Extensive research has been conducted on unmanned ground vehicles (UGVs), used for critical applications, such as military or search and rescue operations. As all those unmanned vehicles use wireless communications due to mobility constraints, it is therefore important to further define the limits of high reliability communication links in operational environments. The practical importance of this study relates to applications where antennas are located very close to plane surfaces e.g. small, unmanned, vehicles used for exploration, monitoring or rescue purposes in confined spaces. An empirical channel model allows better understanding of the RF propagation mechanisms and enables optimisation of the sensor network with certain reliability levels.