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Leaf Area Index (LAI) Retrieval using Remote Sensing

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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: closed (15 February 2019) | Viewed by 87848

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Special Issue Editors

Dr. Roshanak Darvishzadeh

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Guest Editor

Department of Natural Resources, Faculty of Geo-Information Science and Earth Observation, University of Twente, Enschede, The Netherlands
Interests: remote sensing; vegetation physiological properties; imaging spectroscopy; radiative transfer models; smart agriculture; biodiversity
Special Issues, Collections and Topics in MDPI journals

Dr. Abel Ramoelo

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Guest Editor

Department of Geography, Geoinformatics and Meteorology, University of Pretoria, Hatfield, Pretoria 0001, South Africa
Interests: vegetation assessments; biodiversity monitoring including species mapping; nutrients (nitrogen, phosphorus); biophysical parameters (biomass, leaf area index); hyperspectral; multispectral; radar; lidar; machine learning; random forest
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Leaf area index (LAI) is the key biophysical variable influencing land surface photosynthesis, energy balance, and transpiration, and it is closely related to the net primary production of terrestrial ecosystems. Since green leaves play a critical role in controlling many physical and biological processes of plant canopies, LAI, being the key structural characteristic of vegetation, is also widely used as an indication of vegetation status. Thus, accurately estimating and mapping LAI at regional, national, and global scales is crucial. However, LAI measurement either using destructive or un-destructive methods is challenging and requires a great amount of labour and, hence, cost.

Remote sensing has played an imperative role in obtaining LAI estimates for its rapid, cost-effective, reliable, and objective estimation. A large number of relationships have been discovered between remote sensing data obtained from optical, thermal, LiDAR, and radar sensors at laboratory, field, airborne, or satellite levels, utilizing various physical or empirical models. However, regardless of remote sensing data type and models, challenges, such as saturation at high LAI values, canopy structure, and heterogeneity, as well as the type of underlying background soil, impede the retrieval accuracy of LAI and need to be further addressed.

This Special Issue, "Leaf Area Index (LAI) Retrieval using Remote Sensing", is calling for papers that demonstrate original research that can overcome or address the above challenges and gaps and develop corresponding solutions, in particular using remote sensing recent advances.

Dr. Roshanak Darvishzadeh
Dr. Abel Ramoelo
Guest Editors

Keywords

Vegetation Canopy
Leaf Area Index
Vegetation Indices
Empirical
Radiative Transfer Modelling

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Published Papers (13 papers)

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Research

16 pages, 3731 KiB

Open AccessArticle

Relating X-band SAR Backscattering to Leaf Area Index of Rice in Different Phenological Phases

by Sonia Asilo, Andrew Nelson, Kees de Bie, Andrew Skidmore, Alice Laborte, Aileen Maunahan and Eduardo Jimmy P. Quilang

Remote Sens. 2019, 11(12), 1462; https://doi.org/10.3390/rs11121462 - 20 Jun 2019

Cited by 12 | Viewed by 4514

Abstract

The objective of this study is to provide complete information on the dynamic relationship between X-band (3.11 cm) backscattering intensity (σ°) and rice crop’s leaf area index (LAI) at all growth phases. Though the relationship between X-band σ° and LAI has been previously explored, details on the relationship at the reproductive phase remain unstudied. LAI at the reproductive phase is important particularly at the heading stage where LAI reaches its maximum as it is closely related to grain yield, and at flowering stage where the total leaf area affects the amount of photosynthates. Therefore, this study examined the relationship of increasing LAI (vegetative to reproductive phase) and decreasing LAI (ripening phase) with TerraSAR-X (TSX) ScanSAR (3.11 cm) σ° at HH polarisation and 45° incidence angle. The results showed a statistically significant (R² = 0.51, p value < 0.001) non-linear relationship of LAI with σ° at the vegetative to reproductive phase while no significant linear relationship was found at the ripening phase. This study completes the response curve of X-band σ° to LAI by filling in the information on the reproductive phase which more accurately characterises the dynamic relationship between the rice crop’s LAI and X-band’s σ°. This contributes to improved knowledge on the use of X-band data for estimating LAI for the whole crop cycle which is essential for the modelling of crop growth and estimation of yield. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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16 pages, 2467 KiB

