## 4 Results and Evaluation  
### Experimental Deployment Arrangements  
In an attempt to highlight the behavior of the sensor nodes we designed and implemented, a series of experiments were conducted starting from controllable laboratory settings and proceeding with in situ ones in the rural area of the university campus. Figure 8a depicts the former ones and Figure 8b,c the latter ones. Experiments in an open area exhibit more interest due to the exposure to many different factors affecting the performance and longevity of the overall system, and thus the focus of this work emphasizes the open area.  
More specifically, for the rural-area experiments, two units were installed, one close to the other but not having identical setup configurations. Both nodes were equipped with one TEROS 12 unit, one 5 TE unit, one TEROS 10 unit, and one ML2 instrument. All soil-sensing instruments were placed beneath the ground, horizontally, at 15 cm depth; we left a distance of 50 cm from the one from the other, approximately, to avoid interference.  
Figure 8: Characteristic experimental arrangements for multiperspective sensor node performance: (**a**) indoor ones in controllable laboratory environment; (**b**,**c**) outdoor ones in the rural area surrounding the university campus, including complete or partial equipment placement in the ground.  
Experiments also included a 10 HS unit, connected at the fourth socket of node #A1. The second node (node #A2) hosted an Adafruit LM4040 in lieu of a soil instrument at its fourth sensor socket to provide an accurate reference voltage to compare against the performance of the built-in digitizer of the 32u4 throughout the experiments.  
As with the accompanying soil-sensing instruments, the concentrating box enclosure of node #A1 was placed underground, at approximately 10 cm depth; it contained a single-cell Li-Ion battery of the 18,650 type with a 2500 mAh capacity and a small 2 dBi LoRa antenna (i.e., omnidirectional and vertically polarized for the 868/915 MHz bands, as mentioned in Section 3.1), both buried with the rest of the electronic equipment. This quite unorthodox setting protects the sensor node parts from several potentially dangerous factors and yet is expected to maintain LoRa connection quality within an acceptable range, as inferred by studying the results presented in [36; 37].  
On the other hand, for node #A2, while the four soil instruments where buried at 15 cm around it, its box enclosure was fixed on a wooden rod at a 1 m distance above the ground level, facing south, and was equipped with an external 2 dBi antenna LoRa antenna (as mentioned in Section 3.1) and a small solar panel with rated power 0.5 W and voltage 5 V. To avoid extreme thermal stress, affecting performance and limiting charging periods, the battery of node #A2 was buried at 15 cm depth in a similar manner as the soil instruments.  
The soil at the neighboring locations where the instruments of node #A1 and of node #A2 were installed (i.e., five meters away) was almost of the same type, although small variations are expected in the way that the holes hosting the instruments were drug and the instruments were covered. Sources of inaccuracy/diversification among the instrument readings should also be taken under consideration, for example, due to nearby bushes, trees, and ant colonies. The soil-specific information from each location, as prepared and packetized by the corresponding sensor nodes, was collected by the sink/gateway, which is described in Section 3.1, so as to become available for further assessment.  
It should be noted that the experiments took place in the summer of 2024, i.e., an extremely hot and dry season, in Athens, Greece. After a short period of testing operation, the soil sensors were given almost equal quantities of water (three 10 It buckets each) and were left to dry again, while their measurements were acquired and recorded by the monitoring system at five minute intervals.