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1 INTRODUCTION
Thepreparationofthestudiesonforecastingthedrift
of survivors in the Szczecin Lagoon waters was the
inspiration for this topic. The long‐term goal of the
authorsistodevelop driftmodelsofvariousobjects
for employing them in the search‐and‐rescue
operations and for
including them as an additional
sourceoflocationdata.Suchalgorithmsarecurrently
beingdevelopedandtheyfitintotheareaofmodern
navigation[2,14,23,24].
Small boats with limited drafts are main
participantsofsailingintheSzczecinLagoonwaters,
due tothe specificity ofthatreservoir. The Szczecin
Lagoon
characterizeslowdepths.Theaccidentswith
theparticipationofsuchvesselshappenmostoftenon
theSzczecinLagoonwaters.
For example, on 08.05.2017 at noon, three sailors
went on a cruise of the Szczecin Lagoon. On
09.05.2017atafternoon,therescueservicesfoundthe
capsizedyachtoftheBEZtypeand
thebodyofoneof
thosesailors.Theremainingtwomenwerenotfound.
The Rescue Station in Dziwnów and a rescue ship
from Trzebież attended in the rescue operations.
Additionally, the Border Guard also helped on the
water and in the air. In turn, the WOPR and police
searched
an area from the land side [18]. At night,
19.06.2015, the man fell overboard from the S/y
HAARLEMyacht.Despiteanintensivesearchaction,
thesurvivorwasnotfound.Theyachtwastowedon
the island of Wolin. Six search‐and‐rescue units
attended in the rescue operation. Additionally, the
fire
brigadeandpolicesearchedanareafromtheland
side[18].
Comparative Analysis of the Data on the Surface
Currents and Wind Parameters Generated by Numerical
Models on the Szczecin Lagoon Area
M.Kijewska,K.Pleskacz,&L.Kasyk
M
aritimeUniversityofSzczecin,Szczecin,Poland
ABSTRACT:Thisstudyfocuses onthe investigationofavailablesurfacecurrents andwind parametersfor
employingtheminordertopredictthesurvivormovementintheSzczecinLagoonwaters.Forthispurpose,the
surfacecurrentsandwindparametersweregeneratedbyselectednumericalmodelsand
thewindparameters
werealsomeasuredwiththetelemetrydevices.Inthispaper,thePM3DhydrodynamicmodelandtheNEMS,
ECMWF, GFS weather forecast models have been investigated. The measurements of the wind parameters,
recordedattheBramaTorowaIandTrzebieżstations,werealsoanalyzed.Aspartofthe
research,anexpert
methodwas used to evaluate the surface currents parameters. In turn,the method based on comparing the
forecastedwindparameterswiththemeasuredwindparameterswasappliedinordertoassessuncertaintiesof
theseparameters.Thecomparativeanalysesofthedataonthesurfacecurrentsandwindparameters
havebeen
done and probabilistic models for uncertainties of these forecasted parameters have been formulated.
Additionally, relations between the surface currents speeds and the wind speeds, in the case when their
directionswereconsistent,havebeenalsodiscovered.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 12
Number 4
December 2018
DOI:10.12716/1001.12.04.12
730
ThemostimportanttaskoftheSARservicesisto
look for the people who have fallen overboard or
drifting in the water after overturning the boats. In
the literature [3‐7,9,10,13,17,20,21,25,27], the search‐
and‐rescue areas, in waters used for the navigation,
are determined by employing the Monte Carlo
methods,Bayesianmethods,regressionmodelsforan
object’sdriftvelocity,theFokker‐Planckequationsor
certain graph models. To determine such areas, it is
necessary to obtain data about surface currents and
wind. That data are often generated by numerical
models.Theaccesstosuchdatamightbeobtainedby,
e.g., theGeographic Information System such as the
Maritime Network‐Centric Geographic Information
System Gulf of Gdansk [16]. Sometimes, some
relationsbetweenthewindandwind‐drivencurrents
are established [20]. Based on the wind parameters,
theleewayparametersalongwiththeiruncertainties
aredetermined,e.g.,bythelinearregressionor
onthe
basis of constructed probability distributions. The
potentialtotaldriftofasurvivoristhevectorsumof
the current and leeway. The position vector of a
survivoratagiventimetiscalculatedastheintegral
of the survivor’s velocity vector from the initial
momenttothe
timetincreasedbythevelocityvector
fromtheinitialmoment.
