For large-scale monitoring, such as county or countrywide studies, field-based survey methods alone are often considered too labour intensive and both API and satellite imagery interpretation provide more cost-effective alternatives.

However, the restrictions of these methods, which are simultaneously very powerful but extremely limited, must be clearly understood, and their appropriateness for each project must be assessed. Through discussion with each client, together with a full review of the project, we will critically and honestly assess whether the application of these methods will deliver what is really needed. There is a long history of unfulfilled promises associated with these methods, and we will not add to them.

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Manual digitisation of aerial imagery to determine relationship of conservation land in Little Ouse valley

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Manual digitisation of aerial imagery to determine land use in Little Ouse valley project area

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Detailed manual digitisation of aerial imagery to assess extent and age of tree and scrub encroachment as part of conservation planning process for Blo' Norton Fen SSSI




The key to both API and satellite image analysis is classification of the image into requisite categories for the study. It is the ability to distinguish the required classes with sufficient accuracy that can limit the applicability of these method.

As a guide, for general land use classification, these methods will be more than suitable. However, for fine detail habitat/community recognition they are unlikely to work effectively unless the classification is made extremely broad, and this may not then provide the information required.

The choice of using API or satellite imagery will depend on the area of the study site, and or the resolution required.

On-screen digitisation of aerial imagery is ideal for broad land-use classification such as the examples top & middle right. Generally, identification of land use/cover type is made using the imagery and then verified using ground truthing where appropriate.

However, the use of these methods also allows detailed mapping of distinctive vegetation types as well as other features (bottom right).

This can allow reconstruction of past distributions as historical imagery, if available, may be the only accurate record of habitat changes.






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