Zero calibration of bottom pressure gauge in antarctic: A case study at Chinese Zhongshan station using GPS techniques

Tide gauge data are critical for assessing long-term trend of sea level changes, which is a significant consequence of global climate changes, and for providing local height datum. Calibration and vertical datum control of tide gauges are fundamental in studies involving the determination of absolute sea level and its long term trend. The Chinese Zhongshan station, located in Larsemann Hills, East Antarctic(69_22_ S, 76_23_ E), represents one of the few possible locations in the Southern Ocean to measure sea level using traditional tide gauge techniques. The sea ice and atmospheric climatology of the region, coupled with a rugged coastline, makes installing a modern tide gauge extremely difficult. To overcome many of these difficulties, we use a bottom pressure gauge operated within a mooring frame. The frame is weighted by 9 lead weights to fix on the sea floor. The calibration requirements of the gauge zero are problematic and require special consideration for an accurate calculation of mean sea level and its change over time. We present results from an application of GPS to achieve an in situ calibration of the tide gauge zero, solving for the vertical offset and zero drift parameters. Obvious vertical offset has been found of the tide gauge zero, which must be removed from the tide data to calculate the long term sea level change. The methodology provides a new and high-precision technique using available instrumentation, allowing users to maximize the oceanographic and geodetic values of tide gauge observations.