Figure 8a corresponds to the signal backscattered by the crowns of a group of trees located m from the lidar system. Two signal peaks separated by 15 m can be observed. This is because the crowns are comprised of a set of non-homogeneous elements which favour partial impact of the beam on them. In Figure 8b the measurement is shown of the wall of a building located m away.
The SNR estimated for measurement of the trees is 71 highest peak , while the corresponding SNR for the signal backscattered by the wall is The procedure explained in [ 14 ] was used to calculate the SNR. Range profile of lidar signal backscattered by several topographic targets. Range profile of lidar signal backscattered by a mountain located at m from the lidar.
Figure 9a shows the signal peak backscattered by a mountain located at a distance of m. The estimated SNR is 11, a far higher value than the threshold of 5 considered in the simulations of Section 2. This result shows that the system is capable of detecting with clarity topographic targets over 2 km away. It can be observed how the SNR improves up to a value of Due to their high dynamics, shot averaging cannot be used for the measurement of drift clouds in cases in which there is a desire to know their temporal evolution.
However, this method raises the possibility of monitoring other cloud typologies with slower dynamics, as for example of atmospheric clouds ceilometry or those generated in forest fires. Figure 10 shows the measurements of two spray clouds generated by an air-assisted sprayer operating in an area without vegetation.
During these tests, the sprayer was kept in a static position at a distance of 90 m from the lidar system. The signal obtained shows two peaks which correspond to the two emission sides of the sprayer. Figure 10b shows a particular type of plot called range-time intensity RTI.
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These were created from various consecutive measurements, in this case one each second, and show the evolution in time and distance of the cloud. The gradation of colours corresponds to the intensity of the received signal.
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- Eye-Safe Lidar System for Pesticide Spray Drift Measurement?
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In this test, spray measurement was performed from its initiation to its conclusion, with detection also of the residual drift in the air once the spraying had terminated. Detection of pesticide clouds generated by a cross-flow air-assisted sprayer. The sprayer was in a static position and located in a place with no crop. Figure 11 shows the typical set-up of a lidar system during a spray drift study.
In this test, the spray drift was generated by an air-assisted sprayer treating a vineyard background , while the lidar system is placed at a distance of 80 m away foreground.
The laser was pointed perpendicularly to the orchard and above it, to prevent any signal distortion by trees. The backscattered signal due to the interaction with the spray drift cloud is detected by the optoelectronic receiver and through the digitizer is sent to the PC so that the signal is displayed in real-time. The air-assisted sprayer was positioned in one of the orchard inter-rows while the laser beam was aimed at the neighbouring inter-row, parallel to it. The aim of the tests was to detect the fraction of spray able to get past the vegetation or, in other words, the spray drift.
The drift generated during the application is shown in Figure 12a until the cloud signal dies out. In this test, the sprayer was kept in a static position so that the small variations in distance correspond to movement of the cloud caused by air currents. Figure 12b is similar to Figure 12a except that the sprayer was moved along the inter-row at constant speed as would take place in a real application. It can be seen how the drift cloud moves away as the sprayer advances along the inter-row.
Detection of the pesticide spray drift in an apple orchard. In this work, the key parameters wavelength, pulse energy, emission frequency, reception area, etc. The methodology used is based on SNR simulations and on the study of the MPE for different wavelengths nm, nm and 1. An erbium-glass laser based lidar prototype with 3-mJ of pulse energy, emitting at nm has been constructed. Initial tests with topographic targets and spray drift clouds have validated the correct operation of this instrument. The instrument that has been developed meets the design specifications that were established initially since it is capable of measuring mid-range spray drift as shown by the tests conducted, has high distance 2.
Laser remote sensing : fundamentals and applications
However, it should be noted that this prototype was developed in the framework of a research project and not as a commercial product. A scanning system will need to be implemented in more advanced versions so that the system is able to provide a bi-dimensional image of pesticide plumes. Another aspect that will need to be examined is the possibility of using a coaxial configuration to reduce the minimum detection distance.
