Level 2 OCN Ocean Swell Spectra (OSW) Component

Sentinel-1 SAR Technical Guide - Level-2 OCN OSW Product

The OSW component is a two-dimensional ocean surface swell spectrum and includes an estimate of wind speed and direction per swell spectrum. The OSW component provides continuity measurement of SAR swell spectra at C-band. OSW are estimated from Sentinel-1 SLC images by inversion of the corresponding image cross-spectra.

The OSW is generated from Stripmap and Wave modes only and is not available from the TOPSAR IW and EW modes. For Stripmap mode, there are multiple spectra derived from the Level-1 SLC image. For Wave mode, there is one spectrum per vignette.

Ocean wave height spectra are provided in units of m4 and given on a polar grid of wavenumber in rad/m and direction in degrees respect to North.

The OSW product also contains one estimate of the wind speed in m/s and direction in degrees (meteorological convention) per ocean wave spectrum, as well as parameters derived from the ocean wave spectra (integrated wave parameters) and from the imagette (image statistics).

The spatial coverage of the OSW product is equal to the spatial coverage of the corresponding Level-1 WV SLC or Level-1 SM SLC product, limited to ocean areas.

OSW Characteristics
Coordinate System Ground Range
Incidence angle [*] S1 22.3 S2 25.6 S3 31.2 S4 36.4 S5 41.0 S6 43.8
WV1 23 WV2 36.5
Ocean Swell Spectra
30 wave number bins
(rad/m, {2Π/800...2Π/30} x 36 directional bins (degrees, equidistantly{0, 10,...,350})
Quality cross spectra
30 wave number bins
(rad/m, {2Π/800...2Π/30} x 36 directional bins (degrees, equidistantly{0, 10,...,350})
for both imagery and real part
Ocean Swell Spectra Spatial Resolution
[km x km]
SM: 20x20
Product splits 170km x 80km SM image into 8 x 4 images
of 20km x 20km for OSW estimation.
WV: 20x20
Ocean Swell Spectra Resolution
On Average, between 30 and 220 m depending on
wave direction relative to azimuth direction
Ocean Swell Spectra Grid Dimension
[azimuth cell x ground range cell]
SM: 2x2
WV: 1x1
Number of Waves Partitions 2
SAR Significant Wave Height
>0 , RMSe < 0.5, Bias < 0.1
Dominant Wave Length
∈ {30,500}, RMSe < 50, Bias < -10
Dominant Wave Direction
∈ {0,360}, RMSe < 40, Bias < 10
Azimuth Cutt-off Wavelength
∈ {15,800}, 210m < Mean < 260m
Confidence Flag for Wave Direction Retrieval
0 or 1

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