It sounds very doable to me. Depending on what kind of data you are collecting, it should be fairly easy. You can take the output and the input source and readily work out, through division, the transfer function in frequency space. From that, you can work out the Z, knowing the R. But perhaps you should talk more about the application, in detail, and what kind of data (and if it is z-space sampled data.) One of the editions of
Numerical Recipes will have everything you need to know.