AccordingtoIAMSAR(InternationalAeronautical
and Maritime Search and Rescue Manual) [8], an
estimation of the surface current and wind
parameters can be derived from direct observations,
diagrams,charts, wind roses, reliablehydrodynamic
models and weather forecast models. The direct
observations may be obtained from the in situ
measurements,fromvesselspassingthroughanarea;
aircrafts flying over an area, installed appropriately
buoys,platformsorsatellitemeasurements.However,
suchdataarenotalwaysavailable.Bydiagramsand
charts,thelong‐termaverageseasonalparametersof
the currents and wind could
be determined.
However,thesesourcesareemployedintheareasfar
away from shores. Nevertheless, an estimation of
these parameters provided by these sources should
not be used in coastal areas, and especially in the
offshore areas less than 25 nautical miles distance
from the shore and less than 300 feet
(100 meters)
water depth. Reliable hydrodynamic models with
high resolution and weather forecasts models are
other sources of such. The authors consider these
sourcesofdata.
The first aim of this paper is to verificate the
available data on the surface currents and wind
parameters on the Szczecin Lagoon area
for the
summer season in 2017. The forecasted surface
currentsparameters have beenexamined with using
an expert method. In turn, the real and forecasted
wind parameters have been compared. Some
statisticalcharacteristics of the uncertainties of those
parameters havebeen presented. Furthermore, some
probabilisticmodelsfortheobtaineduncertaintiesof
the considered parameters have been determined.
Additionally, linear relations between the surface
currentsandwindspeedswereestablished.
The remainder of this paper is organized as
follows.InSection2,researchareaanditshydrology
conditions are described. In Section 3, the materials
and methods are presented. Section 4 contains
a
comparative analysis of numerical data on surface
currents and wind parameters collected for the
SzczecinLagoonduring thesummer season in2017.
InSection5,adiscussionoferrorsinforcingfieldsis
conducted.Section6concludes.
2 RESEARCHAREAANDITSHYDROLOGY
CONDITIONS
2.1 Researcharea
The Szczecin Lagoon
(Polish: Zalew Szczeciński)
coverswaters atthemouth ofthe Odra River. From
thenorthernsideofthislagoon,theislandsofWolin
and Uznam separate it from the Baltic Sea. In the
middle part of this lagoon, it is subdivided into the
LargeLagoon(Polish:WielkiZalew),with
thesurface
areaof
2
488 km lyingwithinPoland,andtheSmall
Lagoon(German:KleinesHaff),coveringtheareaof
2
424 km ,whichbelongsalmostentirelytoGermany.
The Szczecin Lagoon lies on the longitude: approx.
'
13 53 E
'
14 36 E
and the latitude: approx.
'
53 42 N
'
53 52 N
.Itisabout 28 km long and
over
52 km wide [1]. The southern limit of the
Szczecin Lagoon is designated by the Jasienica
channel outlet (on the west bank)and the mouth of
theKrępaRiver(intheeast).
ThePomeranianBay(Polish:ZatokaPomorska)is
connected with the Szczecin Lagoon via the straits:
Dziwna,Świna and Peennestrom.Ś
wina is the most
important for the Szczecin Lagoon hydrological
system. These straits are not the Odra River arms,
becausetheircurrentisnotarivercurrent,butitisthe
result of the constant sea and the Szczecin Lagoon
waterlevelling.
TheaveragedepthoftheSzczecinLagoonisabout
3,8 m . The largest natural depth of the Szczecin
Lagoon is
8,5 m . However, it is not a region
deprivedofshoalsandshallows.Nearly
25% ofthe
areais
02
‐meterdeep,andthehighaverageisdue
tothefactthatthereisthe
10,5 ‐meterdeepchannel
across the Szczecin Lagoon from Szczecin to Baltic
waters [1]. This channel is called the Szczecin‐
Świnoujście fairway. The Szczecin‐Świnoujście
fairway is the dredged channel in the Szczecin
Lagoonarea.
2.2 Descriptionofthehydrologicalconditionsonthe
SzczecinLagoon
TheSzczecinLagoonis
perceivedasasmallandfairly
safeareaforsailingandmotorboatsport.Thedanger
is the shape of its coastline and bottom, which in a
combination with varying hydrodynamic conditions
led already too many woes. Particularly dangerous
are squalls, which are strong and unexpected. In
addition to the wind
dynamic action, generated
waves affect also boats. The wave height is directly
relatedtothedepthofalagoonarea.
Windwavesaretheimmediatethreats.Thewave
dimensionsaredeterminedbythewind.Theduration
of the wind forcing practically does not affect the
developmentofthewave.Thefull
wavedevelopment
can take place within a period of no more than one
hour. After the wind stopping, the wave quickly
731
disappears. The currents directions in the Szczecin
Lagoon generally lay along the dredged channel.
