separate scenarios for evaluating the readiness of the technology for practical use: the first scenario uses a subset of the data with five species and a testing set that has a very similar percentage of each species to those present in the training set. The models studied reach very high performances with over 99 Accuracy and 98 F1 Score (the harmonic mean of Precision and Recall) for image classification and biodiversity estimates under 1% error. The second scenario uses the full dataset with nine species and large variations in class balance between the training and testing datasets, which is often the case in practical use situations. The results in this case remained fairly high for Accuracy at 90.64% but dropped to 51.77% for F1 Score. The relatively low F1 Score value is partly due to a small number of misclassifications having a disproportionate impact in the final measure, but still, the large difference between the Accuracy and F1 Score highlights the complexity of finely evaluating the classification results of Deep Learning Networks. Even in this very challenging scenario, the biodiversity estimation remained with relatively small (6–14%) errors for the most detailed indices, showcasing the readiness of the technology for practical use. Full article
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25 pages, 3397 KiB  
Article
Hyperspectral Imaging for Phenotyping Plant Drought Stress and Nitrogen Interactions Using Multivariate Modeling and Machine Learning Techniques in Wheat
by Frank Gyan Okyere, Daniel Kingsley Cudjoe, Nicolas Virlet, March Castle, Andrew Bernard Riche, Latifa Greche, Fady Mohareb, Daniel Simms, Manal Mhada and Malcolm John Hawkesford
Remote Sens. 2024, 16(18), 3446; https://doi.org/10.3390/rs16183446 - 17 Sep 2024
Viewed by 1590
Abstract
Accurate detection of drought stress in plants is essential for water use efficiency and agricultural output. Hyperspectral imaging (HSI) provides a non-invasive method in plant phenotyping, allowing the long-term monitoring of plant health due to sensitivity to subtle changes in leaf constituents. The [...] Read more.
Accurate detection of drought stress in plants is essential for water use efficiency and agricultural output. Hyperspectral imaging (HSI) provides a non-invasive method in plant phenotyping, allowing the long-term monitoring of plant health due to sensitivity to subtle changes in leaf constituents. The broad spectral range of HSI enables the development of different vegetation indices (VIs) to analyze plant trait responses to multiple stresses, such as the combination of nutrient and drought stresses. However, known VIs may underperform when subjected to multiple stresses. This study presents new VIs in tandem with machine learning models to identify drought stress in wheat plants under varying nitrogen (N) levels. A pot wheat experiment was set up in the glasshouse with four treatments: well-watered high-N (WWHN), well-watered low-N (WWLN), drought-stress high-N (DSHN) and drought-stress low-N (DSLN). In addition to ensuring that plants were watered according to the experiment design, photosynthetic rate (Pn) and stomatal conductance (gs) (which are used to assess plant drought stress) were taken regularly, serving as the ground truth data for this study. The proposed VIs, together with known VIs, were used to train three classification models: support vector machines (SVM), random forest (RF), and deep neural networks (DNN) to classify plants based on their drought status. The proposed VIs achieved more than 0.94 accuracy across all models, and their performance further increased when combined with known VIs. The combined VIs were used to train three regression models to predict the stomatal conductance and photosynthetic rates of plants. The random forest regression model performed best, suggesting that it could be used as a stand-alone tool to forecast gs and Pn and track drought stress in wheat. This study shows that combining hyperspectral data with machine learning can effectively monitor and predict drought stress in crops, especially in varying nitrogen conditions. Full article
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18 pages, 7349 KiB  
Article
Temporal Patterns of Vegetation Greenness for the Main Forest-Forming Tree Species in the European Temperate Zone
by Kinga Kulesza and Agata Hościło
Remote Sens. 2024, 16(15), 2844; https://doi.org/10.3390/rs16152844 - 2 Aug 2024
Cited by 1 | Viewed by 648
Abstract
In light of recently accelerating global warming, the changes in vegetation trends are vital for the monitoring of the dynamics of both whole ecosystems and individual species. Detecting changes within the time series of specific forest ecosystems or species is very important in [...] Read more.
In light of recently accelerating global warming, the changes in vegetation trends are vital for the monitoring of the dynamics of both whole ecosystems and individual species. Detecting changes within the time series of specific forest ecosystems or species is very important in the context of assessing their vulnerability to climate change and other negative phenomena. Hence, the aim of this paper was to identify the trend change points and periods of greening and browning in multi-annual time series of the normalised difference vegetation index (NDVI) and enhanced vegetation index (EVI) of four main forest-forming tree species in the temperate zone: pine, spruce, oak and beech. The research was conducted over the last two decades (2002–2022), and was based on vegetation indices data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). To this end, several research approaches, including calculating the linear trends in the moving periods and BEAST algorithm, were adapted. A pattern of browning then greening then constant was detected for coniferous species, mostly pine. In turn, for broadleaved species, namely oak and beech, a pattern of greening then constant was identified, without the initial phase of browning. The main trend change points seem to be ca. 2006 and ca. 2015 for coniferous species and solely around 2015 for deciduous ones. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Plant species classification and biodiversity estimation from UAV images with Deep Learning
Authors: Marco Conciatori; Nhung Tran Cam Thi; Yago Diez; Alessandro Valletta; Andrea Segalini; Maximo Larry Lopez Caceres
Affiliation: Faculty of Science, Yamagata University, Yamagata, Japan
Abstract: Biodiversity is a characteristic of Ecosystem that plays a crucial role in the study of their evolution. In order to estimate it, the species of all plants needs to be determined. In this study we used Unmanned Aerial Vehicles to gather RGB images of mid-to-high altitude ecosystems in Zao mountains (Japan). All data collection missions took place in Autumn so plants present distinctive seasonal coloration. Deep Learning image classification networks were used to automatically determine the species of each tree or bush and estimate biodiversity. Both Convolutional Neural Networks (CNNs) and Transformer-based models were considered (ResNet, RegNet, ConvNeXt, and SwinTransformer). In order to measure and estimate biodiversity, we relied on the Gini-Simpson Index, the Shannon-Wiener Index, and Species Richness. In order to evaluate the level of readiness of the technology for practical use, we present two separate scenarios: The first scenario uses a subset of the data with five species and a testing set that has very similar percentage of each species to those present in the training set. The models studied reach very high performances with over 99% accuracy and 98% F1 Score for image classification and biodiversity estimates under 1% error. The second scenario uses the full dataset with 9 species and large variations between class balances between the training and testing datasets, which is often the case in practical use situations. The results in this case remained fairly high for accuracy at 90.64% but dropped to 51.77% for F1. The relatively low F1 value is partly due to a small number of misclassification having a disproportionate impact in the final measure, but still, the large difference between accuracy and F1 score highlights the complexity of finely evaluating the classification results of Deep Learning networks. Even in this very challenging scenario, the biodiversity estimation remained with relatively small (6-14%) errors for the most detailed indices, showcasing the readiness of the technology for practical use even in challenging scenarios.

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