I’ll add a different perspective as someone who designs operational radars for a living:
Yes, the CFAR threshold absolutely depends on the radar system at hand. Ignoring the academic topics of detection theory and such which we use to set the CFAR bias, operational radars need a bit more than statistical rigor. Most commonly you’ll see CFAR detectors implemented in what’s called “cell-averaging CFAR” (CA-CFAR) where a local noise floor is estimated using a sliding window, and then some bias term is added such that a specific probability of detection is achieved given some probability of false alarm. There are several types of CA which are all basically just riffs on estimating a local mean. Depending on the operational environment, you may prefer some methods over the others.
For you second question, obviously the thermal noise of the system is a driving factor in choosing how you calculate your CFAR, but there are loads of others.
- How stationary is the noise floor?
- Are there a lot of targets closely spaced together?
- How wide/extended are your targets after pulse compression? You’ll want to set up a “guard band” if they’re more than a few samples wide
- Are you expecting any interference of any sort? This may introduce a non-stationary response that you should adjust for
- What kind of clutter are you dealing with (ground, sea, airborne), and can you sufficiently cancel it? I
Here’s an example:
Let’s say I have one low power target and one high power amplitude target in very close proximity. If I just do a regular sliding window, the power from the big target will corrupt/skew my moving average very high, and therefore I might miss the detection of the small target. In this case you would want to use some form of censoring or two-pass CFAR to try to alleviate this issue.
Let’s say you have a lot of sea clutter with nasty sidelobes that you can’t 100% remove. This may skew your local noise floor, so with the help of some clutter mapping you may be able to construct a CFAR implementation that purposefully excludes the clutter region.
I recognized I’ve used some jargon in this post, but these are all pretty standard things in the radar community, so do consult a textbook/IEEE papers if you’re looking for more specifics.