Don't get me wrong Steve, you can get very accurate ultrasonic instruments. A company in the UK, Gill Instruments, makes the research quality sensors I used to use and the present price for those is over ?9000. For that you get good measurements of mean wind and turbulence in 3 components from a relatively large sensor. A quick look at the Gill web site suggests that for 2 component mean winds their cheapest products are in the ?1000 - ?1500 range. I know of Airmar and Maretron weather stations being offered in the yacht equipment market - at around ?600 - ?700 in the UK and cheaper in the States. There may be others. Airmar quote 1 or 2 knot accuracy in the dry but only 5 knots rms in "wet conditions" and they say wet conditions include "moisture, rain, frost, dew, snow, ice and/or sea spray". Maretron quote 5% or 1 knot without any proviso with regard to rain. However they do say that "The WSO100 unit itself, especially the area between the transducers, must be kept clean and free of debris for maximum wind speed and direction accuracy". It would be interesting to see how the Maretron instruments perform with rain or ice in the sensing volume! I don't know if they also measure the temperature from the sound speed - if they do that could deteriorate too during rain. These ultrasonic instruments are certainly getting much less expensive and are certainly worth keeping an eye on but I just wanted to warn people that they may well come with a different set of problems than you are used to with cup (or propeller vane) instruments. Peter.
