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Abstract: The spaceborne platform has unprecedently provided the global eddy-permitting (typically ~0.25°) products of Sea Surface Salinity (SSS), however the existing SSS products can hardly resolve mesoscale motions due to the heavy noises therein and the over-smoothing in denoising processes. By means of the Multi-fractal Fusion (MFF), the high-resolution SSS product is synthesized with the template of Sea Surface Temperature (SST). Two low-resolution SSS products and four SST products are considered as the source data and the templates respectively to determine the best combination. The fused products are validated by the in situ observations and intercompared via SSS maps, Singularity Exponent maps and wavenumber spectra. The results demonstrate that the MFF can perform a good work in mitigating the noises and improving the resolution. The Climate Change Initiative (CCI) SSS + the REMote Sensing System (REMSS) SST can produce the 0.1° denoised product whose global mean STandard Derivation (STD) against Argo is 0.21 psu and the feature resolution can reach 30-40 km.
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Key words:
- sea surface salinity /
- multi-fractal fusion /
- high resolution
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Figure 1. The meridional wavenumber spectra for the four SST products. From (a) to (d): Southern Indian Ocean (SIO), Gulf Stream (GS), Kuroshio Current (KC) and Tropical Pacific (TP).
Figure 2. The differences between the different salinity products and Argo (located at the pixels). BEC: BEC-based products; CCI: CCI-based products; ori: original product; Gauss: Gaussian-filtered product; OISST: multi-fractal fusion product with OISST template; REMSS: multi-fractal fusion product with REMSS template.
Figure 3. The statistics for the different SSS products with respect to Argo. Eight regions were examined. For each panel, the bias, the STD, and the correlation coefficient are plotted from top to bottom, respectively. From (a) to (h): Global ocean between 60oS and 60oN (Glo); South Indian Ocean (SIO); Gulf Stream (GS); Kuroshio Current (KC); Tropical Pacific (TP); Agulhas Current (AC); Bay of Bengal (BoB); Amazon plume (Amazon). BEC: BEC-based products; CCI: CCI-based products; ori: original product; Gauss: Gaussian-filtered product; OISST: multi-fractal fusion product with OISST template; REMSS: multi-fractal fusion product with REMSS template.
Figure 4. The bias (panel (a)), the STD (panel (b)) and correlation coefficient (panel (c)) for the different SSS products with respect to the series of TAO. Each star point labels the position of the mooring buoy, encompassed by the distribution of 2 × 4 pixels. As shown in the diagram at the bottom, the upper four pixels represent the BEC-based products while the lower four pixel represent the CCI-based products. BEC: BEC-based products; CCI: CCI-based products; ori: original product; Gauss: Gaussian-filtered product; OISST: multi-fractal fusion product with OISST template; REMSS: multi-fractal fusion product with REMSS template.
Figure 5. Maps of the different SSS products in the region of the Kuroshio Current on March 15th 2016. The same contours are plotted in each panel ranging from 32 psu to 35.5 psu at the interval of 0.1 psu. BEC: BEC-based products; CCI: CCI-based products; ori: original product; Gauss: Gaussian-filtered product; OISST: multi-fractal fusion product with OISST template; REMSS: multi-fractal fusion product with REMSS template.
Figure 6. Maps of the singularity exponents for the different SSS products in the region of the Kuroshio Current. The same contours are plotted in each panel ranging from -0.5 to 0.5 at the interval of 0.01. BEC: BEC-based products; CCI: CCI-based products; ori: original product; Gauss: Gaussian-filtered product; OISST: multi-fractal fusion product with OISST template; REMSS: multi-fractal fusion product with REMSS template.
Figure 7. The meridional wavenumber spectra for the SSS products. From (a) to (d): Southern Indian Ocean (SIO), Gulf Stream (GS), Kuroshio Current (KC) and Tropical Pacific (TP). BEC: BEC-based products; CCI: CCI-based products; ori: original product; Gauss: Gaussian-filtered product; OISST: multi-fractal fusion product with OISST template; REMSS: multi-fractal fusion product with REMSS template.
Table 1. The statistics of TAO 137e5e corresponding to Figure 4.
ori Gauss MFF_OISST MFF_REMSS bias BEC 0.05 0.06 0.05 0.06 CCI 0.05 0.07 0.06 0.06 STD BEC 0.25 0.19 0.21 0.20 CCI 0.14 0.11 0.12 0.11 Corr BEC 0.43 0.54 0.50 0.52 CCI 0.79 0.85 0.84 0.85 
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