Ballard did not know exactly where the Titanic's wreak was located. How did he overcome this problem. (Need answer and Explanation)

The following is an exerpt from “Finding The Titanic“

(from Planet-Science.com)

”The traditional way to search for wrecks was to use sonar. Sonar uses sound to detect objects underwater. As well as using sonar, Ballard searched for the Titanic's trail of debris. He estimated that it would be over 2km long. Ballard had just 12 days to find it, in an area of ocean five times the size of New York.

To find the trail, Ballard used a deep-sea vehicle called Argo. Argo had lots of cameras and was towed behind the ship. Argo floated just above the sea floor, 2.5 miles down in the cold, dark Atlantic.

After days of searching, Ballard found the trail. He knew the currents would take the trail northwards. Ballard followed the trail and sailed right up to the Titanic!”