A single beam LIDAR would suffer the same problem. That is, the radar was accurate, the problem was the team hadn't foreseen the probe flying over such a deep

A single beam LIDAR would suffer the same problem. That is, the radar was accurate, the problem was the team hadn't foreseen the probe flying over such a deep crater, thus the threshold for failing the sensor in case of a sudden large change in apparent altitude was set too low. This is why I suggested a visual-based sensor, since it would be using a very different measuring scheme, and one which could also be used to cross-check the IMU data.