An obstacle detector configured to identify negative obstacles in a vehicle's path responsive to steering a laser beam to scan high priority areas in the vehicle's path is provided. The high priority areas can be identified dynamically in response to the terrain, speed, and/or acceleration of the vehicle. In some examples, the high priority areas are identified based on a projected position of the vehicles tires. A scan path for the laser, scan rate, and/or a scan location can be dynamically generated to cover the high priority areas.