Major studies have been undertaken to evaluate the catch ratio of the more common and some alternative shield configurations All of these studies use the resultant total accumulation of some reference standard to evaluate the performance of various shield configurations. To fully understand the effectiveness of the various wind shield configurations, several wind shield studies were conducted to evaluate the airflow at and near the gauge orifice placed in several wind shield configurations. The mean and turbulent flow fields around each wind shield configuration were characterized with sonic anemometers which can rapidly measure the three dimensional flow vectors. In particular, the wind speed at the gauge was compared to a reference sonic anemometer located on a small mast some distance away from the fences.
Remarkably, the ranking of the wind shields by reduction in the mean wind speed at the gauge similar to the catch ratios published in major WMO studies, suggesting that the flow field measurements may provide a useful tool for designing and quantifying catch ratios for existing and new wind shield configurations. The results also suggest that the low porosity double Alter, which is smaller in footprint than the DFIR or SDFIR, may generate the necessary flow field characteristics to provide catch ratios similar to the DFIR.