Design of remote acquisition node of low-cost multispectral image for field monitoring

Analyzing the multispectral images of sensitive bands of crops obtained through multispectral image acquisition devices, has currently become an important means to assess the growth status of crops. However, the existing multispectral image acquisition devices have some shortcomings, such as expensive in price, huge in volume, low in resolution. Further, it is labor-intensive and time-consumed to carry the device to reality environment. To this end, a low cost and high resolution multispectral image remote acquisition node is designed in this paper, and it is deployed in a field to capture multispectral images of crops in real time which are remotely transmitted to the server in order to achieve continuous monitoring for the growth status of crops. The designed node can simultaneously capture RGB images and spectral images in 3 different bands with the resolution of up to 5 mega pixels, and its filters are replaceable. Thus, the node can be deployed in different environments to capture images of different crops. The system control module of the node is constructed by integrating a low-cost high-performance S3C6410 chip produced by Samsung Electronics Co., Ltd, and a peripheral circuit designed by ourselves. The multispectral image acquisition module of the node is constructed by combining a CMOS image sensor OV5640 with a mechanical filters switching device designed by ourselves. To transmit the images remotely, a third generation (3G) module is integrated into the node, which communicates through 3G wireless networks widely used in China. S3C6410 is a low cost chip, OV5640 as a CMOS sensor is much cheaper than CCD sensors, and the mechanical filters switching method is much cheaper than others, so the cost of the node is inexpensive. To ensure the stability and reliability of the node, the powerful embedded Linux operating system is employed as the software development platform. And based on this platform, a modular designing method is adopted to program the software system of the node, realizing the drive control of the filter switching device, capturing images periodically, compressing images and transmitting images through 3G networks in C/C++ language. In order to verify the performance of the node, the node is deployed in a farmland for a series of experiments. To ensure the node works stably in the field, where the climate is changeable and the infrastructure is absent, the node is encapsulated in a waterproof spherical shield, and a solar panel plus rechargeable batteries are used to supply power for it. The experimental results indicate that the node can automatically capture RGB images and images of 3 different bands of 550, 650 and 800 nm, and transmit them to the server through 3G wireless communication networks. The total time consumed to capture and transmit 4 images with a size of 133 kB is about 45.27 s. Aiming at the package loss problem arising in experiments, an image automatic retransmission mechanism is designed based on selective repeat ARQ (Automatic Repeat reQuest) protocol, which makes the package loss rate dropped to 0.54%, realizing the reliable transmission of images. The experiments validate the node designed in this work can capture multispectral images in real time and transmit them remotely, and satisfy the requirements of multispectral image acquisition in real agricultural field environments.