INVESTIGATIONS OF TEMPERATURE EFFECTS ON NOAAS NEXT-GENERATION WATER-LEVEL MEASUREMENT SYSTEM

The National Oceanic and Atmospheric Administration collects tide and water-level data by using an air acoustic tide gauge in its Next Gener ation Water Level Measurement System (NGWLMS). The elevation of the wa ter is calculated from the round-trip travel time of an acoustic wave generated from a source mounted above the water. At some sites, solar radiation on the tide well can set up a nonuniform temperature structu re in the well. This temperature effect can modify the travel time of the sound pulse, thereby introducing an offset into the estimate of th e water level and hence into the computation of datums, such as mean s ea level, which is a significant global change index. This diurnal tem perature effect was quantified by computing day and night datums for t ide stations located at La Jolla, California, and Baltimore, Maryland. By employing the difference in these datums, a method of delineating and removing this temperature effect was developed. This analysis resu lted in 1) a quantifiable method for determining the need fur maintain ing temperature sensors at NGWLMS locations, 2) an optimized temperatu re correction formula, and 3) an important finding that in most cases the temperature effect will have little impact on significant global c hange indices such as the yearly mean sea level.