Open AccessArticle

Comparison of Landsat-8 and Sentinel-2 Data for Estimation of Leaf Area Index in Temperate Forests

by Lorenz Hans Meyer, Marco Heurich, Burkhard Beudert, Joseph Premier and Dirk Pflugmacher

Remote Sens. 2019, 11(10), 1160; https://doi.org/10.3390/rs11101160 - 15 May 2019

Cited by 56 | Viewed by 7861

Abstract

With the launch of the Sentinel-2 satellites, a European capacity has been created to ensure continuity of Landsat and SPOT observations. In contrast to previous sensors, Sentinel-2′s multispectral imager (MSI) incorporates three additional spectral bands in the red-edge (RE) region, which are expected to improve the mapping of vegetation traits. The objective of this study was to compare Sentinel-2 MSI and Landsat-8 OLI data for the estimation of leaf area index (LAI) in temperate, deciduous broadleaf forests. We used hemispherical photography to estimate effective LAI at 36 field plots. We then built and compared simple and multiple linear regression models between field-based LAI and spectral bands and vegetation indices derived from Landsat-8 and Sentinel-2, respectively. Our main findings are that Sentinel-2 predicts LAI with comparable accuracy to Landsat-8. The best Landsat-8 models predicted LAI with a root-mean-square error (RMSE) of 0.877, and the best Sentinel-2 model achieved an RMSE of 0.879. In addition, Sentinel-2′s RE bands and RE-based indices did not improve LAI prediction. Thirdly, LAI models showed a high sensitivity to understory vegetation when tree cover was sparse. According to our findings, Sentinel-2 is capable of delivering data continuity at high temporal resolution. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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16 pages, 3293 KiB

Open AccessArticle

Comparison of Vegetation Indices for Leaf Area Index Estimation in Vertical Shoot Positioned Vine Canopies with and without Grenbiule Hail-Protection Netting

by Pedro C. Towers, Albert Strever and Carlos Poblete-Echeverría

Remote Sens. 2019, 11(9), 1073; https://doi.org/10.3390/rs11091073 - 07 May 2019

Cited by 57 | Viewed by 5354

Abstract

Leaf area per unit surface (LAI—leaf area index) is a valuable parameter to assess vine vigour in several applications, including direct mapping of vegetative–reproductive balance (VRB). Normalized difference vegetation index (NDVI) has been successfully used to assess the spatial variability of estimated LAI. However, sometimes NDVI is unsuitable due to its lack of sensitivity at high LAI values. Moreover, the presence of hail protection with Grenbiule netting also affects incident light and reflection, and consequently spectral response. This study analyses the effect of protective netting in the LAI–NDVI relationship and, using NDVI as a reference index, compares several indices in terms of accuracy and sensitivity using linear and logarithmic models. Among the indices compared, results show NDVI to be the most accurate, and ratio vegetation index (RVI) to be the most sensitive. The wide dynamic range vegetation index (WDRVI) presented a good balance between accuracy and sensitivity. Soil-adjusted vegetation index 2 (SAVI₂) appears to be the best estimator of LAI with linear models. Logarithmic models provided higher determination coefficients, but this has little influence over the normal range of LAI values. A similar NDVI–LAI relationship holds for protected and unprotected canopies in initial vegetation stages, but different functions are preferable once the canopy is fully developed, in particular, if tipping is performed. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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14 pages, 1840 KiB

Open AccessArticle

Numerical Assessments of Leaf Area Index in Tropical Savanna Rangelands, South Africa Using Landsat 8 OLI Derived Metrics and In-Situ Measurements

by Timothy Dube, Santa Pandit, Cletah Shoko, Abel Ramoelo, Dominic Mazvimavi and Tatenda Dalu

