When I work at military facilities in the US, they use wet bulb globe temperature (WBGT) which adds the heating effect of direct sunlight.
We use it to prevent heat stroke. DoD has a system of colored flags that index to the WBGT. Red and black flags indicate that folks working outside need to take breaks at some increased frequency.
The digital Through-The-Earth (TTE) communication system can be used to provide communications links from the surface to below-ground locations. The system can be used to provide real-time monitoring of equipment sensors. The TTE communication uses very low frequency (VLF) transmission (transmission is usually done with magnetic induction, at frequencies below 30 kHz) to provide reliable data links through environments surrounded by rock, but this system in turn severely limits the bandwidth available for information transmission with data rates ranging from 9 bps to 1 kpbs43. However, since both reference and receiver detectors have their own clock, the information that would have to be transferred to the counterpart detector to be effective is just n and t. Therefore, this data rate is sufficient for MuWNS communication requirements.