Drone radar facilitates agricultural monitoring

 In agriculture, drones distribute seeds or fertilizers with precision, saving both time and money. When combined with sensors and artificial intelligence, they can perform remote sensing, similar to satellites and airplanes, monitor large crops, conduct detailed analyses of soil’s chemical elements, and identify issues such as erosion. One of the most advanced techniques in this field, Synthetic Aperture Radar (SAR), has been enhanced by Radaz, a startup founded in 2017 at the University of Campinas (UNICAMP) and now based in São José dos Campos, São Paulo.

“It’s an innovative technology with enormous potential to generate a wide variety of products, serving various market segments,” says electrical engineer Hugo Enrique Hernández Figueroa from UNICAMP’s School of Electrical and Computer Engineering (FEEC), who led the team responsible for developing a radar mounted on a small drone. To achieve this, the team had to miniaturize the radar’s electronic hardware and antennas. The idea behind SAR, explains the researcher, involves using a moving radar to simulate an antenna significantly larger than the radar’s physical components. As the antenna’s directivity increases with its size, the system’s resolution also improves.

Through its antenna, the radar emits pulsed electromagnetic waves that are reflected by obstacles on the ground. These waves are then detected by the antenna while the radar is in motion, whether on an airplane, satellite, or drone. The movement of the radar along its trajectory creates a large virtual antenna, allowing for high resolutions and precise observations.

The operating principle of SAR is similar to that of interferometry, where the combination of multiple radio antennas simulates a single large antenna corresponding to the path traveled. If the drone moves 100 meters (m) in a straight line, the SAR can simulate a 100-meter aperture antenna; if the trajectory is circular, with a radius of 300 meters, the radar will simulate a spiral-shaped antenna with a 300-meter radius.

Developed in the United States in the 1950s and used in satellites and space probes since the 1960s, Synthetic Aperture Radar (SAR) has been employed to map the terrain of Venus, which is obscured by clouds made of microscopic drops of sulfuric acid and other aerosols. In the early 2000s, SAR was integrated into large drones for military purposes. With the growing miniaturization of electronic components and the proliferation of drones, it became apparent that SAR systems could be attached to small, civilian devices.

“The challenge was to do it, and nobody was doing it,” says Figueroa. The first recorded instance of SAR on a drone dates back to 2016, from the University of Texas, United States, but this version was handmade and produced low-quality images. The São Paulo-based company took a different approach, developing a system with three spectral bands, including an advanced inertial navigation system (see infographic).