There are a many sensors that can be used for localization of an outdoor mobile agricultural robot. Common ones are wheel encoders, GPS, inertial measurement unit (IMU) and machine vision [1],[2]. Usually these are used in combination to provide a global position estimate. This position can be fairly accurate if expensive sensors are used. On an agricultural robot, the global position does not always have to be that accurate when operating on a field. More important are the robot’s position relative the crops, if the aim is agricultural operation on crop-scale. This requires an ability to navigate locally at high precision [3]. An
example is a robot having a camera sensor detecting and classifying crops, and an active tool performing individual plant operations out of sight of the camera, Fig. 1. The position measurement of the tool relative the camera has to be done with high accuracy, to perform close to crop operations. Further there is an advantage to keep a tool, like a mechanical weed tool, far away from the camera sensor to prevent dust and soil from covering the lens. In these situations there is a need for a non-contact sensor that can measure short distances with high precision.