# Contrails and Their Dependence on Meteorological Situations
## 2 Materials and Methods
### Measured Contrail Data  
For the purposes of this work, the collected data on contrails were used, which are observed by the camera system that monitors flight paths around Decin and Prague. Flight data containing information about the aircraft that created a particular contrail are available. The result is a.csv file containing the following data for each aircraft: latitude, longitude, altitude, heading, GS, TAS, and Mach number. From the pairing of the camera and ADS-B data, dataset 1 was obtained to investigate the occurrence of contrails, which contains video and Mode S reports from 68 days. A total of 1778 contrails were observed on randomly selected days from September 2018 to July 2020. The specific days are listed in Appendix B in Table 1.  
Furthermore, measurements of dataset 2 were made: contrails in the vicinity of Prague on 42 days with low cloud cover. Measurements of 160 contrails were carried out in the vicinity of the aerological probe 1 h before the launch of the probe and up to 1 h after the launch of the probe. Data on the position of the probe were obtained using the website [[https://sl.radiosondy.info](https://sl.radiosondy.info)]([https://sl.radiosondy.info](https://sl.radiosondy.info)) (accessed on 10 August 2023), as well as data on the position of the aircraft using the Flightradar24 application. The camera was continuously set to the indicated position of the probe, and when the probe reached an altitude of 10,000 m, the camera was fixed. Only the contrails that were in the image were measured. The measurements were carried out in days from January 2022 to July 2023. The specific days are given in Appendix B in Table 1. The times in UTC of the contrail formation, duration of the contrail location, barometric altitude, and identification of the aircraft that created the contrail were recorded. Suitable meteorological data were obtained, and the quality was checked to ensure the research. Aerological measurements were used as the primary source of meteorological data, which provide basic meteorological elements even at altitudes near the tropopause and are the most accurate source of directly measured meteorological data. Of the other sources of meteorological information previously discussed, the data were not sufficiently accurate for the research and did not particularly contain a sufficient amount of humidity data. For all measured contrails, a meteorological dataset from the aerological sounding of the CHMI was created, which was obtained from the website [[https://ruc.noaa.gov/raobs/](https://ruc.noaa.gov/raobs/)]([https://ruc.noaa.gov/raobs/](https://ruc.noaa.gov/raobs/)) (accessed on 15 August 2023), where raw data of sounding measurements from 2018 are available. The records of the received values of meteorological elements from the sounding measurements of the CHMI, related to the geopotential altitude, are stored in individual rows of this matrix. For the purpose of this work, the geopotential height can be considered as a geometric height; the difference between the two heights in the territory of the Czech Republic is about 10 m at an altitude of 10 km. The columns of the meteorological datasetcontain the respective values of pressure, temperature (T), dew point temperature (T\({}_{d}\)), ice point temperature (T\({}_{ice}\)), wind direction, wind speed, and tropopause height for each given altitude. In order to create classification models for determining the dependence of contrails, other meteorological variables were calculated in Scilab 6.1.1. Ref. [21] for each contrail record, namely relative humidity with respect to water (RH\({}_{w}\)) and relative humidity with respect to ice (RH\({}_{i}\)), according to an equation:  
\[RH(T,Td)=e^{-\frac{L_{ww}T-Td}{\hbar\omega Td}}, \tag{1}\]  
where Lvw is the latent heat of condensation and Rv = 461.5 [J.kg\({}^{-1}\).K\({}^{-1}\)] is the specific gas constant of water vapor [21].