Support the spread of “good practice” in generating, managing, analysing and communicating spatial information Using Remote Sensing Imagery By: J.Verplanke, ITC Unit: M11U04

Content Introduction Purpose and method Which satellite image is suitable for which purpose? Familiarisation Drawing directly on image hard copies or using overlays Scale issues Local spatial knowledge

Introduction The document deals with: –remote sensing imagery; –mapping with false colour composites and large-scale images; –usefulness of false colour and true colour images; –tips on participatory mapping.

Purpose and method Identify the purpose. Is conformity needed (e.g. fit to existing maps)? Who owns the product? Who receives copies? Will you draw "on top" or on overlays?

Purpose and method Existing topographic maps contain required information.

Which satellite image is suitable for which purpose? Determine: –amount of detail needed –desired scale

Which satellite image is suitable for which purpose? High-resolution imagery is needed if: –individual houses or plot boundaries must be discernable; –objects smaller than cars should be identified. Use QuickBird or IKONOS satellites

Which satellite image is suitable for which purpose? Use lower resolution for general land- cover and land-use mapping. Aster or Landsat satellites

Which satellite image is suitable for which purpose? Detail level of IKONOS Detail level of Landsat

Which satellite image is suitable for which purpose? Most satellite imagery provides different spectral bands. When combining green, red and infrared, the image, represented in blue, green and red, is suitable to show vegetation.

Which satellite image is suitable for which purpose? “False” colour images are particularly useful for land-cover mapping. Forest Agricultural crops

Familiarisation When using aerial photographs or “true colour” images, not much familiarisation is needed. If false or pseudo colour images are used, it is important to explain what the colours represent. Most commonly, vegetation is represented in red colours in false colour imagery.

Familiarisation B&W aerial photo Landsat (pseudo colour) IKONOS (true colour) Landsat (true colour)

Familiarisation Image courtesy J. Verplanke©/ITC

Familiarisation

Drawing directly on images Mapping directly on images is the simplest approach and has advantages: –It allows for easy interpretation. –People can easily see features and boundaries. However, mapping on an image requires using proper pens and adhering to pre- defined coding.

Drawing directly on images Images courtesy J. Verplanke©/ITC

Drawing directly on images Direct mapping gives a sense of permanence. It reduces the risk that outsiders may alter the output. The immovability of traits also represents a disadvantage: there is no room for errors.

Drawing directly on images Direct mapping has to be repeated to make needed copies. Copying involves extra work and cost. There is a risk of creating discrepancies in each copy.

Using overlays Using transparent overlays is cheaper and more versatile. Copies can easily be traced from each other. Ordinary (colour or grease) pencils may be used on overlay paper (acetate or mylar).

Using overlays Overlays may become separated from the underlying base map. A legend must be added to the overlay, and numbers that identify the image must be recorded. The reference marks of the photo (fiducial marks) are always transferred on to the overlay.

Using overlays Reference marks on the photo are unique to the camera, not to the photo

Scale issues Enlargements to 70 cm x 70 cm or 100 cm x 100 cm are useful for participatory work. People can gather around and jointly input data. In participatory mapping, it is important that all stakeholders participate, and that no one is excluded.

Scale issues Image courtesy G. Rambaldi ©/CTA

Scale issues Always ensure that the mapping scale is in accordance with other spatial data. Satellite images cover large areas, and likely only a small portion of an image is required. A small scale is useful for large-area interpretation such as land cover. A large scale is useful for detailed mapping of features (e.g. trees, houses)

Scale issues Small scale, useful for large-area interpretation (land cover) Large scale, useful for detailed mapping (trees, houses, etc.)

Local spatial knowledge Objectivity is needed: only map information which is relevant to the mapping purpose. Be flexible in the interpretation method, but apply the method consistently. Use local spatial knowledge to derive the map legend. If a certain feature is unknown, leave it “blank”, and conduct a field visit to verify.