## 3 Deployment Strategies at Offshore Platforms  
All lidars in the NORSEWiND project were planned to provide stand-alone wind profile observations offshore over many months of operation, _i.e._, there would not be nearby meteorological masts for comparison during the offshore deployment. This prompted a need for careful pre- and post-deployment validations. Access to the lidars at the offshore platforms is limited thus it was necessary to plan carefully.  
The lidars were selected by the industrial partners and encompassed focused cw Doppler wind lidars of the type ZephIR(r)[16, 17] and pulsed wind lidars of the type WindCubeWLST(r)[18, 19]. Dependent upon the height of the platform at which each lidar would be installed there were specific deployment plans for the two types of lidars. The key aim was to observe wind profiles without significant flow distortion from the platforms and to observe winds at several heights in free stream conditions. It was decided as most important to observe winds at 100 m above mean sea level (AMSL) as it is expected to be close to the hub heights of future offshore wind turbines. A wind turbine with a rotor diameter of 120 m will sweep from 40 to 160 m AMSL. The wind profiles were planned to be observed within these height ranges in steps of 20 m, typically at 5 or 6 heights for the ZephIRs and at 10 heights for the WindCubes.  
The deployment requirements for each platform or rig included technical and legal considerations. From the technical perspective it was important to clarify the access to the platform and to ensure the installation would be at a suitable location with a level and vibration-free position and the mounting would be with free view for all laser beam directions. The free view may potentially be disturbed by the rig, cranes, derricks, building, _etc_. As an example Figure 3 shows photographs of some lidars in situ to demonstrate the selected installation spots. On oil and gas rigs the installation location was selected to be as far as possible from exhausts and flares. It was important to avoid high aerosol  
Figure 2: Overview of observation period from the lidars.  
concentrations that could either corrupt the measured wind speed or cause complete extinction of the laser light and thus prevent valid measurements.  
The lidars need a power supply and a communication network. Thus it was important to ensure a suitable and uninterrupted power supply and to check if un-regulated or un-buffered power supply could occur. Furthermore, the communication network was required to allow remote control, data retrieval access and time synchronization. At some platforms cable line was hooked up at Ethernet and using VPN. The time synchronization was important since the internal clocks of unattended lidars may significantly drift if they are not actively synchronized (there were unfortunately examples of this). The drift is typically around one to three seconds per day; thus it needs update once per day or hour. A network time server (if available) or an onboard Global Positioning System (GPS) device can be used as reference time sources. NTP protocol was used once per day typically. On offshore platforms debris from birds is common. This should not fall on the lidar's optical port. Therefore spikes or cages were established. Large amounts of the wiper fluids were provided and connected to keep the lidar windows/lenses clean. The wash and wipe systems were regularly revisited.  
On the un-manned platforms theft protection was carried out. At manned platforms/rigs the personnel were instructed to perform operation and maintenance of the remote sensing instruments. In fact, it proved very important that this instruction/training was carefully undertaken to allow best operation of lidars. After installation a thorough on-site test was done. The systems were configured for immediate safe shutdown.  
Figure 3: Photograph of selected lidars on platform.