Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986 
755 
Satellite data in aquatic area research: Some ideas 
for future studies 
Jouko T.Raitala 
Jet Propulsion Laboratory, Caltech, Pasadena, Calif., USA (on leave from Dept, of Astronomy, University of Oulu, Finland) 
ABSTRACT: Computer-aided digital remote sensing techniques were used to evaluate the usefulness of Landsat MSS 
data in aquatic area studies. These investigations unravelled some of the Landsat data potentials in monitoring 
factors critical to limnology, aquatic botany, geomorphology and engineering: 1) Besides depth (in relatively 
shallow Finnish lakes) the MSS data may also include useful information about Secchi disc values, humus content 
in water (colour, iron) and productivity (nutrients, chlorophyll). 2) Aquatic vegetation classification is 
possible only where vegetation units are big enough in respect to the 0.5 hectares ground resolution. Different 
life-forms (helophytes, nympheids, elodeids, bryophytes etc.) are mapped quite easily, but when using the super 
vised classification procedure even some minor nuances can be traced. 3) Multitemporal satellite imagery has 
been used to evaluate alterations within the littoral areas of some Finnish water reservoirs between successive 
periods of high water and also along the shallow coastal sea of the Gulf of Bothnia. 
The limitations of the MSS data in exact small-scale interpretations are, however, so apparent that the most 
critical support of relevant water chemical and field data must not be underestimated. The use of MSS data with 
poor ground resolution and with too broad and too few spectral channels represents only a small range of the 
possibilities which will be gained by using the more advanced TM and SPOT data. The MSS data may nevertheless 
be important when trying to trace the changes in aquatic and other environments during the last decade. 
1. INTRODUCTION 
Different lakes and coastal sea areas are amongst 
the few most essential environments in Finland 
forming a natural surrounding for almost all activi 
ties of men. This means that aquatic areas are the 
object of various and often conflicting efforts of 
utilization. Research, investigation and planning 
of water areas for recreational and residential use 
and as a source of livelihood and raw water or as a 
dumping place for waste water all require accurate 
information, some of which can in principle be 
obtained and prepared by using Landsat or other 
satellite data and the computer-aided analysis of 
such data. 
The Landsat MSS data includes information of 
aquatic areas down to the Secchi disc depth. The 
green and yellow wavelengths of channel 4 indicate 
variations within a few uppermost metres in brownish 
Finnish lakes and water features even down to tens 
of metres within certain open ocean areas. The red 
radiation of channel 5 usually comes from within the 
uppermost one metre water layer, and the near-in 
frared channels 6 and 7 include information from 
within the uppermost centimetres or millimetres, re 
spectively. In addition the uppermost part of the 
water column is best represented within all recorded 
channels. 
The present study describes some attempts to apply 
aquatic remote sensing to the preparation of 
parametric map-like presentations, quantitative 
evaluations and time-related investigations within 
various water areas in Finland. 
2. WATER QUALITY 
Laborious and expensive efforts are called for when 
attempts are made to inspect water quality and its 
changes over large Finnish lake areas by means of 
field work. Satellite images and their computer- 
aided analysis may help to locate the most critical 
areas where changes in water quality have taken 
place. Continuous satellite monitoring of water 
areas -- in terms of data availability -- can 
provide information for example of movements of dif 
ferent water bodies, changes in production rate, 
overgrowth, pollution and purification. 
However, more basic studies and progress are still 
needed before remote sensing will be able to answer 
all questions unambiguously. The wavelength 
channels of the Landsat MSS sensor are too wide and 
too few to allow distinct parametric map-like 
presentations of only one of the aquatic variables 
to be performed. Indications of different phenomena 
are intermingled, resulting in difficulties and mis 
interpretations in monitoring. Naturally brownish 
Finnish lake waters are easily confused with waste 
water pollution and even a sparse nymphaeid vegeta 
tion may prevent recognition of water quality. We 
must, then, be extremely cautious when trying to 
generalize results obtained from one water area to 
another. 
In applying the remote sensing technique to 
studies of aquatic areas the most critical support 
of the relevant water chemical data acquired by the 
Water District Offices of Finland makes it possible 
to find the main differences between various water 
areas in advance and to limit studies to within the 
same type lakes. Satellite data is thus not used to 
find major differences but rather to indicate minor 
variations within basically similar water units. 
Even certain small nuances and changes in water 
quality can be traced and followed once a critical 
choice has first been made of what factors can be 
monitored and when and where (Lindell 1980, Raitala 
et al. 1984c). Channel 7 for example displays very 
sensitively changes in the quality of the uppermost 
surface water and in vegetation above, on and just 
below the water surface. Near-infrared radiation is 
almost totally absorbed by even a thin water layer, 
while the existence of green vegetation, turbidity, 
algae production and surface-reaching shallows in 
crease the quantity of reflected radiation. 
Statistical correlation between certain water 
chemical values and Landsat record derivatives from 
within the Kuusamo and Kemijarvi areas in north-