# Remote Image Capture System to Improve Aerial Supervision for Precision Irrigation in Agriculture
## 3 Results and Discussion
### Experiments on Capture Distance  
The maximum distance allowed from the remote node to the control node is another important factor to be analyzed. Therefore, an extensive series of experiments has been done to find the optimal working distances. Since the system was designed for horticultural crops, such as lettuce, the signal loss due to intermediate obstacles can be neglected. This means that the line-of-sight of the different nodes can be maintained, which in general allows for much greater distances.  
The experiment consisted in placing the control node at a fixed position of the crop, near the farm house, and 11 remote capture nodes at different distances from 150 m to 1125 m. For each distance, between 20 and 50 images were captured and transmitted to the control node. This way, the error rate, defined as the percentage of images that produced any transmission error, was calculated. Figure 11 contains an aerial view of the crop where the experiments were conducted, with the location of the RICS nodes and the control node.  
Figure 10: Some sample images received in the coordinator node with different transmission speeds: (a) 57,600 bps; (b) 38,400 bps; (c) 28,800 bps; (d) 19,200 bps (image received without errors).  
The obtained graph of the transmission error as a function of the distance is presented in Figure 12. In these tests, the images have a resolution of 320 \(\times\) 240 pixels.  
As is evident from Figure 12, the error progressively increases with distance. The error is 0 for all the distances below 600 m, meaning that no error occurred in the transmission of these images. It remains at low values until the distance reaches 750 m. However, the error grows very quickly from 800 m, being unacceptable for distances greater than 1000 m. Thus, if the local controller node is situated in the center of the crop, the system can cover effectively an area with a diameter around 1500 m, which should be enough for most small and average farms. Figure 13 shows some of the typical errors in the images produced by loss of packages due to the distance.  
Figure 11: Aerial view of the location of the local control node and the remote capture nodes (source: DigitalGlobe, European Space Imaging).  
Figure 12: Error rates in the transmission of images from the remote RICS nodes to the local coordinator node, as a function of the distance between them. The speed is 19,200 bps and the resolution is 320 \(\times\) 240 pixels.  
In the experiments, it has been observed that the loss of data in the transmission affects the final size of the received images. For example, the files received in Figure 13a-d have sizes 50.5 Kb, 44.1 Kb, 25.1 Kb and 13.0 Kb, respectively. This allows detecting errors in the transmission of the images and, consequently, automate the request of a new image to the active remote node. Thereby, the embedded microprocessor of the coordinator node verifies the integrity of the image file by checking the header and end-of-file according to the JPEG image format, as well as the size of the received data stream.