This thesis consists of the results of a Ph.D. study
that was focused on the development of the system of three
time-space synchronized pulsed coherent Doppler scanning
lidars, which are coordinated by a remote ’master computer’.
This system has the unique capability to measure a
complete three-dimensional flow field by emitting the laser
beams from the three spatially separated lidars, directing
them to intersect, and moving the beam intersection over
an area of interest.
Each individual lidar was engineered to be powered
by two real servo motors, and one virtual stepper motor.
The stepper motor initiates the laser pulse emission and
acquisition of the backscattered light, while the two servo
motors conduct the scanner head rotation that provides
means to direct the laser pulses into the atmosphere.
By controlling the rotation of the three motors from the
motion controller the strict synchronization and time
control of the emission, steering and acquisition were
achieved, resulting that the complete lidar measurement
process is controlled from the single hardware component.
The system was formed using a novel approach, in
which the master computer simultaneously coordinates the
remote lidars through a UDP/IP and TCP/IP network by
exchange of network packets. Since the size of the packets
is roughly 1 kB, this approach allows an uninterrupted and
fast coordination of the lidars, even in the case of mobile
networks such as GSM. With this approach a maximum
lag of 10 ms was observed in terms of the scanner heads’
rotation and the measurements among the lidars in the
The laser beam pointing accuracy of each lidar was
estimated to ±0.5° for the laser beam direction, and
roughly ±5 m for the sensing distance. A set of procedures
were proposed that can improve the pointing accuracy by
a factor of 20.
Subsequently, two experiments were carried out in
which the developed multiple lidars system was used to
synchronously measure wind velocity fields in multiple
points in the atmosphere.
|Publisher||DTU Wind Energy|
|Number of pages||176|
|Publication status||Published - 2014|
|Series||DTU Wind Energy PhD|
- DTU Wind Energy PhD-0027
- DTU Wind Energy PhD-27