Hyperspectral Reflectance Characteristics of Rice Canopies under Changes in Diffuse Radiation Fraction

To analyze the hyperspectral reflectance characteristics of rice canopies under changes in diffuse radiation fraction, experiments using different cover materials were performed in Nanjing, China, during 2016 and 2017. Each year, two treatments with different reduction ratios of diffuse radiation fraction but with similar shading rates were set in the field experiment: In T1, total solar radiation shading rate was 14.10%, and diffuse radiation fraction was 31.09%; in T2, total solar radiation shading rate was 14.42%, and diffuse radiation fraction was 39.98%, respectively. A non-shading treatment was included as a control (CK). Canopy hyperspectral reflectance, soil and plant analyzer development (SPAD), and leaf area index (LAI) were measured under shading treatments on different days after heading. The red-edge parameters (position, λ0; maximum amplitude, Dλ; area, α0; width, σ) were calculated, as well as the area, depth, and width of three absorption bands. The location of the first absorption band appeared in the range of 553–788 nm, and the second and third absorption bands appeared in the range of 874–1257 nm. The results show that the shading treatment had a significant effect on the rice canopy’s hyperspectral reflectance. Compared with CK, the canopy reflectance of T1 (the diffuse radiation fraction was 31.09%) and T2 (the diffuse radiation fraction was 39.98%) decreased in the visible light range (350–760 nm) and increased in the near-infrared range (800–1350 nm), while the red-edge parameters (λ0, Dλ, α0), SPAD, and LAI increased. On the other hand, under shading treatment, the increase in diffuse radiation fraction also had a significant impact on the hyperspectral spectra of the rice canopy, especially at 14 days after heading. Compared with T1, the green peak (550 nm) of T2 reduced by 16.12%, and the average reflectance at 800–900 nm increased by 10%. Based on correlation analysis, it was found that these hyperspectral reflectance characteristics were mainly due to the increase in SPAD (2.31%) and LAI (7.62%), which also led to the increase in Dλ (8.70%) and α0 (13.89%). Then, the second and third absorption features of T2 were significantly different from that of T1, which suggests that the change in diffuse radiation fraction could affect the process of water vapor absorption by rice.

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Spaceborne Estimation of Leaf Area Index in Cotton, Tomato, and Wheat Using Sentinel-2

Land ◽

10.3390/land10050505 ◽

2021 ◽

Vol 10 (5) ◽

pp. 505

Author(s):

Gregoriy Kaplan ◽

Offer Rozenstein

Keyword(s):

Water Vapor ◽

Leaf Area Index ◽

Leaf Area ◽

Vegetation Index ◽

Near Infrared ◽

Linear Regression Models ◽

Area Index ◽

Estimation Performance ◽

Red Edge ◽

Sentinel 2

Satellite remote sensing is a useful tool for estimating crop variables, particularly Leaf Area Index (LAI), which plays a pivotal role in monitoring crop development. The goal of this study was to identify the optimal Sentinel-2 bands for LAI estimation and to derive Vegetation Indices (VI) that are well correlated with LAI. Linear regression models between time series of Sentinel-2 imagery and field-measured LAI showed that Sentinel-2 Band-8A—Narrow Near InfraRed (NIR) is more accurate for LAI estimation than the traditionally used Band-8 (NIR). Band-5 (Red edge-1) showed the lowest performance out of all red edge bands in tomato and cotton. A novel finding was that Band 9 (Water vapor) showed a very high correlation with LAI. Bands 1, 2, 3, 4, 5, 11, and 12 were saturated at LAI ≈ 3 in cotton and tomato. Bands 6, 7, 8, 8A, and 9 were not saturated at high LAI values in cotton and tomato. The tomato, cotton, and wheat LAI estimation performance of ReNDVI (R2 = 0.79, 0.98, 0.83, respectively) and two new VIs (WEVI (Water vapor red Edge Vegetation Index) (R2 = 0.81, 0.96, 0.71, respectively) and WNEVI (Water vapor narrow NIR red Edge Vegetation index) (R2 = 0.79, 0.98, 0.79, respectively)) were higher than the LAI estimation performance of the commonly used NDVI (R2 = 0.66, 0.83, 0.05, respectively) and other common VIs tested in this study. Consequently, reNDVI, WEVI, and WNEVI can facilitate more accurate agricultural monitoring than traditional VIs.

