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areal photo or satallite image interpretation

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4.1 Introduction
In order to take advantage of and make good use of remote sensing data, we must be able to
extract meaningful information from the imagery. This brings us to the topic of discussion in
this chapter - interpretation and analysis - the sixth element of the remote sensing process
which we defined in Chapter 1. Interpretation and analysis of remote sensing imagery involves
the identification and/or measurement of various targets in an image in order to extract useful
information about them. Targets in remote sensing images may be any feature or object which
can be observed in an image, and have the following characteristics:
􀂄 Targets may be a point, line, or area feature. This means that they can have any form,
from a bus in a parking lot or plane on a runway, to a bridge or roadway, to a large
expanse of water or a field.
􀂄 The target must be distinguishable; it must contrast with other features around it in the
image.
Section 4.1 Introduction Page 141
Canada Centre for Remote Sensing
Much interpretation and identification of targets in remote sensing imagery is performed
manually or visually, i.e. by a human interpreter. In many cases this is done using imagery
displayed in a pictorial or photograph-type format, independent of what type of sensor was
used to collect the data and how the data were collected. In this case we refer to the data as
being in analog format. As we discussed in Chapter 1, remote sensing images can also be
represented in a computer as arrays of pixels, with
each pixel corresponding to a digital number,
representing the brightness level of that pixel in the
image. In this case, the data are in a digital format.
Visual interpretation may also be performed by
examining digital imagery displayed on a computer
screen. Both analogue and digital imagery can be
displayed as black and white (also called
monochrome) images, or as colour images (refer
back to Chapter 1, Section 1.7) by combining different
channels or bands representing different
wavelengths.
When remote sensing data are available in digital format, digital processing and analysis
may be performed using a computer. Digital processing may be used to enhance data as a
prelude to visual interpretation. Digital processing and analysis may also be carried out to
automatically identify targets and extract information completely without manual intervention
by a human interpreter. However, rarely is digital processing and analysis carried out as a
complete replacement for manual interpretation. Often, it is done to supplement and assist the
human analyst.
Manual interpretation and analysis dates back to the early beginnings of remote sensing for
Section 4.1 Introduction Page 142
Canada Centre for Remote Sensing
air photo interpretation. Digital processing and analysis is more recent with the advent of
digital recording of remote sensing data and the development of computers. Both manual and
digital techniques for interpretation of remote sensing data have their respective advantages
and disadvantages. Generally, manual interpretation requires little, if any, specialized
equipment, while digital analysis requires specialized, and often expensive, equipment.
Manual interpretation is often limited to analyzing only a single channel of data or a single
image at a time due to the difficulty in performing visual interpretation with multiple images.
The computer environment is more amenable to handling complex images of several or many
channels or from several dates. In this sense, digital analysis is useful for simultaneous
analysis of many spectral bands and can process large data sets much faster than a human
interpreter. Manual interpretation is a subjective process, meaning that the results will vary
with different interpreters. Digital analysis is based on the manipulation of digital numbers in a
computer and is thus more objective, generally resulting in more consistent results. However,
determining the validity and accuracy of the results from digital processing can be difficult.
It is important to reiterate that visual and digital analyses of remote sensing imagery are not
mutually exclusive. Both methods have their merits. In most cases, a mix of both methods is
usually employed when analyzing imagery. In fact, the ultimate decision of the utility and
relevance of the information extracted at the end of the analysis process, still must be made
by humans.
Section 4.1 Introduction Page 143
Canada Centre for Remote Sensing
4.2 Elements of Visual Interpretation
As we noted in the previous section, analysis of remote sensing imagery involves the
identification of various targets in an image, and those targets may be environmental or
artificial features which consist of points, lines, or areas. Targets may be defined in terms of
the way they reflect or emit radiation. This radiation is measured and recorded by a sensor,
and ultimately is depicted as an image product such as an air photo or a satellite image.
What makes interpretation of imagery more difficult than the everyday visual interpretation of
our surroundings? For one, we lose our sense of depth when viewing a two-dimensional
image, unless we can view it stereoscopically so as to simulate the third dimension of
