ADCP and CTD
The research Vessel RV/ Samudrikabelong to National Aquatic Resources Research
and Development Agency (NARA) equipped with Acoustic Doppler Current Profiler
(ADCP) and Conductivity Temperature Depth (CTD) profiler to measure physical
oceanographic parameters such as current velocity, temperature and conductivity of
water column. Those instruments are advance technologies which can be utilised in
oceanographic applications.
ADCP
The RV/Samudrika equipped with hull mounted ADCP which can be used to measure
sound velocity profiles towards down (downward looking). The instrument set in the
ship as given in the diagram 1. The data bins are designed at 2.5m from the instrument
up to 35meters with 1m bin intervals. The instrument consists of four beam
transducers transmits a pulse of energy along beam directions inclined typically at 30
degrees from the vertical.Particles in the water column and in homogeneities reflect
some sound energy back to the transducer. The motion of the reflectors relative to the
transducer causes a Doppler shift in the frequency of the received echo. On average
these particles will move at the average velocity of the water surrounding them.
Therefore, we can determine the velocity component along each beam at any point
from the Doppler shift. In practice, we use the echoes returning at later and later times
to determine the velocity component further and further from the transducer. By
combining the measurements from the 3 or 4 beams we can calculate the horizontal
and vertical components of velocity at different depths. So, it provides the current
velocity profiles in different depth levels. The data can be utilised to study the
generation of internal waves, surface friction velocity and the stress.
Fig.1 Ship mounted ADCP in Samudrika
Conductivity Temperature Depth Profiler
Fig.2 Operation of CTD with Rosette water sampler
CTD profiler measures variation of Conductivity and Temperature of sea water as a
function of Depth. Conductivity is important parameter because it determines the
dissolved salts in the sea water. From the conductivity, temperature and depth of any
measurement we can calculate the salinity, density and other properties that allow us
to trace movement and processes such as mixing in the ocean.
The vessel Samudrika equipped with seabird9plus and 19plus CTD’s. The
instruments have capacity to take measurements from top to 3000m and 600m
respectively. The available sensors allows to measure, conductivity, temperature,
density, dissolved oxygen and chlorophyll. Those parameters can be utilized to study
the oceanic processes, fish forecasting and seasonal variation of thermocline depths.
In addition to the CTD, the vessel equipped with the 2000m long coaxial cable and
winch to operate the instrument. The figure 2 illustrates the CTD operation with
rosette water samplers.
Side scan sonar investigations
Side scan sonar is mainly used for detection of underwater objects such as sunken
ships, aero planes, pipe lines, and geo-morphological features on the sea bed. Main
advantages of this technology are time effective for searching, safe deep water
operations and large spatial coverage within short time. In addition, this gives chance
to work in more risky environments even in murky or black waterless visibility. The
lack of good last observed point, information can extend the search area to tens or
hundreds of square kilometers instead of small area. In many cases there are no
accurately identified locations where the drowning objects last observed. Therefore
side scan sonar can effectively use under these conditions.
RV/ Sumudrikaarealso equipped with Yellowfin side scan sonar. It is an instrument
with triple frequencies. The instrument has two data acquisition cables with 30m and
150m length respectively. Currently, the instrument is used for offshore sand deposit
and underwater heritage (shipwrecks) investigation around the country.
Underwater heritage investigations
Side scan sonar is a very good instrument to locate underwater heritages specially in
shipwreck investigations around the country. Some findings from NARA research
team is given in the diagram.
Fig. Some shipwrecks found in east coast of Sri Lanka
Sand depositsinvestigation
Side scan sonar is an important instrument for sand deposits. Some side scan sonar
images are given in the following diagrams.
Underwater pipe line investigation
Fig. Side scan images from east coast of Sri Lanka
Moorings and Profiling
The vessel Sudrika is equipped with three winches. One is with 2000m coaxial cable
to be used for CTD deployments and other two with 100m and 300m fibre optic cable
used for offshore coring and trawling respectively. The possible deployments and
moorings will be discussed as follows.
Deployment of Drifters and Argoprofilers
RV/ Samudrika have enough deck space, winch and A-Frame facilities for Drifter and
Argo float deployments. Currently, NARA engaging drifter deployments but new
research vessel will increase efficiency of the deployments. The diagrams show the
drifter and Argo deployments by NARA Oceanographic research team.
Fig: Drifter and Argo deployment in the offshore southern Sri Lanka
ADCP moorings
Samudrika can be utilised for shallow water Acoustic Doppler Current Profiler
(ADCP) moorings around the continental shelf of Sri Lanka. A-Frame belongs to
vessel can be used for this moorings. Some ADCP moorings are given in the
diagrams.
Fig. ADCP moorings
Geological and Geophysical Exploration of Continental shelf
Recognizing the importance of the marine sciences, Oceanography Division of
NARA is conducting research and surveys within the continental shelf of Sri Lanka.
Geological and Geophysical exploration initiated by NARA include the investigation
of heavy minerals and stratigraphic variations beneath the sea floor mainly in coastal
and offshore regions.
Sub Bottom Profiling
Sub-bottom profiling systems identify and measure various marine sediment layers
that exist below the sediment/water interface. Anenergy source emits seismic signal
vertically downwards into the water and a receiver monitors the return signal that has
been reflected off the seafloor. The system uses this reflected energy to provide
information on sediment layers beneath the sediment-water interface.
Capabilities
Sub-bottom profiling systems useful for characterizing benthic habitats, since they
provide information about sub-surface sediment structure. No other techniques
provide this type of information, and only physical sampling via cores will allow for
characterization of subsurface structures.
Uses
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Detect and measure the thickness of dredged material deposits.
Detect hard substrate that has been covered by sedimentation.
Identify buried objects (such as cables and pipelines).
Define the basement (or bedrock) layer for potential confined aquatic disposal
sites for dredged material.
Fig. Illustrate the sub-bottom profiling apparatus and survey results
Geological Exploration
Oceanography division is mainly conducting geological exploration for study surface
geological variations and placer mineral surveys for identifying economically
potential areas for mining. Some sampling devices and separation equipment’s are
given in the diagram.
Fig. Wet lab apparatus to be used in onboard sample collection and analysis