Signature of Arctic first-year ice melt pond fraction in X-band SAR imagery
The Cryosphere Discussions
In this paper we investigate the potential of melt pond fraction retrieval from X-band polarimetric synthetic aperture radar (SAR) on drifting first-year sea ice. Melt pond fractions retrieved from a helicopter-borne camera system were compared to polarimetric features extracted from four dual polarimetric X-band SAR scenes, revealing significant relationships. The correlations were strongly dependent on wind speed and SAR incidence angle. Co-polarisation ratio was found to be the most
... SAR feature for melt pond fraction estimation at intermediate wind speeds (6.2 m/s), with a correlation coefficient of 0.46. At low wind speeds (0.6 m/s), this relation disappeared due to low backscatter from the melt ponds, and backscatter VV-polarisation intensity had the strongest relationship to melt pond fraction with a correlation coefficient of &minus;0.53. From the results, an intermediate and a low-wind speed empirical model for melt pond fraction estimation were suggested and evaluated. The models gave good estimates of mean melt pond fraction for the full satellite scenes, deviating with less than 4&thinsp;% from the airborne retrieved melt pond fractions in the investigated area. A smoothing window of 51&thinsp;&times;&thinsp;51 pixels gave the best reproduction of the width of the melt pond fraction distribution. A considerable part of the backscatter signal was below the noise floor at SAR incidence angles above ~&thinsp;40 degree, restricting the information gain from polarimetric features above this threshold. Compared to previous studies in C-band, limitations concerning wind speed and noise floor set stricter constraints on melt pond fraction retrieval in X-band. Despite this, our findings demonstrate new possibilities in melt pond fraction estimation from SAR, opening for expanded monitoring of melt ponds during melt season. In the next step, melt pond estimation from SAR may supplement surveillance from optical satellites, providing melt pond information to climate applications during cloudy conditions.