Transcript TELEFOS : A new surface drifter for coastal and lake studies

TELEFOS:
A new surface drifter for
coastal and lake studies
V. Zervakis1, M. Ktistakis2, D. Georgopoulos1 and A. Kantidakis2
2
1
TELEFOS: the concept
The idea of designing and building TELEFOS was generated
at the Hellenic National Centre for Marine Research, when
it was realized that almost the entirety of the Aegean Sea
is by now fully covered by cellular telephony:
Coverage by the three main companies:
VODAFON
COSMOTE
TELESTET
The initial idea
NCMR researchers realized that cellular telephony (GSM) could be
significantly more advantageous than satellite or UHF tracking of
the floats, in terms of:
•
Communication cost
•
Real-time access to the information
•
Flexibility to monitor the floats from anywhere
•
Flexibility to reprogram the floats for easier retrieval.
Based on that idea, we started looking for partners to build a surface
drifter specially designed for the Greek Seas.
The Consortium
A manufacturing company with great experience in manufacturing
navigational equipment, MARAC Electronics, was interested, and a
common project started under the auspices (and 50% funded) by
the General Secretariat for Research and Technology of the
Hellenic Republic.
The new drifter
Through our interactive work, we believe that we have come up with a new
drifter that is characterized by the following novelties:
•
GSM communication (with option for ARGOS)
•
Short-range communication (and programming) through UHF (no
hussling with connectors…)
•
Novel design, allowing the very easy conversion from measuring
surface currents (“Davis type”) to subsurface currents (kite down
to 50 m depth).
•
Low-cost accessories (alkaline batteries)
•
A user-friendly, highly capable software
As the real-time data acquisition will permit the easy tracking and
retrieval of the drifters, the instruments will acquire a semiexpendable character.
This lowers the real cost of the initial investment.
The Hardware
Characteristics
• Hull constructed of PVC
• Weight < 5Kgs (float
only)
• Hull 90cm X 15cm
• Sail area ~1m2
TELEFOS is designed to
measure both surface and
subsurface currents
In “surface mode”, the
design is based on the
Davis type.
In “subsurface mode”, the
inner body of the drifter is
turned into the surface
buoy, and the hollow outer
body forms the spine of
the kite.
One of TELEFOS novelties lies in the design:
The modification of a drifter from the
“surface mode” to “subsurface mode” takes
place in a couple of minutes:
Surface mode
Simply
pulling the
float off
the kite
Subsurface mode
The Software
As “Telefos” is targeted to a wider market than
marine scientists, the software is designed from the
start to be as user-friendly and comprehensive as
possible.
Selecting the geographic area is a click away….
The software is comprised of
•
the project scheduling/drifter programming
mode
•
The real-time drifter monitoring mode, and
•
The data analysis mode.
project scheduling/drifter programming mode
the user sets:
•
Region and length of the experiment
•
Number and identification of drifters to be used
•
Sampling rate (GPS interrogation)
•
Reporting rate (GSM calling home)
real-time drifter monitoring mode
the user can:
•
Observe his/her drifters in real time (and know their
positions)
•
Change the reporting rate to facilitate drifter chase and
recovery
The data analysis mode
A more extensive presentation of the data analysis mode
follows. We should just point out that the analysis can be
performed not just on TELEFOS data but also on any
Lagrangian drifter data, surface or subsurface.
The graphical interface provides a user-friendly way to
filter out bad data.
The following computations are possible with the data
analysis module:
• Lagrangian velocities, accelerations and Rossby numbers
(along the path of the drifters)
• Eulerian statistics (Velocity fields)
• Lagrangian statistics (integral time scales, eddy
diffusivities)
• Semi-Lagrangian Spectra
Example with
borrowed data-set
from WOCE drifters
in the Aegean Sea:
Each drifter can be
identified by a
different color,
determined
interactively.
