A comparison of cylindrical and flat plate sensors for surface wetness duration

Gillespie, T. J.; Duan, R.-X

doi:10.1016/0168-1923(87)90055-4

Cited by 32 publications

(33 citation statements)

References 7 publications

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“…Hourly average values of wetness duration and air temperature were also measured in a maize canopy at a height of 1.5 m, near the position of maize ears (total canopy height about 2.5 m). The temperature sensors were shielded thermistors and the wetness sensors followed the design of Gillespie and Duan (1987), where the presence of liquid water modifies the electrical impedance between adjacent wires wound onto a cylinder about 10 cm long and 1 cm in diameter. The cylinder was painted an appropriate shade of green to mimic the drying rate of liquid water on nearby ears.…”

Section: Methodsmentioning

confidence: 99%

Estimating wetness duration on maize ears from meteorological observations

Rao¹,

Gillespie²,

Schaafsma³

1998

Can. J. Soil. Sci.

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Estimating wetness duration on maize ears from meteorological observations. Can. J. Soil Sci. 78: 149-154. The onset and cessation of surface wetness on maize ears were simulated with six models, using hourly meteorological data, to examine the linkage between wetness duration and possible forecasting of fungal infections that produce mycotoxins. Two threshold models (using relative humidity and dew point temperature), one regression model (using humidity and wind speed), and three physical models based on the energy balance approach, were compared. Also, spatial and temporal variability in wetness duration was measured and simulated at three sites located at distances up to 29 km from a central weather station. The estimated wetness values were compared with observations from cylindrical wetness sensors placed near ear level in maize canopies. The results relate to potential mycotoxin warning systems and indicate that threshold models can provide reasonable estimates of ear wetness duration in this region, that a comprehensive physical model can give superior estimates, and that wetness estimates made from a central weather station data can be extended to nearby crop fields with a moderate degree of confidence.Key words: epidemiology, mycotoxins, surface wetness models Rao, P. S., Gillespie, T. J. et Schaafsma, A. W. 1998. Estimation de la durée d'humectation des épis de maïs à partir des observations météorologiques. Can. J. Soil Sci. 78: 149-154. Étant donné le lien observé entre la durée d'humectation et l'apparition éventuelle des infections fongiques mycotoxinogènes, nous avons simulé au moyen de 6 modèles, à partir des données météorologiques horaires, le début et la fin de l'humectation superficielle des épis de maïs. Deux modèles à seuils (utilisant l'humidité relative et la température au point de rosée), un modèle de régression utilisant l'humidité et la vitesse du vent et 3 modèles physiques basés sur le bilan énergétique étaient comparés. En outre, la variabilité dans le temps et dans l'espace de la durée d'humectation était mesurée et simulée à 3 emplacements situés à des distances allant jusqu'à 29 km d'une station météorologique centrale. Les valeurs d'humectation estimées étaient comparées à des observations enregistrées par des capteurs d'humectation cylindriques posés à la hauteur approximative des épis dans une culture de maïs. Les résultats sont intéressants pour les futurs systèmes d'avertissement de production de mycotoxines. Ils montrent aussi que les modèles à seuils peuvent fournir des valeurs raisonnables de la durée d'humectation des épis dans cette région. Ces valeurs peuvent encore être améliorées par l'utilisation d'un modèle physique intégré. On a enfin constaté que les valeurs de durée d'humectation provenant d'une station météorologique centrale peuvent être étendues aux cultures avoisinantes avec un degré de confiance modéré.

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Section: Methodsmentioning

confidence: 99%

Estimating wetness duration on maize ears from meteorological observations

Rao¹,

Gillespie²,

Schaafsma³

1998

Can. J. Soil. Sci.

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“…Most electronic sensors were based on a design developed by Davis & Hughes (1970), which sensed the presence of wetness as a drop in electrical resistance across two adjacent circuits etched onto a printed-circuit board. Later workers found that coating these sensors with latex paint enhanced their sensitivity to wetness (Gillespie & Kidd, 1978;Sentelhas et al, 2004a) (Figure 1), that height and angle of deployment influenced sensitivity (Figure 2), and that electronic sensors could also be fabricated as cylinders rather than flat plates (Gillespie & Kidd, 1978;Gillespie & Duan, 1987;Lau et al, 2000;Sentelhas et al, 2004b;Sentelhas et al, 2007a). A recent innovation in flat-plate sensor design operates on the principle of electrical capacitance rather than resistance (Decagon Devices, Inc., Pullman, WA, U.S.A.).…”

Section: The Challenge Of Timelinessmentioning

confidence: 99%

Obtaining weather data for input to crop disease-warning systems: leaf wetness duration as a case study

Duttweiler

Batzer

Taylor

et al. 2008

Sci. agric. (Piracicaba, Braz.)

