Several months ago, I got a one-month freelance job in Geohazard Survey. My previous work experience in 11 years was mainly
focused on streamers seismic survey & Ocean Bottom Node (OBN). The
experience in the field of Geohazard Survey was quite an exciting and
challenging experience.
I have a principle that
"The glass must always be emptied, so that it can be fully filled."
In essence, if we master a field, we should never stop learning only in one
area but continue to learn other new things by always giving room to add new
broader experiences.
After I was on board, I
learned many new things. The navigation system used is Qinsy, then the MBES
processing used is Qimera. As an online surveyor, I operate Qinsy a lot daily,
so I have added a lot of new learning to the Geohazard survey.
In addition to the
navigation system, there are also many other Analog and Digital hardware that I
have studied. These instruments are widely used in the field of Geohazard
Surveys, including:
a. Multi-Beam Echosounder
(MBES)
An instrument for measuring
the depth of the seabed by emitting a large number of beams from the left to the
right of the vessel at a certain angle. So that the seabed surface can be
described accurately with close distribution.
=> MBES Input = ZDA + GGA, PRH Motion, PPS
=> Real Time Input to Navigation
System = Sound Velocity
b. Single Beam
Echosounder (SBES)
This instrument is widely
used in 3D seismic, so I am familiar with it even though the brands
operated are different, but the use of SBES is to measure the depth of the
seabed using a single beam.
To determine the accuracy
of SBES, it is necessary to do Bar check Calibration from a depth of 5 - 10
meters so that the bar check depth and the depth from the echosounder should be
the same, and take attention to the Index on high and low frequency, draft, and monitor
the power and gain levels.
=> SBES Input = PRH Motion
c. Side Scan Sonar (SSS)
This instrument is towed behind the vessel, which serves to record images of the seabed in dual-frequency (High and Low) on the left and right of the unit in real-time. SSS requires data string from the navigation system in GLL (Latitude & Longitude), VTG (Heading & Speed) and Fix number.
SSS already has an independent PRH Motion,
so there is no need for PRH Motion data string output from the navigation system.
d. Ultra-Short Baseline (USBL)
This instrument
determines the position of the Side Scan Sonar (SSS), which is towed behind the vessel. In principle, the USBL beacon is mounted on the SSS. After the SSS is
towed behind the vessel and the USBL is activated, the USBL transceiver mounted
on the side pole will transmit an acoustic signal to the beacon on the SSS so
that the accurate position of the SSS will be known.
Every time you replace a
beacon, one of the reasons is because the beacon battery runs out, the ID of
the beacon in the USBL software needs to be inputted into the Navigation System
used. So the SSS position will be displayed in the Navigation system.
=> USBL Input = GGA
(Position) and HDT (Heading)
=> USBL Output = USBL data string (to navigation software for beacon position)
e. Sub Bottom Profiler
(SBP)
An instrument that
functions to record sectional layers on the seabed. The more pinger instrument
used, the deeper the penetration rate into the seabed, which is can be more than 50
meters.
These pingers are small
but can be used in large quantities (according to the specifications
requested). These pingers are then connected to a cable and connected directly
to the top side of the Sub Bottom Profiler.
=> SBP Input =
Easting/Northing of the Pinger and
Heading from the navigation system to the top unit, and PRH Motion data string.
f. 2D Hi-Res Streamer
In my previous
experience, I used to do seismic surveys with 4-16 streamers with length of more than 4-6
km, but in this survey, I used a short streamer with 48 channels, so it
was easy when navigating the vessel. One of the challenges is creating a
driver in the navigation system to receive data string from birds in heading
and depth.
Then it was also necessary
to take attention to the GPS position of the Tail Buoy, which was at the very
back of the streamer to be always active and steady.
g. Sound Velocity
Profiler (SVP)
This instrument is widely
used before starts acquisition in a specific area within 2 km, then used again after acquisition in that area is finished. The data was obtained in the form of depth and Sound
Velocity.
So the newly
obtained Sound Velocity data can be immediately updated into the navigation system,
MBES and SBES.
(****)
In addition, besides learning a lot of new hardware and software, I also got a lot of new friends in the field of Geohazard survey who are very supportive and willing to share their knowledge.
This Geohazard Survey project had been completed faster than the
specified time and all done safely.
I am very grateful to
have been given this opportunity. Hopefully, this valuable experience can be useful in the future, and I always have the spirit of continuous improvement and learning.
All the best.
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