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VIS-NIR, Red-Edge and NIR-Shoulder Based Normalized Vegetation Indices Response to Co-Varying Leaf and Canopy Structural Traits in Heterogeneous Grasslands

Remote Sensing ◽

10.3390/rs12142254 ◽

2020 ◽

Vol 12 (14) ◽

pp. 2254 ◽

Cited By ~ 1

Author(s):

Hafiz Ali Imran ◽

Damiano Gianelle ◽

Duccio Rocchini ◽

Michele Dalponte ◽

M. Pilar Martín ◽

...

Keyword(s):

Near Infrared ◽

Spatial Scales ◽

Vegetation Indices ◽

Radiative Transfer Model ◽

Transfer Model ◽

Sharp Change ◽

Full Potential ◽

Area Index ◽

Red Edge ◽

Temporal And Spatial

Red-edge (RE) spectral vegetation indices (SVIs)—combining bands on the sharp change region between near infrared (NIR) and visible (VIS) bands—alongside with SVIs solely based on NIR-shoulder bands (wavelengths 750–900 nm) have been shown to perform well in estimating leaf area index (LAI) from proximal and remote sensors. In this work, we used RE and NIR-shoulder SVIs to assess the full potential of bands provided by Sentinel-2 (S-2) and Sentinel-3 (S-3) sensors at both temporal and spatial scales for grassland LAI estimations. Ground temporal and spatial observations of hyperspectral reflectance and LAI were carried out at two grassland sites (Monte Bondone, Italy, and Neustift, Austria). A strong correlation (R2 > 0.8) was observed between grassland LAI and both RE and NIR-shoulder SVIs on a temporal basis, but not on a spatial basis. Using the PROSAIL Radiative Transfer Model (RTM), we demonstrated that grassland structural heterogeneity strongly affects the ability to retrieve LAI, with high uncertainties due to structural and biochemical PTs co-variation. The RENDVI783.740 SVI was the least affected by traits co-variation, and more studies are needed to confirm its potential for heterogeneous grasslands LAI monitoring using S-2, S-3, or Gaofen-5 (GF-5) and PRISMA bands.

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Evaluation of Different Radiation and Albedo Models for the Prediction of Solar Radiation Incident on Tilted Surfaces, for Four European Locations

Journal of Solar Energy Engineering ◽

10.1115/1.2870939 ◽

1996 ◽

Vol 118 (3) ◽

pp. 183-189 ◽

Cited By ~ 10

Author(s):

B. E. Psiloglou ◽

C. A. Balaras ◽

M. Santamouris ◽

D. N. Asimakopoulos

Keyword(s):

Solar Radiation ◽

Diffuse Radiation ◽

Vertical Surface ◽

Mean Bias Error ◽

Bias Error ◽

Total Solar Radiation ◽

Total Radiation ◽

Radiation Incident ◽

Tilted Surface ◽

Significant Difference

The diffuse radiation incident on an inclined surface is composed of both the sky diffuse radiation and the ground-reflected radiation. Depending on the model used to calculate the sky diffuse radiation and the estimated albedo value, it is possible to introduce a significant error in the prediction of the total radiation incident on a tilted surface. Twelve sky diffuse submodels associated with four different albedo submodels are used to estimate the total radiation on the tilted surface from data on the horizontal plane. The predicted total solar radiation values are compared with measured data on a south facing vertical surface, from four representative south and north European locations. Root mean square error, mean bias error, and a t-test are used to determine the intrinsic performance of each combination of diffuse tilt and albedo submodel. Accordingly, the various model combinations do not exhibit a statistically significant difference between measured and calculated values.

