1. 1 Lecture 4 Photographic Systems, Aerial Photography, and Image Interpretation 11 September 2008

2. 2 Reading Assignment Campbell, Chapters 3 (3.1-3.8) and 5 (5.1 to 5.11) Unless otherwise noted, all images in this lecture are from –Jensen, J.R., Remote Sensing of the Environment - An Earth Resource Perspective, 544 pp., Prentice Hall, Upper Saddle River, NJ, 2000.

3. 3 Lecture 4 Outline and Key Points 1.Components of a camera system 2.Collection of aerial photographs 3.Categories of aerial photographs 4.Photogrammetry 5.Definition of image interpretation 6.Reasons for using image interpretation 7.Key elements of image interpretation

4. 4 Source of image from the internet

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7. 7 Early pioneers in photography Joseph Niepce – 1826 Created first photographic image in France Used a camera obscura, exposed the scene for 8 hours Photographic plate was made of pewter and was coated by bitumen suspended in lavender oil Bitumen is a tar like substance found in crude oil – today it is used in roofing tar and asphalt pavement When exposed to light, bitumen/oil hardened and adhered to the pewter plate Non-hardened areas washed away

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9. 9 Emulsion layer Base layer Anti-halation layer Figure 5

10. 10 Film Layers Emulsion layers – contain light sensitive particles (silver-halide crystals) suspended in gelatin Base or support material (polyester or cellulose acetate) Anti-halation layer – absorbs all light that gets through first two layers to prevent reflection back into the emulsion

11. 11 Additive Color Theory Based on three primary colors (red, green, blue) When added together, these three primary colors produce white light ACT is the basis for human vision and photographic systems

12. 12 Photographic films Color films have 3 emulsion layers – filters are used to expose the emulsion layers to different regions of the EM spectrum 0.4 to 0.5  m: blue region of the EM spectrum 0.5 to 0.6  m: green region of the EM spectrum 0.6 to 0.7  m: red region of the EM spectrum 0.7 to 1.1  m: near infrared region of the EM spectrum

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14. 14 Lecture 4 Outline and Key Points 1.Components of a camera system 2.Collection of aerial photographs 3.Categories of aerial photographs 4.Photogrammetry 5.Definition of image interpretation 6.Reasons for using image interpretation 7.Key elements of image interpretation

15. 15 Aerial metric camera Figure 6

16. 16 Invention of Digital Cameras Throughout most of the 20 th century, aerial camera systems used film to record information Aerial cameras used black and white, color and color- IR film to record data This changed in 1986, when Kodak invented the first charged couple device that was capable of sensing and recording an entire photographic image –The first digital camera recorded 1.4 million picture elements (pixels) in a 5 by 7 inch format Now, digital aerial camera systems are quite common

17. 17 Digital Aerial Camera System from Vexcel Corp. Figure 7

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19. 19 One can alter the focal length of the lenses used in a camera system to vary the area of coverage of the system Figure 9

20. 20 Focal Length Focal length (f) – is the distance, when the lens is focused on infinity from the center of the lens to the film or focal plane where the image is in focus –Wide angle lenses, have short focal lengths –Telescopic lenses have longer focal lengths –Area of coverage ~ 1 / f

21. 21 Relationship between aircraft altitude and ground coverage – two ways to change FOV a.Changing the focal length of the camera lens will alter the angular coverage of the system – as the focal length gets smaller, the angular coverage increases b.As the angular cover increases (focal length decreases), the FOV increases Figure 23

22. 22 Relationship between aircraft altitude and ground coverage – two ways to change FOV Changing the aircraft altitude will alter the ground coverage of the system

23. 23 Lecture 4 Outline and Key Points 1.Components of a camera system 2.Collection of aerial photographs 3.Categories of aerial photographs 4.Photogrammetry 5.Definition of image interpretation 6.Reasons for using image interpretation 7.Key elements of image interpretation

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26. 26 Figure 12

27. 27 Categories of Aerial Photographs Vertical Photograph –Camera optical axis < 3° off vertical Low-Oblique –Camera optical axis > 3° off vertical –Horizon not in image High Oblique –Camera optical axis > 3° off vertical –Horizon in image

28. 28 Lecture 4 Outline and Key Points 1.Components of a camera system 2.Collection of aerial photographs 3.Categories of aerial photographs 4.Photogrammetry 5.Definition of image interpretation 6.Reasons for using image interpretation 7.Key elements of image interpretation

29. 29 What is Photogrammetry? The science of making accurate measurements by means of aerial photography –Requires development of specific skills Photomensuration –Techniques used by interpreters to obtain quantitative information from aerial photographs

30. 30 What is Photogrammetry? Analogue photogrammetry –Visual interpretation using hard copy (photographs or transparencies) Digital or analytical photogrammetry –Computer analysis on digitized photography

31. 31 For More Background Collection of aerial photography – Section 3.9 to 3.14 Photogrammetry – Sections 5.12 to 5.14

32. 32 Lecture 4 Outline and Key Points 1.Components of a camera system 2.Collection of aerial photographs 3.Categories of aerial photographs 4.Photogrammetry 5.Definition of image interpretation 6.Reasons for using image interpretation 7.Key elements of image interpretation

33. 33 Image/Photo Interpretation The examination and analysis of images for the purpose of identifying objects and features and judging their importance

