Is the mridang the same as the Carnatic mridangam?

No: in North India, mridang is a current alternative name for the pakhawaj, and the scholar Aneesh Pradhan warns against confusing it with the Carnatic mridangam. The two drums are close relatives. The mridangam uses a jackwood shell and a semolina (rava) patch on its bass head; the pakhawaj takes wheat dough on its bass.