[Namikaze]

Thing is, Namikaze, Voice Control states it can't emit things outside human possibility, giving as specific examples both ultrasonic and infrasonic emitting, as I quoted above.

Poop.  I missed that part in the wall of posts. 

[Hibiki54]

If you want a new sense that does not enhance your vision or audio etc and still leet you "see" even while blindfolded then you might want to look at astral perception rather than ultrasound....

So, explain to me how you would traverse a man-made bunker while blindfolded? You cannot do that with Astral Perception because you do not have any auras to follow. And even if you were in a natural cave, you could not really

Ultrasound is like having the radar senses of a bat.

[Xenon]

Mundane, factory-made walls and furniture are "seen" from the astral as featureless grey shadows of their physical form. As I see it, Astral Perception would be perfectly viable to navigate the bunker while blind-folded.

The earth not only have an astral aura, it have a tangible astral form. A natural cave would be more colorful and bright than even regular Auras. A natural cave would be "Astrally Real". Unlike a mundane man made wall, you can't even astrally project through the walls of a natural cave.

[Namikaze]

Astral perception is nearly useless underground.  The gaiasphere has an aura, which would prevent any astral perception within it's borders.  Assuming the man-made bunker was recent, the gaiasphere probably wouldn't have adapted to the change yet.  In a cave though, astral perception is probably fine since the gaiasphere has adapted to the cave's structure (because it's natural).