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Table of Contents
Foreword
Preface
Glossary

Chapter 1: Introduction

Introduction

Remote Sensing and Air Photo Interpretation

This collection aims to show the geography of Manitoba using remote sensing, a process that involves obtaining information about the earth’s surface without coming into contact with it. A range of instruments can sense much of the electromagnetic spectrum, whereas the human eye can sense only a narrow band of wavelengths from 0.4 to 0.7 micrometres, the so-called visible part of the spectrum. Most people are now familiar with at least air photographs, obtained using cameras, and with radar images. Radar has the advantage of not requiring light to operate and some radar wavelengths can penetrate clouds. Many Manitobans are familiar with the spectacular radar images of the Red River Plain obtained during the height of the 1997 “flood of the century.”

In remote sensing the remoteness of the sensor can vary enormously. Photographs can be taken from a few metres above the ground using a camera mounted on a “cherry picker” but most air photographs are taken from planes flying between 5,000 and 30,000 feet[i] above sea level. Photographs and other forms of images are obtained from satellites at heights up to thousands of kilometres. Despite the development of many new remote-sensing techniques, air photographs are still the best known and, for the non-expert, the most easily interpreted of all images; consequently, most images in this collection are air photographs.

Air photographs come in several different forms, the most obvious division being into colour or black and white (panchromatic) photos. Colour photos are more impressive and more easily interpreted because they are more like what people are used to seeing. However, they have some drawbacks vis-à-vis “black and white” photos. Despite modern developments, colour photos are more demanding with respect to light conditions, a factor that limits their availability. Consequently, colour air photo coverage of the province is limited to a few areas and was usually taken for specialized purposes such as vegetation mapping. In contrast “black and white” images are available for every part of the province and often coverage of the same area for several different dates is available. These so called “sequential air photos” are particularly useful for the interpreter trying to detect changes over the years, for example, at the edges of urban areas and along meandering rivers (figures 1.1, 1.2, and 1.3).

Another standard sub division of air photos is into verticals, obliques, and mosaics. As the name suggests, verticals are taken with the camera pointing directly downwards from the plane[ii]. These are the most readily available of the categories; consequently, most images in this collection are verticals. Obliques are taken at an angle of less than 90 degrees to the earth’s surface. They are easily recognizable by most people because they resemble the view passengers get from a plane window. They are, though, much less readily available than verticals, and, because the scale varies from place to place on the photo, measurements on them are complicated. Mosaics are secondary photographs made by re-photographing a series of verticals placed in their correct position with respect to one another. The result is a good overview of an area. Mosaics are available for all of Agro Manitoba[iii] and were used extensively in trying to locate the exact position of verticals used in this collection.

Air Photographs vs Maps

Geography “seeks to understand where things are and how and why they got there by studying—with an emphasis on location—the connections and interactions among people, places, and environments."[iv] Maps are useful in showing locations, patterns and the interrelatedness of things. They are indispensable to the geographer, so much so that some claim that if you cannot show it on a map it is not geography. Photos also show locations, patterns and the interrelatedness of things and have some additional merits compared to maps. An air photograph shows the surface of the earth as an observer looking at the ground from a plane would see it and, as most people who use this collection will have flown, the photos will be familiar to them. An air photo shows everything “seen” by the camera at a specific instant; maps on the other hand are sets of symbols. Although people become familiar with the map symbols over time, it takes skill and experience to become a good map interpreter. Moreover, the cartographer—mapmaker—cannot show every aspect of the earth’s surface, as the resulting map would be cluttered. Consequently a map is selective in what is shown.

A point against the air photo is that its time specificity gives the interpreter no indication of seasonal changes of the landscape. Most photos are taken during the summer, when the sun is high in the sky and the days long. Consequently winter photos are rare and few were available for inclusion in this collection. Nor do air photos show abstract things such as political boundaries, although different land use on either side of a boundary may give it physical representation as for example along the Canada/U.S.A. border (figures 2.5 and 2.6).

One further difference between air photos and maps is that maps are drawn as if it were possible for an observer to be directly above each point on the earth’s surface. A map is therefore a true plan view or orthogonal projection. In contrast when a vertical air photo is taken, the camera is directly above only one point on the ground; all other points are seen slightly “sideways on.” So, vertical air photos are perspective projections and as a result some points on the ground may be hidden from the camera by tall objects or high ground. This is particularly troublesome in mountainous areas (so it is not a major problem in Manitoba) and in areas with many tall buildings (limited in Manitoba to Winnipeg only-- Figure 1.13).

Air Photo Interpretation: The Process

Although we aim to keep this description non-technical, the reader needs to know how air photos are interpreted, which involves the introduction of some terms. Interpreting air photos is like detective work; a series of clues is assembled in an orderly fashion and then a solution is arrived at which best fits the clues. The interpreter uses seven criteria in the interpretation of photo images: tone, texture, pattern, shape, size, shadow, and location (or association).

Tone is a measure of the amount of light reflected by an object and recorded on a panchromatic (black and white) photograph. Tones are shades of grey; strictly speaking they range from very dark grey to very light grey—not from black to white. Tones vary greatly depending on the time of day, which influences the sun’s angle; the type of film and filter used; and the development process. On the whole, dark coloured objects appear dark grey and light coloured objects, light grey. There are, though, exceptions; two water surfaces on the same photo can vary from almost black to almost white, depending on the relationship between the sun’s angle, the water surface and the camera (figure 1.4); tonal contrast is more important than the actual tone. The human eye is sensitive to very small tonal differences and minor variations can represent significant differences on the earth’s surface (figure 1.12). Tone is a characteristic of all the other interpretation criteria.

