A New Threshold-Based Method for Extracting Canopy Temperature from Thermal Infrared Images of Cork Oak Plantations

Canopy temperature (Tc) is used to characterize plant water physiology, and thermal infrared (TIR) remote sensing is a convenient technology for measuring Tc in forest ecosystems. However, the images produced through this method contain background pixels of forest gaps, thereby reducing the accuracy of Tc observations. Extracting Tc data from TIR images is of great significance for understanding changes in ecosystem water status. In this study, a temperature threshold method was developed to rapidly, accurately, and automatically extract forest canopy pixels for Tc data obtention. Specifically, this method takes the temperature corresponding to the point with a slope of 0.5 in the curve composed of the normalized average temperature and the normalized cumulative number of pixels as the segmentation threshold to separate the forest gap pixels from the forest canopy pixels in the TIR images and extract the separated forest canopy pixels based on the pixel coordinates for Tc data obtention. Taking the Tc values, measured using a thermocouple, as the standard, Tc extraction using the new temperature threshold method and traditional methods (the Otsu algorithm and direct extraction) was compared in cork oak plantations. The results showed that the temperature threshold method offered the highest extraction accuracy, followed by the direct extraction method and the Otsu algorithm. The temperature threshold method was determined to be the most suitable for extracting Tc data from the TIR images of cork oak plantations.

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A New Low-Cost Device Based on Thermal Infrared Sensors for Olive Tree Canopy Temperature Measurement and Water Status Monitoring

Remote Sensing ◽

10.3390/rs12040723 ◽

2020 ◽

Vol 12 (4) ◽

pp. 723 ◽

Cited By ~ 3

Author(s):

Miguel Noguera ◽

Borja Millán ◽

Juan José Pérez-Paredes ◽

Juan Manuel Ponce ◽

Arturo Aquino ◽

...

Keyword(s):

Water Stress ◽

Water Status ◽

Low Cost ◽

Canopy Temperature ◽

Olive Tree ◽

Thermal Infrared ◽

Tree Canopy ◽

Coefficient Of Determination ◽

Crop Water ◽

Olive Orchard

In recent years, many olive orchards, which are a major crop in the Mediterranean basin, have been converted into intensive or super high-density hedgerow systems. This configuration is more efficient in terms of yield per hectare, but at the same time the water requirements are higher than in traditional grove arrangements. Moreover, irrigation regulations have a high environmental (through water use optimization) impact and influence on crop quality and yield. The mapping of (spatio-temporal) variability with conventional water stress assessment methods is impractical due to time and labor constraints, which often involve staff training. To address this problem, this work presents the development of a new low-cost device based on a thermal infrared (IR) sensor for the measurement of olive tree canopy temperature and monitoring of water status. The performance of the developed device was compared to a commercial thermal camera. Furthermore, the proposed device was evaluated in a commercially managed olive orchard, where two different irrigation treatments were established: a full irrigation treatment (FI) and a regulated deficit irrigation (RDC), aimed at covering 100% and 50% of crop evapotranspiration (ETc), respectively. Predawn leaf water potential (ΨPD) and stomatal conductance (gs), two widely accepted indicators for crop water status, were regressed to the measured canopy temperature. The results were promising, reaching a coefficient of determination R2 ≥ 0.80. On the other hand, the crop water stress index (CWSI) was also calculated, resulting in a coefficient of determination R2 ≥ 0.79. The outcomes provided by the developed device support its suitability for fast, low-cost, and reliable estimation of an olive orchard’s water status, even suppressing the need for supervised acquisition of reference temperatures. The newly developed device can be used for water management, reducing water usage, and for overall improvements to olive orchard management.