Simply moving and letting
the mouse over a drifter
position, a box appears
showing
•the drifter’s code #
•date and time
•Position
•estimated speed
•estimated direction
•Rossby number
•surface temperature
(for the WOCE drifters;
TELEFOS are not yet
equipped with thermistors)
Using the “zoom” button,
we can focus in an area
to view details of the
tracks
Removing “bad” data,
either by deleting single
points or by selecting a
group of points, is done
easily with the mouse.
The details of single
points to be erased are
shown in inset boxes.
The Lagrangian velocity is
estimated just by clicking
to the folder “velocity”
and leaving the option
“grid” unchecked
Checking the option “grid”,
we obtain Eulerian means
over a grid laid on the
region of interest
Moving the mouse
over the center
of a grid point,
we see its
statistics.
The size of the grid
is controlled by a
slide-ruler
The variance ellipse is
displayed by clicking to
the folder “confidence”
A slide-ruler controls
the desired confidence
interval
There is also a folder
option providing the mean
kinetic energy
…and one for the “eddy”,
or fluctuating kinetic
energy
These autocorrelation
functions are the first
step in estimating integral
time scales and horizontal
diffusivities.
The work is under
progress.
Conclusions
• Telefos will constitute a low-cost, very versatile
instrument.
• Telefos novelties improve its cost-efficiency, while
facilitating its use.
• We seek to expand the market to non-marine
scientists by offering ease of use and user-friendly
data analysis.
• The first prototypes have been built; the first four
instruments will be delivered to NCMR for sea trials
in January 2003, and six more (production-type) will
be ready until the summer 2003.
Additional Information:
Vassilis Zervakis (NCMR), at [email protected]
Antonis Kantidakis (MARAC) at [email protected]
What is TELEFOS?
MARAC ELECTRONICS and the
HELLENIC CENTRE FOR MARINE RESEARCH
present a new surface drifter (Telephonic monitored
drifters for ecological studies - TELEFOS), designed
for use in semi-enclosed seas, coastal areas and
lakes.
Monitoring surface currents
TELEFOS is a state of the art system for measuring currents and calculating dispersion
(e.g. pollutants) in the near surface waters. Its concept is based on a new design on an
old idea, i.e. of using drifters to monitor the circulation in aquatic bodies.
The system consists of a monitoring station (which may be placed either on land or
aboard the deployment/retrieval vessel), and the drifter fleet. The drifters’ positioning
exploits the highly accurate GPS system.
The main innovations that TELEFOS brings are:
Use of GSM and RF technology for communication.
A modular design allowing two configurations, thus enabling the monitoring of surface
and subsurface currents (down to 50 m).
A potent, user-friendly software offering real-time monitoring and interactive
programming during the mission, a vessel-guiding module for the retrieval of the
drifters, and extensive data analysis features (assessment of mean and eddy velocity
and kinetic energy fields, lagrangian statistics, horizontal diffusion coefficients,
spectral analysis).
The software allows the import and analysis of any drifter data.
Area
selection
tool
APPLICATIONS
• Environmental impact studies
 Port construction
 Sewage dispersion from point
sources
 Aquacultures
 Experimental validation of
numerical simulations of
circulation
 Calibration of coastal HF
current/wave radars
Monitoring sub-surface
currents
Real-time drifter-monitoring screen
POSITIONING
GPS
COMMUNICATION
ISM433
GSM
DIMENSIONS
Vessel-guidance module
Weight < 5Kgs
Hull 90cm X 15cm
Drogue surface ~ 1m2
OPERATIONAL LIMITS
-5oC to 50oC Air Temperature
-2oC to 45oC Water Temperature
OTHER DETAILS
•
•
•
•
•
•
Lagrangian Statistics – decorrelation scales
•
Operation depth 0-50m
Weeks or months of operation (depending on the sampling and
communication strategy)
Low cost operation due to:
High drifter retrievability due to the monitoring and boatguidance modules.
Use of data compression algorithms.
Use of alkaline “D”-cell batteries for low cost and high
flexibility.
Low cost materials and accessories
www.marac.gr - www.hcmr.gr