# Remote Image Capture System to Improve Aerial Supervision for Precision Irrigation in Agriculture
## 2 Materials and Methods
### Description of the Remote Image Capture System (RICS)
#### Solar Power Supply of the RICS Node  
An important constraint of capture nodes is their reduced power capacity. Different energy-efficient methods have been proposed in existing works to deal with the power battery problem of the notes. For example, energy harvesting techniques has been introduced as a way to recover energy. Some of these methods include solar panels, mechanical vibration, wireless power transfer (WPT), kinetic and wind energy [48]. These mechanisms allow obtaining rechargeable nodes that are able to operate uninterruptedly for longer periods. Solar energy using photovoltaic systems have been used in agricultural applications of the WSNs [49]. Solar panels offer an excellent solution to guarantee the operation of the agricultural monitoring system [50]. Solar cells have been previously used in some studies to provide long-term power to sensor motes in agronomy. For example, an irrigation system is developed in [51] based on the ZigBee wireless protocol and powered by rechargeable batteries and solar panels.  
The direct current (DC) power system of the RICS node consists of a pair of 1.5 W photovoltaic solar panels (in total 3 W), connected to a Sunny Buddy module (SparkFun Electronics, Boulder, CO, USA), with a maximum power point tracking (MPPT) system which provides an efficient management of the energy coming from the solar panels, as well as an adequate management of the battery charge based on the LT3652 chip (Analog Devices Inc., Norwood, MA, USA). The photovoltaic panels use polycrystalline silicon with a size of 15 cm \(\times\) 15 cm, and have a maximum power point voltage of 6 V and a maximum power point current of 0.25 A. The battery used in the remote node has been dimensioned to achieve the appropriate days of autonomy considering the meteorology and the average rate of cloudy days at the installation place. According to the measurements and calculations of energy needs, approximately 2000 mAh are required for 7 days of autonomy, i.e., 7 days with null radiation. The selected battery will be of Li-ION technology since it provides the best energy performance. The work load is considered with power on and in automatic standby mode during 24 h at a capture rate of 1 image per hour. In the case of intensive use of image capture on demand, the consumption of energy can be increased in a timely manner. However, in the typical use, a rate of 1 image per day should be enough to monitor crop canopy due to its slow growth rate.  
If this happens, the local control node will take into account this increase of energy consumption. Thus, it will reduce image captures at the following time intervals to allow for recovery of the energy stored in the battery in case of solar radiation deficit. The typical consumption pattern of the remote node in image capture mode at intervals of one hour is depicted in Figure 5.  
The wireless communication modules (XBee 868 LP) and the image capture processor in low-power/sleep mode will be configured to achieve the maximum efficiency in the management of the energy of the remote nodes. The functional tests performed showed consumption data in the different operations with the values presented in Table 1.  
In relation to the amount of energy available in the batteries of a remote system to capture images, and from the point of view of the use of drones, essential maintenance tasks and recharges are needed to maintain their operability. In addition to the necessary infrastructure to perform this process, it cannot be done automatically without human operators. A problem in this energy supply can cause an accident and endanger the material and human elements nearby, as well as the structure of the drone itself. However, the proposed solution can operate continuously for very long periods of time.