Texture is difficult to define and is best described by reference to the texture of cloth. The same sort of terminology is used, so photo surfaces may be rough (figure 1.9), mottled (figure 1.4), or silky (figure 1.7). The texture displayed on a photo results from the arrangement of tiny images expressed by the tone, shape, size, and pattern of the object displayed. The texture of an area does not always remain the same; for example, a lake surface in calm weather will be expressed as smooth or even textured (figure 1.6) whereas with a strong wind blowing, the surface will be rough and will be expressed as a rough texture on an air photo. Texture also depends on the scale of the photos (explained later). For example, rows of trees in an orchard will show up as a series of round objects arranged in lines on a large scale photo, but on a smaller scale photo, the individual images merge to produce a rough texture. At a very small scale, all variations may disappear to produce a smooth texture (figures 1.15a, 1.15b, and 1.15c).

Pattern refers to the orderly arrangement of features. Some elements of the natural landscape form patterns; for example, under the right circumstances, river channels may be arranged into distinctive drainage patterns. However, more obvious patterns are associated with human activity. In much of Agro-Manitoba, for example, the pattern of square fields resulting from the Dominion Lands Survey (DLS) system is distinctive (figures 1.14, 1.15a, 1.16), but land that was settled by people of French heritage exhibits the equally distinctive long lot system (figure 1.12).

Shape is the general form or configuration of an object. Some landforms have distinctive shapes, for example, the loops of meanders (figure 1.2a, 1.2b); however, as with patterns, human-made objects tend to have more clearly defined and easily interpreted shapes. The “fish-like” appearance of golf courses (figures 17.15, 17.16) is often seen near the edges of towns and cities, as are oval shaped racetracks (figure 1.9). Also, the fan shape of drive-in cinemas (figure 12.12)—now almost extinct—and the triangular shape of small prairie airfields (figures 18.45 to 18.48) point to their functions.

Size, both actual and relative, is another criterion used. Even though the interpreter may be unable to determine the exact size of an object, it is usually possible to obtain a comparative size with respect to something whose size is known. An object at the edge of a field may be wider than a nearby road so the object is clearly not a car. Also the relative size of objects on a road may indicate whether they are buses, trucks, or cars (figure 1.13).

Shadow: Photographs are usually taken when the sky is cloud-free so ground objects will throw shadows; only rarely do cloud shadows appear on photos (figure 1.14). The length of the shadow will depend on the time of day the photo was taken: a long shadow, early and late in the day; a short shadow, near midday. Often the shadow shape will point to the nature of the object; for example, coniferous trees have different shadow shapes from deciduous trees (figure 1.6, 1.13). Experienced interpreters can even determine tree species from their shadows. Human-made objects such as electricity pylons, TV towers, bridges and the old wooden grain elevators (figure 1.9) throw distinctive shadows. Also because shadows are thrown generally northward, rather than to the south, the orientation of the photograph can be determined if it is not known from other information.

Location (sometimes referred to as association) is another useful criterion. The interpreter is concerned with the location of an object with respect to other things. Is the object in the middle of a city or in an open field? Is it at the top of a hill or the bottom of a valley? Is it closely associated with railway tracks or roads? The answers to these questions can lead to a positive identification or at least the elimination of some possibilities (figures 1.8, 1.13).

Scale is a factor that has an influence on all the photo identification criteria. Scale is the ratio between a distance on the photo and the distance it represents on the ground. It is usually expressed in the form, 1:20,000, meaning that one unit of measurement on the photo represents 20,000 of the same units on the ground. Scale is influenced by the height from which the photos were taken. Assuming the focal length of the camera remains the same, as the plane carries the camera higher, more ground is covered on an individual photo but at the same time there is a loss of detail as the scale decreases. Conversely, photos taken from low flight heights cover less ground but more detail is shown at a larger scale (figures 1.15a, 1.15b, 1.15c).

Stereoscopic Vision

People with two good eyes see things in three dimensions; i.e., they see stereoscopically. This is because they see objects from two different viewpoints—the right eye and the left eye. The two sight lines converge on the object being viewed and the two images are processed in the brain to give a three dimensional impression. Taking photographs from two different plane positions simulates this situation. The most common situation is for a plane to fly over an area with a camera automatically taking photos so that photo two overlaps photo one by 60 percent and photo three overlaps photo two by 60 percent and so on. In this way each point on the ground is photographed from two different viewpoints, duplicating the position of the two eyes. Two photos with one overlapping the other are known as a stereopair and three as a stereotriplet (figure 1.16a, 1.16b, 1.16c). To view the photographs, one arranges them side by side with the correct orientation and observes them through a stereoscope. The stereoscope is merely a device to help the observer to look at the left-hand image with the left eye and the right-hand image with the right eye. The brain fuses the two images to give a three dimensional (stereoscopic) effect. Usually the relief is exaggerated over reality. If the photographs are taken closely together to more closely resemble the sight lines from the two eyes, the exaggeration is reduced. Conversely, decreasing the overlap increases the exaggeration. Usually the vertical exaggeration is a bonus in areas of “moderate” relief such as Manitoba where minor landforms with little amplitude of relief—vertical distance from top to bottom—are more easily detected and interpreted.

Air photos should be arranged so that shadows fall towards the viewer. Failure to do so can result in pseudoscopic vision; that is, the topography is reversed—valleys look like ridges and ridges look like valleys (figure 1.17).

Organization

This collection follows the same outline as the book, The Geography of Manitoba: Its Land and Its People[v] so that the book and air-photo collection can be used in conjunction with each other. However, it has to be acknowledged that while some aspects of Manitoba’s geography are well displayed on air photographs, others are not. For example, landforms are very well shown but climate is not. Consequently the relative weighting of topics varies from that given in the book. Nevertheless, the sequence of topics is essentially the same but in the collection we treat transport as a major topic. In the book it was subsumed under other headings.



