I was recently on a project where I had to collect ground penetrating radar data on a steep slope.
Using the GPR, I traversed the slope since the slope was too steep to collect up and down in any systematic way.
But, I had two issues:
1) the antenna was producing a signal at a 45 degree angle (the approximate angle of the slope), and
2) the wheels were turning at different rates making it impossible to create any accurate 3D map or time-slice.
If you have had issues, tell me in the comments what they were!!