## 1 Introduction  
The advantages of non-equilibrium plasmas generated by pulsed low-current high-voltage discharges at atmospheric pressure have contributed to the fact that such discharges are now well established industrially and are constantly growing [1, 2]. In the automotive and packaging industries, for example, surfaces are treated with such plasmas before bonding, printing or painting [3, 4, 5, 6] to improve the quality of the following process. Surfaces are hydrophilized or hydrophobized by the deposition of layers as a result of a chemical reaction induced by such plasmas [7, 8]. Various layers of low-melting materials are coated onto temperature-sensitive substrates [9, 10, 11, 12]. The antibacterial properties of non-equilibrium plasmas are used and intensively explored in food and medical industries [13, 14, 15, 16]. In the environmental sector, such plasmas are used to neutralize industrial waste gases by the selective removal of chemical compounds [8, 17, 18]. Moreover, possible applications to increase efficiency in the production of synthetic fuels are being explored [19, 20]. As a result of the ever-widening range of applications, especially in the environmental and health fields [13, 20, 21, 22, 23], the need for the comprehensive characterization of non-thermal plasmas seems to become more and more important. Due to the wide application field and industrial spread of pulsed low-current discharges, a plethora of publications exist in which this type of discharge is studied. However, often it is not the physical effects that occur in plasma that are characterized, but the effects achieved as a result of a plasma treatment, as presented in [4, 6, 14, 24, 25, 26, 27], to name a few. In references dealing with the characterization of such discharges, researchers often describe their behavior using electrical measurements [10; 28; 29; 30] or emission spectroscopy. The latter diagnostic method is primarily used to qualitatively describe the composition of the plasma [12; 24; 31; 32]. Only a few authors estimated the temperature of heavy particles or, more precisely, the rotational and vibrational temperatures of molecular bands based on the fitting of the recorded spectra for pulsed low-current nitrogen discharges in the analyzed power range [3; 33; 34; 35; 36; 37]. In some cases, the estimation of the gas temperature is also conducted by thermocouple measurements [10; 12; 38]. The last technique may be easy to implement, but the gas temperature values that can be assessed are significantly limited by the sensor used and are subsequently less accurate than those determined spectroscopically. Furthermore, due to the ratio of the sensor size to the measured object size, this method only allows the recording of integral values. Therefore, spectroscopic measurements or laser scattering diagnostics should be preferred over thermocouple-based ones for the evaluation of the heavy particle temperature \(T_{h}\) with regard to the chemical reactivity of the plasma under study, while calorimetric measurements as presented in [39; 40] are preferable if the thermal load of the substrate is to be evaluated. As mentioned above, the temperature of heavy particles can be assessed experimentally by emission spectroscopy measurements and subsequent fitting of synthetic spectra. In comparison, the determination of the electron parameters of non-equilibrium plasmas based on spectroscopic measurements is not so straightforward. Several research groups estimated the electron density or temperature through modelling [35; 37; 41; 42; 43]. Thereby, in addition to the estimation of rotational and vibrational temperatures, the measured spectra are used to estimate the diameter of the discharge channel, which is then used to determine the current density. Thereafter, the electron parameters can be obtained by solving the Boltzmann equation [37], an Elenbaas-Heller [43] or a collisional-radiative model [35].