Notes

[i] Even today, flight heights are given in feet rather than in metres. On the other hand, lens focal length—needed in order to calculate the scale of an air photo—is given in millimetres.

[ii] Good quality vertical air photos are no more than one degree removed from 90 degrees.

[iii] Agro-Manitoba is that part of southern Manitoba in which agriculture is practised. Usually not included is a small area of agricultural land south of The Pas.

[iv] National Geographic. The National Geographic Desk Reference. Washington D.C.: National Geographic, 1999, 4.

[v] Welsted, J., Everitt, J., and Stadel, C., eds. The Geography of Manitoba: Its Land and Its People. Winnipeg: The University of Manitoba Press, 1996.

1.1: Sequential Air Photos of the Junction of the Assiniboine and Little Saskatchewan Rivers

Sequential air photos (taken of the same area at different times) reveal changes that have occurred over time. Many geomorphological processes are so slow that no change can be detected even by comparing very old photos with recent ones (the time span is after all little more that 100 years). However, prairie streams flowing across easily eroded sediments assume a meandering form, the position of the meanders changing relatively quickly.

Figure 1.1a: 1947 Photo

The Little Saskatchewan River 1 flows southward onto the floor of the Assiniboine spillway, bounded roughly by provincial road (PR) 459 2. From that point south, it assumes an indirect meandering course 3 to the Assiniboine River 4. Several previous routes can be seen both west 5 and east 6 of the present course. Note also the dam 7 across the Little Saskatchewan River with a reservoir 8 to the north. This was the location of the first hydroelectric power station in Manitoba. Between 1900 and 1930 it supplied electricity to Brandon during the summer months. The dam was washed away and the reservoir emptied in 1949

Figure 1.1.a: 1947 Photo

Figure 1.1.a: 1947 Photo

Figure 1.1a

Vertical air photo: A11041-201

Flight height: 9,520 feet a.s.l.; lens focal length: 152.4 mm

Scale: 1: 16,700 (approx.)

Date: May 19, 1947

Location: Township 10, Range 20 WI

Map sheets: 1:250,000 62F Virden

1:50,000 62F/16 Alexander

Notes

[i] For a ground level photo of the dam see figure 16.26.


Figure 1.1b: 1968 Photo

Twenty years after photo 1.1a was taken, the Little Saskatchewan River 1 takes a more direct route to the Assiniboine River 2 (the 1948 route is indicated by a dashed line) and has deposited sediment 3 in the larger river.

This photograph also illustrates several of the criteria used in air-photo interpretation.

1)  Tone. Tones are in shades of grey, ranging from almost white, to almost black. Fields on which crops have been grown, and at least partly harvested, appear in light tones 4 whereas the relatively clear water of the Little Saskatchewan River is dark toned 5. The Assiniboine River, which carries more suspended sediment than the Little Saskatchewan River, is lighter toned than the latter. Also some deciduous trees, probably aspen (Populus tremuloides) appear light toned 6 because in this fall photo the leaves have changed colour to bright yellow.

2)  Texture. A field east of the Little Saskatchewan River 7, which has been left fallow, exhibits a smooth texture because of its uniform medium grey tone. On the other hand the treed area south of the Assiniboine River 8 has a mottled texture resulting from the various tones of the constituent trees.

3)  Pattern. East of the fallow field are two other fields exhibiting the characteristic pattern of grain crops that have been harvested. The westernmost 9 has a pattern of narrow lines typical of a field that has been swathed whereas the field to its east 10 has wider rows resulting from the fact that it is being combined.

4)  Shape/shadow. Shadows thrown by trees west of the Little Saskatchewan River are rounded 11, indicating that they are deciduous rather than coniferous. South of the Assiniboine River, tree shadows indicate that the trees have lost their leaves so that their branched form can be seen 12.

5)  Location and size. At the north end of the field being combined are eight vehicles 13. Given their location it is a reasonable assumption that they are combine harvesters accompanied by trucks to receive the grain. At least four vehicles can be seen on the Trans-Canada Highway 14, 15, and 16. Given their location it can be assumed that they are trucks or cars; the largest of the four is a truck 16.


Figure 1.1.b: 1968 Photo

Figure 1.1.b: 1968 Photo

Figure 1.1b

Vertical air photo: A20811-97

Flight height: 7,200 feet a.s.l.; lens focal length: 152.07 mm.

Scale: 1:12,000 (approx.)

Date: September 29, 1968

Location: Township 10, Range 20 WI

Map sheets: 1:250,000 62F Virden

1:50,000 62F/16 Alexander


1.2: Sequential Air Photos of the Assiniboine River Near the Junction with Birdtail Creek

Figure 1.2a: 1946 Photo

The photo shows a stretch of the south flowing Assiniboine River 1 just above (0.75 miles: 1.2 km) its junction with Birdtail Creek. The river meanders freely across the floor of the Assiniboine Spillway, a flat-floored valley that used to carry water from glacial lakes in Saskatchewan to glacial Lake Agassiz in southern Manitoba. Several abandoned channel sections 2 can be seen, all of which were abandoned before the first map of the area was made in 1882. Note two narrow meander necks 3 and 4 in the southern half of the photo.

Note also: 1) the relatively light tone of the sediment-laden Assiniboine River 5, compared with the dark sediment-free water 6 in abandoned channels; and 2) the mottled texture 7 in the area of deciduous woodland west of the river where trees are changing colour at the beginning of fall resulting in various tones.

Figure 1.2b: 1981 Photo

In this 1981 photo the narrow neck 1 (3 in figure 1.2a) has broken resulting in an abandoned channel 2. The meander neck in the centre 3, although narrower than on the older photo, is still extant but looks as if it will break any time.

Note also: 1) the uniform dark tone of the deciduous trees west of the Assiniboine 4 in this summer photo when all the leaves were green; and 2) a small recently abandoned channel 5 in the south.

