Remote Sensing

Chapter 8Remote Sensing and GIS Integration Concepts and Techniques of Geographic Information Systems, 2e by C.P Lo and Albert K.W. Yeung

Definition ► The

acquisition of information about an object without physical contact.

► Includes

gathering and processing of information about the Earth’s environment through the use of photographs and related data acquired from an aircraft or satellite.

Remote Sensing ► Can

be digital or analog

► The

term “photograph” usually associated with analog, while imagery from a spectral scanner.

► Spectral

scanners usually operate with EM radiation outside of visible light.

► Easy

to use with and update raster GIS layers.

What type of data do you get? ► Synoptic

maps ► Land cover ► Planimetric location ► Elevation ► Spectral Signature ► Chlorophyll absorption characteristics ► Biomass ► Moisture content ► Temperature ► Roughness

Principles of Electromagnetic Remote Sensing ►

Record data of reflected or emitted electromagnetic energy.

►

EM radiation is energy capable of transmission through empty space in a plane harmonic wave pattern at the velocity (C) of light.

►

The frequency of oscillation (f) is related to wavelength (λ) by c = λf

►

EM occurs as a continuum of wavelengths and frequencies from short wavelength, high-frequency cosmic waves to longwavelength, low-frequency radio waves (aka ELECTROMAGNETIC SPECTRUM)

Figure 8.1

Figure 8.3

Principles of Electromagnetic Remote Sensing ► EM from the sun is seriously attenuated by passage through the atmosphere, which particles scatter or absorb certain wavelengths. ► Scattering

decreases with increase in wavelength.

► Wavelengths

shorter than 0.3 micrometers are completely absorbed by ozone.

► There

exists “transmission windows,” which are exploited for imagery remote sensing.

Figure 8.4

►

► ► ► ► ► ►

Once EM energy reaches the surface, it is further modified through interacting with features on the Earth’s surface (reflected, refracted, transmitted, or absorbed). Absorbed energy will usually be emitted in a different form. Reflection depends on surface material and roughness. A rougher surface will give rise to more diffused and brighter reflection. Smooth surfaces look dark because they reflect away from sensor. Hot objects emit more IR than cool, through the “windows” All surface objects have their own spectral signature-allowing it to be characterized and mapped.

Remote Sensing System Classifications ► Passive

and active. ► Passive = analog or digital ► Active = Synthetic Aperture radar and others ► Can also be based on aerial or space based systems

Imaging Characteristics ► Remote

sensing imaging systems possess four major resolution characteristics that determine the type of geographic data that can be detected. ► Spatial resolution ► Spectral resolution ► Radiometric resolution ► Temporal resolution

Plate 8.1

Plate 8.2

Figure 8.6

Imaging Characteristics ► Remote

sensing imaging systems possess four major resolution characteristics that determine the type of geographic data that can be detected. ► Spatial resolution ► Spectral resolution ► Radiometric resolution ► Temporal resolution

Spatial Resolution ► Most

important ► Ability of system to record detail. ► Analog = photograph sharpness; up to 60 lp/mm. ► The number of line pairs per millimeter does not take into account the scale of the aerial photo, GR combines scale and resolution  GR = W*SF  1:10,000 scale photo at 60 lp/mm =0.17 m

Spatial Resolution for Scanners ► Measured

in instantaneous field of view (IFOV) or the angle through which the detector is sensitive to energy. ► D = H*B; D = ground dimension (resolution); H = height of platform; B = IFOV in milliradians. ► SPOT = 10 m resolution ► IKONOS-2 = 1 m resolution ► Landsat = 15 m.

Spectral Resolution ► Two

things considered here. ► Number of Wavelength Bands ► Wavelength of Bands ► More bans with smaller wavelengths means higher resolution.

Radiometric Resolution ► The

smallest difference in radiant energy that can be detected by a sensor. ► Inversely proportional to contrast of film=film can pick up more subtle changes ► For digital images, number of discrete levels into which a signal may be divided, 6 bit vs. 8 bit, etc.

Temporal Resolution ► Frequency

data is collected. ► Clouds play a role usually. ► Landsats 1-3 capture the Earth every 18 days ► Landsats 4-7 capture the Earth every 16 days = better temporal resolution ► Import for many studies like vegetation growth.