Manual - International Environmental Technology Centre

Also helpful in woodland identification is species
phenology. In early spring deciduous trees are leafless.
That allows not only for easy differentiation
of forests, but makes analysis of the land structure
easier. Identification of deciduous and coniferous
trees is also easy with photos taken in autumn.
For the purposes of forest identification,
the most useful are pictures at a medium
scale of up to 1:20 000.
Meadows
They are recognizable as dark-gray or dark-green
areas sometimes having a cloudy texture. After
grass harvesting a picture may be different with
very strong visible strips, the effect of using harvesting
equipment (Box 4.3).
Arable land
On aerial photos arable land is clear and brighter
in colour, especially during summer months, and
is characterized by a specific texture reflecting
equipment use. Unfortunately, crop analysis is one
of the biggest challenges in photointerpretation.
It requires very detailed study of the brightness
indicator of different crops on photos taken at
particular times of the year.
Urban areas
Aerial photography is one of the most valuable
sources of information about human settlement.
In the case of villages, the most important pro-
perties are: shape, number of farms, building density
or, for long-term documentation, also the rate
of development as a result of interactions between
a settlement and surrounding environment.
In the case of towns these interactions are expressed
by the arrangement of streets. History and
functions of the city may be deduced from the
distribution of buildings of different sizes and uses.
IMPORTANT PARAMETERS - QUANTIFICATION OF
INFORMATION
How is the area of objects measured?
The area of objects may be measured directly on
the picture if the topographic profile of the land
is not very diversified. This is possible using a planimeter,
but first the scale of the picture has to
be calculated (Box 4.4). Because there are picture
deformations, increasing from the centre to the
edge, the most accurate estimations may be conducted
only for objects situated in the centre.
How do you measure lengths?
On pictures of areas showing small elevation differences
(up to 100 m) lengths may be measured
directly with a ruler. If the lines are curved, the
easiest way is to divide them into straight sections
and to measure each separately. An alternative
method is to use a curvometer. Very small
objects require application of a Brinell magnifying
glass or Brinell microscope.
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Surveys & Assessments: Landscape