Figure 1.2.a: 1946 Photo

Figure 1.2.a: 1946 Photo

Figure 1.2a

Vertical air photo: A10707-57

Flight height: 9,800 feet a.s.l.; lens focal length: 152.4 mm

Scale: 1:17,000 (approx.)

Date: October 4, 1946

Location: Township 15, Range 27/28 WI

Map sheets: 1:250,000 62K Riding Mountain

1:50,000 62K/6 Birtle




Figure 1.2.b: 1981 Photo

Figure 1.2.b: 1981 Photo

Figure 1.2b

Vertical air photo: 8126-00-037

Flight height?: lens focal length: 152.034 mm

Scale: 1:15,800 (approx.)

Date: August 16, 1981

Location: Township 15, Range 27/28 WI

Map sheets: 1:250,000 62K Riding Mountain

1:50,000 62K/6 Birtle 


1.3: Sequential Air Photos of the Assiniboine River West of Brandon

Figure 1.3a: 1945 photo

The Assiniboine River 1 flows from west to east with a large meander loop 2 to the north. Below the meander the river is remarkably straight, hugging the south bank of the Assiniboine Spillway the south side of which is more heavily wooded 3 than the north side 4. This is a result of a wetter microclimate on steep north-facing slopes. The photo was taken in the early winter after a light snowfall. Snow—very light-toned—has accumulated more in some places than in others; for example, it is more obvious on a rough field surface in the northwest 5 than over the fields just to the south 6. At this early stage of winter, the Assiniboine is not frozen and appears as a characteristic light tone due to high-suspended sediment content.

Figure 1.3b: 1968 photo

The area shown in figure 1.3a is in the northwest corner of this smaller scale photo. Twenty-two years after 1.3a was taken, the meander loop has been cut across 1. Given the width of the meander neck, it would seem that the river was artificially straightened. A small causeway across the north end of the meander 2 hints at the reason for the straightening. Land within the loop is now cropped 3 while it was not on figure 1.3a. To gain access to the area it was possible for the farmer to build a causeway across the static water of the cutoff whereas this could not be done with a flowing river. Note also the contrast between the light tone of the sediment-laden Assiniboine River 4 and the dark tone of the sediment-free cutoff 5. The Little Saskatchewan River can be seen in the northeast 6 following much the same route as it did in figure 1.1b.

Figure 1.3.a: 1945 Photo

Figure 1.3.a: 1945 Photo

Figure 1.3a

Vertical air photo: A7566-5

Flight height: 12,400 feet a.s.l.; lens focal length: 209.55 mm

Scale: 1:13,900 (approx.)

Date: April 13, 1945

Location: Township 10, Range 20 WI

Map sheets: 1:250,000: 62F Virden

1:50,000: 62F/16 Alexander




Figure 1.3.b: 1968 Photo

Figure 1.3.b: 1968 Photo

Figure 1.3b

Vertical air photo: A20470-66

Flight height: 21,950 feet a.s.l.; lens focal length: 152.73 mm

Scale: 1:39,000 (approx.)

Date: May 21, 1968

Location: Township 10, Ranges 20 and 21 WI

Map sheets: 1:250,000 62F Virden

1:50,000 62F/16 Alexander


1.4: Tonal Variations in the Landscape East of Elphinstone

In this area of hummocky ground moraine topography, numerous small lakes (sloughs) can be seen. In the centre and north they are dark-toned 1 whereas in the southeast they are light-toned 2. The light tone is a result of the relationship between the camera angle, the sun angle, and the water surface, a phenomenon known as specular reflection. The diagram below shows the conditions under which specular reflection occurs. Objects at E would show the effect whereas objects at F would not.

The very light-toned lake in the west 3 is probably a dried up lake with a salt surface resulting from evaporation. The same process seems to be starting at another lake further south 4, which was obviously once much larger 5 and now has white deposits along its shore 6.

The photo also illustrates the interpretation criterion “texture.” The central lake 7 is uniformly dark-toned and has a smooth texture whereas wooded areas to the north 8 and south 9 have variable tones resulting from the way light falls on tree crowns and sides. The result is a mottled texture.

Figure 1.4: Tonal Variations in the Landscape East of Elphinstone

Figure 1.4: Tonal Variations in the Landscape East of Elphinstone

 

Figure 1.4

Vertical air photo: A11569-201

Flight height: 7,920 feet a.s.l.; lens focal length: 152.4 mm

Scale: 1:14,700 (approx.)

Date: August 18, 1948

Location: Township 18, Range 21 WI

Map sheets: 1:250,000: 62K Riding Mountain

1:50,000: 62 K/9 Elphinstone

 


1.5: Tonal Variations North of Elphinstone

Shown here is an area of lake-strewn ground moraine in the east and the valley of the upper part of the Little Saskatchewan River 1 in the west. The lakes are mainly dark-toned 2 except for those in the southeast 3 where specular reflection is occurring. The large lake in the extreme southeast 4 is Thomas Lake; it is large enough that winds blowing across it can produce waves leading to slight tonal variations and a silky texture 5. Note also tonal variations in harvested fields in the north centre: light-toned areas 6 are covered by stubble, whereas irregularly shaped dark-toned areas 7 result from stubble burning, a common practice in southern Manitoba in 1947.

Figure 1.5: Tonal Variations North of Elphinstone

Figure 1.5: Tonal Variations North of Elphinstone

 

Figure 1.5

Vertical air photo: A11614-73

Flight height: 7,920 feet a.s.l.; lens focal length: 152.4 mm

Scale: 1:15,000 (approx.)

