Measurements

The Purposes of the Measurements
In the spring of 1999 an extensive measurement programme was launched at Horns Rev to survey the wind and sea conditions at Horns Rev.

Based on the measurement data and on calculations of the wind and sea conditions, the purposes of the measurement programme are to be able to calculate important data. These data may be production prognoses, loads (wind loads, wave loads, currents and ice loads) and to estimate possible changes of the sea bed in the long run as well as local erosion around the foundations.

Extent of Measurements
It is a big challenge to make offshore measurements and immense resources are invested into obtaining as much information as possible over a certain period of time. Based on these requirements, and after thorough considerations, a 'stand-alone' solution was chosen for the supply of electricity and the measuring equipment, designed to work for years and years. Close to the reef a square lattice mast has been erected on a single ø1700 mm-pile. In May 1999 the first measurements were made and later, in June the same year, the sea measurements were commenced.

Meteorological Measurements
The met measurements include measurements of wind speeds and directions at four levels; temperature; atmospheric pressure, influx of light and registration of lightning. The measurements were made at the following four levels: 62, 45, 30 and 15 meters above DNN, please refer to the below figure.

In the top section of the mast, at level 58, an extra and completely separate system for the measurement of wind speeds, direction and atmospheric pressure has been installed. This provides the possibility and safety of recording data in case of errors and these measurements can also be used for verifying the principal measurements.

The Sea Measuring System
The sea measuring system consists of two wave riders, which constantly measure the movements of the sea surface. It also consists of an acoustic Doppler radar, which measures current, water depth, temperature and salinity from the seabed. All stored data from the measurements of the met conditions and current/level activities are sent ashore via a GSM connection.

Presentation of Data
A presentation of the stored and processed data is transferred from the database to an Internet-based Geographical Information System (GIS), which guarantees fast and instant transfer to internal and external project partners. The figure below shows an example with wind speeds (level 62) and atmospheric pressure measured on Horns Rev at the peak of the storm on December 3, 1999.