Modelling wind speeds for cup anemometers mounted on opposite sides of a lattice tower : a case study

Abstract

When mounted at an intermediate monitoring level on a meteorological mast or tower, a cup anemometer’s horizontal wind speed reading is influenced by the structure’s construction type, the anemometer’s relative position to the structure itself and by the wind vector angle. Although measurements at the topmost level of the structure are a basic prerequisite for wind resource characterisation, intermediate height measurements are also required to calculate wind shear characteristics at the site of interest. Cup anemometers mounted at intermediate levels will, to a certain degree, always be influenced by the meteorological mast. Locating the sensors on opposite sides of the structure allows the wind analyst to filter the data according to wind direction, thereby reducing the largest interference effects. Failure of one of these same-level, opposite cup anemometers would curtail the possibility of data filtering by direction. A technique that would redress the consequences of cup anemometer breakdown during a measurement campaign was thus devised and validated. The capability of the Levenberg–Marquardt (LM) method to model data from one cup anemometer to the other sensor on the opposite side of the tower was assessed by comparing the modelled (LM-generated) data with measured data. The LM algorithm was then used to build a relationship between wind speed records for different concurrent and ever-increasing measurement programme time frames from the two active, same-level anemometers and then failure of one of the sensors was simulated. This paper presents results from a case study using 12 months of wind speed and direction data captured by two, same-level cup anemometers attached to opposite sides of a lattice-type telecommunications tower on the Mediterranean island of Malta.