Date: September 30, 1948

Location: Township 18, Range 21 WI

Map sheets: 1:250,000: 62K Riding Mountain

1:50,000: 62K/9 Elphinstone


1.6: Tonal Variations in Riding Mountain National Park

The large lake in the east 1 is Edwards Lake. In the north it is dark-toned 2 but in the southeast specular reflection can be seen 3. Waves on the lake produce a silky texture in the east 4. Other slightly lighter-toned areas 5 may result from sediment stirred up by waves or from algae growth. A small round lake 6 west of Provincial Trunk Highway (PTH) 10 7 is dark-toned and smooth textured. The photo also illustrates the use of the criterion “shadow” in identification. Coniferous trees, in addition to being dark-toned, throw triangular shadows 8 well seen close to PTH 10 that runs between Wasagaming (to the south) and Dauphin (to the north).

Figure 1.6: Tonal Variations in Riding Mountain National Park

Figure 1.6: Tonal Variations in Riding Mountain National Park

Figure 1.6

Vertical air photo: A20375-189

Flight height: 10,320 feet a.s.l.; lens focal length: 152.47 mm

Scale: 1:15,800 (approx.)

Date: May 21, 1968

Location: Township 22, Range 19 WI

Map sheets: 1:250,000: 62K Riding Mountain

1:50,000: 62K/6 Whitewater Lake

1:125,000: MCR 207 Riding Mountain National Park


1.7: Tonal Variations Exhibited by Water Surfaces

Figure 1.7a: large-scale photo

Shown on this large-scale photo is the east flowing light-toned Assiniboine River 1 with some spectral reflection in the east 2. Just downstream from the confluence of Chater Creek 3 are the City of Brandon’s sewage lagoons, medium grey-toned 4, except in the east where spectral reflection occurs 5. Slight variations in tone resulting from a rough water surface produce a silky texture in the extreme east 6. Note also the dark-toned, rough textured woodland along the Assiniboine River 7 and Chater Creek 8.

Figure 1.7.a: large-scale photo

Figure 1.7.a: large-scale photo

Figure 1.7a

Vertical air photo: A25396-159

Flight height: 9,700 feet a.s.l.; lens focal length: 152.034 mm

Scale: 1:17,100 (approx.)

Date: June 4, 1980

Location: Township 10, Range 18 WI

Map sheets: 1:250,000: 62G Brandon

1:50,000: 62G/13 Brandon

Figure 1.7b: smaller scale photo

This photo covers a larger area than 1.7a including all the land shown on 1.7a. Here the Assiniboine River 1 is darker toned except in the south 2 where spectral reflection occurs. On this photo the sewage lagoons 3 are very dark toned, probably the result of different photo paper and processing. Note also the distinctive checkerboard pattern produced by the DLS system of land division 4.


Figure 1.7.b: smaller-scale photo

Figure 1.7.b: smaller-scale photo

Figure 1.7b

Vertical air photo: A25656-42

Flight height: 17,384 feet a.s.l.; lens focal length: 88.19 mm

Scale: 1:57,600 (approx.)

Date: April 9, 1981

Location: Township 10, Range 18 WI

Map sheets: 1:250,000: 62G Brandon

1:50,000: 62G/13 Brandon

 


1.8: Air Photo Interpretation Criteria Applied to an Area South of Wawanesa

This photo illustrates the use of the air photo interpretation criteria: tone, texture, location, and shadow (shape). A field in the south-centre 1 is uniformly dark-toned and consequently has a smooth texture. It is characteristic of fallow fields in this area developed on flat, lake-bottom sediments that produce black chernozem soils. The field to the northeast 2 has supported a grain crop that has been harvested, the remaining stubble producing a light tone. However, the farmer has “cultivated” the edge of the field producing a dark-toned fringe 3. Located in the middle of two fields to the west are irregular masses 4 which, as they throw a shadow, have some vertical extent. Their locations in the centre of cropped fields suggest that they are straw piles. Another possible explanation might be that they are stone piles, but given the obvious fertility of the fields in the area, this explanation is less likely. The river in the north is the Souris 5 flowing from west to east. Some of the trees near the meander are light-toned 6 suggesting first that they are deciduous trees (in this area, probably aspen-Populus tremuloides) and second that the photo was taken in the fall when the leaves turn yellow. The direction in which the shadows—of trees 7, buildings 8, and a river cliff 9—fall is towards the top of the photo suggesting that the top of the photo is north.

Figure 1.8: Air Photo Interpretation Criteria Applied to an Area South of Wawanesa

Figure 1.8: Air Photo Interpretation Criteria Applied to an Area South of Wawanesa

Figure 1.8

Vertical air photo: A11123-224

Flight height: 12,400 feet a.s.l.; lens focal length: 8 inches

Scale: 1:15,000 (approx.)

Date: October 4, 1947

Location: Township 7, Range 17 WI

Map sheets: 1:250,000: 62G Brandon 

1:50,000: 62G/12 Wawanesa


1.9: Air Photo Interpretation Criteria Applied to an Area Near Carberry

This photo of Carberry and surrounding area illustrates the application of the photo interpretation criteria—tone, texture, shape, and location—to the identification of surface features. Several fields have a uniform dark-grey tone 1 characteristic of grain crops at an early growth stage while they are still green. The uniformity of tone results in a smooth texture 2. Northwest of town, several fields show gradations from very light tone 3 to medium-grey tone 4. These fields are developed on an irregular sandy surface; the light-toned areas are higher and drier than the dark-toned areas. Also west of Carberry are dark-toned areas with a rough texture 5; these are areas of deciduous woodland. On the southwestern edge of town is the characteristic oval shape 6 of a racetrack. Finally north of town are two squared areas 7, one divided into quarters by tree belts 8. This is a typical arrangement for cemeteries, an identification supported by the location, a half-mile (0.8 km) out of town. A railway line 9 runs south of town with a branch leading off to the north 10. An elevator 11 identified by its distinctive shadow shape is located on this line.