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High resolution imaging of maize (Zea mays) leaf temperature in the field: the key role of the regions of interest

Functional Plant Biology ◽

10.1071/fp15024 ◽

2015 ◽

Vol 42 (9) ◽

pp. 858 ◽

Cited By ~ 5

Author(s):

Taha Jerbi ◽

Nathalie Wuyts ◽

Maria Angela Cane ◽

Philippe-François Faux ◽

Xavier Draye

Keyword(s):

Zea Mays ◽

Water Status ◽

Canopy Temperature ◽

Regions Of Interest ◽

Average Temperature ◽

Remote Sensors ◽

Single Leaf ◽

Mutual Shading ◽

Resolution Imaging

The use of remote sensors (thermometers and cameras) to analyse crop water status in field conditions is fraught with several difficulties. In particular, average canopy temperature measurements are affected by the mixture of soil and green regions, the mutual shading of leaves and the variability of absorbed radiation. The aim of the study was to analyse how the selection of different ‘regions of interest’ (ROI) in canopy images affect the variability of the resulting temperature averages. Using automated image segmentation techniques we computed the average temperature in four nested ROI of decreasing size, from the whole image down to the sunlit fraction of a leaf located in the upper part of the canopy. The study was conducted on maize (Zea mays L.) at the flowering stage, for its large leaves and well structured canopy. Our results suggest that, under these conditions, the ROI comprising the sunlit fraction of a leaf located in the upper part of the canopy should be analogous to the single leaf approach (in controlled conditions) that allows the estimation of stomatal conductance or plant water potential.

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Indirect Measurement of Forest Canopy Temperature by Handheld Thermal Infrared Imager through Upward Observation

Remote Sensing ◽

10.3390/rs12213559 ◽

2020 ◽

Vol 12 (21) ◽

pp. 3559

Author(s):

Anni Su ◽

Jianbo Qi ◽

Huaguo Huang

Keyword(s):

Measurement Method ◽

Forest Canopy ◽

Atmospheric Correction ◽

Canopy Temperature ◽

Thermal Infrared ◽

Absolute Error ◽

Indirect Measurement ◽

True Temperature ◽

Infrared Imager ◽

Thermal Infrared Imager

The influence of leaf temperature on transpiration, photosynthesis, respiration, and other metabolic activities is critical to plant growth, development, production and distribution. However, traditional measurement of canopy temperature by thermocouples or thermal infrared thermometers is laborious and difficult, especially for tall trees. The recent development of a handheld thermal infrared imager has made it possible to perform high temporal and spatial canopy temperature measurements efficiently. However, the signal recorded by the sensor is often a mixture of radiation from the target and the atmosphere, which must be corrected to get the true temperature. In this study, we propose a ground-based indirect measurement method of canopy temperature by a handheld thermal infrared imager through upward observation. Visible and thermal images are combined to distinguish the canopy pixels and sky pixels. To remove the atmospheric radiation from the sky, an empirical atmospheric model is established, which can perform atmospheric correction accurately and efficiently. To validate the proposed method, we collected canopy temperatures of 36 species of trees with a FLIR T420 thermal infrared imager and compared the estimated temperatures with those directly measured by thermocouples. The accuracy of the corrected canopy temperature has been significantly improved with mean absolute error reduced from 3.73 °C to 0.64 °C. This proposed canopy temperature measurement method can be used to various applications in remote sensing product validation, and ecosystem and forestry studies.

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Spatial and Temporal Variation Characteristics of Snowfall in the Haihe River Basin from 1960 to 2016

Water ◽

10.3390/w13131798 ◽

2021 ◽

Vol 13 (13) ◽

pp. 1798

Author(s):

Xu Wu ◽

Su Li ◽

Bin Liu ◽

Dan Xu

Keyword(s):