34. 34 Lecture 4 Outline and Key Points 1.Components of a camera system 2.Collection of aerial photographs 3.Categories of aerial photographs 4.Photogrammetry 5.Definition of image interpretation 6.Reasons for using image interpretation 7.Key elements of image interpretation

35. 35 Why is image interpretation such an important tool? 1.Represents the fundamental process for human (visual) analysis of remote sensing imagery 2.Provides a unique spatial observation perspective 3.Provides information that cannot easily be obtained in other ways 4.Provides ability to do accurate mapping, including 3-D information 5.Can provide information beyond our visual perception range 6.Allows for change detection analyses of specific regions where satellite data are not available

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38. 38 Image from -http://rs.gso.uri.edu/amy/avhrr.html AVHRR Image of land and sea surface temperature from thermal IR radiance measurements Red – warmest Orange Yellow Green Blue Purple - coldest

39. 39 Why is image interpretation such an important tool? 1.Represents the fundamental process for human (visual) analysis of remote sensing imagery 2.Provides a unique spatial observation perspective 3.Provides information that cannot easily be obtained in other ways 4.Provides ability to do accurate mapping, including 3-D information 5.Can provide information beyond our visual perception range 6.Allows for change detection analyses of specific regions where satellite data are not available

40. 40 Unique perspective of aerial imagery – the aerial/regional perspective While human vision provides a unique perspective, it is a limited perspective Humans primarily observe the world from a limited, ground-level view – vertical perspective Aerial platforms allow the viewing of an area from a more synoptic, horizontal perspective

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43. 43 Why is image interpretation such an important tool? 1.Represents the fundamental process for human (visual) analysis of remote sensing imagery 2.Provides a unique spatial observation perspective 3.Provides information that cannot easily be obtained in other ways 4.Provides ability to do accurate mapping, including 3-D information 5.Can provide information beyond our visual perception range 6.Allows for change detection analyses of specific regions where satellite data are not available

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45. 45 Lillesand and Kiefer 2000 Figure 4.32

46. 46 Why is image interpretation such an important tool? 1.Represents the fundamental process for human (visual) analysis of remote sensing imagery 2.Provides a unique spatial observation perspective 3.Provides information that cannot easily be obtained in other ways 4.Provides ability to do accurate mapping, including 3-D information 5.Can provide information beyond our visual perception range 6.Allows for change detection analyses of specific regions where satellite data are not available

47. 47 Stereoscopic viewing Can create a 3-D view using aerial photographs collected from slightly different vantage points Using a stereoscope, allows an interpreter to view the earth’s surface in three dimensions Extremely valuable for interpreting landforms and other 3-D features Stereoscopic imagery can be processed to generate accurate 3-d maps (e.g., accurate in the x,y,z dimensions) of the earth’s surface

48. 48 Why is image interpretation such an important tool? 1.Represents the fundamental process for human (visual) analysis of remote sensing imagery 2.Provides a unique spatial observation perspective 3.Provides information that cannot easily be obtained in other ways 4.Provides ability to do accurate mapping, including 3-D information 5.Can provide information beyond our visual perception range 6.Allows for change detection analyses of specific regions where satellite data are not available

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50. 50 Why is image interpretation such an important tool? 1.Represents the fundamental process for human (visual) analysis of remote sensing imagery 2.Provides a unique spatial observation perspective 3.Provides information that cannot easily be obtained in other ways 4.Provides ability to do accurate mapping, including 3-D information 5.Can provide information beyond our visual perception range 6.Allows for change detection analyses of specific regions where satellite data are not available

51. 51 Lillesand and Kiefer 2000 Figure 4.26 Monitoring Land Cover Change 1937 1955 1968 1990

52. 52 Lecture 4 Outline and Key Points 1.Components of a camera system 2.Collection of aerial photographs 3.Categories of aerial photographs 4.Photogrammetry 5.Definition of image interpretation 6.Reasons for using image interpretation 7.Key elements of image interpretation

53. 53 Key Steps in Image Interpretation Analysis of the cartographic information in the image Examination of image characteristics

54. 54 Key Steps in Image Interpretation Analysis of image characteristics Size (length, width, perimeter, area) Shape Shadow Tone/color Pattern Texture Site/situation/association

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57. 57 Shape

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60. 60 The presence of a shadow provides important information on the relative positions of objects

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62. 62 Lillesand and Kiefer 2000 Figure 4.41

63. 63 4 important aspects of shadows 1.Provide information on relative height 2.Contain indirect information on geometric characteristics of some features 3.Provide a unique means for interpreting topographic features 4.Areas that are in shadows lack information

64. 64 BW photograph collected with Near infrared film Image tone – variations in image tone (e.g., the grey scale from white to black) allow for discrimination of different forest cover types Dark area is a pine stand and the light colored forests are deciduous trees (see next slide)

65. 65 Maple trees have a brighter tone Pine trees have a darker tone Reflectance controls image tone

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67. 67 Texture and Pattern Texture – characteristic placement and arrangement of repetitions of tone and color in an image Pattern – systematic or random arrangement of discrete objects within a scene

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71. 71 Importance of Location Determining where an image was collected often provides key information on features within the image Location provides context for interpreting an image

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73. 73 Aspen or birch forests Black spruce forests