ERT247 GEOMATICS ENGINEERING

1. PERPARED BY: SAMERA BINTI SAMSUDDIN SAH SCHOOL OF BIOPROCESS ENGINEERING AIRBORNE IMAGERY ERT247 GEOMATICS ENGINEERING

2. Aerial Camera Systems • The recent introduction of digital cameras has revolutionized photography. • Digital and film-based cameras both use optical lenses. • Film-based cameras: use photographic film to record an image. • Digital cameras: record image data with electronic sensors. • Advantage of digital camera: can store, transmit and analyze the image data. • Types of camera systems: small-format and large-format.

3. Small-format system • Consists one or more cameras • Using smaller photographic format (negative size-35mm) • Do not have high-quality lens to meet the normal measurement accuracies. • Very useful and inexpensive for updating land-use changes.

4. Large-format system • Consists only single camera. • Uses fixed focal length, large-format negative (230mm by 230mm). • Strictly used for aerial photography. • Equipped with a highly corrected lens and vacuum pressure to minimize distortion.

5. Flight Lines and Photograph Overlap • Factors need to consider: • Using suitable aircraft and technical staff. • The study area must be outlined carefully – using GPS to maintain flight line alignment. • Photographs must be taken under cloudless skies.

6. Figure 1: Flight line and photograph overlap

7. Figure 2: Photograph overlap along flight line

8. The number of air photos required to cover study area is very important. • For photographic scale of 1: 10,000 • 1 photograph cover 1 km2 • if area need to cover 500 km2 , the number of air photos is 500/1 = 500 nos . • But, if the scale decreased to 1:5000, the number of air photos is 500 x (10000/5000)2 = 2000 nos.

9. Ground Control for Mapping • Aerial photography is not perfect if it involves exposure to sudden and a flat surface. • Ground control points is the best way to overcome this problem. • To establish the control point; • Existing photography used for mapping. • Prior to the acquisition of the air photos.

10. Ground control is required for each data point positioning. • The accuracy depending on following requirements: • Measurements of distances and elevations • Preparation of topographic maps • Construction of controlled mosaics • Construction of ortho-photos and rectified photographs

11. Selection of ground control points for existing photograph based on following criteria: • Must be separated in the overlap area – model more stable and result more accurate. • Must be easily identifiable on both air photos – useless (if not) • Should be selected on the assumption that there are no changes since using the existing photographs. • Surveyor should consider ease of access to all points to minimize open-ended traverse lines.

12. For new photography, there are criteria need to follow; • The areas containing few identifiable ground control points. • Legal surveys of densely developed areas. • Municipal survey of roads and services

13. Mosaics • An assembly of two or more air photos to form one continuous picture of the terrain. • Extremely useful for the following application; • Plotting of ground control points at the optimum locations to ensure the required distribution and strength of figure. • A map substitute for field checkpoint locations and approximate locations of natural and cultural features. • A medium for presenting ground data.

14. Advantages: • Can be produced more rapidly. • Less expensive (cheaper). • Shows more terrain details. • Can interpreting subtle terrain characteristics ( tone, texture , and vegetation) • Disadvantages: • Horizontal scale measurements are limited due to relief displacement. • Not topographic maps (do not show elevations)

15. Aerial Surveying and Photogrammetric Mapping • Advantages using AS and PM over traditional ground surveying methods: • Low cost. • Reduced field work. • Faster in compilation (time saving). • Easy to record inaccessible terrain conditions. • Provide an accurate record of the terrain features. • Flexibility in term of scale. • More relevant (new technology)

16. Disadvantages: • Cannot get the real picture at dense vegetation area. • Cannot show the contour line • Need to do site visit - type of roads, surfacing etc

17. Aerial Photography Interpretation • Image interpretation is achieved by a combination of direct human analysis and by automated soft-copy processes. • Image interpretation techniques are based on 3 fundamental assumptions: • The remotely sensed image are records of the results of long- and short-term natural and human processes. • The surface features can be grouped together to form patterns that are characteristic of particular environmental conditions. • The environmental conditions and reflected image patterns are repeated within major climatic zones.

18. Applications of Air Photo Interpretation for Engineer and the Surveyor. • Can identify the land forms and site conditions (type of soil, soil depth, average topographic slopes, etc) • Can examine the topographic slopes, areas of unstable ground and density, and type of vegetation cover. • Air photo provide an excellent overview of the site and surrounding area. • Soil test holes should be used to verify the results of the air photo interpretation.

19. THE END….