Boundary-layer height detection with a ceilometer at a coastal ... - Orbit

3 Site and measurements
In this section the site location is presented and some of the instruments used there. The
theoretical background of the ceilometer, wind lidar and sonic anemometer measurements is
explained, along with a presentation of the available data from the site database.
3.1 Høvsøre
Høvsøre is a farm area located at the westcoast of Jutland, seen in Figure 5(a). Here, a
ceilometer has operated almost continuously since january 2007. The location of Høvsøre was
chosen in 2002 to be a national test facility for large wind turbines, seen in Figure 5(b). Due
to the location and the type of terrain, wind speeds are very high 4 and general wind patterns
are very well understood, providing excellent conditions for the testing (Høvsøre infofolder,
2013).
5 ◦ E 7 ◦ E 9 ◦ E 11 ◦ E 13 ◦ E
NORTH SEA
Høvsøre
DENMARK
56 ◦ N 56 ◦ N
Copenhagen
km
0 50 100
7 ◦ E 9 ◦ E 11 ◦ E 13 ◦ E
(a)
(b)
Figure 5: (a): Map of Jutland, with Høvsøre indicated (map made by Rogier Floors). (b):
View of Høvsøre test station, with operational wind turbines. Picture from Høvsøre infofolder
(2013).
3.2 The ceilometer
The ceilometer is a single lens LIDAR (Light Detection And Ranging) device, which is primarily
used to detect cloud base and vertical visibility. It transmits short pulses of light in the
near-vertical direction. The light is scattered by particles in the air, aerosols, cloud droplets
and precipitation. The returned light is then collected in a receiver inside the ceilometer
(Vaisala User’s Guide, 2004). The height h from which the returned signal comes from may
be estimated as
h = ct
(14)
2
where c is the speed of light and t the time delay. As the speed of light is taken as a constant,
the height may be calculated directly from the time delay. The signal strength as a
4 the annual mean wind speed is ∼9.3 m/s at 80 m
16