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Inici > English version > GRAP research > GRAP works > Drift detection with lidar sensors

Drift detection with lidar sensors

 

 

Spray drift measurement

There are several techniques used to measure the airborne spray drift. Some of the most used are the chemical analysis, the tracers and LIDAR (Light Detection and Ranging) systems. Chemical analyses are based on the extraction and analysis of pesticides in the air by chromatographic techniques. Tracers are substances used to simulate the transport of pesticides in the air. Most popular tracers are visible and fluorescent dyes, metal salts and radioactive isotopes.

 

Spray drift studies are usually carried out by means of field experiments using in-situ collectors placed near the application site. The function of these collectors is to intercept the drift cloud generated by the sprayer (Figure 1). Main limitations of this methodology are (Gregorio, E., 2012):

  • Does not provide information about the temporal evolution of the drift cloud.
  • Only provide information about a single point.
  • 2 or 3 dimensional information is not obtained.
  • The collector’s efficiency depends on the meteorological conditions. Significant personnel and time resources are required to carry out the trials.

 

 

Figure 1. Spray drift measurement, extracted from Gregorio (2012). Four poles are shown: one to subject the anemometer and the other three to hold the nylon lines (2 mm diameter). Horizontal collectors (filter paper sheets) are also used to measure the terrestrial spray drift.

The application of LIDAR remote sensing technique allows overcoming the previous limitations.

 

LIDAR systems

A LIDAR system is a remote sensing device similar to a radar, except for the fact that emits light (laser) instead of radio waves. Its principle of operation is based on the emission of a pulsed laser beam towards a target (in this application, the target is a drift cloud) that partially backscatters this light. Photons arriving at the receiver are collected by a telescope and a photodetector module. The receiving signal is recorded as a function of time (Figure 2). It is possible to calculate the distance to the target measuring the time this light requires to go and back (time of flight). The interaction between the laser beam and the aerosol and the atmospheric molecules follow the scattering laws (Rayleigh, Mie and Raman). In addition, the extinction of the emitted energy follows the Beer’s law.

Figure 2. Outline of an elastic LIDAR system (Gregorio et al., 2011).

 

LIDAR systems have applications in many fields, including the measurement of the wind speed and direction, to obtain the concentration of chemical species, in ceilometry (height and thickness of clouds). In the environmental field, LIDAR systems are used to monitor the spread of aerosols and other pollutants.

 

Spray drift measurement using LIDAR systems

Over recent years, several studies have used LIDAR systems to measure spray drift. In 2009, our group carried out an extended spray drift study using a UV (ultraviolet) LIDAR system and two types of passive collectors (nylon lines and water-sensitive papers) (Gregorio, E., 2012). This work concluded that LIDAR is a suitable technique to measure the spray drift. It is possible to relate the LIDAR measurements with those obtained by passive collectors (Gregorio et al., 2014).

As a continuation of previous works, a new LIDAR system, specifically designed for spray drift measurement, has been developed by our research group. This instrument consists of a laser transmitter and a receiver system that allows capturing a fraction of the backscattered light. The steering of the LIDAR is made by an electromechanical system with two freedom degrees (azimuth and elevation). The light captured by the photodetector module is converted into electrical signal by a digitizer and sent to a PC.

 

Figure 3. LIDAR prototype (Gregorio et al., 2015).

 

Main features of the LIDAR system developed by the GRAP are listed in the following table:

 

Table 1. LIDAR system specifications (Gregorio et al., 2015).

 

Figure 4 shows the developed LIDAR system performing spray drift measurements in a vineyard orchard.

 

Figure 4. Lidar system deployed in the field during a drift measurement (Gregorio et al., 2015).

 

References.

  • Gregorio, E., 2012. Lidar remote sensing of pesticide spray drift. Tesi Doctoral. Departament d’Enginyeria Agroforestal. Universitat de Lleida.
  • Gregorio, E., Solanelles, F., Rocadenbosch, F., Rosell, J.R., Sanz, R. 2011. Airborne spray drift measurement using passive collectors and lidar Systems.
    SPIE. Praga (República Txeca). Proc. SPIE 8174, 81741I. DOI: 10.1117/12.903723.
  • Gregorio E; Rosell-Polo JR; Sanz R; Rocadenbosch F; Solanelles F; Garcerá C; Chueca P; Arnó J; del Moral I; Masip J; Camp F; Viana R; Escolà A; Gràcia F; Planas S; Moltó E. (2014). LIDAR as an alternative to passive collectors to measure pesticide spray drift. Atmospheric Environment 82: 83-93. DOI: 10.1016/j.atmosenv.2013.09.028.
  • Gregorio E; Rocadenbosch F; Sanz R; Rosell-Polo JR. 2015. Eye-Safe Lidar System for Pesticide Spray Drift Measurement. Sensors 15(2): 3650-3670. DOI: 10.3390/s150203650.
  • Subias, M. 2014. Configuració i programació d’un sistema d’adquisició de dades per a un radar làser (LiDAR). Projecte Final de Carrera. Universitat de Lleida.

 

 

 

Last modified: 13/05/2015
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