No longer ago than early 2015 sea ice was being cored. I remember one sample off the coast of Alaska that turned out to be only one meter thick. It was not really something that had to be done Arctic wide. If you know what the exact measurement is in one place and get readings that it is 32% thicker in another place, you can calculate the depth. They measure many things with satellites using this method, not just ice.
That being said, I personally would not want to go out on the ice, especially nowadays. I do not blame anyone else for trying to use safer methods, whether by airplane, submarine, helicopter, or whatever.