Figure 1.9: Air Photo Interpretation Criteria Applied to an Area Near Carberry

Figure 1.9: Air Photo Interpretation Criteria Applied to an Area Near Carberry

Figure 1.9

Vertical air photo: A23996-91

Flight height: 13,200 feet a.s.l.; lens focal length: 153.22 mm

Scale: 1:24,400 (approx.)

Date: June 18, 1975

Location: Townships 10/11, Ranges 14 and 15 WI

Map sheets: 1:250,000 62G Brandon

1:50,000 62G/14 Carberry


1.10: Air Photo Interpretation Criteria Applied to an Area on the Assiniboine River South of Long Plain First Nation

The Assiniboine River 1 flows from west to east and then turns north. The photo illustrates the use of the criterion, tone, in interpretation of landforms. The tone of the river is light grey 2 indicating high suspended sediment content; at several locations in the channel very light-toned areas 3 are sandbars. South of the west-east river section and west of the south-north section are linear dark-toned features 4 and 5. These are meander scrolls left as relics of former positions on the river as it migrated north and east. Southeast of the river is a field in which the tone varies from very light 6 to very dark 7, a reflection of water content of the soil; dark grey indicates high water content, and light grey suggests low water content. This type of variation is characteristic of sandy soils.  Dark-toned, rough-textured areas 8 cover much of the photo. These are areas of deciduous woodland, an interpretation supported by rounded shadows 9 thrown by the trees near clearings.

Figure 1.10: Air Photo Interpretation Criteria Applied to an Area on the Assiniboine River South of Long Plain First Nation

Figure 1.10: Air Photo Interpretation Criteria Applied to an Area on the Assiniboine River South of Long Plain First Nation

Figure 1.10

Vertical air photo: A16574-44

Flight height: 8,800 feet a.s.l.; lens focal length: 6 inches

Scale: 1:15,100 (approx.)

Date: June 19, 1959

Location: Township 9, Range 8 WI

Map sheets: 1:250,000: 62G Brandon

1:50,000: 62G/16 Portage la Prairie


1.11: Air Photo Interpretation Criteria, Tone and Shadow, Applied to an Area in the Upper Part of Elm River Southeast of Portage la Prairie

This very large-scale photo (1:3,000) shows the upper part of Elm River, a palaeochannel (former channel) of the Assiniboine River, across an alluvial fan south of Portage la Prairie[i]. In this area the creek is really a series of small lakes 1 rather than a continuous flow to the east. In the northwest tonal variations from very light 2 to dark 3 indicate meander scrolls left behind as Elm River migrated to the southeast. At this large scale, rounded shadow shape 4 is a good indicator of deciduous trees including those growing along the river course 5 and those planted in a shelterbelt around a farm 6. Also shadows of poles 7 carrying a power line can be seen along a light-toned north/south road 8.

The notation in the top right hand corner of the photo indicates that photo A20774-21 is the first in a line flown from east to west that includes photos 21-33. The photographs were taken on July 7, 1968 from a height of 2,400 feet above ground level[ii] using a camera having a lens with focal length 152.24 mm.

Figure 1.11: Air Photo Interpretation Criteria, Tone and Shadow, Applied to an Area in the Upper Part of Elm River Southeast of Portage la Prairie

Figure 1.11: Air Photo Interpretation Criteria, Tone and Shadow, Applied to an Area in the Upper Part of Elm River Southeast of Portage la Prairie

Figure 1.11

Vertical air photo: A20774-21

Flight height: 2,400 feet a.g.l.; lens focal length: 152.52 mm.

Scale: 1:4,800 (approx.)

Date: July 2, 1968

Location: Township 11, Range 6 WI

Map sheets: 1:250,000 62G: Brandon

1:50,000 62 G/16: Portage la Prairie

Notes

[i] W. F. Rannie, “The Portage la Prairie ‘Floodplain Fan’,” in Alluvial Fans: A Field Approach. eds. A. H. Rachocki and M. Church. Chichester, England: John Wiley and Sons, 1990, 179-193.

[ii] This is a mistake. Using the given data for flight height and lens focal length results in a scale of 1:4,800. However, when the photo is compared with the relevant 1:50,000 topographic map a scale of 1:3,000 is obtained, which is what it would be if a flight height of 2,400 feet above sea level were used in the calculation of the scale.


1.12: Patterns at St. Francois Xavier

The DLS system, used over most of Agro-Manitoba, produces a pattern of squares (a checkerboard pattern) based on sections one square mile in area. The DLS system is seen in the northeast 1. However, along the Red River, the Assiniboine River as far west as Portage la Prairie, as well as in several other small areas in southeastern Manitoba, the French-based long lot system is used. In this system strips of land, often narrow, run back from the river. This system is clearly seen in the centre of the photo with strips 2 based on the east flowing Assiniboine River 3. The saw-edged contact between the two systems 4 is the boundary between the RM of St. Francois Xavier and the RM of Rosser to the north.

Both systems have a profound influence on road locations and directions and on the distribution of settlements. Note for example the road running northeast 5 from St. Francois Xavier parallel to the strips of the long lot system and compare this with gravel roads running north/south and east/west along section lines in the northeast 6. In the latter area farmsteads are widely distributed along section lines 7, whereas close to the river farmsteads are closely spaced at the south end of strips of land 8.

The photo also illustrates the capacity of the human eye to distinguish minor variations in grey tone. On the northeast side of First Creek 9, which flows southeast to join the Assiniboine River, numerous fields can be identified simply on the basis of their tone ranging from almost white 10 to very dark grey 11. Fields that have a uniform tone exhibit a smooth texture 12, whereas the more irregular tones of the areas within meander necks of the Assiniboine (areas of deciduous woodland) have a rough texture 13.