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Disease-warning systems are decision support tools designed to help growers determine when to apply control measures to suppress crop diseases. Weather data are nearly ubiquitous inputs to warning systems. This contribution reviews ways in which weather data are gathered for use as inputs to disease-warning systems, and the associated logistical challenges. Grower-operated weather monitoring is contrasted with obtaining data from networks of weather stations, and the advantages and disadvantages of measuring vs. estimating weather data are discussed. Special emphasis is given to leaf wetness duration (LWD), not only because LWD data are inputs to many disease-warning systems but also because accurate data are uniquely challenging to obtain. It is concluded that there is no single "best" method to acquire weather data for use in disease-warning systems; instead, local, regional, and national circumstances are likely to influence which strategy is most successful. Key words: integrated pest management, site-specific weather data, disease forecasting, disease prediction, sustainable agriculture OBTENÇÃO DE DADOS METEOROLÓGICOS PARA SISTEMAS DE ALERTA FITOSSANITÁRIO: O CASO DA DURAÇÃO DO PERÍODO DE MOLHAMENTO FOLIARRESUMO: Os sistemas de alerta fitossanitário são ferramentas de suporte à decisão desenvolvidos para ajudar os agricultures a determinar o melhor momento da aplicação das medidas de controle para combater as doenças de plantas. As variáveis meteorológicas são dados de entrada quase que obrigatórios desses sistemas. Este trabalho apresenta uma revisão sobre os meios pelos quais as variáveis meteorológicas são coletadas para serem usadas como dados de entrada em sistemas de alerta fitossanitário e sobre os desafios associados à logística de obtenção desses dados. Essa revisão compara o monitoramento meteorológico ao nível do produtor, nas propriedades agrícolas, com aquele feito ao nível de redes de estações meteorológicas, assim como discute as vantagens e desvantagens entre medir e estimar tais variáveis meteorológicas. Especial ênfase é dada à duração do período de molhamento foliar (DPM), não somente pela sua importância como dado de entrada em diversos sistemas de alerta fitossanitário, mas também pelo desafio de se obter dados acurados dessa variável. Pode-se concluir, após ampla discussão do assunto, que não há um método único e melhor para se obter os dados meteorológicos para uso em sistemas de alerta fitossanitário; por outro lado, as circunstâncias a nível local, regional e nacional provavelmente influenciam a estratégia de maior sucesso. Palavras chave: manejo integrado de doenças, dados meteorológicos específicos do local, previsão de doenças, estimativa de doenças, agricultura sustentável

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“…The use of low alternating currents in the sensor minimizes self heating and electrolytic depositions on the wires or fingers as suggested by Gillespie & Kidd (1978) Both cylindrical and flat plate LWD sensors were white latex painted in order to increase their sensitivity to microscopic wetness droplets as well as to simulate leaf optical proprieties, following the recommendation of Gillespie & Kidd (1978) and Sentelhas et al (2004a). The sensors were submitted to an oven heat treatment at 65ºC for 12 h in order to remove the hygroscopic components of the paint, following the procedures proposed by Gillespie & Duan (1987). After this, laboratory tests were performed in order to establish a threshold of resistance, expressed by the ratio between the measured voltage and the excitation voltage provided by the data logger (Vs/Vx), for which the sensors were considered initially wet.…”

Section: Laboratory Assessmentmentioning

confidence: 99%

“…Gillespie & Duan (1987) developed a low cost cylindrical sensor of easy construction. Its sensing surface faces a solid angle of 2π radians (360 degrees), which represents better some organs, such as stems.…”

Section: Introductionmentioning

confidence: 99%

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Performance of cylindrical leaf wetness duration sensors in a tropical climate condition

Santos

Sentelhas

Gillespie

et al. 2008

Sci. agric. (Piracicaba, Braz.)

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Leaf wetness duration (LWD) measurements are required for disease warning in several agricultural systems, since it is an important variable for the diagnose of plant disease epidemiology. The cylindrical sensor is an inexpensive and simple electronic LWD sensor initially designed to measure this variable for onions, however some studies show that it may be helpful for standard measurements in weather stations and also for different crops. Therefore, the objective of this study was to assess their performance under tropical climate conditions, in Brazil, having as standard measurements those obtained by flat plate sensors, which have presented very good performance when compared with visual observations. Before field assessments, all LWD sensors used in our study (flat plates and cylinders) were white latex painted and submitted to a heat treatment. Laboratory tests were performed in order to determine the resistance threshold for the sensor to be considered wet and the time response of the sensors to wetness. In the field, all cylindrical sensors were initially deployed horizontally 30-cm above a turfgrass surface in order to assess the variability among them with respect to LWD measurements. The variability among the horizontal cylindrical sensors was reduced by using a specific resistance threshold for each sensor. The mean coefficient of variation (CV) of LWD data measured by the cylindrical sensors was 9.7%. After that, the cylindrical sensors were deployed at five different angles: 0º, 15º, 30º, 45º, and 60º. Data of measurements made at these angles were compared with the standard measurement, obtained by flat plate sensors at the same height and installed at 45°. The deployment angle had no systematic effect on LWD measurements for the local tropical conditions, since the correlations between flat plate and elevated cylinder measurements were very high (R 2 > 0.91), which differed from the results obtained under temperate climatic conditions, where LWD measured by cylinders were two hours longer than by flat plate sensors.

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A comparison of cylindrical and flat plate sensors for surface wetness duration

Cited by 32 publications

References 7 publications

Estimating wetness duration on maize ears from meteorological observations

Estimating wetness duration on maize ears from meteorological observations

Obtaining weather data for input to crop disease-warning systems: leaf wetness duration as a case study

Performance of cylindrical leaf wetness duration sensors in a tropical climate condition

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