## 3 Results and Discussions
#### 3.3.2 The Spatial Characteristics  
Beside the above summarized variations of environmental parameters over time, to further explore their patterns of distribution across the swine confinement building, the three-dimensional surface plots and corresponding contour plots of so's respiratory zone (60 cm height) and upper region above sow's head (150 cm height) on 15:04 August 13 are  
Figure 12: Four environmental parameters recorded by indoor nodes varied from August 13 to August 14.  
Figure 13: Substantial records of rather high relative humidity (over 85%) of the two consecutive days’ entire observations recorded by nodes from Column A and Column B.  
shown in Figure 14. The overall temperature in this commercial pig house at 15:04 exceeded the comfortable limit 20 \({}^{\circ}\)C but maintained under the UCT 27 \({}^{\circ}\)C, and there were four regions that displayed higher temperatures than their nearby surroundings. They were located on both the front (Units 2-14) and rear (Units 21-28) parts of pig house, and were primarily spotted by nodes from Column A, Column C, and Column D which represented the sow's respiration zone (60 cm height) and upper area of the sow's head (160 cm height), respectively. This spatial distribution feature implied that further cooling measures should be taken to prevent sows there from reducing welfare due to the heat stress. The spatial characteristic of relative humidity sustained its negative correlation relationship with temperature, which was pointed out previously in the process of temporal characteristic analysis. Benefitting from this distribution characteristic, it is favorable for sow's health to avoid staying in a both hot and humid barn that will cause severe uncomfortableness and thereby reduce animal welfare. Regions that exhibited higher relative humidity than the recommended value 86% primarily appeared in the front parts of Units 1-3 and 13-15. Therefore, timely and accurate suggestions to improve the management efficiency of temperature and relative humidity in the commercial swine confinement building could be provided by this WSN system.  
Figure 14: (a,b) The three-dimensional surface plots and corresponding contour plots of sow’s respiratory zone and upper region above sow’s head recorded on 15:04 13 August.  
CO\({}_{2}\) concentrations of two small regions which were located near the side wall, referring to Units 1-4 and Units 24-28 in the middle, showed extremely high levels that far more exceeded the recommended 2700 mg/m\({}^{3}\). This phenomenon was probably due to the poor air exchange rate, and thereby CO\({}_{2}\) was prone to accumulating in those areas. Moreover, nodes mounted on Units 24-28 were 60 cm high, thus could well represent sow's respiration area, given that respiration of sows is one main source of CO\({}_{2}\) release and is proportional to the total heat production and the maximum accepted CO\({}_{2}\) concentration inside the pig building [36]. Therefore, it is of vital importance to timely exhaust this greenhouse gas from the pig barns especially in the hot summer, and the WSN system is capable of accurately identifying those abnormal regions in real-time. Although the overall NH\({}_{3}\) concentration in this swine building was much less than the recommendation 20 mg/m\({}^{3}\), high levels of ammonia accumulated in many Units in Columns A, B, and C near the side wall, which might imply that the air exchange rates in those regions were quite slow.