Evaluation of ocean tide models in coastal ocean regions of northern Australia and Papua New Guinea using an updated set of short term tide gauges

The accuracy of global ocean tide models (OTMs) in shallow waters and along coasts impacts on their numerous applications. For example, the use of OTMs to provide tide corrections (‘de-tiding’) for satellite altimetry observations is required for, e.g., sea level studies and marine gravity field recovery. OTMs are also indispensable in the mitigation of striping errors in GRACE and GRACE-FO time-variable gravity field solutions. It therefore follows that OTM errors in coastal and shelf ocean may then introduce biases into the ‘corrected’ satellite altimetry and gravimetry observations with the potential to impact models using these data. The purpose of our study is to assess the accuracy of two high resolution assimilated OTMs (TPXO9v5, and FES2014b) using an updated set of >100 coastal and shelf tide gauges across the northern Australia and Papua New Guinea region. TPXO9v5 and FES2014b are used here because they have previously compared better than other tidal models in adjacent coastal and shelf areas. This study will also provide insight into the tides in this region which contain a mix of shallow and medium depth waters adjacent to the coast, in addition to land and island barriers that result in a complex tidal regime. This study takes advantage of the large number of short-term tide gauges situated on the coast or offshore islands in Northern Australia and Papua New Guinea. This set of tide gauges have observation periods of >30 days, with a number being more than 90 days long which allows the resolution of the major semidiurnal and diurnal tidal constituents. We use harmonic analysis to estimate tidal constants of major diurnal and semi-diurnal constituents from tide gauges then compare them with corresponding values from TPXO9v5 and FES2014b at the tide gauge location. This comparison identifies improvements and also limitations in these OTMs in this region, and their potential impact on tide corrections provided for satellite altimetry products that may propagate into coastal sea surface, and gravity at the coast. The results also provide additional insight into the local tidal patterns in this region, with particular interest in the Torres Strait and surrounding area.