Energy efficiency in wireless sensing networks (WSN) is the last-mile challenge when deploying a WSN for field-based monitoring task to environmentally hard-access, remote, and geospatial large or complex spaces. In this paper, we propose a novel aerial-ground and energy efficient sensing network for meeting the need of geospatial field monitoring by using an aerial UAV as the mobile gateway to wireless sensor nodes in the ground (or in ground structures). Then the focus of this paper is on achieving energy efficiency for ground sensor nodes. In this paper, the authors develop an active radio-frequency (RF) based wake-up mechanism for data transmission in the aerial-ground sensing network. To prove the energy efficiency, several sensor wake-up solutions are physically implemented and evaluated. The results show that the RF-based wake-up mechanism can potentially save more than 98.4% of the energy that the traditional duty-cycle method would otherwise consume, and 96.8% if an infrared-receiver method is used.