Offshore Wind Energy: Wind and Sea Surface Temperature from Satellite Observations

Abstract

As the land space suitable for wind turbine installations becomes saturated, there is a growing interest for oshore locations. There, available measurements of various environmental parameters are limited and the physical environment is still not well understood. Thus, there is a need for readily available wind speed and direction observations over the ocean and for a better understanding of the marine atmospheric boundary layer (MABL). The sea surface temperature (SST) has a direct impact on the marine atmospheric boundary layer, as the top few meters of the ocean have the same heat capacity as the entire atmosphere above. Under conditions of light winds and strong solar insolation, warming of the upper oceanic layer may occur. In this PhD study, remote sensing from satellites is used to obtain information for the near-surface ocean wind and the sea surface temperature over the North Sea and the Baltic Sea. The aim is to evaluate their potential use and demonstrate their applicability within the context of offshore wind energy; for the quantication of the wind resources and for the identication of diurnal warming of the sea surface temperature. Space-borne observations of wind are obtained from scatterometers and Synthetic Aperture Radars (SAR); active microwave radars that relate radiation backscattered from the sea surface to wind. Scatterometers are characterized by global spatial coverage and long temporal availability, while their resolution is 25 km. SARs are characterized by very high resolution, 600 m, and infrequent temporal and spatial coverage. Twice daily wind speed and direction measurements from scatterometers are used in the present study for an evaluation of the wind resources. The spatial spectral properties of wind fields from scatterometers and SARs, evaluated in this study, demonstrate that wind information from SAR is more appropriate when small scale local features are of interest, not resolved by scatterometers. Hourly satellite observations of the sea surface temperature, from a thermal infra-red sensor, are used to identify and quantify the daily variability of the sea surface temperature. This is found to occur from April to August mostly in the Baltic Sea and the eastern North Sea. Finally, as very often information on the daily variability of sea surface temperature is not available from measurements, three models that predict this variability are applied and compared with the observed warming patterns from the satellite observations.