Environmental Engineering Reference
In-Depth Information
specifically adapted for harsh and remote offshore environments, the time between
visits will increase. Scheduled lidar and sodar maintenance activities can include
replenishing window-washing fluid, changing wiper blades, removing bird droppings,
and replacing desiccant to control humidity.
Offshore power supplies also require periodic maintenance. On unmanned plat-
forms, birds have a tendency to congregate on all available perches. For this reason,
where solar panels are used, their output should be monitored and compared to read-
ings from a pyranometer to determine if the panels are becoming excessively soiled.
It is recommended that bird deterrents be considered for all critical equipment. If they
are not implemented or if they prove ineffective, it may be necessary to manually
wash off solar panels and other equipment from time to time. When a generator is
part of the power supply system, serving as either a primary or an emergency backup
power source, it will require not only refueling but also periodic maintenance such
as oil changes and perhaps engine overhauls, depending on how often it is used. Pre-
cautions should be taken if the storage batteries in the power supply are housed in
a confined space, as they may pose an air quality hazard for which additional safety
training and equipment (such as an air quality monitor) may be needed.
During operation, it is important to monitor the health of the sensors by analyzing
their data on a regular basis. Furthermore, it is recommended that status indicators
from ancillary equipment on the tower, such as warning lights and power supply,
be included in the data transmitted from the station. This information can be moni-
tored to verify that the systems are operating normally and to support maintenance
planning.
Because of the cost and effort needed for a maintenance visit to an offshore mon-
itoring station, it is recommended that ample spare parts for critical equipment be
brought along during maintenance visits. This is particularly true for equipment that
typically has an extended replacement lead time, such as calibrated anemometers.
14.4 SATELLITE-BASED MICROWAVE SENSORS
Given the costs and inconveniences of surface-based wind monitoring systems, it is
natural that there should be a strong interest in other potential sources of offshore
wind resource measurements. The leading candidates are satellite-based microwave
sensors, and in particular, microwave radiometers, scatterometers (SCATs), and SARs.
All these instruments operate on the principle that winds create waves, which affect the
roughness of the sea surface. The degree of roughness, and specifically the size distri-
bution of the small wavelets
2
that form almost instantly in response to the wind, is in
turn related to the amount of microwaves emitted or reflected from the surface at differ-
ent frequencies. Using mainly speed measurements from weather buoys as the standard
2
The signal detected by microwave sensors is most sensitive to waves that are about the same size as the
microwave wavelength. This ranges from about a millimeter to several centimeters for most satellite-based
microwave instruments.
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