Temporal Variation ◽

River Basin ◽

Spatial And Temporal Variation ◽

Haihe River Basin ◽

Temperature Threshold ◽

Threshold Method ◽

Exponential Equation ◽

Haihe River ◽

The Haihe River Basin ◽

Different Levels

The spatio-temporal variation of precipitation under global warming had been a research hotspot. Snowfall is an important part of precipitation, and its variabilities and trends in different regions have received great attention. In this paper, the Haihe River Basin is used as a case, and we employ the K-means clustering method to divide the basin into four sub-regions. The double temperature threshold method in the form of the exponential equation is used in this study to identify precipitation phase states, based on daily temperature, snowfall, and precipitation data from 43 meteorological stations in and around the Haihe River Basin from 1960 to 1979. Then, daily snowfall data from 1960 to 2016 are established, and the spatial and temporal variation of snowfall in the Haihe River Basin are analyzed according to the snowfall levels as determined by the national meteorological department. The results evalueted in four different zones show that (1) the snowfall at each meteorological station can be effectively estimated at an annual scale through the exponential equation, for which the correlation coefficient of each division is above 0.95, and the relative error is within 5%. (2) Except for the average snowfall and light snowfall, the snowfall and snowfall days of moderate snow, heavy snow, and snowstorm in each division are in the order of Zones III > IV > I > II. (3) The snowfall and the number of snowfall days at different levels both show a decreasing trend, except for the increasing trend of snowfall in Zone I. (4) The interannual variation trend in the snowfall at the different levels are not obvious, except for Zone III, which shows a significant decreasing trend.

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Association between meteorological factors and reported cases of hand, foot, and mouth disease from 2000 to 2015 in Japan

Epidemiology and Infection ◽

10.1017/s0950268817001820 ◽

2017 ◽

Vol 145 (14) ◽

pp. 2896-2911 ◽

Cited By ~ 11

Author(s):

A. SUMI ◽

S. TOYODA ◽

K. KANOU ◽

T. FUJIMOTO ◽

K. MISE ◽

...

Keyword(s):

Relative Humidity ◽

Foot And Mouth Disease ◽

Entropy Method ◽

Temperature Data ◽

Mouth Disease ◽

Lower Threshold ◽

Control Measures ◽

Temperature Threshold ◽

Average Temperature ◽

Foot And Mouth

SUMMARYThe purpose of this study was to clarify the association between hand, foot, and mouth disease (HFMD) epidemics and meteorological conditions. We used HFMD surveillance data of all 47 prefectures in Japan from January 2000 to December 2015. Spectral analysis was performed using the maximum entropy method (MEM) for temperature-, relative humidity-, and total rainfall-dependent incidence data. Using MEM-estimated periods, long-term oscillatory trends were calculated using the least squares fitting (LSF) method. The temperature and relative humidity thresholds of HFMD data were estimated from the LSF curves. The average temperature data indicated a lower threshold at 12 °C and a higher threshold at 30 °C for risk of HFMD infection. Maximum and minimum temperature data indicated a lower threshold at 6 °C and a higher threshold at 35 °C, suggesting a need for HFMD control measures at temperatures between 6 and 35 °C. Based on our findings, we recommend the use of maximum and minimum temperatures rather than the average temperature, to estimate the temperature threshold of HFMD infections. The results obtained might aid in the prediction of epidemics and preparation for the effect of climatic changes on HFMD epidemiology.

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CANOPY TEMPERATURE AS AN INDICATOR OF WATER STATUS IN CITRUS TREES

Acta Horticulturae ◽

10.17660/actahortic.2011.889.42 ◽

2011 ◽

pp. 347-353 ◽

Cited By ~ 2

Author(s):

F. Stagno ◽

A. Giuffrida ◽

F. Intrigliolo

Keyword(s):

Water Status ◽

Canopy Temperature ◽

Citrus Trees

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Microtensiometers Accurately Measure Stem Water Potential in Woody Perennials

Plants ◽

10.3390/plants10122780 ◽

2021 ◽

Vol 10 (12) ◽

pp. 2780

Author(s):

Victor Blanco ◽

Lee Kalcsits

Keyword(s):