Remote Sens. 2019, 11(7), 829; https://doi.org/10.3390/rs11070829 - 07 Apr 2019

Cited by 26 | Viewed by 4658

Abstract

Knowledge on rangeland condition, productivity patterns and possible thresholds of potential concern, as well as the escalation of risks in the face of climate change and variability over savanna grasslands is essential for wildlife/livestock management purposes. The estimation of leaf area index (LAI) in tropical savanna ecosystems is therefore fundamental for the proper planning and management of this natural capital. In this study, we assess the spatio-temporal seasonal LAI dynamics (dry and wet seasons) as a proxy for rangeland condition and productivity in the Kruger National Park (KNP), South Africa. The 30 m Landsat 8 Operational Land Imager (OLI) spectral bands, derived vegetation indices and a non-parametric approach (i.e., random forest, RF) were used to assess dry and wet season LAI condition and variability in the KNP. The results showed that RF optimization enhanced the model performance in estimating LAI. Moderately high accuracies were observed for the dry season (R² of 0.63–0.72 and average RMSE of 0.60 m²/m²) and wet season (0.62–0.63 and 0.79 m²/m²). Derived thematic maps demonstrated that the park had high LAI estimates during the wet season when compared to the dry season. On average, LAI estimates ranged between 3 and 7 m²/m² during the wet season, whereas for the dry season most parts of the park had LAI estimates ranging between 0.00 and 3.5 m²/m². The findings indicate that Kruger National Park had high levels of productivity during the wet season monitoring period. Overall, this work shows the unique potential of Landsat 8-derived metrics in assessing LAI as a proxy for tropical savanna rangelands productivity. The result is relevant for wildlife management and habitat assessment and monitoring. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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16 pages, 2552 KiB

Open AccessArticle

Estimating the Seasonal Dynamics of the Leaf Area Index Using Piecewise LAI-VI Relationships Based on Phenophases

by Kun Qiao, Wenquan Zhu, Zhiying Xie and Peixian Li

Remote Sens. 2019, 11(6), 689; https://doi.org/10.3390/rs11060689 - 22 Mar 2019

Cited by 49 | Viewed by 4612

Abstract

The leaf area index (LAI) is not only an important parameter used to describe the geometry of vegetation canopy but also a key input variable for ecological models. One of the most commonly used methods for LAI estimation is to establish an empirical relationship between the LAI and the vegetation index (VI). However, the LAI-VI relationships had high seasonal variability, and they differed among phenophases and VIs. In this study, the LAI-VI relationships in different phenophases and for different VIs (i.e., the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI) and near-infrared reflectance of vegetation (NIRv)) were investigated based on 82 site-years of LAI observed data and the Moderate Resolution Imaging Spectroradiometer (MODIS) VI products. Significant LAI-VI relationships were observed during the vegetation growing and declining periods. There were weak LAI-VI relationships (p > 0.05) during the flourishing period. The accuracies for the LAIs estimated with the piecewise LAI-VI relationships based on different phenophases were significantly higher than those estimated based on a single LAI-VI relationship for the entire vegetation active period. The average root mean square error (RMSE) ± standard deviation (SD) value for the LAIs estimated with the piecewise LAI-VI relationships was 0.38 ± 0.13 (based on the NDVI), 0.41 ± 0.13 (based on the EVI) and 0.41 ± 0.14 (based on the NIRv), respectively. In comparison, it was 0.46 ± 0.13 (based on the NDVI), 0.55 ± 0.15 (based on the EVI) and 0.55 ± 0.15 (based on the NIRv) for those estimated with a single LAI-VI relationship. The performance of the three VIs in estimating the LAI also varied among phenophases. During the growing period, the mean RMSE ± SD value for the estimated LAIs was 0.30 ± 0.11 (LAI-NDVI relationships), 0.37 ± 0.11 (LAI-EVI relationships) and 0.36 ± 0.13 (LAI-NIRv relationships), respectively, indicating the NDVI produced significantly better LAI estimations than those from the other two VIs. In contrast, the EVI produced slightly better LAI estimations than those from the other two VIs during the declining period (p > 0.05), and the mean RMSE ± SD value for the estimated LAIs was 0.45 ± 0.16 (LAI-NDVI relationships), 0.43 ± 0.23 (LAI-EVI relationships) and 0.45 ± 0.25 (LAI-NIRv relationships), respectively. Hence, the piecewise LAI-VI relationships based on different phenophases were recommended for the estimations of the LAI instead of a single LAI-VI relationship for the entire vegetation active period. Furthermore, the optimal VI in each phenophase should be selected for the estimations of the LAI according to the characteristics of vegetation growth. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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22 pages, 4021 KiB