However, there may also be the currents which are
perpendiculartoit.Thecurrentsduringtheinflowof
Balticwaterscanreach
24 knonthestraits:Świna
andDziwna.
Thechangeofthewaterlevelmaycausecurrents.
Itis importantto note that large, sudden, butshort‐
termfluctuationsinthewaterlevelcausestorms.The
stormy winds from the northern sector cause the
water level increasing of
0,7 1,0 m
, while the
southern winds – the decreasing of
0,6 m . The
winds, with the speed of more than
10 /ms
, cause
the water‐level variation. The north or south
variations rarely exceed
0,1 m , and in the west or
east direction –
0, 2 m
. However, the stormy
southwest winds cause the water‐level difference of
0,6 m .
Thesurfacecurrentsandalsowindareimportant
forestablishingtheparametersofthesurvivor’sdrift
inthe water. In order to develop and determine the
potentialsearcharea,thedirectionofthewaterflow
should be taken into account in addition to the
direction and force of the wind
parameters. The
fluctuationsinthewaterleveldependmainlyonthe
windparameters.ForthewindfromNWtoNE,the
water level can rise by about
1 m per day. In turn,
forthewindfromthesouthernsector,itdecreasesby
0,6 m in the relation to the average level. The
exemplary fluctuations of the water level on the
indicator at the Trzebież hydrological station are
presentedin Figure 1. With such shallow water and
mostlyswampyandlowbanks,suchamplitudeofthe
water level radically changes the shape of the
shoreline
insomeareas.
Figure1. Change in the water level on the Trzebież
indicator–from25.06to03.07.2017.
3 MATERIALSANDMETHODS
Foranalysispurposes,theauthorschosethemonths:
July and August in 2017, since experiments will be
donebythisseasoninthefeature.Theanalysiscovers
only this season due to the unavailability of any
forecasted wind parameters generated by the
consideredweatherforecastmodels:ECMWF,
NEMS,
GFS fromtheprevious summer seasons. In order to
discuss the surface currents parameters on the
Szczecin Lagoon, the authors generated the surface
currents charts by the SatBałtyk system [19]. The
parametersofthesurfacecurrentswerederivedfrom
the PM3D hydrodynamic model [15]. The PM3D
hydrodynamic model
works at the Institute of
OceanographyattheUniversityofGdańskinPoland
[11]. The PM3D model covers the Szczecin Lagoon
with 1/6NM resolution (approximately 300 m). It is
worth adding that thishigh resolution of the PM3D
modelfortheSzczecinLagoonareaaffectsthemuch
better description
of this area’s bathymetry and
coastline [12]. It may be seen that the widths of the
narrow straits connecting the Szczecin Lagoon with
the Pomeranian Bay (Świna, Dziwna, Peennestrom)
areclosetotheirrealsize[12].TheSatBałtyksystem
data, e.g., the surface currents parameters, are
updated four
times a day: 0000UTC, 0600UTC,
1200UTC,1800UTC.
Itisworthaddingthatthevalidationofthesurface
currents parameters with using the in situ
measurements was not possible. By this reason, the
generated surface currents fields were discussed by
the expert method. The expert method utilizes the
knowledge of experiencedprofessionals
in
evaluating the goodness of the generated surface
currents fields. The authors presented the generated
chartsofthesefieldstotheexperts–thegroupofport
pilots – which know the hydro meteorological
conditions of the Szczecin Lagoon. Additionally, the
authors created the list of the questions which
facilitated
the evaluation of these charts. These
expertsassessedthereceivedchartsandrespondedto
the submitted questions. These questions concerned
thehydrologicalandmeteorologicalconditionsonthe
Szczecin Lagoon area, e.g., whether the information
contained on the generated charts coincides with
many years of experience of the practitioners – the
pilots;
what are the directions and speeds of the
surface currents on the Szczecin Lagoon; what do
their directions and speeds depend on; how the
shapingoftheshorelineandlandaffectsthedirection
and speed of the wind at various points of the
SzczecinLagoon;duetothevariabilityof
parameters,
i.e.,theshapeofthebottomprofileandshoreline,the
impact of the Odra River; in which areas of the
Szczecin Lagoon the currents are the most variable
andunpredictable,etc. Itisworthnotingthat,upto
this date, there exists no research work that has
attempted to validate
the surface currents fields
presentedintheSatBałtyksystem.
In the world, currently in certain water areas,
measurements ofthe sea currents are carried out
using the High Frequency Surface Wave Radars
(HFSWR).However,suchradarsarenotavailablein
the Polish zone of responsibility. Indeed, the typical
range
of the surface velocity measurements is
30 100 km
from the coast and inthe case of high
spatial resolution depending on the radar working
frequency– a fewkilometres. Due tothesizeof the
Szczecin Lagoon, it is currently too expensive
solution.
