"Breaking in" to reading papers in an unfamiliar field? I graduated from my undergraduate degree about a year ago and took a job in industry.  While completing that degree, I did research with a professor related to machine learning.  However, after finishing that project, I don't think ML is where I'd want to do my research if I decide to reenter the academic world.

The advice I've received regarding applications to grad school is to be reading papers of a professor I want to work with, at least with enough understanding to suggest a new idea/direction of my own.  However, I don't really know exactly what I'd like to research, but I do have some general topics I'm interested in (categories on the level of "robotics" or "cyber-physical systems") --- figuring out what areas are still active research and what is ancient history is a bit harder than when I could just turn to my advisor and ask "what/who is at the cutting edge in this field?"

Aside from just "jump in the deep end and keep reading until it makes sense," are there methods or techniques that might help me build context or evaluate the areas I'm interested in?
You could use a database, thorough your university library for example, to search for papers in your area of interest (with keywords or author names etc). This will help you see what others are researching and publishing and to determine if that is what you want to do too.

Reading relevant blogs and forums (that deal with same or similar topics as the one/s you're interested in) may also give you some ideas. 

Similarly, talking to academics you may wish to work with is a good idea, as already suggested to you by others. 

I would also make sure that the academic I am working with is someone who is going to be supportive (and have time for me) to make sure that I get some help (rather than being completely on my own). If this relationship doesn't work, your job is going to be much harder. You can change direction of your research later in the degree or post graduation.