Amarine biologist is working on a research vessel to study whale calls. his recording devices are measuring depths above 1,000 meters. as his vessel travels to cooler waters and begins to measure at greater depths, the marine biologist needs to make adjustments to his monitoring devices. why is that?

It's due to more pressure as the sound is searched deep into the waters. The adjustments were done to adapt and make clearer sounds.
Animal researchers use hydrophone arrays to determine the location of the whale calls. Another equipment is the Sound Surveillance system, it is used on the sea floor once during the cold war to detect warships and submarines. But now it is used in researchers to understand animals in the ocean. 

Which of the following is an example of an opposing signal? no examplthates given.   i would say, that traffic lights in a city at major intersections direct the flow of traffic in opposite directions so would be an example.also, stop signs on either side of the same street would be an example. at a train crossing, the light for allowing car traffic in opposite directions or not would be another example.