Figure 1.12: Patterns at St. Francois Xavier

Figure 1.12: Patterns at St. Francois Xavier

Figure 1.12

Vertical air photo: MB89021-6-153

Flight height: 30,800 feet a.s.l.; lens focal length: 152.860 mm.

Scale: 1:59,200 (approx.)

Date: August 7, 1989

Location: Junction of the Trans-Canada Highway and PTH 26 Latitude: 49º 53'N

Longitude: 97º 30'W

Map sheets: 1:250,000 62H Winnipeg

1:50,000 62H/13 Elie

 


1.13: Air Photo Interpretation Criteria Applied to an Area at the Forks in Winnipeg

This very large-scale (1:5000) photo of the junction of the Red River 1 and the Assiniboine River 2 was taken at an early stage of redevelopment of “the Forks.” Some early construction can be seen at three locations north of the junction 3. The main Canadian National (CN) lines 4 with Union Station 5 can be seen in the north, and to the east 6 are the CN rail yards—now gone. Two railway bridges 7 cross the Assiniboine River, and west of them is the Bridge of the Old Forts—a road bridge 8.

The photograph illustrates the use of the criteria—tone, shape (shadow), size, and location—in identification of objects. The tone of the Red River is light 9 compared with the Assiniboine 10; the junction of the two is easily seen 11. The Red carries more suspended sediment than the Assiniboine. Individual branches in the shadows of trees on the southeast bank of the Red River 12 indicate that at the time they were leafless, and based on the umbrella shape of some of the shadows, the trees are probably elms. A few ornamental coniferous trees 13 can be seen in Bonnycastle Park 14 north of the Assiniboine, identification being on the basis of the triangular shadow shapes. Also, using the criterion of shape; the rounded roof form of a building in the southwest corner 15 is typical of indoor sports facilities, in this case a curling club. Shadow length gives an idea of the relative heights of objects; for example, at the Forks building 16 is higher than building 17, and, on the St. Boniface side of the river, building 18 is the tallest of all. If the actual height of one object is known, the heights of other objects can be determined from their shadows on a ratio basis. Finally, the criterion of location suggests that objects on the southern approaches to the Norwood Bridge 19 are buses, trucks, and cars, buses being the largest 20, trucks next 21 and cars the smallest 22.

Figure 1.13: Air Photo Interpretation Criteria Applied to an Area at the Forks in Winnipeg

Figure 1.13: Air Photo Interpretation Criteria Applied to an Area at the Forks in Winnipeg

Figure 1.13

Vertical air photo: AS88013-43

Flight height: 3,250 feet a.s.l; lens focal length: 152.03 mm.

Scale: 1:5,000 (approx.)

Date: April 24, 1988

Location: Latitude: 49º 53'N Longitude: 97º 07'W

Map sheets: 1:250,000 62H Winnipeg

1:50,000 62H/14 Winnipeg


1.14: Landscape Near the Manitoba/Saskatchewan Border

The stepped border between Manitoba and Saskatchewan runs along the west side of this photo 1, and Swan River 2 runs across the northwest corner.

The aim of the air photographer is to take photos under cloudless conditions which makes this photo unusual in that clouds 3, almost white, and their shadows 4, almost black, thrown to the north, are visible. The photo also shows the checkerboard pattern of the sections of the DLS system especially in the southeast 5. This, the first photo in a job, contains all the details of the photography in the bottom left hand corner 6.

Photo A21810-1 was the first photo of line 23 that was flown from west to east and includes photos 1-16. This line was flown on August 4, 1970. Line 21, including photos 17-40 was also flown from west to east but on August 5, 1970. Line 22, which includes photos 41-50, was flown from east to west also on August 5, 1970. Finally line 23, which includes photos 51-59, was also flown from east to west on August 5, 1970. The flight height in all cases was 25,100 feet above sea level and the camera used had a 88.214 mm focal length lens.

Figure 1.14: Landscape Near the Manitoba/Saskatchewan Border

Figure 1.14: Landscape Near the Manitoba/Saskatchewan Border

Figure 1.14

Vertical air photo: A21810-1

Flight height: 25,100 feet a.s.l.; lens focal length: 88.214 mm.

Scale: 1:83,400 (approx.)

Date: August 4, 1970

Location: Townships 34 and 35, Ranges 28 and 29 WI

Map sheets: 1:250,000 62N Duck Mountain

1:50,000 62N/14 Durban


1.15: The Influence of Scale Illustrated by Photos of Part of the Assiniboine River Southwest of Lavenham

a) Smallest scale:

This high level, small-scale photo shows a large stretch of the eastward flowing Assiniboine River 1 and the junction with Cypress River 2. Specular reflection results in both rivers having a very light tone near their junction 3. In this area the Assiniboine River is incised into the Assiniboine Delta. Dunes 4, now mainly stabilized by grasses 5 and trees 6, have been created by wind action.

The area covered measures 11.375 miles (18.3 km) by 11.375 miles (18.3 km) for a total area of 129.4 square miles (335.1 square km). The sections of the DLS system (one square mile in area) 7 are a good rough indicator of the area covered. PTH 34 8 crosses the area from north to south.

b) Larger scale:

This larger scale photo covers only a small part of the area shown on figure 1.15a. The side of the photo measures 5 miles (8 km) for an area of 25 square miles (64 square km). However, more detail can be observed than on 1.15a; for example, sand bars 1 can be seen along the course of the Assiniboine River 2. But perhaps the clearest example is the possibility of locating individual trees 3, some of which can be identified as coniferous trees 4 on the basis of their shadow shapes. Note also south of the Assiniboine, east of PTH 34 5 an area of deciduous woodland has tonal variations 6 which produce a mottled texture, whereas the same area at the smaller scale of figure 1.15a has a uniform tone that produces a smooth texture.

c) Largest scale:

The increase in scale results in an even smaller area covered; the photo side is 2.27 miles (3.7 km) with an area of 5.15 square miles (13.34 square km). This results in much more detail being detectable, particularly when compared with figure 1.15a (smallest scale). Details seen along the Assiniboine River 1 are sand bars 2 and the exact location of the mouth of the Cypress River 3. Meander scrolls 4 indicate previous river positions. Tonal variations in the woodland produce a mottled texture 5, and deciduous trees with rounded shadows 6 can easily be distinguished from coniferous trees with triangular shadows 7. Details of a gravel pit 8 east of PTH 34 9 can be obtained whereas the pit is only just identifiable in figure 1.15a. One final detail observable is supports for the bridge across the Assiniboine, five of them in all 10.

