satellite radar altimeters measure the ocean surface height (sea level) by measuring the time it takes a radar pulse to make a round-trip from the satellite to the sea surface and back. Features on the sea floor such as mountains add extra pull to Earth’s gravity field, drawing more water around them and bulging the sea surface outward. The sea surface height can then be used to estimate ocean bathymetry. In 2014 satellite based bathymetry could resolve features of approximately 1.5 km (0.93 miles) or larger.