Sewers are often below several meters of concrete/rock/earth, interwoven with steel reinforcements, metal tubing, wires, power conduits and other stuff that wou

Sewers are often below several meters of concrete/rock/earth, interwoven with steel reinforcements, metal tubing, wires, power conduits and other stuff that would make for very poor wireless reception even when directly above the ratbot. The airborne approach on the other hand guarantees maximum range. Perhaps a small, solar-powered dirigible would be a better approach? They don't require massive amounts of power just to stay airborne and solar cells (battery buffered) could arguably provide enough power to stay stationary in most wind situations. A miniaturized version of this perhaps: http://www.popularmechanics.com/science/space/4324155 http://www.popularmechanics.com/science/space/4324155