Three-dimensional (3D) laser technology has been tested for assessing the performance of air-assisted spraying. A static test using an air-assisted sprayer equipped with two axial fans (front and back) with opposing directions of rotation was developed. The sprayer was adjusted to spread water in a static mode, at a pressure of 10 bars, with four air volumetric flow rates. Measurements were performed using a Leica HDS6000 3D laser scanner. In addition, the flow and velocity of air generated by the air-assisted sprayer were measured using a hot-wire anemometer and a 3D sonic anemometer with the objective of estimating the influence of air flow on the spatial distribution of spray droplets. To carry out the analysis, all of the droplets detected by the laser were considered to be of the same size. The distribution of products was asymmetric when the machine only worked with the back fan, with 41% of the product distributed on the left side versus 59% on the right side, as referenced to the direction of the machine’s advance. This asymmetry was corrected when the machine functioned with the two fans activated. These spray data were concordant with the measured air flow generated by the machine in the different working conditions. For the different regulation settings of the machine, taking the vertical of the machine as 0°, the angular region comprised between 40° and 60° was the one that received the highest quantity of product. The increase of the air flow produced a greater distance of the product. For the highest air flow configuration, 99% of the product detected by the laser was detected within a distance of 16 m from the axis of the machine.
Air-assisted sprayers used in fruit production must be carefully and effectively regulated to ensure that crops are successfully treated. Four main factors affect the deposition efficiency [
The use of experimental methods to characterize the product distribution by a sprayer would be difficult and expensive [
To determine the deposition of the product as a function of distance, quantification tests of the deposition are required through the use of collector elements. Distance of deposition defines the spray drift which is considered as the main source of contamination of pesticide applications in tree crops [
The pattern of spray deposition is affected by droplet size and air flow. Droplets in flight are often measured using laser-based spatial (number-density weighted) and temporal (number-flux weighted) techniques [
The distribution of the spray in the vicinity of the sprayer is often estimated by measuring the air flow generated by the fans. In this sense, the air flow generated by the sprayer can be characterized using high-precision anemometers such as sonic anemometers (two-dimensional or three-dimensional) which are used to measure the velocity components for different heights, sections, and distances from the sprayer [
Laser technology has been used successfully to measure the tree canopy geometry in real time with the goal of implementing variable application rate techniques [
Another application of laser technology is its use in validating equipment design and for analysis of different regulations prior to field trials, as a validation tool for the design of the manufactured prototypes. In this case, the laser can be used statically to analyze the distribution of the product [
In conclusion, methodologies used to measure the spray drift and the spray distribution are expensive, time consuming and, in many cases, not practical for the manufacturer’s day-to-day tests. For these tests, manufacturers require rapid measurement methods with a reasonable precision to test different configurations of their machines, which, in most cases, have been previously simulated through the use of computational fluid dynamics (CFD). Therefore, an easy estimation of the spray plume generated in the vicinity of the sprayer (maximum distance of deposition of the product and its spatial distribution) for a specific configuration of air flow, nozzle pressure, and nozzle orientation would be of great help to validate key design parameters of the sprayer such as nozzle position, nozzle type, air conducts geometry, and fan regulation.
The present study is aimed at analyzing the viability of using three-dimensional (3D) laser scanner technology to assess the effectiveness of an air-assisted sprayer used in fruit orchards in terms of the two aforementioned critical criteria: the deposition of the product as a function of distance and the product distribution in the vicinity of the machine.
The operation of an air-assisted sprayer equipped with two reversed-rotation axial fans (Gar-melet S.L., Huesca, Spain), one placed behind the tank and the other placed in front, was analyzed. The diameter of the front fan was 800 mm and that of the back fan was 830 mm. When viewed from the tractor, the front fan spins anticlockwise and the rear fan clockwise. Each fan sucks air axially from the outer area of the machine and expels it radially (Figure
Air-assisted sprayer equipped with two reversed-rotation axial fans (1: PTO; 2: pump; 3: front fan; 4: rear fan; 5: tank; 6: front nozzles; 7: rear nozzles).
A Leica HDS6000 3D laser scanner (Figure
Leica HDS6000 3D laser scanner. (a) Global view; (b) relative position of laser and sprayer during testing.
During the scan, the instrument head automatically rotates while a mirror oscillates in the vertical direction. Both movements can be programmed to cover the selected area with user-specified vertical and horizontal angular steps. The angular accuracy (vertical and horizontal) is 60
Under the experimental conditions used in the present study, the equipment surveyed about 1500 points s-1. The laser spot varies according to the distance; at a distance of 50 m, the laser spot is 4 mm in diameter. To detect a particle, the laser scanner must receive about 35% of the emitted energy. Because of this fact, the density of the cloud of drops present in the laser spot affects the sensitivity of the measurement. Tests carried out using LIDAR sensors have shown the difficulty of the laser beam to impact on a less dense cloud, even if these droplets have bigger size [
The scanner registers Cartesian coordinates of the laser reflection point. The precision of the scanner was adjusted such that at a distance of 30 m, data would be recorded every 20 mm. The scanned area was defined through a rectangular window.
Back and front fans can be regulated, in a range labelled 1–5, to supply different air flows from rotating fan blades. The air flows in the present study were measured according to the method given in [
In addition, the velocity of the air generated by the sprayer was measured in the absence of any wind using a WindMaster 3D sonic anemometer (Gill Instruments, UK) according to the methodology developed by [
Laser measurements were carried out with the sprayer static, establishing three regulations of the fans (Table
Air flows generated by the sprayer with different configurations of settings and PTO working at 540 rpm.