Figure 1.15.a: smallest scale

Figure 1.15.a: smallest scale

Figure 1.15a

Vertical air photo: A21666-116

Flight height: 22,420 feet a.s.l.; lens focal length: 3.5 inches

Scale: 1:79,200 (approx.)

Date: July 21, 1970

Location: Townships 8 and 9, Ranges 10, 11, and 12 WI

Map sheets: 1:250,000 62G Brandon

1:50,000 62G/10 Treherne


Figure 1.15.b: larger scale

Figure 1.15.b: larger scale

Figure 1.15b

Vertical air photo A15577-24

Flight height: 20,000 feet a.s.l.; lens focal length: 6 inches

Scale: 1:35,800 (approx.)

Date: October 11, 1951

Location: Township 8 and 9, Range 11 WI

Map sheets: As for 1.15a


Figure 1.15.c: largest scale

Figure 1.15.c: largest scale

Figure 1.15c

Vertical air photo: A16574-86

Flight height: 9,000 feet a.s.l.; lens focal length: 6 inches

Scale: 1:16,050 (approx.)

Date: June 19, 1959

Location: Township 8, Range 11 WI

Map sheets: as for 15.1a

 

 

 


1.16: Transect Across the Assiniboine Valley North of Miniota

This stereo triplet transect across the Assiniboine Valley shows the standard 60 percent overlap: A15528:44 (centre photo) overlaps A15528:43 (right photo) by 60 percent, and A15528:45 (left photo) overlaps A15528:44 by 60 percent. So each part of the earth’s surface is shown on two photos (stereopairs) thus enabling stereoscopic viewing. Dashed lines on figure 1.16b bound the Assiniboine Spillway 1 that carried water from glacial lakes in Saskatchewan to glacial Lake Agassiz in Manitoba . The spillway occupies the centre of the area, with the south flowing Assiniboine River 2 on its floor. At least five cut offs can be seen 3. The spillway has steep sides, both on the east 4 and west 5, but two creek valleys 6 dissect the west wall.

These photos also illustrate the use of photo interpretation criteria: tone, texture, pattern and shape.

Tone: the sediment-laden Assiniboine River has a light-grey tone 7 whereas a prominent cut off in the north 8 is dark-toned because it carries no suspended sediment. Numerous sloughs east and west of the spillway 9 are dark-toned for the same reason.

Texture: the water surfaces are mainly smooth textured 10; whereas the valley walls, especially the east wall 11, have a mottled texture.

Pattern: elements of the checkerboard pattern of the DLS are seen in the east 12 and west 13.

Shape: the river displays the distinctive meandering form 14 with crescent-shaped cut offs 15. Curved meander scrolls 16 indicate previous positions of the river.

Figure 1.16.a: Transect Across the Assiniboine Valley North of Miniota

Figure 1.16.a: Transect Across the Assiniboine Valley North of Miniota

Figure 1.16

Vertical air photos: A15528-43, 44,45

Flight height: 20,000 feet a.s.l.; lens focal length: 6 inches

Scale: 1:37,300 (approx.)

Date: October 7, 1956

Location: Townships 13 and 14, Ranges 26 and 27 WI

Map sheets: 1:250,000 62K Riding Mountain

1:50,000 62K/3 Miniota


Figure 1.16.b: Transect Across the Assiniboine Valley North of Miniota

Figure 1.16.b: Transect Across the Assiniboine Valley North of Miniota


Figure 1.16.c: Transect Across the Assiniboine Valley North of Miniota

Figure 1.16.c: Transect Across the Assiniboine Valley North of Miniota


1.17: An Example of Pseudoscopic Vision

This photo has been arranged so that shadows 1 fall away from the viewer resulting in the possibility of pseudoscopic vision. Shown here is a series of steep-sided creek valleys 2 etched by streams that rise on the Riding Mountain Plateau 3 and deeply dissect the escarpment as they flow northeast. Some disappear into alluvial deposits at the base of the escarpment 4.

It is possible that the viewer sees the valleys as ridges (pseudoscopic vision). Turning the photo upside down can reverse this optical effect. The photo also illustrates the criteria, “tone” and “shape” (shadow) in identification. Very light-toned areas 5 are bedrock outcrops along the valley sides. The dark-toned areas are groups of coniferous trees 6; individual coniferous trees can be identified from their triangular-shaped shadows 7.

Figure 1.17: An Example of Pseudoscopic Vision

Figure 1.17: An Example of Pseudoscopic Vision

 

Figure 1.17

Vertical air photo: A20374-115

Flight height: 10,020 feet a.s.l.; lens focal length: 152.47 mm

Scale: There is enough height variation here to produce a measurable difference in scale. At the top of the escarpment 1:15,440 (approx.) At the foot of the escarpment 1:17,540 (approx.)

Date: May 14, 1969

Location: Township 20, Range 16 WI

Map sheets: 1:250,000 62J Neepawa

1:50,000 62J/12 Wasagaming

1:125,000 MCR 207 Riding Mountain National Park