For this site study, CLS has used its large SAR archive, acquired by ASAR instrument aboard ENVISAT satellite (which is no longer functional). Figure 1 : Density map of SAR images used over the area From each of the SAR image collected, the 10-m high wind information was extracted. To better assess the wind conditions over the Syrian coast, CLS conducted a regional analysis following this principle: - Results from a low resolution atmospheric model are analyzed over years to establish the most probable wind regimes over the area.
- Each SAR wind measurement at high resolution is associated to a low resolution wind regime.
- High resolution wind measurements are combined by regime in order to estimate the mean wind field (or other statistical parameters) at high resolution over the area.
This study led to the highlighting of 7 main wind regimes off the Syrian coast. Two of these 7 regimes are shown on the figures 4 and 5. Figure 2: Regime 1: 52,04%Left: surface wind model results; Right: SAR-derived surface wind results |
The first regime over the area is likely to happen at 52.04%. On Figure 4, despite their different resolution, one can observe the SAR wind measurement and model output are in good agreement. However, on figure 5, high resolution features depicted by the SAR appear essential for the correct estimation of the surface wind conditions over the area. Figure 3 : Regime 5: 3.99%Left: surface wind model results Right: SAR-derived surface wind results
The high resolution SAR images show very high speed wind regions located near the coast which are note visible on the model output because of their inability to resolve fine scale phenomenon impacted by the topography. This information is of a great help when considering the location of the platform, and in that case the model alone is not sufficient to meet this requirements. In parallel of the regional analysis, some locations were selected to perform an wind regime analysis, using a so-called virtual buoy methodology: all the wind speed and direction measurements are collected at points of interest to derive on the wind statistics. Thereby, the virtual buoy approach avoids the deployment and maintenance costs of an in situ buoy. For each selected location, the estimated wind rose provides a succinct view of the wind speed and direction distribution.
Figure 4 : Example of wind rose
Figure 5 : Wind roses at the 5 points selected off the Syrian coast This type of tools is of a great help when deciding on which coordinate to locate the drilling ring. To know the probability of high wind speed as well as its direction is an essential parameter to take into account during the site survey. |