Activated fans | Fan gear box setting | Blade setting | Air flow (m3/h) |
---|---|---|---|
Back | Low | 3 | 31,981 |
4.5 | 37,624 | ||
Back | High | 3 | 38,654 |
4.5 | 42,831 | ||
Back | Low | 3 | 31,981 |
Front | Low | 3 | 26,635 |
The droplets (or group of droplets) detected by the laser scanner in each test, referenced with Cartesian coordinates
Polar coordinates versus Cartesian coordinates.
The sprayer was positioned so that the rear fan coincided with the
Tests carried out on sprayers using LIDAR technology, which has common characteristics to the one used in this test, have shown that measurements cannot be linked to droplet size [
Considering all drops of the same size requires prior analysis to correctly interpret the information provided by the laser. The droplet population generated by a nozzle presents a great variability in sizes and, at the same time, is conditioned by the working pressure. Among the various parameters used in characterizing the range of droplet sizes in a spray, the most commonly used is the volumetric median diameter (VMD or D50). Additionally, relative span is an indicator of the distribution uniformity. Larger droplets are deposited at a closer distance than smaller ones that are more susceptible to drift. For a specific air velocity, the percentage of product deposited at a given distance is related to an inverse function with D50 [
In order to establish direct correlations between the information supplied by the laser and the volume of product applied at different distances, it would be necessary to carry out quantification tests to collect the quantity of product deposited in different areas near the sprayer. In this article, a first step has been taken to demonstrate the feasibility of the 3D scanner technique in providing relevant information. However, the authors plan to carry out quantification trials in the future in order to obtain complete information to establish precise models for estimating product deposition from the information provided by the laser.
Analysis of the experimental data has been carried out leading to three key results: (1) spray deposition as a function of the distance from the machine, (2) symmetry of spray distribution, and (3) spray distribution in angular sectors in a plane (rear fan) perpendicular to the longitudinal axis of the machine.
Considering the center of the rear fan as the coordinate axis, the amount of product applied by the sprayer in circular crowns of 1 m in width was measured.
This methodology allowed the analysis of the spray deposition distance as a function of the regulation of the sprayer. A 100% output of the product from the nozzles was assumed, and using this, the percentage of product that reached the volume of each circular crown was computed.
Figure
Percentage of spray volume detected by the laser within circular crowns of 1 m width for five air flow regulation settings.
Moreover, Figure
Results were concordant with those obtained using other methodologies. In [
The axial fans, due to their direction of rotation, distribute the air flow with some asymmetry, usually applying greater volume of air to the area coincident with the direction of rotation. This fact produces an asymmetry in the spray distribution.
Laser technology was used to assess the symmetry of the spray distribution by quantifying the amount of product applied by the machine to the left and right sectors.
For the data shown in Figure
Percentage of spray volume detected by the laser on the right and left sides of the sprayer.
These results were concordant with those shown in [
The amount of products applied by the sprayer in angular sectors of a plane located at the rear fan was analyzed. For this goal, angular sectors of 10° were used for the left and right sides of the machine, considering the vertical as 0° (Figure
Angular sectors used in the analysis of spray direction.
Figures
Percentage of spray volume for each angular sector for the right side of the sprayer.
Percentage of spray volume for each angular sector for the left side of the sprayer.
According to this result, the laser technique is a useful tool to regulate correctly the position of the nozzles and the direction of the air flow generated by the fans, with the aim of directing the pesticide to the canopy of the tree, reducing the spray drift and increasing the efficiency of the treatment.
The laser sensor was capable of estimating the spray volume in the different areas surrounding the sprayer. The measured movement of the product detected by the laser was in agreement with the air flow generated by the sprayer. Figure
Magnitude of air velocity at the plane of the back fan of the sprayer from 3D anemometer measurements, obtained with the sprayer in a low gear and with a blade setting of 4.5.
Droplets detected by the laser scanner in the plane of the back fan of the sprayer functioning in a low gear and with a blade setting of 4.5.
The flow rate of liquid supplied by the equipment was constant during all the tests as the working pressure was set at 10 bars. However, when comparing the number of droplets obtained for different air flows, the number of droplets detected at high speed of the fan was 36.8% lower than that at low speed for blade setting 3 and 40.4% lower considering blade setting 4.5. Analyzing the number of droplets detected at a distance of 7 to 12 m, the number of droplets detected at high speed of the fan was 32.7% lower than that at the low one, at blade setting 3, and 53.4% considering blade setting 4.5. These data are consistent with those obtained by [
The laser technique examined in this study provides useful information on of air-assisted sprayers for evaluating their function with the aim of improving efficiency of application in the field.
Measurements using the laser sensor allowed the quantification of the maximum distance of deposition of the product. Such data facilitates quantification of the risk of drift and, therefore, the risk of contamination of elements adjacent to the treatment plot: water channels, populations, roads, farms, orchards, and so on.
The left-right asymmetry of the spraying can be estimated in a straightforward manner for the different configurations of the fans. Furthermore, the laser allows quantification of the amount of products applied in different areas in the vicinity of the sprayer. The results of this study also showed that information supplied by the laser on the spraying pattern is concordant with the air flow pattern of the sprayer as measured using 3D anemometers.
When considered together, our results indicate that laser technology can be used for the validation of sprayer machine design. Moreover, as the next step, the regulation of the function of the sprayer, depending on the vegetative state of the crop and the geometry of the orchard, can be established and checked. The air flow, air direction, fan setting, pressure, nozzle type, and nozzle position can be optimized using this laser technique.
The “excel spreadsheet format” data used to support the findings of this study may be released upon application to the main author of the research (F. Javier García-Ramos), who can be contacted by email at
The authors declare that they have no conflicts of interest.