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Sensor Evaluation for Autonomous Surface Vehicles in Inland Waterways

In this paper, we evaluate and discuss various sensors that may be used by an autonomous surface vehicle (ASV) to detect and classify objects. These sensors were each evaluated quantitatively and qualitatively for effectiveness (range, accuracy, resolution, field of view, height information) and practicality (marinization, effectiveness in various weather conditions, use in darkness, cost). In brief, LIDAR was found to be extremely accurate, although the maximum range (100m for our unit) is too short for most marine applications, the hardware is expensive, and most units are not marinized. Although marine radar is properly marinized and works well in all-weather at acceptable ranges, returns are often reduced to amorphous blobs with little fine detail to aid identification or even proper boundary definition of obstacles. Additionally, marine radar has no concept of height in its return, collapsing all vertical returns to the ground plane, thus obscuring covered passageways, such as those under bridge archways. Visible light cameras perform well at high resolution and long ranges, but only operate in daylight during good weather and are blinded by glare on the water or by the sun itself. Although stereocameras suffer the same drawbacks as visible light cameras, they have potential for short range obstacle detection. Thermal cameras operate day or night and provide an interesting supplement to other sensors, because water is a different temperature and has different emissivity characteristics than most objects. This enables buoys, vessels, structures, etc. to be discerned from the background using a thresholding method. Thermal cameras are limited by weather conditions and are often most affordable in low resolution, low field of view models.