This is going to be more than 'a bit of work'. Over 3G means you will have to downsample (which is ok, you don't need a new image every 2.5s for your purpose.)
The only doppler radar that has been reverse engineered is the
Navico HALO radar, but we have not yet mastered how it does doppler. This is waiting for a volunteer, which could be you.
The best codebase to look at is the new 'generic all-brand-radar plugin' at
https://github.com/opencpn-radar-pi/radar_pi/ that some people (including me) are working on. At the moment we are waiting for the
Raymarine guy to show up (or some other volunteer(s)) as the
Garmin xHD and
Navico work is pretty much finished.