1 Validation and Application of Jason-1 and Envisat Significant Wave Heights

Satellite altimetry provides an immensely valuable source of operational Hs data. Currently, altimeters on-board Jason-1 and Envisat provide global Hs observations, available within 3-5 hours of real time. In this work, Hs data from these altimeters are validated against in situ buoy data from the National Data Buoy Center (NDBC) and Marine Environmental Data Service (MEDS) buoy networks. Data covers a period of three years for Envisat and over four years for Jason-1. Co-location criteria of 50 km and 30 minutes yield 3452 and 2157 co-locations for Jason-1 and Envisat respectively. Jason-1 is found to be in no need of correction, performing well throughout the range of wave heights, although it is notably noisier than Envisat. An overall RMS difference between Jason-1 and buoy data of 0.229 m is found. Envisat has a tendency to overestimate low Hs and underestimate high Hs. A linear correction reduces the RMS difference by 8%, from 0.219 m to 0.202 m. A systematic difference in the Hs being reported by MEDS and NDBC buoy networks is noted. Using the altimeter data as a common reference, it is estimated that MEDS buoys are underestimating Hs relative to NDBC buoys by about 10%. The corrected altimeter data are used to make preliminary assessments of two potential upgrades to the Bureau of Meteorology’s wave forecasting system – specifically, an increase in the directional resolution of the wave spectrum and the expansion of the data assimilation system to include Envisat Hs data as well as Jason-1. In situ buoy data are also used to assess the improvements in model forecast skill and the computational requirements of the potential upgrades are evaluated. It is concluded that in order to gain improvements in skill for both short-range and long-range (up to 72-hour) forecasts, then both of the proposed enhancements need to be incorporated