I was trying to model constant acceleration from a device that gives less than great outputs (it's method of determining acceleration isn't perfect). Does this not constitute process (or plant) noise? I think what has me really confused is some of the Kalman output equations have measurement noise added to y(t) where y(t) is of the form: $$y(t) = C*x(t) + noise$$

Could you please elaborate on your statement: "But then your true state generation is wrong." I've updated the model to include what I believe is both Process and Measurement noise inputs.

Ok, well running velocity into the filter with a MUX was not as straight forward as I hoped. I have some input/output dimension errors to fix.

Thanks for the helpful reply! So I clearly have some confusion regarding process noise and measurement noise. I was intending to inject measurement noise for my (at the moment) constant acceleration. Would my measurement noise have to be injected right before the zero-order hold? Both position and velocity are my states, so I'll update the model to include a velocity measurement (I think I can do that with a MUX). I did not intend for acceleration to be a state.

I think that's the answer I was looking for...confirming that these duplicate "images" represent the signal frequencies that can be perfect aliases of the base signal (the signal between -fs/2 and fs/2. Now, you just used a word which I think is significant - folded. When the aliasing occurs, are the two aliased points between the two signals at the exact same position in the images, or is it reversed? For example, if I fold a sheet of paper in half, the left most edge becomes the right most edge and now your points look reversed, albeit symmetric.

Thank you for this - it is helpful, but I think I'm still confused with what it means to have a duplicate image centered at some integer multiple of the sampling frequency. When I think of aliasing, I usually do think of the typical example you have shown above. My confusion is with what does that duplicated image centered on the frequency line really mean? If I'm sampling at 20 Hz, and I have an image at 100 Hz, does it mean the sampled value at the same relative location in the other mage will be exactly the same as the original, but just happens to come from a higher frequency signal?