Aerial Photography and Remote Sensing (GEOG2112)
Instructor: Dr. M. M. Yagoub
URL: https://www.angelfire.com/mo/yagoub
Questions and Answers (Q/A) on Eelectro-optical Sensors
Chapter 6: page 109-160
Textbook: Thomas Eugene Avery and Graydon Lennis Berlin, Fundamentals of Remote Sensing and Airphoto Interpretation, Fifth Edition, Macmillan Publishing Company, New York, 1992.
What is the difference between photographic camera and electro-optical scanner?
Camera record radiation reflected from ground onto film while electro-optical scanner use non-film detectors (signal). The signal can be converted to Digital Numbers (DN) and from which images can be generated
List four examples of electro-optical scanners?
Video camera, Vidicon camera, along-track scanners, across-track-scanners
List 5 advantages of electro-optical scanner?
1. Operate in numerous bands (UV, visible, Infrared, Thermal)
2. Images can be transmitted over radio link (satellite to ground receiving station)
3. Ground scene can be viewed in real time (e.g. video display onboard aircraft)
4. System operate in Thermal Infa-Red (TIR) have a day and night capability
5. Detection process is renewable (non-film-signal, camera needs film to store photos)
Discuss briefly video-graphy? (see page 109-111, and Plate 7)
- Video-graphy (compare with photo-graphy) is the process of obtaining video images (bands: 0.4-1.1 um).
- Images can obtained from more than one camera (each camera sensitive to specific band-filter)
- The main components use in video-graphy include video camera, Video Cassette Recorder (VCR), and TV monitor for displaying the image.
- Solid state detectors such as Charge Couple Devices (CCD) are widely used for video cameras.
- The main video formats are NTSC, VHS, PAL, an BETA.
- Video images can be interpreted on TV screen or by generation of hardcopy film products by directly photographing the TV screen.
- Advantages of video-graphy include Exposure and flight line can be adjusted in real time and images can be acquired immediately.
- Such real time images are important in some applications (e.g. flood monitoring, water pollution studies).
Some of its disadvantages are coarse resolution (see Plate 7) and difficulty to register to maps.
Discuss briefly Vidicon camera?
Vidicon camera has the same concept as video camera, but images are sent as signal to ground receiving stations. The camera has been used for imaging moon and mars and a modified version of it (Return Beam Vidicon Camera- RBV) was also used onboard Landsat 3.
Discuss briefly across-track scanner, illustrate by figures?
Reflected or emitted signal from ground is converted to Digital Numbers (DN) and from which images can be generated (Draw Figure 6.5 Page 113).
Rather viewing entire ground scene (as in photographic camera), across-track scanner, through rotating or oscillating mirror, scan a contiguous narrow ground strips at right angle to the flight line (see the Figure). Ground swath (length of ground strip-see the Figure) depends on altitude above mean terrain (H) and angular Field of View (FOV).
Discuss briefly the types of across-track scanners, illustrate by figures?
There are two types of across-track scanners:
1. Multi-spectral scanner: Operate in multi-bands (UV, visible, Infrared) (Figure 6.8 page 115)
2. Thermal Infra-Red scanner (TIR): Operate in thermal IR regions (3-5 um and 8-14 um)(Figure 6-9 and 6-11 Page 116). The scanner can operate day and night because it does not depend on reflected energy, but emitted energy (which depends on temperature of body). Warmer bodies appeared whiter while cold objects appeared darker in the image. It has important application in geology (rock types), police investigations, and utilities (detection of pipes).
