Monitoring of Pollution by Means of Remote Sensing
535
iii) Standardized Principal Components Analysis: The analysis of principal
components is a technique widely used in digital image processing to synthesize
the information from a group of bands into a reduced set of bands (Picchioltti et
al., 1997). In the case of multitemporal applications such as this, the first principal
component tends to show stable information that which is common to all images.
The successive components show the information that is not held in common and
thus are normally used as a change detection technique
The analysis of principal components was applied to each group on the previously
normalized band 2 images with the land masked out. In this case we are concerned to
detect precisely the elements which are stable within each group of images for which
we are left with just the first principal component of each group. However, in all three
cases, this contains almost 99% of the variation in the original images and shows the
most common distribution of water masses in the estuary for each of the tidal
circumstances considered. In all three cases the different images correlate positively
with the first principal component in that high values in the principal component can
be interpreted as zones of high turbidity in all images in the group and vice-versa. The
high and low tide results, which are the most interesting for the sampling issue, are
considered below.
HIGH TIDE
Four water masses are clearly discernable in order of increasing turbidity (Fig. 5)
the upper Tinto channel has a very turbid water mass with a gradual
transition to less turbid water at the confluence of the two rivers
the upper Odiel channel has a medium-low turbidity water mass
the lower reaches of the two rivers before their confluence have similar
characteristics, with medium-high turbidity which in the case of the Odiel
penetrates El Burro channel, demonstrating the link already detected with
the Punta Umbría channel which, as the tide falls, will drain part of the
Odiel's waters
the channels of Padre Santo and Punta Umbría are also homogenous zones, in
this case with medium-low turbidity because of the arrival of coastal waters
which push the more turbid estuarine waters upstream
the zone outside the estuary is occupied by clear coastal waters except for a
narrow zone anchored to the coastline. The orange coloured zones in the
mouth of the Punta Umbría channel relate to the sandy shallows of this zone
535
iii) Standardized Principal Components Analysis: The analysis of principal
components is a technique widely used in digital image processing to synthesize
the information from a group of bands into a reduced set of bands (Picchioltti et
al., 1997). In the case of multitemporal applications such as this, the first principal
component tends to show stable information that which is common to all images.
The successive components show the information that is not held in common and
thus are normally used as a change detection technique
The analysis of principal components was applied to each group on the previously
normalized band 2 images with the land masked out. In this case we are concerned to
detect precisely the elements which are stable within each group of images for which
we are left with just the first principal component of each group. However, in all three
cases, this contains almost 99% of the variation in the original images and shows the
most common distribution of water masses in the estuary for each of the tidal
circumstances considered. In all three cases the different images correlate positively
with the first principal component in that high values in the principal component can
be interpreted as zones of high turbidity in all images in the group and vice-versa. The
high and low tide results, which are the most interesting for the sampling issue, are
considered below.
HIGH TIDE
Four water masses are clearly discernable in order of increasing turbidity (Fig. 5)
the upper Tinto channel has a very turbid water mass with a gradual
transition to less turbid water at the confluence of the two rivers
the upper Odiel channel has a medium-low turbidity water mass
the lower reaches of the two rivers before their confluence have similar
characteristics, with medium-high turbidity which in the case of the Odiel
penetrates El Burro channel, demonstrating the link already detected with
the Punta Umbría channel which, as the tide falls, will drain part of the
Odiel's waters
the channels of Padre Santo and Punta Umbría are also homogenous zones, in
this case with medium-low turbidity because of the arrival of coastal waters
which push the more turbid estuarine waters upstream
the zone outside the estuary is occupied by clear coastal waters except for a
narrow zone anchored to the coastline. The orange coloured zones in the
mouth of the Punta Umbría channel relate to the sandy shallows of this zone