Water Potential ◽

Leaf Gas Exchange ◽

Water Status ◽

Full Range ◽

Canopy Temperature ◽

Plant Water ◽

Stem Water Potential ◽

Woody Tissue ◽

Woody Perennials ◽

Stem Water

Stem water potential (Ψstem) is considered to be the standard measure of plant water status. However, it is measured with the pressure chamber (PC), an equipment that can neither provide continuous information nor be automated, limiting its use. Recent developments of microtensiometers (MT; FloraPulse sensors), which can continuously measure water tension in woody tissue of the trunk of the tree, can potentially highlight the dynamic nature of plant water relations. Thus, this study aimed to validate and assess the usefulness of the MT by comparing the Ψstem provided by MT with those same measurements from the PC. Here, two irrigation treatments (a control and a deficit treatment) were applied in a pear (Pyrus communis L.) orchard in Washington State (USA) to capture the full range of water potentials in this environment. Discrete measurements of leaf gas exchange, canopy temperature and Ψstem measured with PC and MT were made every two hours for four days from dawn to sunset. There were strong linear relationships between the Ψstem-MT and Ψstem-PC (R2 > 0.8) and with vapor pressure deficit (R2 > 0.7). However, Ψstem-MT was more variable and lower than Ψstem-PC when Ψstem-MT was below −1.5 MPa, especially during the evening. Minimum Ψstem-MT occurred later in the afternoon compared to Ψstem-PC. Ψstem showed similar sensitivity and coefficients of variation for both PC and MT acquired data. Overall, the promising results achieved indicated the potential for MT to be used to continuously assess tree water status.

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On-the-go thermal imaging for water status assessment in commercial vineyards

Advances in Animal Biosciences ◽

10.1017/s204047001700108x ◽

2017 ◽

Vol 8 (2) ◽

pp. 520-524

Author(s):

S. Gutiérrez ◽

M. P. Diago ◽

J. Fernández-Novales ◽

J. Tardaguila

Keyword(s):

Thermal Imaging ◽

Water Status ◽

Canopy Temperature ◽

Stress Index ◽

Coefficient Of Determination ◽

Stem Water Potential ◽

Water Stress Index ◽

Status Assessment ◽

Commercial Vineyard ◽

East And West

The goal of this work was the assessment of commercial vineyard water status using on-the-go thermal imaging. On-the-go thermal imaging acquisition was conducted with a thermal camera operating at 1.20 m distance from the canopy, mounted on a quad moving at 5 km/h. Canopy temperature, cross water stress index (CWSI) and stomatal conductance index (Ig) were strongly and significantly correlated to stem water potential (Ψstem) in east and west side of the canopy. For CWSI, the values of the coefficient of determination (R2) were 0.88*** and 0.73*** for east and west sides, respectively. As regards the index Ig, its relationships with Ψstem showed R2=0.89*** and R2=0.77*** for east and west sides, respectively. These results are promising and evidence the potential of on-the-go thermal imaging to become a new tool to evaluate the vineyard water status.

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Thermal Imaging Reliability for Estimating Grain Yield and Carbon Isotope Discrimination in Wheat Genotypes: Importance of the Environmental Conditions

Sensors ◽

10.3390/s19122676 ◽

2019 ◽

Vol 19 (12) ◽

pp. 2676 ◽

Cited By ~ 3

Author(s):

Sebastián Romero-Bravo ◽

Ana María Méndez-Espinoza ◽

Miguel Garriga ◽

Félix Estrada ◽

Alejandro Escobar ◽

...

Keyword(s):

