We've had a few articles on our blog in the past discussing split shots. Also known as "over-under shots", split shots include both the underwater and
4 steps to keeping a clear dome port (water drop free)
Dome vs. Flat Glass Ports for Underwater Photography
Shooting Split Shotswith a Small Dome Port
SJPRO DOME
Ask the Pros: Split shots
Best GoPro Dome Port for Over/Under Split Shot Water Photos
Over-Unders and Split-Shot Underwater Photography - Underwater
Mastering the Split Shot - Waterproof Magazine
Split Water Shots - Ocean Trials with the AquaTech PD16 MegaDome
Shooting Split Shotswith a Small Dome Port
Creating Half-and-Half (Split Shot) Underwater Photos – Kate
Seagoing Solutions
Shooting Split Shotswith a Small Dome Port