Geographical Information Systems

Geog 481/506                                                                                                  Tu Th 3:30-4:50pm
Fall 2011                                                                                                          Fillmore 170

Instructor: Ling Bian                                                                                          LabA: Tue:   5-6:20pm, W145, Chunyuan diao
Office: 120 Wilkeson                                                                                        LabB: Thur:  6:30-7:50pm, W145, Tong Sun
Office hours: Tu Th 2-3pm  or by appt.                                                             LabC: Fri:  10-11:20am, W145, Tong Sun

Remote Sensing

1. Definition

    The technique of collecting information from a distance (without physical touch).
    Remotely sensed data: aerial photography, digital satellite images, etc.

2. Properties of electromagnetic (EM) energy

    EM travels at the speed of light, 3x108/sec
 
    Wavelength l and frequency n

    Electromagnetic spectrum
        The type of energy is defined by the position in the EM spectrum
        in terms of wavelength, measured by mm

 1m = 1,000mm, 1mm = 1,000mm (micrometer)

    Major divisions of EM spectrum
       X rays, UV, visible, infrared, microwave, TV

    Response of earth features to EM energy
        Reflection (%)

  Transmission (%)

  Absorption (%)

  Reflection + Transmission + Absorption = 100%

  Emission
 

    Atmospheric effects
        Atmospheric absorption: H2O, CO2, O3

  Atmospheric windows: UV and visible, near infrared, mid infrared, far infrared, and microwave

  Atmospheric scattering: radiation of short wavelengths are easier to be scattered
 

3. Major sensor systems

        (1) Photographic cameras
            Uses aerial camera and film
            Mounted on a aircraft

            Produces aerial photographs

        (2) Electro-Optical scanners
            Uses light-sensitive detectors
            Generates electrical signals
            Mounted on spacecrafts or aircrafts

        (3) Microwave
           Uses antennas as detectors
           Passive microwave systems
           Active microwave systems: RADAR

4. Operation of digital remote sensing
          Moving mirror

    Pushbroom
 
    Pixel
    IFOV

    Each sensor system contains a set of detectors, each sensitive to a certain range of wavelength (band)

    Detector(s) of each band produce a digital image, which is a matrix consisting of rows and columns of pixels
    The digital number of each pixel measures the intensity of energy received from the IFOV area on the ground
    The response of earth features to energy varies with wavelength.

    Images of several bands result in a composite image.

5. Types of resolution

        (1) Spectral resolution
           The dimension and number of specific wavelength intervals in the EM spectrum to which a sensor is sensitive to

        (2) Spatial resolution
          A measurement of the smallest angular or linear separation between two objects that can be resolved by the sensor

        (3) Radiometric resolution
          The sensitivity of a detector to differences in signal strength as it records the radiant levels

        (4) Temporal resolution
          How often a given sensor obtains imagery of a particular area
 

6. Commonly used satellite image data

        Moderate resolution land satellites, Landsat, SPOT
        High resolution land satellites, IKONOS
        Meteorological satellites, AVHRR, EOS
        Radar systems, RADARSAT, LIDAR
        Digital aerial photographs, DOQQ

7. Processing remotely sensed data
      Corrections and enhancements
      Image classification

8. GIS vs. remote sensing
     
 
 
 

9. Reading: Chpt 8