Catch-can performance under a line-source sprinkler

A line-source sprinkler configuration provides a linearly decreasing irrigation application rate perpendicular to the sprinkler line and has been utilized to study crop response to variable irrigation amounts. The effect on measured irrigation application depths from using various types of catch-cans in those studies is not known. Derived relationships between crop yield and applied water is dependent on the accuracy of measured catch-can water volumes. The purpose of this study was to evaluate catch-can characteristic effects on measurement of sprinkler irrigation depths in a line source. This was accomplished by evaluating six types of catch-cans: (1) 83 mm diameter polypropylene separatory funnel (with evaporation-suppressing oil), (2) 82 mm diameter PVC reducer can (with evaporation-suppressing oil), (3) 151 mm diameter metal can, (4)64 x 59 mm wedge rain gauge, (5) 146 mm white plastic bucket, and (6) 100 mm diameter clear plastic funnel rain gauge. The cans were placed at five application rate conditions (2.8, 5.5, 8.7, 12.6, and 14.8 mm/h). Cumulative catch depths differed among the catch-can types. However, only the metal can and white bucket cumulative application depths at the lowest application rate were statistically different from those of the control (separatory funnel). Catch-cans with a larger diameter opening exhibited less variation in catch depths. Measured evaporation of standing water from catch-cans varied from 0.04 mm/h (funnel rain gauge) to 1.81 mm/h (separatory funnel without evaporation-suppressing oil). Water applied to a bucket's sidewall evaporated at a higher rate than standing water. Inaccuracy of application depth measurement may occur at low application rates even when catch-cans meet the ASAE Standard. The relatively good performance of the funnel rain gauge and catch-cans with evaporation-suppressing oil (and subsequently less depth than the ASAE Standard requires) suggests that it may be appropriate to re-evaluate the standard to consider such devices

Laser precipitation monitor for measurement of drop size and velocity of moving spray-plate sprinklers

Sprinkler drop size distribution and associated drop velocities have a major influence on sprinkler performance in regards to application intensity, uniformity of water application, wind drift, evaporation losses and kinetic energy transferred to the soil surface. Sprinkler drop size measurements are either labor intensive or require use of expensive equipment, both of which limit data availability. Sprinkler drop velocity data are more limited than drop size data due to measurement difficulty and associated cost of labor and instrumentation. An economical laser instrument commercially marketed for real-time rainfall measurements as a Laser Precipitation Monitor (LPM) was used to measure drop size and velocity from ten moving spray-plate type sprinklers. Measured drop size and velocity were used to determine sprinkler drop size distribution and kinetic energy applied to the soil by sprinkler discharge. Drop size distributions measured by the LPM were compared to drop size distributions measured in earlier studies using the traditional flour pellet method. Eight of the ten measured drop size distributions were not significantly different between measurement methods. However, the operating conditions when the two methods did not compare well were outside sprinkler manufacturer specifications. Based on this limited study the results from the two drop size measurement methods can be vastly different for sprinklers with relatively compact streams of water drops. Which method is more accurate for this condition remains unknown. Kinetic energy values calculated using measured drop size and velocity data were not significantly different from values determined using flour pellet drop size data and a ballistic model for estimating sprinkler drop tangential velocity. The economical laser instrument used in this study provided a relatively easy means to obtain reliable estimates of sprinkler kinetic energy per unit volume of applied water for various moving spray-plate sprinkler types and operating conditions. Estimated drop size distribution and computed kinetic energy applied by sprinkler discharge is sufficient for practical field application purposes

Comparison of drop size and velocity measurements by a laser precipitation meter and low-speed photography for an agricultural sprinkler

Kinetic energy of water droplets has a substantial effect on development of a soil surface seal and infiltration rate of bare soil. Methods for measuring sprinkler droplet size and velocity needed to calculate droplet kinetic energy have been developed and tested over the past 50 years, each with advantages, disadvantages, and limitations. Drop size and velocity of an impact sprinkler at three operating pressures and one nozzle size were measured using a laser precipitation meter and compared with published values obtained using a photographic method. Significant differences in cumulative volume drop size distributions derived from the two measurement methods were found, especially at the highest operating pressure. Significant differences in droplet velocities were found between measurement methods as well. Significant differences were attributed to differences in minimum drop sizes measured; 0.5mm for the photographic method versus 0.2 mm for the laser precipitation meter. The laser precipitation meter provided smaller cumulative volume drop size distributions compared to the photographic measurement method. The laser precipitation meter tended to provide greater drop velocities which were attributed to altitude differences at experimental sites. The difference in calculated droplet kinetic energy per unit drop volume based on drop and size velocity data from the laser precipitation meter and the photographic method ranged from +12.5 to -28%. The laser precipitation meter generally provided a lower estimate of sprinkler kinetic energy due to the measurement of a greater proportion of smaller drop sizes. Either method can be used to obtain drop size and velocity sprinkler drops needed to calculate sprinkler kinetic energy. The laser precipitation meter requires less skill and labor to measure drop size and velocity

Comparison of sprinkler droplet size and velocity measurements using a laser precipitation meter and photographic method