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Developing and Evaluation of Various Correlations for Diffuse Solar Radiation for Urla (Izmir, Turkey)

Journal of Solar Energy Engineering ◽

10.1115/1.4007855 ◽

2012 ◽

Vol 135 (2) ◽

Cited By ~ 6

Author(s):

Orhan Ekren

Keyword(s):

Solar Radiation ◽

Solar Energy ◽

Tracking System ◽

Diffuse Radiation ◽

Energy System ◽

Solar Irradiation ◽

Total Solar Radiation ◽

Total Radiation ◽

Diffuse Solar Radiation ◽

Tilted Surface

Characteristics of site-specific solar irradiation is required to optimize a solar energy system. If no tracking system is used, the amount of electricity or heat produced by solar energy depends on the total solar radiation on a tilted surface. Although pyranometer measures direct plus diffuse solar radiation on a horizontal surface, there are many locations where diffuse radiation is not measured. Also, diffuse radiation is necessary to determine the total radiation on a tilted surface. Therefore, in this study, new correlations for diffuse solar radiation is proposed as a function of atmospheric parameters for Urla (Izmir, Turkey). After applying the statistical procedure on the measured data, seven new correlations are proposed for the ratio of hourly average diffuse and total radiation. Also, the ratio of monthly average daily diffuse and total radiation for this region is proposed.

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Accurately Shaping Supercontinuum Spectrum via Cascaded PCF

Sensors ◽

10.3390/s20092478 ◽

2020 ◽

Vol 20 (9) ◽

pp. 2478

Author(s):

Jifang Rong ◽

Hua Yang ◽

Yuzhe Xiao

Keyword(s):

Photonic Crystal ◽

Pump Power ◽

Near Infrared ◽

Cost Effective ◽

Infrared Range ◽

Crystal Fiber ◽

Red Edge ◽

Supercontinuum Spectrum ◽

Cost Effective Alternative ◽

Near Infrared Range

Shaping is very necessary in order to obtain a wide and flat supercontinuum (SC). Via numerical simulations, we accurately demonstrated shaping the SC using the fiber cascading method to significantly increase the width as well as the flatness of the spectrum in silica photonic crystal fiber (PCF). The cascaded PCF contains two segments, each of which has dual zero-dispersion frequencies (ZDFs). The spectral range of the SC can be expanded tremendously by tuning the spacing between the two ZDFs of the first segmented cascaded PCF. Increasing the pump power generates more solitons at the red edge, which accelerates solitons trapping and improves the spectral flatness of the blue edge. Furthermore, cascading the second segmented PCF by choosing appropriate fiber parameters ensures the flatness of the red end of SC. Therefore, a cost-effective alternative method for broad and flat supercontinuum generation in the near-infrared range is proposed here, which can be implemented easily in any photonics laboratory, where dual ZDFs PCFs are commonly found.

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Long-term variations in solar radiation, diffuse radiation, and diffuse radiation fraction caused by aerosols in China during 1961–2016

PLoS ONE ◽

10.1371/journal.pone.0250376 ◽

2021 ◽

Vol 16 (5) ◽

pp. e0250376

Author(s):

Hongfei Xie ◽

Junfang Zhao ◽

Kaili Wang ◽

Huiwen Peng

Keyword(s):

