Test och implementering av en laserbaserad havsnivåmätare

Abstract

Measuring sea level has been of interest in Sweden since the discovery of the land uplift and today one reason for measurements is the current climate change. By accurately measuring the sea level, vulnerable coastlines can be detected at an early stage and appropriate measures can be taken. The two types of sensors, radar and pneumatic bubbler gauge, that are mounted at the tide gauge well at Onsala Space Observatory both have a best case measurement uncertainty of 3 mm. This report will study another method based on an optical distance sensor, a laser, that will be a complement to the other two. Before an implementation of such an optical distance sensor the devices accuracy have to be examined. Given the specifications of the wells dimensions measurements related to repeatability, linearity and temperature depence will be carried out. The report conclude that an optical distance sensor has the smallest standard deviation of the three sensors, based on an experiment lasting slighly longer than one day, and that no significant temperature dependence can be found. The laser will sample the reflected light from a reflector that floats on the water surface. Calculations show that this reflector has insignificant impact on the total measurement accuracy. Therefore an optical distance sensor is a useful alternative to the already mounted sensors at Onsala Space Observatory for measuring the sea level.