LED Mini-lidar for Mars Rover and its Dust Flow Measurement

Abstract

A mini-lidar to observe the activity of Martian atmosphere/dust was developed. Many researchers focused on the Martian atmosphere because of its unique and original activities. One of them is “Dust Devil”, which is a whirlwind on the ground. It is said that the dust devil will affect the atmospheric circulation and electric field of Mars. The 10cm-cube LED mini-lidar was designed to be onboard a Mars rover. A high power LED at 385nm wavelength was employed as a light source of the mini-lidar. LED was adopted as light source because of its toughness against circumference change and physical shock during launch. The pulsed power and the pulse repetition frequency of LED beam were designed as 0.75W (＝7.5 nJ / 10ns) and 500kHz, respectively. Lidar echoes were received by the specially designed Cassegrain telescope, which has the shorter telescope tube than the usual to meet the 10cm-cube size limit. The transmitting beam had a diameter of 30mm with a divergence of 67 mrad. The receiver’s field of view was set as 3 mrad. The ratio of the transmitted energy and received energy was estimated. The receiver always put its field within the transmitted beam even in rough treatment. The high-speed photon counter was also designed and developed to follow to the pulse repetition frequency of the LED light. The measurement range is longer than 30m. Its spatial resolution was improved as 0.15m (＝1ns) by this photon counter. The demonstrative experiment was conducted at the large wind tunnel facility of Japan Meteorological Agency. The measurement target was smoke of glycerin particles. The smoke was released in the wind tunnel with a wind speed of 0-5m/s. Smoke diffusion and convection due to the wind flow were evaluated by the LED mini-lidar. This result suggests that the developed lidar can measure the structure and the motion of dust devil of larger than 2m.