Open AccessFeature PaperArticle

Analysis of Sentinel-2 and RapidEye for Retrieval of Leaf Area Index in a Saltmarsh Using a Radiative Transfer Model

by Roshanak Darvishzadeh, Tiejun Wang, Andrew Skidmore, Anton Vrieling, Brian O’Connor, Tawanda W Gara, Bruno J. Ens and Marc Paganini

Remote Sens. 2019, 11(6), 671; https://doi.org/10.3390/rs11060671 - 20 Mar 2019

Cited by 49 | Viewed by 10714

Abstract

The Sentinel satellite fleet of the Copernicus Programme offers new potential to map and monitor plant traits at fine spatial and temporal resolutions. Among these traits, leaf area index (LAI) is a crucial indicator of vegetation growth and an essential variable in biodiversity studies. Numerous studies have shown that the radiative transfer approach has been a successful method to retrieve LAI from remote-sensing data. However, the suitability and adaptability of this approach largely depend on the type of remote-sensing data, vegetation cover and the ecosystem studied. Saltmarshes are important wetland ecosystems threatened by sea level rise among other human- and animal-induced changes. Therefore, monitoring their vegetation status is crucial for their conservation, yet few LAI assessments exist for these ecosystems. In this study, the retrieval of LAI in a saltmarsh ecosystem is examined using Sentinel-2 and RapidEye data through inversion of the PROSAIL radiative transfer model. Field measurements of LAI and some other plant traits were obtained during two succeeding field campaigns in July 2015 and 2016 on the saltmarsh of Schiermonnikoog, a barrier island of the Netherlands. RapidEye (2015) and Sentinel-2 (2016) data were acquired concurrent to the time of the field campaigns. The broadly employed PROSAIL model was inverted using two look-up tables (LUTs) generated in the spectral band’s settings of the two sensors and in which each contained 500,000 records. Different solutions from the LUTs, as well as, different Sentinel-2 spectral subsets were considered to examine the LAI retrieval. Our results showed that generally the LAI retrieved from Sentinel-2 had higher accuracy compared to RapidEye-retrieved LAI. Utilising the mean of the first 10 best solutions from the LUTs resulted in higher R² (0.51 and 0.59) and lower normalised root means square error (NRMSE) (0.24 and 0.16) for both RapidEye and Sentinel-2 data respectively. Among different Sentinel-2 spectral subsets, the one comprised of the four near-infrared (NIR) and shortwave infrared (SWIR) spectral bands resulted in higher estimation accuracy (R² = 0.44, NRMSE = 0.21) in comparison to using other studied spectral subsets. The results demonstrated the feasibility of broadband multispectral sensors, particularly Sentinel-2 for retrieval of LAI in the saltmarsh ecosystem via inversion of PROSAIL. Our results highlight the importance of proper parameterisation of radiative transfer models and capacity of Sentinel-2 spectral range and resolution, with impending high-quality global observation aptitude, for retrieval of plant traits at a global scale. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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15 pages, 1346 KiB

Open AccessArticle

Integration of Landsat-8 Thermal and Visible-Short Wave Infrared Data for Improving Prediction Accuracy of Forest Leaf Area Index

