## 5 Conclusions  
In this work, the key parameters (wavelength, pulse energy, emission frequency, reception area, _etc._) were determined for the design of an eye-safe lidar system for pesticide spray drift measurement. The methodology used is based on SNR simulations and on the study of the MPE for different wavelengths (905 nm, 1064 nm and 1.5 \(\upmu\)m). A wavelength of 1.5 \(\upmu\)m was chosen which, though requiring system constants between 2 and 3.6 times higher than at 905 nm, allows eye safety to be attained with reasonable expansion diameters, between one and two orders of magnitude below those at 905 or 1064 nm.  
An erbium-glass laser based lidar prototype with 3-mJ of pulse energy, emitting at 1534 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 (2.4 m) and temporal (100 ms at maximum PRF) resolution, is eye-safe and weighs less than 15 kg (not including the data acquisition system). The cost of this prototype is about 40 k\(\upmu\), a value significantly lower than the price of lidar systems commonly used to atmospheric sounding. 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. It is expected that the developed instrument will enable estimation of the spray drift flux [\(\upmu\)g/m\({}^{2}\)]. 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 (1.5 \(\upmu\)m) as that used in the present work.  
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.