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Using Aerial Photos for Nutrient Management Planning

Important Terms

Table 3.2.1 Key Terms and Definitions

Term Definition

Spatial

Relating to, occupying, or having the character of space. Relating to the three dimensional positioning of an object in space.

An aerial photo shows spatial relationships between features in a field. Aerial photos can be used to estimate total available area for nutrient application, while considering application setbacks from sensitive areas. Interpreting aerial photos involves identifying features, assessing their significance, and determining their spatial relationship to other features in the field. An aerial photo provides a different perspective of the landscape than ground-based observation. An aerial perspective reveals the horizontal orientation of a feature in a landscape, but the trade-off is the inability to judge the height or elevation of a feature.

There are two important points to remember when using aerial images:

Aerial photos complement, but should not replace, •

a ground-based site assessment. They provide a complete perspective of the relative location and orientation of features within a field. The usefulness of aerial photos depends on the •

user’s ability to interpret qualitative and quantitative information in the image.

Interpreting aerial photos involves considering the following aspects:

Scale • is the ratio of the distance between two points on an aerial photo to the actual distance between those two points on Earth’s surface (Table 3.2.2). For example, an aerial photo with a scale of 1:15,000, one unit of measurement (centimeters or inches) on the photo is equal to 15,000 of these same units on the ground.

The relative • size of known features can be used to estimate their relative “footprint” on the landscape as well as the approximate size of surrounding features.

The • shape of an object from an aerial view can help distinguish human-made features (e.g., buildings) from natural features (e.g., water bodies).

The • shadows cast by objects in a photo will depend on the time of day and year the photo was taken. This may affect the interpretation of the objects casting the shadow.

Tone • refers to the colour or shade of grey of objects in a photo, and the pattern in which these colours are reflected (uniform, mottled or banded). Tone is influenced by several factors including soil moisture, vegetation type and density, time of day and year the photo was taken (Table 3.2.3).

Texture • is the impression of “smoothness” or “roughness” of an image. Texture offers the ability to distinguish boundaries between individual objects in a photo. Objects that are too small to be distinguished from each other tend to appear “smooth” (e.g., grass, cement, water), while objects with more distinguishable boundaries appear “rough” (e.g., forest canopy).

Pattern • refers to the spatial arrangement of objects in an aerial photo. Patterns can be natural (e.g., forested area) or the result of human activities (e.g., cultivated woodlot).

Unknown objects • can be identified in an aerial photo by considering their location and association to known objects.