The authors further have established the linear
relations between the surface currents and wind
parameters
at two points of the Szczecin Lagoon:
Brama Torowa I (longitude:
'
014 20
E; latitude:
'
53 49
N) and at the point in the area nearby the
Trzebież (longitude:
'
014 28
E; latitude:
'
53 41
N).The Szczecin Lagoonis aflowable reservoirand
the water flow at these two points reflects to a
significantextentthewatermovementinthislagoon.
Inturn,theprobabilisticapproachwasusedinorder
732
todescribeuncertaintiesfortheparametersachieved
withtheobtainedformulas.
In turn, for a comparative analysis of the wind
parameters, the authors firstly generated charts
depictingthewindyconditionsforJulyandAugustin
2017. These charts were generated on the website
https://www.windy.comForthisresearch,thedataon
the wind parameterswere collected from the Brama
Torowa I and Trzebież meteo stations. These data
were recorded by the Maritime Office in Szczecin
(UMS) and the Institute of Meteorology and Water
ManagementinWarsaw(IMGW).Theforecastsofthe
wind parameters were obtained from the NEMS,
ECMWForGFS
models.Thedatafromthesemodels
are generally available in [26]. The NEMS (NOAA
Environmental Modelling System) model has the
resolution of approximately
4 km and its data are
updated every
12 hours: 0830UTC, 2030UTC. The
ECMWF (European Center for Medium‐Range
Weather Forecasts) model, with the resolution of
approximately
9 km , is updated every
12
hours:
0715UTC, 1915UTC. The GFS (Global Forecast
System) model has the resolution of approximately
13 km and it is updated every 6 hours: 0615UTC,
1215UTC,1815UTCand0015UTC.TheNEMSmodel
is a local European model. The ECMWF and GFS
modelsareglobalweathermodels.
Inthispartofthepaper,theauthorscomparedthe
measuredandforecastedwindparameters. Moreover,
the authors described statistically the differences
betweentheseparameters.Inturn,
theprobabilistic
models for the absolute values of the differences
between the measured and forecasted wind
parametersareachieved.
4 COMPARATIVEANALYSISOFTHE
NUMERICALDATAONTHESURFACE
CURRENTSANDWINDPARAMETERS
COLLECTEDFORTHESZCZECINLAGOON
WATERSDURINGTHESUMMERSEASON
4.1 Thesurfacecurrentsparameters
In general, the
experts did not have any significant
objections to the water circulation presented on the
generated charts of the Szczecin Lagoon. They
observed that, substantially the charts appropriately
reflect the wind‐driven currents. For example, the
experts, analyzing the surface currents chart for
08.07.2017at12:00UTC,establishedthattheimpactof
the wind field has been reflected in the surface
currents field, that is, the surface currents field was
directlydependenton changes inthe air flowat the
air‐water interface. Moreover, they noted that the
generated surface currents field was quite uniform.
Thatis,thisfieldwasclosetothe
stationaryfield.The
differencesinthecurrentsdirectionsandspeedswere
not significant in the central part of the Szczecin
Lagoon. By these reasons, the experts recommended
thatdownscalingcouldbeconsideredinthefeature.
The hydrodynamic model, generating the surface
currents, could be adapted in order to describe
conditions
intheSzczecinLagoonalmosttwoorders
of magnitude smaller. Furthermore, this approach
couldunveilsub‐gridwatermovements,providinga
more complicated description of the water transport
process on the Szczecin Lagoon. The experts also
observed that the surface currents circulation was
strictlyconnectedwiththeshoreline’sshape,butthe
waterexchangebetweentheSzczecinLagoonandthe
PomeranianBaywaspreserved.
However, in the area of complicated shoreline
configuration and significant shallows, there are
clearly noticeable differences between the display of
the charts and the experts’experience. Indeed, there
are areas on the Szczecin Lagoon where the PM3D
model
forecasts the surface currents directions
opposite to those estimated by the experts. In such
areas,thesurfacecurrentdirection,forecastedbythe
PM3Dmodel,isnotjustifiedbythebathymetryofthe
lagoon.Duringthebackflow(thatis,thewaterinflow
from the Baltic Sea to the Szczecin Lagoon),
particularlystrong
surfacecurrentsoccurinthearea
ofthemouthofthePiastowskiChaneltotheSzczecin
Lagoon. The similar phenomenon, wherein the
currentdirectionisopposite,occurs