Global absolute sea level: The Hawaiian network

Abstract

NOAA has begun work on a pilot absolute sea level network in Hawaii. Tide gauge stations on the islands of Hawaii, Maui, Oahu, and Kauai have been upgraded by installing Next Generation Water Level Measurements Systems (NGWLMS). A regular program of monitoring the stability of each tide gauge in the International Earth Rotation Service (IERS) conventional terrestrial reference frame has begun. Two primary IERS stations are located in Hawaii: the NASA Very Long Baseline Interferometry (VLBI) observatory at Kokee Par, Kauai, and the University of Hawaii lunar and satellite laser ranging station, Haleakala, Maui. During March and April 1987, and again during April 1988, geodetic surveys using the Global Positioning System (GPS) were performed to determine the positions of the tide gauges relative to these observatories. The vectors between the stations range from about 10 to more than 350 kilometers, with height differences as large as 3,050 meters. The RMS scatter of repeated measurements on the longest lines was approximately 1 centimeter in latitude, 2–3 centimeters in longitude (equivalent to better than 1 part in 10 million), and 5–6 centimeters in height, excellent results for the current status of the partially completed GPS satellite constellation and the available satellite ephemerides. A second independent method of monitoring changes in the heights of stations, by measuring changes in absolute gravity, is being tested at stations on Kauai, Oahu, and Maui. The first observations, made during October 1987, have uncertainties equivalent to approximately 2–3 centimeters in height.