Digital Output Wind System for Airport Use

Abstract

The workload in Air Traffic Control Centers often prohibits the controllers from making lengthy observations of the moving pointer indicators in order to obtain sufficiently representative estimates of the current surface wind. A requirement for wind instruments permitting read-out of the current wind information in digital form has been advanced by the International Civil Aviation Organization. Consequently, a project was initiated at the Instrument Division, Atmospheric Environment Service, to develop a wind system capable of providing representative estimates of the current wind automatically. In this paper the present status of the above-mentioned project is discussed. The system developed to date consists of a standard Atmospheric Environment Service 3-cup anemometer and wind vane, a signal processing unit, and a digital display panel. The wind speed and direction information is displayed to the observer in the form of a one-sided 2-min running mean, while the gustiness is indicated by the peak gust in the last 10 min, decayed at a rate of 1 mph min−1. A high-speed Hewlett-Packard 2010 series data logger was used to evaluate the system. The analog signal from the cup anemometer was recorded by the data logger directly, and also through the signal processing unit. Similarly, the wind direction signal from the vane-driven Muirhead 18M4J1 synchro motor was recorded by the data logger through a low-torque Baldwin 80 Series optical encoder and also through the signal processing unit. Thus, simultaneous records of the processed and unprocessed wind signals were obtained for further analysis. These records were then read into a PDP-10/50 computer and direct comparisons were made between the computed one-sided running means and those given by the wind processing unit. The analysis showed that the root-mean-square difference between the computed and the indicated mean wind speeds was 0.3 mph. The data provided by the wind system were compared with those data satisfying the standard airport wind algorithm. According to this algorithm the airport wind speed and direction are given as 2-min running means, while for the gustiness value the peak gust in the preceding 10 min is indicated. It was found that the largest difference between the wind information supplied by the wind system and that specified by the algorithm was less than 10°, 2 mph and 4 mph, respectively, for direction, speed and gustiness. The chief advantage of the system is that it is relatively inexpensive and that it possesses typical analog accuracy, which is more than adequate for aeronautical applications. Furthermore, by using simple logic circuits no special consideration has to be given to the 360° crossover when averaging the wind direction. The system is intended primarily for airport use; however, it also holds considerable promise as a sensor for automatic weather stations.