Study on direction dependence of the fully polarimetric wind-induced ocean emissivity at L-band using a semi-theoretical approach for Aquarius and SMAP observations

[摘要] The wind direction dependence of the fully polarimetric ocean emissivity at L-band is studied using a semitheoretical approach. The model, which is tuned and validated against Aquarius and Soil Moisture ActivePassive (SMAP) mission observations, incorporates the two-scale polarimetric ocean emission model, an improved directional wave spectrum, the Anguelova and Gaiser, 2013 (AG13) foam emissivity model and a novel foam coverage model. Wind speeds up to 35 m/s are considered. Comparisons of model simulations to satellite data show that the overall accuracy of model could reach 0.2 K, which is slightly worse than the Aquarius geophysical mode function (GMF) error of about 0.14 K. The negative and positive upwind-crosswind asymmetries of L-band ocean emission and the transition of the phase signatures versus wind speed are well reproduced for all polarizations by the proposed model. The average standard deviations of the differences of polarimetric brightness temperature (TB) between observations and model are less than about 0.16 K for wind speeds up to 15 m/s. Simulations also indicate the anisotropy of L-band ocean emissivities for V- and H- pol would be saturated at high wind speeds. The directional signals at the third Stokes component begin to converge at around the wind speed of 24 m/s. The L-band TB variations due to wind direction for the third Stokes parameter show less sensitivity to wind speed at larger observation angles, while the direction-induced TB variations for the fourth Stokes are more sensitive to wind speed with the increase of observation angle.

[发布日期] 2021-11-01

[关键词] Fully polarimetric ocean emissivity;L-band;Passive remote sensing;Directional wave spectrum;Foam;Aquarius;SMAP