by Elnaz Neinavaz, Roshanak Darvishzadeh, Andrew K. Skidmore and Haidi Abdullah

Remote Sens. 2019, 11(4), 390; https://doi.org/10.3390/rs11040390 - 15 Feb 2019

Cited by 16 | Viewed by 5834

Abstract

Leaf area index (LAI) has been investigated in multiple studies, either by means of visible/near-infrared and shortwave-infrared or thermal infrared remotely sensed data, with various degrees of accuracy. However, it is not yet known how the integration of visible/near and shortwave-infrared and thermal infrared data affect estimates of LAI. In this study, we examined the utility of Landsat-8 thermal infrared data together with its spectral data from the visible/near and shortwave-infrared region to quantify the LAI of a mixed temperate forest in Germany. A field campaign was carried out in August 2015, in the Bavarian Forest National Park, concurrent with the time of the Landsat-8 overpass, and a number of forest structural parameters, including LAI and proportion of vegetation cover, were measured for 37 plots. A normalised difference vegetation index threshold method was applied to calculate land surface emissivity and land surface temperature and their relations to LAI were investigated. Next, the relation between LAI and eight commonly used vegetation indices were examined using the visible/near-infrared and shortwave-infrared remote sensing data. Finally, the artificial neural network was used to predict the LAI using: (i) reflectance data from the Landsat-8 operational land imager (OLI) sensor; (ii) reflectance data from the OLI sensor and the land surface emissivity; and (iii) reflectance data from the OLI sensor and land surface temperature. A stronger relationship was observed between LAI and land surface emissivity compared to that between LAI and land surface temperature. In general, LAI was predicted with relatively low accuracy by means of the vegetation indices. Among the studied vegetation indices, the modified vegetation index had the highest accuracy for LAI prediction (R²_CV = 0.33, RMSE_CV = 1.21 m²m⁻²). Nevertheless, using the visible/near-infrared and shortwave-infrared spectral data in the artificial neural network, the prediction accuracy of LAI increased (R²_CV = 0.58, RMSE_CV = 0.83 m²m⁻²). The integration of reflectance and land surface emissivity significantly improved the prediction accuracy of the LAI (R²_CV = 0.81, RMSE_CV = 0.63 m²m⁻²). For the first time, our results demonstrate that the combination of Landsat-8 reflectance spectral data from the visible/near-infrared and shortwave-infrared domain and thermal infrared data can boost the estimation accuracy of the LAI in a forest ecosystem. This finding has implication for the prediction of other vegetation biophysical, or possibly biochemical variables using thermal infrared satellite remote sensing data, as well as regional mapping of LAI when coupled with a canopy radiative transfer model. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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18 pages, 11011 KiB

Open AccessArticle

Effects of Growth Stage Development on Paddy Rice Leaf Area Index Prediction Models

by Li Wang, Qingrui Chang, Fenling Li, Lin Yan, Yong Huang, Qi Wang and Lili Luo

Remote Sens. 2019, 11(3), 361; https://doi.org/10.3390/rs11030361 - 11 Feb 2019

Cited by 26 | Viewed by 5038

Abstract

A in situ hyperspectral dataset containing multiple growth stages over multiple growing seasons was used to build paddy rice leaf area index (LAI) estimation models with a special focus on the effects of paddy rice growth stage development. The univariate regression method applied to the vegetation index (VI), the traditional multivariate calibration method of partial least squares regression (PLSR), and modern machine learning methods such as support vector regression (SVR), random forests (RF), and artificial neural networks (ANN) based on the original and first-derivative hyperspectral data were evaluated in this study for paddy rice LAI estimation. All the models were built on the whole growing season and on each separate vegetative, reproductive and ripening growth stage of paddy rice separately. To ensure a fair comparison, the models of the whole growing season were also validated on data for each separate growth stage of the standalone validation dataset. Moreover, the optimal band pairs for calculating narrowband difference vegetative index (DVI), normalized difference vegetation index (NDVI) and simple ratio vegetation index (SR) were determined for the whole growing season and for each separate growth stage separately. The results showed that for both the whole growing season and for each single growth stage, the red-edge and near-infrared band pairs are optimal for formulating the narrowband DVI, NDVI and SR. Among the four multivariate calibration methods, SVR and RF yielded more accurate results than the other two methods. The SVR and RF models built on first-derivative spectra provided more accurate results than the corresponding models on the original spectra for both whole growing season models and separate growth stage models. Comparing the prediction accuracy based on the whole growing season revealed that the RF and SVR models showed an advantage over the VI models. However, comparing the prediction accuracy based on each growth stage separately showed that the VI models provided more accurate results for the vegetative growth stages. The SVR and RF models provided more accurate results for the ripening growth stage. However, the whole growing season RF model on first-derivative spectra could provide reasonable accuracy for each single growth stage. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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18 pages, 4655 KiB

Open AccessArticle

Retrieval of High Spatiotemporal Resolution Leaf Area Index with Gaussian Processes, Wireless Sensor Network, and Satellite Data Fusion

by Gaofei Yin, Aleixandre Verger, Yonghua Qu, Wei Zhao, Baodong Xu, Yelu Zeng, Ke Liu, Jing Li and Qinhuo Liu

