Is there a way to calculate modulation depth after the modulation process?
If you look at the envelope of an AM signal then for 100% modulation the amplitude of the envelope will vary between 0 and 2 * Ac, where Ac is the amplitude of the carrier. It's a linear relationship, so for e.g. 50% modulation the amplitude will vary between 0.5 * Ac and 1.5 * Ac. So as long as you know that you have a full scale modulation signal then you can derive Ac from the max and min envelope amplitude (mean of Amax and Amin) and from there you can calculate the modulation depth (Amax / Ac).