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Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Remote sensing of flow characteristics of the strait of Öresund
L.Jonsson
Dept, of Water Resources Engineering, University of Lund, Sweden
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ABSTRACT: The strait of Öresund is located in a densely populated region and subject to many activities. Thus,
it is important to understand the flow characteristics of the strait properly. The paper presents results of the
use of NOAA and Landsat imagery for exracting information on the large-scale flow pattern and the possibility
of distinguishing certain flow phenomena. These findings are discussed in relation to known properties of the
hydrography of Öresund. The remotely sensed flow information is also discussed as far as numerical modelling of
the flow in Öresund is concerned.
RESUME: Le détroit d 1 Öresund est situé dans une region populeuse exposé a beaucoup d'activités. Ainsi c'est
important de savoir les mouvements de l'eau profondément. Cet article present des résultats de l'utilisation de
NOAA et Landsat data pour l'extraction d'information sur la circulation a grande échelle et sur la possibilité
de découvrir certains phénomènes hydrodynamiques. Ces résultats sont discutés en relation avec la nature de
l'hydrographie d'Öresund. L'information d'écoulement obtenu avec télêdetéction est aussi discuté en relation
avec des modèles numériques d'écoulement en Öresund.
1 INTRODUCTION
Knowledge of hydrodynamic processes and circulation
patterns in coastal waters is important when conside
ring resource or quality aspects of the waters or in
connection with technical/constructional measuers in
the coastal zone. Data on large-scale water circula
tion by means of satellite imaging provide one type
of information which could be used either directly
or in connection with numerical flow models for in
creasing this knowledge. This paper discusses the use
of NOAA and Landsat data from the strait of Oresund.
The study has been made possible by the support of
the Swedish Space Corporation, the Swedish Natural
Science Research Council and the University of Lund.
2 BACKGROUND
The strait of Öresund forms one connection between
the southern part of the Baltic Sea and Kattegatt
(Fig. 1). The length is approximately 100 km and the
width 10-20 km.
The flow in the strait is rather complex and at
times one could distinguish three different water
types - Baltic water with salinity S = 8-10 o/oo,
Kattegatt surface water S = 18-24 o/oo and Kattegatt
bottom water S = 30-34 o/oo. The surface flows to
the north 66% and to the south 34% of the time mainly
due to wind and pressure induced water level diffe
rences between Kattegatt and the Baltic. The most
common overall flow could be described as a two-layer
flow situation with northbound surface flow and
southbound bottom flow. However, the bottom flow is
normally blocked by the shallow-8-10 m - depth in the
southern part of the strait. Thus one could think of
Öresund as an estuary for the "river" Baltic most of
the time (HarremoBs et al 1966). The main types of
surface flow patterns based on (rather scarce) field
measurements are shown in Fig. 1.
Öresund is bordered by densely populated areas im
plying a heavy demand on the coastal water for a num
ber of sometimes conflicting uses. This is one rea
son, besides purely technical aspects, why detailed
investigations of the consequences of interferences
with the coastal waters are often needed. Thus a num
ber of studies have been performed involving knowled
ge of and consequences for the flow behaviour in more
or less detail. In several cases numerical modelling
of the flow has been used. In other cases the prob
lems have been approached by means of physical model
ling, prototype simulations or rather simplified cal
culations. Some examples are given below (ref. Fig. 2)
A - an intended railway tunnel on the bottom of the
strait. Risk for blocking of salt, nutritious bottom
water. Ecological consequences. Numerical models
based on vertically or laterally integrated hydrody
namic equations.
B - planned, extensive land fillings which might
affect water exchange, navigation, erosion. Studied
by means of vertically integrated (shallow water)
flow equations.
C - discharge of cooling water from nuclear power
Figure 1. Large-scale flow pattern in Öresund.
Northbound flow.