Computation of calibrated denoised sigma0

Calibration

Sentinel-1 Level-1 SLC product contains radiometric calibration Look-Up Table (LUT) and denoising LUT to compute the required quantity. This procedure is recalled in this note Nuno Miranda [2015] and detailed in this document. A short summarize recalled below can also be found here.

The radiometric calibration is applied by the following equation:

\[value(i)=\dfrac{|DN_i|^2}{A_i^2}\]

where \(value(i)\) can be \(\beta^0(i)\), \(\sigma^0(i)\) or \(\gamma(i)\) depending of the used calibration table \(A_i\) on the digital number \(DN_i\). The \(A_i\) LUT is provided at a lower resolution than the \(DN\) and should thus be bi-linearly interpolated.

Denoising

The denoising applied on the Sentinel-1 SLC NRCS in Ifremer SARWAVE Level-1B XSP processor is following the procedure described in Piantanida et al. [2017]. The range and azimuth de-noise LUTs must be calibrated matching the radiometric calibration LUT applied to the DN as:

\[noise^{rg/az}(i)=\dfrac{|\eta^{rg/az}_i|^2}{A_i^2}\]

where \(\eta^{rg/az}_i\) are the range and azimuth noise LUTs and \(noise^{rg/az}(i)\) are calibrated noise profiles depending on the used calibration table \(A_i\).

The radiometrically calibrated and denoised \(\sigma^0\) thus writes:

\[\sigma^0(i)=\dfrac{DN_i^2-\eta^{rg}_i\eta^{az}_i}{\Sigma^0_i}\]

where \(\eta^{rg}_i\), \(\eta^{az}_i\) and \(\Sigma^0_i\) are respectively the range noise, azimuth noise and calibration LUT interpolated over the Digital Number locations \(i\).

Note

\(\eta^{rg}_i\) is both range and azimuth dependent and \(\eta^{az}_i\) is azimuth dependent.

Sentinel-1 IW SLC L1B SARWAVE VV polarization sigma0 denoised (one value per intra burst tile) over Tropical Cyclone NIRAN 2021 (New Caledonia).

Sentinel-1 IW SLC L1B SARWAVE VH polarization sigma0 denoised (one value per intra burst tile) over Tropical Cyclone NIRAN 2021 (New Caledonia).