Remote Sens. 2019, 11(3), 244; https://doi.org/10.3390/rs11030244 - 24 Jan 2019

Cited by 15 | Viewed by 4100

Abstract

Many applications, including crop growth and yield monitoring, require accurate long-term time series of leaf area index (LAI) at high spatiotemporal resolution with a quantification of the associated uncertainties. We propose an LAI retrieval approach based on a combination of the LAINet observation system, the Consistent Adjustment of the Climatology to Actual Observations (CACAO) method, and Gaussian process regression (GPR). First, the LAINet wireless sensor network provides temporally continuous field measurements of LAI. Then, the CACAO approach generates synchronous reflectance data at high spatiotemporal resolution (30-m and 8-day) from the fusion of multitemporal MODIS and high spatial resolution Landsat satellite imagery. Finally, the GPR machine learning regression algorithm retrieves the LAI maps and their associated uncertainties. A case study in a cropland site in China showed that the accuracy of LAI retrievals is 0.36 (12.7%) in terms of root mean square error and R² = 0.88 correlation with ground measurements as evaluated over the entire growing season. This paper demonstrates the potential of the joint use of newly developed software and hardware technologies in deriving concomitant LAI and uncertainty maps with high spatiotemporal resolution. It will contribute to precision agriculture, as well as to the retrieval and validation of LAI products. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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20 pages, 4852 KiB

Open AccessArticle

A Recursive Update Model for Estimating High-Resolution LAI Based on the NARX Neural Network and MODIS Times Series

by Jian Wang, Jindi Wang, Yuechan Shi, Hongmin Zhou and Limin Liao

Remote Sens. 2019, 11(3), 219; https://doi.org/10.3390/rs11030219 - 22 Jan 2019

Cited by 6 | Viewed by 2836

Abstract

Leaf area index (LAI) remote sensing data products with a high resolution (HR) and long time series are in demand in a wide variety of applications. Compared with long time series LAI products with 1 km resolution, LAI products with high spatial resolution are difficult to acquire because of the lack of remote sensing observations in long-term sequences and the lack of estimation methods applicable to highly variable land-cover types. To address these problems, we proposed a recursive update model to estimate 30 m resolution LAI based on the updated Nonlinear Auto-Regressive with Exogenous Inputs (NARX) neural network and MODIS time series. First, we used a variety of HR satellite remote sensing observations to produce HR datasets for recent years. Historical low spatial resolution MODIS products were employed as background information and used to calculate the initial parameters of the NARX neural network for each pixel. Subsequently, one year’s reflectance from the HR dataset was used as the new observation that was input into the NARX model to estimate the HR LAI of that year, and the background and HR data were then used for remodeling to update the NARX model parameters. This procedure was recursively repeated year by year until both MODIS background data and all HR data were involved in the modeling. Finally, we obtained an LAI time series with 30 m resolution. In the cropland study area in Hebei Province, China, the results were compared with LAI measurements from ground sites in 2013 and 2014. A high degree of similarity existed between the results for the two study years (

{RMSE}_{2013} = 0.288

and

{RMSE}_{2014} = 0.296

). The HR LAI estimates showed favorable spatiotemporal continuity and were in good agreement with the multisample ground survey LAI measurements. The results indicated that for data with a rapid revisit cycle and high spatial resolution, the recursive update model based on the NARX neural network has excellent LAI estimation performance and fairly strong fault-tolerance capability. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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21 pages, 11170 KiB

Open AccessArticle

Assimilating Multiresolution Leaf Area Index of Moso Bamboo Forest from MODIS Time Series Data Based on a Hierarchical Bayesian Network Algorithm

by Luqi Xing, Xuejian Li, Huaqiang Du, Guomo Zhou, Fangjie Mao, Tengyan Liu, Junlong Zheng, Luofan Dong, Meng Zhang, Ning Han, Xiaojun Xu, Weiliang Fan and Di’en Zhu

