The performance of Harmony's two-dimensional sea-ice-drift observations

Abstract

Sea-ice motion is driven by wind and ocean stress, and varies in space and time.
Small-scale drifts primarily affect the opening of leads, while large-scale drift primarily controls the loss of sea ice.
Both the opening of leads and the loss of sea ice play a major role in the energy balance of the Arctic and Antarctic regions.
Understanding sea-ice drift is therefore important for modelling and projecting regional and global climate change.
Accurately modelling sea ice and its dynamics requires high-resolution vectorized observations in the polar regions. Synthetic Aperture Radar (SAR) has proven to be a useful tool in the observations of sea-ice drift.
Most of the SAR-derived sea-ice-drift estimates make use of feature tracking, which depend on two SAR acquisitions.
This limits the temporal resolution and has the tendency to underestimate the sea-ice drift velocity by 10-20%.
Single-pass sea-ice-drift velocities can be inferred from SAR data using Doppler centroid anomaly estimation, but it is limited to the line-of-sight direction and has a resolution of several kilometers.
The only single-pass interferometric observations of sea ice were made using Tandem-X Along-Track Interferometry (ATI).
Its high sensitivity enables the determination of high-resolution sea-ice drift and also to estimate the rotations of individual floes.
However, as with the other two methods, Tandem-X is only sensitive to the line-of-sight. One of the main objectives of Earth Explorer 10 candidate Harmony is the observation of sea-ice drift.
We will present the first results of a performance analysis of Harmony's observations over sea ice.
The passive instruments onboard the Harmony satellites will use Sentinel-1 as an illuminator to provide multistatic observations of the sea-ice surface.
Harmony's reconfigurable constellation can either be optimized for a large line-of-sight difference (Stereo) or for range-direction sensitivy (ATI).
In the Stereo configuration, it will be possible, for the first time, to obtain instantaneous sea-ice drift vectors.
The ATI configuration enables Harmony to acquire high-resolution sea-ice-velocity estimates.
As Sentinel-1 is operating in the wide-swath mode over most of the sea ice covered areas, the polar region is sampled once every 1-4 days.