International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
or biweekly. However, this will also mean a loss of information
that is required when looking at vegetation types with high
seasonality.
2. DATA
2.1 Satellite data
Weekly composited NDVI images of the NOAA AVHRR
sensor over 4 years (1995-1998) were taken to observe the
dynamics of certain vegetation types in Scotland. The NDVI
data for this study were derived from the German Remote
Sensing Data Centre (DFD). At the DFD, the data were
radiometrically calibrated and geometrically rectified. A couple
of cloud/water tests were performed to ensure that only NDVI-
values over cloud-free land surfaces were derived. Daily maps
were composed on the maximum NDVI value basis at every
pixel's position. The weekly composites were calculated from
the daily maximum NDVI values at every pixel's position.
No atmospheric corrections were performed on the data.
However. there is some evidence to suggest that atmospheric
influences are attenuated to a certain degree through the
calculation of the NDVI (Mather, 1999). This means that it is
very likely that all NDVI values in the images used are lower
than with atmospheric correction. As this is a qualitative study
and as only images from the same sensor and the same pre-
processing chain are compared with each other, qualitative
analysis can be done. What can be observed is the dynamics of
the vegetation and the trend between years.
2.2 Vegetation Dataset
Data on the distribution and state of semi-natural vegetation
was acquired from Scottish Natural Heritage (SNH) who
provided the Land Cover of Scotland 1988 dataset and
Highland Birchwoods who provided the Scottish Semi-Natural
Woodland Inventory.
2.2.1 The LCS88 dataset: The Land Cover of Scotland
1988 (LCS88) survey was the first ever national census of land
cover in Scotland produced by the Macaulay Land Use
Research Institute on behalf of The Scottish Office. It contains
land cover information in digital format in the scale of
1:25 000.
In the LCS88 data set the total area for Scotland is 78 828 km”.
Of this, over 50% is covered by semi-natural ground vegetation,
with heather moorland (8.7%) and peatland (8.4%) as the
largest single features. Heather moorland and peatland in
mosaics represent a further 22.3% of the total land area.
Woodland accounts for a total of 14.7% (mainly in
plantations). The agricultural cover types arable (11.2%) and
improved grassland (13.0%) are the most extensive single
features. Semi-natural vegetation is the most extensive
vegetation feature covering more than 60% of Scotland. The
vegetation is usually less than 0.75 m in height and has not been
subject to reseeding or other major improvement.
478
2.2.2 The Scottish Semi-Natural Woodland Inventory:
This inventory was compiled by Highland Birchwoods Ltd. on
behalf of the Caledonian Partnership and the Millennium
Forest for Scotland Trust. The following types of woodland
have been used for this study: Planted coniferous forest with a
closed broadleaf | (degraded or
fragmented), semi-natural conifer (degraded or fragmented),
mixed broadleaf and conifer, as well as mainly conifer, both
with different stages of naturalness and canopy closure.
canopy. semi-natural
3. METHODOLOGY
3.1 Selection of the landcover areas
Land cover types and areas of the SNH and Highland
Birchwoods Ltd. data sets were selected using ArcView 3.0a.
The criteria were:
e The land cover types have to be representative for
Scotland.
e^ The size of the areas should exceed 400 ha,
corresponding to at least 16 pixel (4 km?) on the
satellite pictures to minimise border effects.
* Compactness: Ideally, the polygons should be as
round as possible which assured the smallest amount
of borderline pixels.
The following land cover types were chosen (see table 1 and
figure 1): Heather moorland and peatland, as they account for
the greatest ground coverage of semi-natural vegetation in
Scotland; montane vegetation, as representative of the montane
zone of the Highlands. and semi-natural grassland in the form of
Nardus stricta and Molinia caerulea ground cover. To compare
these semi-natural cover types with anthropogenic ones,
representative areas of improved pasture and arable land were
also taken into account.
PRINCIPAL
FEATURES
MAJOR
FEATURES
MAIN
FEATURES
Dry heather moorland
Heather moorland
Semisnatural Wet heather moorland
ground Peatland Blanket bog / peat
vegetation Grassland Nardus / Molinia
Montane Montane vegetation
Agricultural Improved pasture
"s Agricultural land
land Arable land
Plantation, full canopy
cover
ne S Mainly coniferous
Coniferous forest forest
Woodland ; La
Semi-natural coniferous
forest
Broadleaf forest Broadleaf forest
Table 1: Selected land cover types (indicated by bold letters)
Internati
Figure 1
32 Cre
After th
polygon:
NDVI ii
one for €
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