this is a very forbidding environment. it's cold. just above freezing. it's completely dark. and we really don't know much about the ocean floor here. you might say why not just drop that robotic sonar imaging device there and let it ride around and start mapping all of this? if you want the best performance out of something like this, you'd like to get it as close to the right distance from the floor as possible. this is right at the range of its functioning level here, 2.5 miles down. they have to make sure they have a better idea before they turn it loose. what that means is up oen the surface they're going to spend a little more time with things like the hms echo trying to get a better map of the ocean floor in general. if they have that they'll know where the obstacles are. they'll know how to place that robot and get better results. >> tom foreman there with some fascinating insight. and each day we learn more about the challenges the searchers face as they try and locate this