Solar Radiation ◽

Atmospheric Aerosols ◽

Terrestrial Ecosystem ◽

Diffuse Radiation ◽

Total Solar Radiation ◽

Total Radiation ◽

Negative Effects ◽

Positive Effects ◽

Sunshine Hours ◽

The Impact

The effects of atmospheric aerosols on the terrestrial climate system are more regional than those of greenhouse gases, which are more global. Thus, it is necessary to examine the typical regional effects of how aerosols affect solar radiation in order to develop a more comprehensive understanding. In this study, we used global AErosol RObotic NETwork (AERONET) data and robust radiation observational evidence to investigate the impact of aerosols on total radiation, diffuse radiation, and the diffuse radiation fraction in China from 1961 to 2016. Our results showed that there were different temporal changes in the aerosol optical depth (AOD), total solar radiation, diffuse radiation and diffuse radiation fraction over the past 56 years. Specifically, the 550 nm AOD from 2005 to 2016 decreased significantly, with annual average AOD of 0.51. Meanwhile, the average total solar radiation reduced by 2.48%, while there was a slight increase in average diffuse radiation at a rate of 3.10 MJ·m-2·yr-1. Moreover, the spatial heterogeneities of AOD, total radiation, diffuse radiation, and the diffuse radiation fraction in China were significant. Aerosol particle emissions in the developed eastern and southern regions of China were more severe than those in the western regions, resulting in higher total radiation and diffuse radiation in the western plateau than in the eastern plain. In addition, aerosols were found to have negative effects on total radiation and sunshine hours, and positive effects on diffuse radiation and diffuse radiation fraction. Further, the diffuse radiation fraction was negatively correlated with sunshine hours. However, there was a positive correlation between AOD and sunshine hours. These results could be used to assess the impacts of climate change on terrestrial ecosystem productivity and carbon budgets.

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Color Assessment of Facing Brick by UV-VIS-NIR Spectroscopy

Stroitel nye Materialy ◽

10.31659/0585-430x-2020-787-12-16-20 ◽

2020 ◽

Vol 787 (12) ◽

pp. 16-20

Author(s):

D.I. Shchikaltsova ◽

◽

Yu.T. Platov ◽

V.A. Rassulov ◽

R.A. Platova ◽

...

Keyword(s):

Absorption Band ◽

Near Infrared ◽

Diffuse Reflection ◽

Nir Spectroscopy ◽

Infrared Range ◽

Absorption Bands ◽

Absorption Intensity ◽

Wide Absorption Band ◽

Near Infrared Range ◽

Facing Brick

Diffuse reflection UV-VIS-NIR spectroscopy was used to study changes in the color of facing bricks from the content of the additive of manganese tetraoxide (Mn3O4) into the ceramic mass. This investigation was shown that with an increase of the additive content, both the intensity of the absorption bands of colored bricks corresponding to hematite decreases, and the absorption intensity increases with a shift in the maximum of the wide absorption band from the visible to the near-infrared range of the spectrum. By changing the values of the color coordinates in the CIE L*a*b* and Mansell systems: lightness and color, and the values of the indicator-relative color ability, it is fixed that the color of a brick depends on the ratio of two pigments: yellowish-red of hematite and black, probably jacobsite in its composition.

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Sentinel-2 Data for Precision Agriculture?—A UAV-Based Assessment

Sensors ◽

10.3390/s21082861 ◽

2021 ◽

Vol 21 (8) ◽

pp. 2861

Author(s):

Josephine Bukowiecki ◽

Till Rose ◽

Henning Kage

Keyword(s):

Precision Agriculture ◽

Near Infrared ◽

Absolute Error ◽

Yield Data ◽

Area Index ◽

Crop Monitoring ◽

Red Edge ◽

Using Data ◽

Simple Ratio ◽

Sentinel 2

An approach of exploiting and assessing the potential of Sentinel-2 data in the context of precision agriculture by using data from an unmanned aerial vehicle (UAV) is presented based on a four-year dataset. An established model for the estimation of the green area index (GAI) of winter wheat from a UAV-based multispectral camera was used to calibrate the Sentinel-2 data. Large independent datasets were used for evaluation purposes. Furthermore, the potential of the satellite-based GAI-predictions for crop monitoring and yield prediction was tested. Therefore, the total absorbed photosynthetic radiation between spring and harvest was calculated with satellite and UAV data and correlated with the final grain yield. Yield maps at the same resolution were generated by combining yield data on a plot level with a UAV-based crop coverage map. The best tested model for satellite-based GAI-prediction was obtained by combining the near-, infrared- and Red Edge-waveband in a simple ratio (R2 = 0.82, mean absolute error = 0.52 m2/m2). Yet, the Sentinel-2 data seem to depict average GAI-developments through the seasons, rather than to map site-specific variations at single acquisition dates. The results show that the lower information content of the satellite-based crop monitoring might be mainly traced back to its coarser Red Edge-band. Additionally, date-specific effects within the Sentinel-2 data were detected. Due to cloud coverage, the temporal resolution was found to be unsatisfactory as well. These results emphasize the need for further research on the applicability of the Sentinel-2 data and a cautious use in the context of precision agriculture.

