Outdoor field performances of Insect-based visual motion sensors

  • Expert Fabien
  • Viollet Stéphane
  • Ruffier Franck


Considerable attention has been paid during the past decade to navigation systems based on the use of visual optic flow cues. Optic flow--based visuomotor control systems have been implemented on an increasingly large number of sighted autonomous robots designed to travel under specific lighting conditions. Many algorithms based on conventional cameras or custom-made sensors are being used nowadays to process visual motion. In this paper, we focus on the reliability of our optical sensors, which can be used to measure the local one-dimensional angular speed of robots flying outdoors over a visual scene in terms of their accuracy, range, refresh rate, and sensitivity to illuminance variations. We have designed, constructed, and characterized two miniature custom-made visual motion sensors: (i) the APIS (adaptive pixels for insect-based sensors)-based local motion sensor involving the use of an array custom-made in Very-Large-Scale Integration (VLSI) technology, which is equipped with Delbrück-type autoadaptive pixels, and (ii) the LSC-based (LSC is a component purchased from iC-Haus) local motion sensor involving the use of off-the-shelf linearly amplified photosensors, which is equipped with an onchip preamplification circuit. By combining these photodetectors with a low-cost optical assembly and a bioinspired visual processing algorithm, highly effective miniature sensors were obtained for measuring the visual angular speed in field experiments. The present study focused on the static characteristics and the dynamic responses of these local motion sensors over a wide range of illuminance values, ranging from 50 to 10,000 lux both indoors and outdoors. Although outdoor experiments are of great interest to equip micro-air vehicles with visual motion sensors, we also performed indoor experiments as a comparison. The LSC-based visual motion sensor was found to be more accurate in a narrow, 1.5-decade illuminance range, whereas the APIS-based visual motion sensor was more robust to illuminance changes in a larger, 3-decade range. The method presented in this study provides a new benchmark test for thoroughly characterizing visual motion and optic flow sensors designed to operate outdoors under various lighting conditions, in unknown environments where future micro-aerial vehicles will be able to navigate safely.