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An affordable Remotely Operated Vehicle (ROV) has been modified for under-ice sensing. In this paper, we present the system upgrade, including sensor integration, electronics and navigation stack. The new ROV is equipped with a Doppler Velocity Log (DVL) and an attitude heading reference system (AHRS) for navigation, and a stereo camera and a forward-looking imaging sonar for perception. Field experiments were conducted in March 2021 on a frozen waterway in Michigan. The ROV was controlled to stay within 2 meters away from the ice keel. Dead-reckoning navigation based on the DVL, AHRS and Extended Kalman Filter (EKF) are implemented with results presented in the paper. Using the navigation result and DVL beam range measurements, ice-thickness was estimated along the vehicle’s path. The ice thickness is found to be about 25 to 30 cm that is coincident with manual observation from drilled ice holes. Besides that, we also present and discuss interesting features embedded in the frozen ice observed by our stereo camera and the forward-looking imaging sonar.