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Characterization of CNx Thin Films Synthesized by Laser Ablation Technique

Materials Science Forum ◽

10.4028/www.scientific.net/msf.609.265 ◽

2009 ◽

Vol 609 ◽

pp. 265-268 ◽

Cited By ~ 1

Author(s):

N. Zouadi ◽

Samira Abdelli-Messaci ◽

N. Gabouze ◽

Tahar Kerdja ◽

D. Bradai

Keyword(s):

Thin Films ◽

Laser Ablation ◽

Carbon Nitride ◽

Near Infrared ◽

Infrared Range ◽

Absorption Bands ◽

Ablation Technique ◽

Krf Excimer Laser ◽

Laser Ablation Technique

In this work we report the optical characteristics of carbon nitride films produced by a KrF excimer laser ablation technique. The ablated materials were collected on different wafers, glass and porous silicon for different N2 pressures (0.1-0.5mbar). The thin films were synthesized at room temperature. The deposited thin films were characterized by spectrophotometry, ellipsometry, scanning electron microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The results show that the optical band gap deduced from optical transmission spectra in the ultraviolet- visible – near infrared range increases with deposition time and with nitrogen pressures increasing. SEM observation indicates that the CNx film is granular. Finally, FTIR spectra reveal carbon nitride absorption bands which do not seem change considerably with N2 pressures.

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Estimating Leaf Area Index with a New Vegetation Index Considering the Influence of Rice Panicles

Remote Sensing ◽

10.3390/rs11151809 ◽

2019 ◽

Vol 11 (15) ◽

pp. 1809 ◽

Cited By ~ 3

Author(s):

He ◽

Zhang ◽

Su ◽

Lu ◽

Yao ◽

...

Keyword(s):

Leaf Area Index ◽

Leaf Area ◽

Spectral Reflectance ◽

Vegetation Index ◽

Near Infrared ◽

Visible Region ◽

Canopy Reflectance ◽

Area Index ◽

Red Edge ◽

Rice Panicles

The emergence of rice panicle substantially changes the spectral reflectance of rice canopy and, as a result, decreases the accuracy of leaf area index (LAI) that was derived from vegetation indices (VIs). From a four-year field experiment with using rice varieties, nitrogen (N) rates, and planting densities, the spectral reflectance characteristics of panicles and the changes in canopy reflectance after panicle removal were investigated. A rice “panicle line”—graphical relationship between red-edge and near-infrared bands was constructed by using the near-infrared and red-edge spectral reflectance of rice panicles. Subsequently, a panicle-adjusted renormalized difference vegetation index (PRDVI) that was based on the “panicle line” and the renormalized difference vegetation index (RDVI) was developed to reduce the effects of rice panicles and background. The results showed that the effects of rice panicles on canopy reflectance were concentrated in the visible region and the near-infrared region. The red band (670 nm) was the most affected by panicles, while the red-edge bands (720–740 nm) were less affected. In addition, a combination of near-infrared and red-edge bands was for the one that best predicted LAI, and the difference vegetation index (DI) (976, 733) performed the best, although it had relatively low estimation accuracy (R2 = 0.60, RMSE = 1.41 m2/m2). From these findings, correcting the near-infrared band in the RDVI by the panicle adjustment factor (θ) developed the PRDVI, which was obtained while using the “panicle line”, and the less-affected red-edge band replaced the red band. Verification data from an unmanned aerial vehicle (UAV) showed that the PRDVI could minimize the panicle and background influence and was more sensitive to LAI (R2 = 0.77; RMSE = 1.01 m2/m2) than other VIs during the post-heading stage. Moreover, of all the assessed VIs, the PRDVI yielded the highest R2 (0.71) over the entire growth period, with an RMSE of 1.31 (m2/m2). These results suggest that the PRDVI is an efficient and suitable LAI estimation index.

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