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Table of Contents
Foreword
Preface
Glossary

Chapter 1: Introduction

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.