height. Indeed, interpretation benefits greatly in many applications when images are viewed in
stereo, as visualization (and therefore, recognition) of targets is enhanced dramatically.
Viewing objects from directly above also provides a very different perspective than what we
are familiar with. Combining an unfamiliar perspective with a very different scale and lack of
recognizable detail can make even the most familiar object unrecognizable in an image.
Finally, we are used to seeing only the visible wavelengths, and the imaging of wavelengths
outside of this window is more difficult for us to comprehend.
Recognizing targets is the key to interpretation and information extraction. Observing the
differences between targets and their backgrounds involves comparing different targets based
on any, or all, of the visual elements of tone, shape, size, pattern, texture, shadow, and
association. Visual interpretation using these elements is often a part of our daily lives,
whether we are conscious of it or not. Examining satellite images on the weather report, or
following high speed chases by views from a helicopter are all familiar examples of visual
image interpretation. Identifying targets in remotely sensed images based on these visual
elements allows us to further interpret and analyze. The nature of each of these interpretation
elements is described below, along with an image example of each.
Tone refers to the relative brightness or colour of objects in an image. Generally, tone is the
fundamental element for distinguishing between different targets or features. Variations in
Section 4.2 Elements of Visual Interpretation Page 144
Canada Centre for Remote Sensing
tone also allows the elements of shape, texture, and pattern of objects to be distinguished.
Shape refers to the general form, structure, or outline of individual objects. Shape can be a
very distinctive clue for interpretation. Straight edge shapes typically represent urban or
agricultural (field) targets, while natural features, such as forest edges, are generally more
irregular in shape, except where man has created a road or clear cuts. Farm or crop land
irrigated by rotating sprinkler systems would appear as circular shapes.
Size of objects in an image is a function of scale. It is important to assess the size of a target
relative to other objects in a scene, as well as the absolute size, to aid in the interpretation of
that target. A quick approximation of target size can direct interpretation to an appropriate
result more quickly. For example, if an interpreter had to distinguish zones of land use, and
had identified an area with a number of buildings in it, large buildings such as factories or
warehouses would suggest commercial property, whereas small buildings would indicate
residential use.
Section 4.2 Elements of Visual Interpretation Page 145
Canada Centre for Remote Sensing
Pattern refers to the spatial arrangement of visibly discernible objects.
Typically an orderly repetition of similar tones and textures will produce a
distinctive and ultimately recognizable pattern. Orchards with evenly
spaced trees, and urban streets with regularly spaced houses are good
examples of pattern.
Texture refers to the arrangement and frequency of
tonal variation in particular areas of an image. Rough textures would
consist of a mottled tone where the grey levels change abruptly in a small
area, whereas smooth textures would have very little tonal variation.
Smooth textures are most often the result of uniform, even surfaces, such
as fields, asphalt, or grasslands. A target with a rough surface and
irregular structure, such as a forest canopy, results in a rough textured
appearance. Texture is one of the most important elements for distinguishing features in radar
imagery.
Shadow is also helpful in interpretation as it may provide an idea of the
profile and relative height of a target or targets which may make
identification easier. However, shadows can also reduce or eliminate
interpretation in their area of influence, since targets within shadows are
much less (or not at all) discernible from their surroundings. Shadow is
also useful for enhancing or identifying topography and landforms,
particularly in radar imagery.
Association takes into account the relationship between other
recognizable objects or features in proximity to the target of interest. The
identification of features that one would expect to associate with other
features may provide information to facilitate identification. In the
example given above, commercial properties may be associated with
proximity to major transportation routes, whereas residential areas would
be associated with schools, playgrounds, and sports fields. In our
example, a lake is associated with boats, a marina, and adjacent recreational land.

السلام عليكم
اشكركم كثيرا على هذه الجهود وجزاكم الله خيرا
في هذا الموقع https://zulu.ssc.nasa.gov/mrsid وجدت خرائط لاند سات ارتفاعات رقمية
ولكن اريد ان اعرف :
1-هل ان الخرائط الرقمية تحتاج الى اى نوع من انواع التصحيح
2-هل هذه الخرائط تحتاج الى ربطها ب GCP من اجل ان تكون الارتفاعات معدلة
3-عندم فتحتها ب global mapper كانت النتائج ب long&latitude هل من الممكن تحويل هذه الاحداثيات الى UTM WGS-84
4-كيف يمكن تحويل هذه النقاط في arcgis 9.3 الى UTM WGS-84

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