The availability of this instrument opens the door to the execution of a wide range of tests. The most immediate of these will comprise an intercomparison campaign with cooperative sensors capable of measuring the concentration and distribution of drift droplet sizes, in order to calibrate the lidar signal. Flux measurement with the lidar may entail a substantial improvement over the present mass balance approach [ 36 , 37 ], the purpose of which is to quantify the fraction of the applied pesticide product which escapes from the treated area. Consideration should also be given to the possible use of the developed instrument in other agroforestry applications such as measurement of the particulate matter PM generated in agricultural and livestock farming, the monitoring of sprinkler irrigation and fertilizer spraying or the prevention of forest fires.
In relation with the latter application, previous studies [ 38 , 39 ] have proposed the development of a lidar system at the same wavelength 1. There is great potential in the use of lidar systems to monitor drift and agricultural air quality in general. The availability of the lidar system presented in this work and specifically designed for these applications, will enable better understanding of the phenomenon of drift and, as a result, the adoption of more efficient techniques to reduce or prevent its occurrence.
IRIS is thanked for his cooperation in the development of the receiving subsystem. Eduard Gregorio designed the lidar system and coordinated the development of the research project; Francesc Rocadenbosch gave scientific advice on the design of the prototype; Joan R. Rosell-Polo and Eduard Gregorio carried out the experimental measurements. National Center for Biotechnology Information , U. Journal List Sensors Basel v. Sensors Basel. Published online Feb 4. Rosell-Polo 3. Find articles by Ricardo Sanz. Joan R. Find articles by Joan R. Author information Article notes Copyright and License information Disclaimer.
Received Sep 29; Accepted Jan This article has been cited by other articles in PMC. Abstract Spray drift is one of the main sources of pesticide contamination. Keywords: lidar, spray drift, optomechanical design, signal-to-noise ratio, eye safety, pesticide, laser, remote sensing, agriculture. Introduction The application of plant protection products by means of sprayers is the most widely used procedure for the protection of agricultural crops against pests and diseases.
An easily transportable instrument suitable for field work is required. Drift plumes generated by ground sprayers have relatively low dimensions, commonly just a few metres thick. For appropriate characterisation, the lidar system must have a high range resolution, ideally not greater than 3 m.
A maximum reach of m is sufficient. Pesticide plumes are highly dynamic, with rapid variations in their shape and concentration.
Eye-Safe Lidar System for Pesticide Spray Drift Measurement
In order to characterise these clouds, the lidar system must be capable of measurements at high frequencies. It was experimentally shown in [ 1 ] that a time resolution of 1 s is suitable for the monitoring of spray drift plumes. The drift clouds generated by ground-based applications are usually suspended at a low height above the sprayed crop [ 7 ]. Therefore, monitoring pesticide drift with terrestrial lidar systems implies a quasi-horizontal sounding, increasing the risk of accidental impinging on bystanders. Performance Assessment In this section, the wavelength, pulse energy and receiving area are determined by taking into account the design specifications of Section 1.
Maximum Permissible Exposure for Different Wavelengths Wavelength is one of the key parameters in the design of any lidar system. Visible radiation used by the Micro Pulse Lidar [ 13 ]. Commonly applied in lidar ceilometry [ 14 ], corresponding to the InGaAs laser diode. Commonly used in eye-safe systems [ 16 ]. Open in a separate window. Figure 1. MPE for an individual pulse vs. Signal-to-Noise Ratio Simulations In this section, the interval of values is determined in which the instrument system constant K s must be found to satisfy the initial specification of pesticide cloud measurement at a distance of m.
Atmospheric Model As explained previously, the lidar system sounding of the atmosphere will be horizontal and so a homogenous optical atmospheric model is considered in the SNR simulations. Table 1 Opto-atmospheric parameters and solar background radiance for the studied wavelengths. Table 2. Figure 2. Signal-to-Noise Ratio Simulations at nm The same photodetector modules, transmission factors and background-radiance system constant as for the nm simulations were considered in the simulations at nm. Figure 3. Table 3.
Signal-to-Noise Ratio Simulations at 1.
Figure 4. Table 4. Table 5.