A method to automatically determine sea level for referencing snow freeboards and computing sea ice thicknesses from NASA IceBridge airborne LIDAR

► We obtained a local sea level reference at the accuracy of centimeters using the ATM L1B data. ► The sea level reference has a spatial gradient from 0.01 m to 0.03 m/km along each L1B profiles. ► The mean snow freeboards are 0.59, 0.67, 0.53, and 0.60 m on the four profiles, respectively. ► The mean ice thicknesses are 1.91, 2.16, 1.76, and 1.94 m on the four profiles, respectively. ► The ATM L2 data can give an overall estimate of ice thickness, but can not accurately resolve leads.