# Correlation and Regression Analysis of Spraying Process Quality Indicators
## 1 Introduction  
One of the primary practices of agricultural production is chemical plant protection because it increases the control of pests and ensures high quantity and quality of yield [1]. The expected effectiveness of spraying involves the need for an adequate amount of plant protection product and uniformity of the liquid distribution in the targeted area. However, during spraying, other phenomena such as drift of spraying, environmental pollution, and poisoning of machine operators and bystanders may occur [2, 3, 4, 5]. The authors emphasized the need to minimize losses and maximize spraying effectiveness [6, 7]. It is therefore important to ensure an appropriate degree of liquid deposition and uniformity of liquid distribution while protecting humans, animals, and the environment. Relevant parameters and working conditions for sprayers in terms of atmospheric conditions should be adapted for this purpose [8]. Among the technical and technological factors include; spraying speed, dose and liquid pressure, the height of the sprayer boom, as well as the nozzles and adjuvants used [9, 10, 11, 12, 13, 14]. The evaluation of spraying quality is conducted based on three indicators. The degree of coverage of sprayed surfaces and the distribution of the spray liquid are qualitative indicators, while the deposition of the liquid is a quantitative indicator. In the literature, the degree of coverage of sprayed surfaces is defined as the ratio of the surface covered by the liquid to the total surface of the sampler. This ratio is calculated on the basis of a computer image analysis. Water-sensitive paper is the most common sampler [15]. Alternatively, the researchers proposed a fluorescent marker and the results were obtained using ultraviolet (UV) radiation [16]. In addition, [PERSON] et al. [17] presented the use of single leaf and Matlab software for the examination of coverage degree. Manyresearch efforts have focused on determining the impact of factors mentioned previously on the degree of coverage of spraying surfaces [18; 19; 20; 21; 22; 23; 24]. The analysis of water-sensitive papers was used to estimate the residues of the plant protection product (pentoconazole) on apple leaves. The applied correction factor was an essential aspect of the analysis. The authors highlighted the need to continue the research to determine whether the presented correction factor would be appropriate during studies with the use of other preparations [25]. The deposition of the spray liquid is a quantitative indicator, calculated as the mass of the product retained on the protected surface. Filter papers are samplers and fluorescent dyes such as rhodamine [26], mylar cards [10], and tartrazine [27] are used during experiments. Studies on the uniformity of the distribution of liquid precipitation are usually carried out by using a grooved table. Experiments are based on the determination of the parameters of the lateral and longitudinal distribution of liquid. The impact of technical and technological factors on this indicator was described based on the results of research [28; 29]. The analysis of the values of a correlation coefficient or regression models are very common approaches in various fields and disciplines such as medicine [30; 31], biology [32; 33], food technology [34; 35], earth sciences [36; 37], economics [38; 39] and agriculture [40; 41; 42; 43; 44]. [PERSON] et al. [45] stated that the coverage degree values obtained on water-sensitive papers were correlated with the deposition of liquid spray. In addition, a model for estimating liquid deposition using the degree of coverage was presented by [PERSON] et al. [46]. The research was carried out in an orchard with the use of an ATR 80 hollow-cone nozzle. A strong correlation between the analyzed indicators was achieved by the authors. [PERSON] et al. [47] obtained a correlation coefficient of deposition and coverage of 0.89. The research was carried out on the crop of cotton with the use of unmanned aerial vehicles.