19:44 Aug 20, 2011
You are right. But for this context (specifically) it takes the same meaning, as it refers to the effect the wind causes on the water. The radar uses the reflection on the water surface waves, which is different for oil and water. If there are no waves, no reflection, no radar sensing. By leeward the effect of the wind is blocked by the vessel causing the wind shade. In this specific case they talk about the final effect, doesn't mind if there's a vessel or not... In the end it's the same.
That's why it took me some time to understand the sense. I had to ask the client. He probably knows better.
In any case, thank you anyway! | 
