which program opens .idx file extension

Can you advise which download will open .idx files? I have underwater survey data with .sl3 extension which are processed files and .idx extensions which I hope are raw data that I am trying to open.

[Walter Roberson]

http://www.sonartrx.com/web/Home/Support possibly

Idx appears to be Hummingbird index files and sl3 appears to have to do with sonar logs.