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Boom Orientation

Anemometers and wind vanes mounted on a meteorological tower are typically mounted at the end of a horizontal boom with a length of 2m or more. Mounting an instrument at a distance from the tower insulates it from the worst of the distorting effects that the met tower has on the wind flow.

The boom orientation is the azimuth of the boom when viewed from above. A boom that points due north from the met tower has an orientation of 0°. One that points due east has a boom orientation of 90°, while one that points due south has an orientation of 180°.

With Windographer 4.1 you can specify the boom orientation for each data column, and it automatically reads boom orientations from RLD, NSD, and NDF files.

Specifying Boom Orientation in Calibration Window

You can enter boom orientation in the Calibration window. That's because, like calibration constants, the boom orientation can change in time. Boom orientation changes often result from small inadvertent shifts that occur when towers are tilted down for maintenance, but they can also happen because of a deliberate re-orientation of a boom. The Calibration window lets you specify any number of changes in the boom orientation over the lifetime of your data set.

Note that boom orientation apply to meteorological towers only. In other types of data sets, such as SoDAR or LiDAR data, or computer modeled data sets such as MERRA-2, the boom orientations is not applicable so you can leave it set to zero.

Flagging Tower Shading by Boom Orientation

One result of specifying the boom orientation is that it makes the flagging of tower shading very easy. Windographer knows that an anemometer experiences tower shading whenever the wind direction is roughly 180° from the boom orientation. So even if the boom orientation changes over time, you can flag all tower shading events in just a single click from the Flag Tower Shading window.

Tower Distortion Analysis Window

Another benefit of specifying the boom orientation is that it allows Windographer to highlight the expected center of the shaded sector, so that you can see how well that agrees with the observed shading patterns.

Combining Anemometers by Boom Orientation

You can also combine co-located anemometers by boom orientation, using the IEC rule of thumb that the optimal boom orientation is 45° away from the wind direction for tubular towers, or 90° in the case of lattice towers. The Combine Anemometers window now offers this option.