# Monitoring System Enhancing the Potential of Urban Bekeeping
## 4 Discussion
The multi-sensor system presented in this work is based on passive exposure, therefore, the unobstructed access of beehive air to the measurement module is critical for attaining credible results. There are multiple examples of sensors located inside beehives, but multi-sensor devices are most willingly localized on the inner side of the beehive base, for convenience [41]. We chose the location directly on the frame amidst brood, honey, and pollen areas, to assure a better quality of data. Ultimately this option showed non-intrusive toward bees. Still, the devices are operated inside the beehive, in its atmosphere. The conditions in the beehive, e.g., thermal and chemical, are distinctive and specific for this kind of environment. Potentially, they could influence the performance of the devices operated there. Our monitoring system is composed of commercially available elements, which have not been optimized for inside-beehive exploitation. The examination of the selected parameters, which characterize the performance of the measurement devices, has shown that the beehive environment does not pose a major threat to their operation. The multi-sensordevices continuously provide exhaustive data on the beehive atmosphere composition and its temporal variation, see Figure 6. Regarding the most commonly monitored parameters, like temperature and relative humidity, their values as well as the patterns of daily variation are coherent with those found by other researchers [27; 30; 42]. Concerning other parameters, in particular, TVOC, NOx, or PM, the data for comparison are difficult to find. The coverage of the period of system operation with the measurement data is very high, which confirms the reliability of the applied data collection and transmission solutions, see Table 2.  
Unfortunately, it is likely that a drift affects the signals of some sensors and respective correction algorithms will have to be developed. Based on our findings, in the case of temperature, NOx, and TVOC measured using SMSs as well as using PID sensors, one could consider the occurrence of a systematic error, see Figure 8. Interestingly, this systematic change was detected in sensors that were exposed to beehive air as well as those exposed to ambient air. Hence, probably the change of the same kind of sensing element with time was encountered irrespective of exposure conditions. Except for the temperature, we could not identify the factors causing the systematic increase in the sensor signal, which would be associated with the measured object. For example, the systematic development of honey bee colonies would be expected to cause a CO\({}_{2}\) concentration increase, but it was not observed. The exhaustive diagnostics of this issue will be possible upon the analysis of the larger set of data, in particular, after completing 1 year of measurements. The completeness of data collected over a long time is very important for overcoming the problem of sensor drift. Various information can be acquired based on beehive weight measurement, in particular, the magnitude and the dynamics of its change. The available information is greatly dependent on the measurement resolution and temporal resolution offered by the measurement device. The typical measurement resolution of the continuously operating beehive scales is 100 g [34], although 10 g has been reported as well [21]. The measurement resolution of our beehive scales is 0.1 g. It greatly enhances the ability to observe small changes in beehive weight. Typically, beehive weight is measured several times a day [34] or with a temporal resolution of 1 h [43]. Our system offers the temporal resolution of 1 s. It is useful to observe the short-term changes in beehive weight.