Observing Sea Surface Height By a Wide-Swath Altimeter and Its Challenges

Abstract:

Ocean circulation at scales down to 1 km is a complex system with rich structures as revealed by satellite images of sea surface temperature and color. Traditional nadir-looking satellite altimeter, measuring sea surface height (SSH) that is diagnostic of surface geostrophic currents, is limited in spatial resolution by instrument errors and sparse cross-track sampling. The popular gridded two-dimensional SSH products from AVISO data center have spatial resolution on the order of 150 km in wavelength. Even the original along-track data are limited to 50-70 km in resolution owing to instrument noise. Using the radar interferometry technique, the proposed SWOT (Surface Water and Ocean Topography) Mission currently in development promises to produce SSH observations over a swath of 120 km with resolution reaching 15 km in most part of the global oceans. To ensure the coverage of the entire earth between the 78-degree latitudes dictated by the mission’s non-sun-synchronous orbit, the orbit repeat period is 21 days. The number of observations in a repeat cycle ranges from 2 near the equator to more than 10 at the highest latitudes. To reconstruct SSH from the irregularly sampled observations with complex error characteristics will pose a significant challenge for advancing the study of ocean circulation from this new type of observation. We offer a simple tool for simulating SWOT observations that can be applied to an ocean general circulation model, allowing the exploration of ideas and methods to optimize information retrieval from the SWOT Mission in the future.