## 3 Results and discussion
### Field Test
#### 3.2.3 Droplet Distribution in Spray Area  
In order to further describe the droplets distribution, the droplet sizes were divided into 0-100 \(\upmu\)m, 100-200 \(\upmu\)m, 201-300 \(\upmu\)m, 301-400 \(\upmu\)m, 401-500 \(\upmu\)m, and more than 500 \(\upmu\)m. The droplet parameters of each sampling point were counted, and Figure 8 is the ratio of the droplet size spectrum of the three types of nozzles and the corresponding deposition and coverage. According to the calculation, the proportion of the droplets in the particle size spectrum of the CP02 nozzle in all droplets were 43.69%, 19.14%, 10.08%, 7.44%, 5.80%, and 13.84%, respectively. CP03 nozzle were 27.76%, 21.46%, 13.40%, 9.59%, 7.68, and 20.11% respectively, CP04 nozzle were 30.55%, 21.56%, 11.91%, 7.54%, 5.93%, and 22.52%. It can be clearly found that 62.83% of the droplets of the CP02 nozzle were distributed in the small particle size spectrum of less than 200 \(\upmu\)m; the droplets of the CP03 nozzle occupied a relatively high range in the particle size spectrum of 201-500 \(\upmu\)m; for the CP04 nozzle, the droplets in the large particle size range of more than 500 \(\upmu\)m were relatively high. This was also consistent with the results of the wind tunnel particle size test, which enhanced the reliability of the test results. In addition, the study also found that the uniformity of the droplet size distribution between the sampling points in the field test area was poor, that is, the coefficient of variation was large. Taking the 3# as an example, the \(CV\) of the CP04 nozzle in the droplet size spectrum were 51.37 %, 22.81%, 33.50%, 35.13%, 38.10%, and 41.86%, respectively, which exposed the common problem of strong randomness and poor reproducibility in the field test [28].  
The droplet deposition and coverage at each sampling point are also important evaluation parameters for the distribution of droplets. Through observation, it can be found that from the sampling position of -20 m to 20 m, the deposition and coverage of each test showed similar trends. After calculation, the average droplet deposition and coverage of each test were 1.043 L/cm\({}^{2}\), 8.04% (CP02 nozzle), 1.248 L/cm\({}^{2}\), 8.89% (CP03 nozzle), and 1.975 L/cm\({}^{2}\), 11.47% (CP04 nozzle), respectively. At the same time, the distribution of droplet deposition and coverage at each sampling point were also not very uniform. It can be seen that the droplet deposition and coverage near the helicopter route were significantly higher than those far from the route. In addition, by comparing with the droplet  
Figure 8: **(a)** Droplet size spectrum percentage of test 1# in the spray area; **(b)** deposition and coverage of test 1# in the spray area; **(c)** droplet size spectrum percentage of test 2# in the spray area; **(d)** deposition and coverage of test 2# in the spray area; **(e)** droplet size spectrum percentage of test 3# in the spray area; **(f)** deposition and coverage of test 3# in the spray area.  
size spectrum percentage, it can also be found that the sampling locations where the deposition and coverage were higher, the proportion of large droplets size measured was also relatively high, which was obvious, so that the above-mentioned droplet size distribution results can be further explained.