SEASTAR

SEASTAR is a new Earth Explorer mission concept dedicated to observing small-scale ocean surface dynamics in coastal seas, continental shelf seas and Marginal Ice Zones (MIZs).

The mission proposes to measure two-dimensional vector fields of total surface current vectors (TSCV) and ocean surface vector winds (OSVW).

SEASTAR is the first mission to offer the sensitivity, fine resolution, high accuracy, wide swath and flexible sampling to observe and characterise these small-scale phenomena. Using highly innovative squinted along-track interferometry on a single independent satellite, SEASTAR will, for the first time, quantify these fast-evolving processes on daily to multi-annual scales, across different ocean conditions and latitudes, over all coastal and shelf seas and MIZs.

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Primary Scientific Objectives

  • Measure

    to measure, for the first time, two-dimensional fields of total surface current and wind vectors at 1-km resolution, with high accuracy, over all coastal seas, shelf seas and MIZs, to characterise their magnitude, spatial characteristics, regional extent, and temporal variability on daily, seasonal to multi-annual time scales

  • Deliver

    to deliver, for the first time, accurate high-order derivative products (e.g. vorticity, strain, divergence) to explore the relations between ocean sub-mesoscale/mesoscale circulation, air-sea fluxes and vertical exchanges

  • Investigate

    to investigate the relations between small-scale dynamics, air-sea interactions, vertical processes and marine productivity using synergy with high-resolution satellite data from optical, thermal and microwave sensors

  • Validate

    to validate high-resolution and coupled models and support the development of new parameterisations to improve operational forecasts and reduce uncertainties in climate projections.

Technology

SEASTAR consists of a single instrument on a single satellite flying in sun-synchronous Low-Earth Orbit. SEASTAR is the first single-platform SAR (synthetic-aperture radar) system dedicated to squinted along-track ocean interferometry from space.

SEASTAR imaging geometry A.

The payload features two squinted SAR beams pointing ±45° in azimuth fore and aft of the satellite plus a standard SAR beam broadside with multi-polarisation capability (VV/VH, HH/HV). This innovative approach makes it possible to retrieve both components of the ocean surface current vector and the wind vector simultaneously in a single pass, with fine resolution and high accuracy.

SEASTAR produces a single-sided continuous swath 100–150km wide with a minimum incidence angle of 20°. The inherent spatial resolution of the SAR images is a trade-off between observing swell waves and achieving high accuracy Level 2 products for ocean surface current vectors and wind vectors at 1-km resolution over the full swath. Scientific objectives are traced to high accuracy requirements at 1-km resolution for TSCV (0.1ms−1) and OSVW (1ms−1).

The instrument operates at Ku-band or Ka-band. The choice of microwave frequency and interferometric baseline must ensure high sensitivity across the wide swath in all sea state conditions, including sheltered coastal regions.

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