Generic Methodology for Field Calibration of Nacelle-Based Wind Lidars

Nacelle-based Doppler wind lidars have shown promising capabilities to assess power performance, detect yaw misalignment or perform feed-forward control. The power curve application requires uncertainty assessment. Traceable measurements and uncertainties of nacelle-based wind lidars can be obtained through a methodology applicable to any type of existing and upcoming nacelle lidar technology. The generic methodology consists in calibrating all the inputs of the wind field reconstruction algorithms of a lidar. These inputs are the line-of-sight velocity and the beam position, provided by the geometry of the scanning trajectory and the lidar inclination. The line-of-sight velocity is calibrated in atmospheric conditions by comparing it to a reference quantity based on classic instrumentation such as cup anemometers and wind vanes. The generic methodology was tested on two commercially developed lidars, one continuous wave and one pulsed systems, and provides consistent calibration results: linear regressions show a difference of ∼0.5% between the lidar-measured and reference line-of-sight velocities. A comprehensive uncertainty procedure propagates the reference uncertainty to the lidar measurements. At a coverage factor of two, the estimated line-of-sight velocity uncertainty ranges from 3.2% at 3 m · s − 1 to 1.9% at 16 m · s − 1 . Most of the line-of-sight velocity uncertainty originates from the reference: the cup anemometer uncertainty accounts for ∼90% of the total uncertainty. The propagation of uncertainties to lidar-reconstructed wind characteristics can use analytical methods in simple cases, which we demonstrate through the example of a two-beam system. The newly developed calibration methodology allows robust evaluation of a nacelle lidar’s performance and uncertainties to be established. Calibrated nacelle lidars may consequently be further used for various wind turbine applications in confidence

“What being healthy means to me”: A qualitative analysis uncovering the core categories of adolescents’ perception of health

BackgroundStudies exploring adolescents' perception of health are still scarce in the international literature. Through a qualitative analysis, this study aims to explore the core categories or themes evoked when adolescents describe what it means to be healthy and unhealthy.MethodsA convenience purposive sample of 34 15-year-old students from three different upper secondary schools took part in a 2-hour group discussion session. During the session, two conceptual projective techniques, the collage creation and the think-aloud technique, were used to elicit perceptions and descriptions of the typical healthy and unhealthy adolescent. Perceptions and descriptions voiced by adolescents were analysed through content analysis, and the key concepts that emerged were grouped so that core categories or themes could be identified.ResultsThe analysis revealed five core categories that adolescents used to describe what being healthy or unhealthy meant to them: physical appearance, personal commitment and goals, possessions and space, use of free time, and social belonging.ConclusionsInstead of those approaches that focuses solely on the avoidance of risk, the identified core categories or themes might be the basics around which health promotion programmes in adolescence should be built. Engaging students in planning for their future and assisting them in mapping out crucial steps to meet their personal goals, including life, academic, and career goals, is a suitable way to address issues that are meaningful to adolescent health