Kinetic energy of water droplets has a substantial effect on development of a soil surface seal and infiltration rate of bare soil. Methods for measuring sprinkler droplet size and velocity needed to calculate droplet kinetic energy have been developed and tested over the past 50 years, each with advantages, disadvantages, and limitations. A laser precipitation meter and photographic method were used to measure droplet size and velocity from an impact sprinkler at three pressures and one nozzle size. Significant differences in cumulative volume drop size distributions derived from the two measurement methods were found, especially at the highest operating pressure. Significant differences in droplet velocities were found between measurement methods as well. Significant differences were attributed to differences in minimum drop sizes measured; 0.5mm for the photographic method versus 0.2 mm for the laser precipitation meter. The laser precipitation meter provided smaller cumulative volume drop size distributions compared to the photographic measurement method. The laser precipitation meter tended to provide greater drop velocities which were attributed to altitude differences at experimental sites. The difference in calculated droplet kinetic energy per unit volume based on drop and size velocity data from the laser precipitation meter and the photographic method ranged from +12.5 to -28%. The laser precipitation meter generally provided a lower estimate of sprinkler kinetic energy due to the measurement of a greater proportion of smaller drop sizes. Either method can be used to obtain drop size and velocity sprinkler drops needed to calculate sprinkler kinetic energy. The laser precipitation meter requires less skill and labor to measure drop size and velocity

Collector design for measuring high intensity time variant sprinkler application rates

Peak water application rate in relation to soil water infiltration rate and soil surface storage capacity is important in the design of center pivot sprinkler irrigation systems for efficient irrigation and soil erosion control. Measurement of application rates of center pivot irrigation systems has traditionally used tipping bucket rain gauges. Calculation of application rate from tipping bucket rain gauge measurements restricts computed application rate to a discrete multiple of the rain gauge resolution and time interval. This limits the resolution of application rate measurement, especially for time intervals less than 15 minutes. A collector was designed to measure time variant high intensity sprinkler application rates under field conditions with greater resolution than a tipping bucket rain gauge. The collector funnels water into a 50 mm (2 in.) diameter tube providing a depth multiplication factor of 18.26:1. The depth of water in the tube is measured with a low pressure piezo-resistive pressure sensor connected to a differential amplifier circuit. Combination of the depth multiplication factor of the collector and differential amplifier circuit provides a collector resolution of 1.4 mm/mV. A data logger is used to record water depth in the collector tube during an irrigation event. A digital differentiating filter was designed and used to reduce the effect of random electrical noise in the sensor output on calculated application rate. The collector was tested in the laboratory and under field conditions emulating center pivot sprinkler irrigation. For a range in application rates from 15 to 200 mm/h in the laboratory, the maximum collector error was 2.1 mm/h. Collector measured application rate patterns under field conditions were well correlated to simulated application rate patterns using radial application rate profiles for the sprinklers tested. Collector measured peak application rates were not significantly different from those predicted by the Kincaid (2005) model. The collector functioned as designed in field tests and provided an effective and efficient means of measuring high intensity application rates from center pivot irrigation systems under field conditions

Catch-can performance under a line-source sprinkler

A line-source sprinkler configuration provides a linearly decreasing irrigation application rate perpendicular to the sprinkler line and has been utilized to study crop response to variable irrigation amounts. The effect on measured irrigation application depths from using various types of catch-cans in those studies is not known. Derived relationships between crop yield and applied water is dependent on the accuracy of measured catch-can water volumes. The purpose of this study was to evaluate catch-can characteristic effects on measurement of sprinkler irrigation depths in a line source. This was accomplished by evaluating six types of catch-cans: (1) 83 mm diameter polypropylene separatory funnel (with evaporation-suppressing oil), (2) 82 mm diameter PVC reducer can (with evaporation-suppressing oil), (3) 151 mm diameter metal can, (4)64 x 59 mm wedge rain gauge, (5) 146 mm white plastic bucket, and (6) 100 mm diameter clear plastic funnel rain gauge. The cans were placed at five application rate conditions (2.8, 5.5, 8.7, 12.6, and 14.8 mm/h). Cumulative catch depths differed among the catch-can types. However, only the metal can and white bucket cumulative application depths at the lowest application rate were statistically different from those of the control (separatory funnel). Catch-cans with a larger diameter opening exhibited less variation in catch depths. Measured evaporation of standing water from catch-cans varied from 0.04 mm/h (funnel rain gauge) to 1.81 mm/h (separatory funnel without evaporation-suppressing oil). Water applied to a bucket's sidewall evaporated at a higher rate than standing water. Inaccuracy of application depth measurement may occur at low application rates even when catch-cans meet the ASAE Standard. The relatively good performance of the funnel rain gauge and catch-cans with evaporation-suppressing oil (and subsequently less depth than the ASAE Standard requires) suggests that it may be appropriate to re-evaluate the standard to consider such devices

Comparison of drop size and velocity measurements by a laser precipitation meter and low-speed photography for an agricultural sprinkler

Kinetic energy of water droplets has a substantial effect on development of a soil surface seal and infiltration rate of bare soil. Methods for measuring sprinkler droplet size and velocity needed to calculate droplet kinetic energy have been developed and tested over the past 50 years, each with advantages, disadvantages, and limitations. Drop size and velocity of an impact sprinkler at three operating pressures and one nozzle size were measured using a laser precipitation meter and compared with published values obtained using a photographic method. Significant differences in cumulative volume drop size distributions derived from the two measurement methods were found, especially at the highest operating pressure. Significant differences in droplet velocities were found between measurement methods as well. Significant differences were attributed to differences in minimum drop sizes measured; 0.5mm for the photographic method versus 0.2 mm for the laser precipitation meter. The laser precipitation meter provided smaller cumulative volume drop size distributions compared to the photographic measurement method. The laser precipitation meter tended to provide greater drop velocities which were attributed to altitude differences at experimental sites. The difference in calculated droplet kinetic energy per unit drop volume based on drop and size velocity data from the laser precipitation meter and the photographic method ranged from +12.5 to -28%. The laser precipitation meter generally provided a lower estimate of sprinkler kinetic energy due to the measurement of a greater proportion of smaller drop sizes. Either method can be used to obtain drop size and velocity sprinkler drops needed to calculate sprinkler kinetic energy. The laser precipitation meter requires less skill and labor to measure drop size and velocity