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ACT Protocols for Wave Measurement Systems
July 2012
16
As reported by Magnusson (2008) “…(Norwegian Meteorological Institute), Phillips Petroleum
Norway, now ConocoPhillips, has recorded waves at or in the vicinity of the Ekofisk complex
since 1980. Different sensors have been used, and mounting locations on the complex have
changed through time. In the years 1991 to 1993, environmental data were available through
modem. Since 1993 data have been transferred in real time through internet. The first winter
season (1991-1992), wave data from two height measuring systems (an EMI radar and a Plessey
radar) were largely affected by lee effects from the tank structure. Focus was thereafter placed
on good quality wave measurements, because forecast skills are highly dependent on measuring
feedback. A WAMOS (www.oceanwaves.de) was installed to measure directional wave spectra
at 2/4-K, and two new sites were chosen for 2 down looking lasers (Optech lasers), one at flare
South, with good exposure to waves from east-west direction, and one at flare North, with
relatively good exposure to northerly directions, and also from the east and west sectors. This
paper only deals with the wave measurements from the in-situ systems (wave profilers). The two
Optech lasers have given relatively good measurements in the period 1995-2005, although with
known problems of possible reflection of waves from the tank in northerly situations at the
northern flare, and sea spray from the platform legs in the vicinity of both sensors when waves
are large, as…” during a storm.
Further Magnusson (2008) goes on to state “Due to decommissioning of the platforms North of
the tank, the sensor at flare North was replaced in 2005 with a new system of 4 lasers in an array
on the bridge between 2/4-K and 2/4-B (Krogstad et al., these proceedings). The bridge is
oriented East-West, with open sector towards North and South. Waves from the westerly sector
may be subject to interference with the 2/4-B platform, which is about 80 meters away. The
sensor at flare South was replaced with a MIROS down-looking radar altimeter, a Miros Range
Finder (MRF).”
9.1 Co-locating Systems
The first and highest priority task of an ACT Test and Evaluation calls for the Datawell
Waverider Buoy to be co-located with this array and evaluated against the LASAR.
Although the scientific community is aware of some of the issues with LASAR, the consensus is
that a co-location exercise with a directional Waverider is necessary. At present, there is a non-
directional Waverider at LASAR. However, ACT will purchase the directional Waverider and be
responsible for buoy deployment at the Ekofisk site with Ekofisk oversight. Pre-deployment
calibration of the Buoy will be performed by Datawell. This same directional Waverider will be
used for all subsequent ACT co-location exercises; thus providing a reference standard for all
future testing and evaluation.
For data review and delivery during the reference standard evaluation, the buoy will be capable
of both iridium and high frequency (HF) radio communication. HF was considered necessary in
case the buoy breaks loose from its mooring. The hand held GPS tracking unit, essential in
recovery, communicates via HF. Iridium communication has proven to be very reliable offshore
and out of range of the HF radio communication.