Using Active Sonar

[Tuee]

Yes, you're right—I see it now. An omni-directional microphone will almost certainly pickup more signal than one only looking in one direction, but obviously it won’t have any directional information about it. The argument that the omni-directional microphone “drowns in noise coming from all directions� is incorrect—it will pick up more of everything, including the signal. To put it in statistical terms, because the “sample� is larger, the power of the test is much stronger. The return-ping ought to “jump out� more against the background of all that sampled data.

With all data gathering sensors, there is a tradeoff between sensitivity and acuity. An interesting illustration of this principle would be the human eye. The indirect (or peripheral) vision has greater sensitivity to light and motion, but images in this region will appear more “blurry�; whereas the direct vision has the ability to see in very fine detail, but has less sensitivity to small amounts of light. The reason it works this way is because the photoreceptors in the indirect vision are networked together by special cells called interneurons which cause neighboring photoreceptors to fire when just one fires—so when one goes off it will trigger a whole bunch, and the overall effect is a brighter (albeit blurrier) picture. The fovia (centre of the retina where the image from the direct vision is projected) has very few interneurons compared to the edges of the retina, thus it is less sensitive but has much higher acuity (which we need in order to read or play computer games).

So LuftWolf is right—a weaker return can’t contain more information than a stronger return, and an omni-directional microphone has the best chance of picking up a weak return.

What about passive contacts—in DW do they appear first in narrowband or broadband? (Does it vary from platform to platform?)