Grain Yield ◽

Thermal Imaging ◽

Mediterranean Climate ◽

Vapor Pressure Deficit ◽

Stress Condition ◽

Water Status ◽

Canopy Temperature ◽

Spring Bread Wheat ◽

Wheat Genotypes ◽

The Relationship

Canopy temperature (Tc) by thermal imaging is a useful tool to study plant water status and estimate other crop traits. This work seeks to estimate grain yield (GY) and carbon discrimination (Δ13C) from stress degree day (SDD = Tc − air temperature, Ta), considering the effect of a number of environmental variables such as the averages of the maximum vapor pressure deficit (VPDmax) and the ambient temperature (Tmax), and the soil water content (SWC). For this, a set of 384 and a subset of 16 genotypes of spring bread wheat were evaluated in two Mediterranean-climate sites under water stress (WS) and full irrigation (FI) conditions, in 2011 and 2012, and 2014 and 2015, respectively. The relationship between the GY of the 384 wheat genotypes and SDD was negative and highly significant in 2011 (r2 = 0.52 to 0.68), but not significant in 2012 (r2 = 0.03 to 0.12). Under WS, the average GY, Δ13C, and SDD of wheat genotypes growing in ten environments were more associated with changes in VPDmax and Tmax than with the SWC. Therefore, the amount of water available to the plant is not enough information to assume that a particular genotype is experiencing a stress condition.

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Assessing canopy temperature-based water stress indices for soybeans under subhumid conditions

10.5194/egusphere-egu2020-16325 ◽

2020 ◽

Author(s):

Angela Morales Santos ◽

Reinhard Nolz

Keyword(s):

Water Stress ◽

Soil Water ◽

Water Status ◽

Canopy Temperature ◽

Irrigation Scheduling ◽

Stress Index ◽

Crop Water ◽

Stress Indices ◽

Soil Water Status ◽

Crop Water Stress

Sustainable irrigation water management is expected to accurately meet crop water requirements in order to avoid stress and, consequently, yield reduction, and at the same time avoid losses of water and nutrients due to deep percolation and leaching. Sensors to monitor soil water status and plant water status (in terms of canopy temperature) can help planning irrigation with respect to time and amounts accordingly. The presented study aimed at quantifying and comparing crop water stress of soybeans irrigated by means of different irrigation systems under subhumid conditions.The study site was located in Obersiebenbrunn, Lower Austria, about 30 km east of Vienna. The region is characterized by a mean temperature of 10.5&#176;C with increasing trend due to climate change and mean annual precipitation of 550 mm. The investigations covered the vegetation period of soybean in 2018, from planting in April to harvest in September. Measurement data included precipitation, air temperature, relative humidity and wind velocity. The experimental field of 120x120 m2 has been divided into four sub-areas: a plot of 14x120&#160;m2 with drip irrigation (DI), 14x120&#160;m2 without irrigation (NI), 36x120&#160;m2 with sprinkler irrigation (SI), and 56x120&#160;m2 irrigated with a hose reel boom with nozzles (BI). A total of 128, 187 and 114 mm of water were applied in three irrigation events in the plots DI, SI and BI, respectively. Soil water content was monitored in 10&#160;cm depth (HydraProbe, Stevens Water) and matric potential was monitored in 20, 40 and 60&#160;cm depth (Watermark, Irrometer). Canopy temperature was measured every 15&#160;minutes using infrared thermometers (IRT; SI-411, Apogee Instruments). The IRTs were installed with an inclination of 45&#176; at 1.8&#160;m height above ground. Canopy temperature-based water stress indices for irrigation scheduling have been successfully applied in arid environments, but their use is limited in humid areas due to low vapor pressure deficit (VPD). To quantify stress in our study, the Crop Water Stress Index (CWSI) was calculated for each plot and compared to the index resulting from the Degrees Above Canopy Threshold (DACT) method. Unlike the CWSI, the DACT method does not consider VPD to provide a stress index nor requires clear sky conditions. The purpose of the comparison was to revise an alternative method to the CWSI that can be applied in a humid environment.CWSI behaved similar for the four sub-areas. As expected, CWSI &#8805; 1 during dry periods (representing severe stress) and it decreased considerably after precipitation or irrigation (representing no stress). The plot with overall lower stress was BI, producing the highest yield of the four plots. Results show that DACT may be a more suitable index since all it requires is canopy temperature values and has strong relationship with soil water measurements. Nevertheless, attention must be paid when defining canopy temperature thresholds. Further investigations include the development and test of a decision support system for irrigation scheduling combining both, plant-based and soil water status indicators for water use efficiency analysis.

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