Remote Sens. 2019, 11(1), 56; https://doi.org/10.3390/rs11010056 - 29 Dec 2018

Cited by 4 | Viewed by 11363

Abstract

The highly accurate multiresolution leaf area index (LAI) is an important parameter for carbon cycle simulation for bamboo forests at different scales. However, current LAI products have discontinuous resolution with 1 km mostly, that makes it difficult to accurately quantify the spatiotemporal evolution of carbon cycle at different resolutions. Thus, this study used MODIS LAI product (MOD15A2) and MODIS reflectance data (MOD09Q1) of Moso bamboo forest (MBF) from 2015, and it adopted a hierarchical Bayesian network (HBN) algorithm coupled with a dynamic LAI model and the PROSAIL model to obtain high-precision LAI data at multiresolution (i.e., 1000, 500, and 250 m). The results showed the LAIs assimilated using the HBN at the three resolutions corresponded with the actual growth trend of the MBF and correlated significantly with the observed LAI with a determination coefficient (R²) value of >0.80. The highest-precision assimilated LAI was obtained at 1000-m resolution with R² values of 0.91. The LAI assimilated using the HBN algorithm achieved better accuracy than the MODIS LAI with increases in the R² value of 2.7 times and decreases in the root mean square error of 87.8%. Therefore, the HBN algorithm applied in this study can effectively obtain highly accurate multiresolution LAI time series data for bamboo forest. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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30 pages, 6793 KiB

Open AccessArticle

Retrieval of Maize Leaf Area Index Using Hyperspectral and Multispectral Data

by Sosdito Mananze, Isabel Pôças and Mario Cunha

Remote Sens. 2018, 10(12), 1942; https://doi.org/10.3390/rs10121942 - 03 Dec 2018

Cited by 38 | Viewed by 5487

Abstract

Field spectra acquired from a handheld spectroradiometer and Sentinel-2 images spectra were used to investigate the applicability of hyperspectral and multispectral data in retrieving the maize leaf area index in low-input crop systems, with high spatial and intra-annual variability, and low yield, in southern Mozambique, during three years. Seventeen vegetation indices, comprising two and three band indices, and nine machine learning regression algorithms (MLRA) were tested for the statistical approach while five cost functions were tested in the look-up-table (LUT) inversion approach. The three band vegetation indices were selected, specifically the modified difference index (mDI_{d: 725; 715; 565}) for the hyperspectral dataset and the modified simple ratio (mSR_{c: 740; 705; 865}) for the multispectral dataset of field spectra and the three band spectral index (TBSI_{b: 665; 865; 783}) for the Sentinel-2 dataset. The relevant vector machine was the selected MLRA for the two datasets of field spectra (multispectral and hyperspectral) while the support vector machine was selected for the Sentinel-2 data. When using the LUT inversion technique, the minimum contrast estimation and the Bhattacharyya divergence cost functions were the best performing. The vegetation indices outperformed the other two approaches, with the TBSI_b as the most accurate index (RMSE = 0.35). At the field scale, spectral data from Sentinel-2 can accurately retrieve the maize leaf area index in the study area. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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14 pages, 2972 KiB

Open AccessArticle

Potential of Red Edge Spectral Bands in Future Landsat Satellites on Agroecosystem Canopy Green Leaf Area Index Retrieval

by Zhaoyu Cui and John P. Kerekes

Remote Sens. 2018, 10(9), 1458; https://doi.org/10.3390/rs10091458 - 12 Sep 2018

Cited by 44 | Viewed by 11401

Abstract

Vegetation biophysical parameter retrieval is an important earth remote sensing system application. In this paper, we studied the potential impact of the addition of new spectral bands in the red edge region in future Landsat satellites on agroecosystem canopy green leaf area index (LAI) retrieval. The test data were simulated from SPARC ‘03 field campaign HyMap hyperspectral data. Three retrieval approaches were tested: empirical regression based on vegetation index, physical model-based look-up-table (LUT) inversion, and machine learning. The results of all three approaches showed that a potential new spectral band located between the Landsat-8 Operational Land Imager (OLI) red and NIR bands slightly improved the agroecosystem green LAI retrieval accuracy (R² of 0.787 vs. 0.810 for vegetation index approach, 0.806 vs. 0.828 for LUT inversion approach, and 0.925 vs. 0.933 for machine learning approach). The results of this work are consistent with the conclusions from previous research on the value of Sentinel-2 red edge bands for agricultural green LAI retrieval. Full article

(This article belongs to the Special Issue Leaf Area Index (LAI) Retrieval using Remote Sensing)

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