Deploy the RAT (ram air turbine) emergency generator and use the RPM and generated power to compute air speed.
The rat will also accrete ice and given that it (probably) isn't heated will ice up pretty quickly.
As an old f@&t, I have to say that if you really get into icing and turbulence (which you should avoid anyway), the way to survive it is to keep the power at cruise settings and fly attitude. Ignore altitude fluctuations. Turn the autopilot OFF or you'll be fighting it constantly. You will move up and down with the air mass but as long as you are stabilized within the air mass, you will get through it.