How do I know my eLearning audience?

Following up on my previous post that talked about the importance of knowing the audience for your eLearning programs. The natural question that was left was "How do I know my audience?" When I am designing my classes they are for a variety of people that range in their occupations, locations, generations, abilities, etc. There is no "one audience" that needs to have the class designed to meet their needs....or at least none that I've found yet. In the ThirdForce blog there is a post entitled Being aware of e-learning gaps... that discusses the accessibility needs for eLearning for the audience. Still the question is how do I know my eLearning audience so I can make the training as accessible as possible? We can survey potential participants, conduct needs analysis, interviews, etc. but does that help us know our audience? I think it has the potential to if the surveys and questions are correctly created and are based on relevant information that is needed by the designers. Follow-up is important with any training program, however, I believe it is even more important with eLearning since we cannot see the participants to judge their reactions. This follow-up give further insight to knowing our audience as well as improving the programs being designed. I think that the more varied the audience the more channels we need to utilize to get to know them both before and after their participation in the programs we've designed.