Introduction to Remote Sensing - PowerPoint PPT Presentation

1 / 26
About This Presentation
Title:

Introduction to Remote Sensing

Description:

The acquisition of information about a target in the absence of physical contact ... Geometric optics (r l), 'specular' Rayleigh scattering (r l) intensity ... – PowerPoint PPT presentation

Number of Views:116
Avg rating:3.0/5.0
Slides: 27
Provided by: vickyha
Category:

less

Transcript and Presenter's Notes

Title: Introduction to Remote Sensing


1
Introduction to Remote Sensing
  • Lecture VEH1
  • 8-26-03

2
What is Remote Sensing?
  • The acquisition of information about a target in
    the absence of physical contact
  • Measure changes in fields
  • Electromagnetic fields (spectroscopy)
  • Acoustic fields (sonar)
  • Potential fields (gravity)
  • Describe as energy intensity vs. wavelength
  • map into spatial or temporal variations
  • use to interpret properties (e.g., chemistry,
    mineralogy, roughness) of the material

3
Remote Sensing Systems
  • Two types
  • Passive detection of energy from natural
    (solar) illumination or emission
  • Active detection of energy after illuminating
    material and observing returned energy
  • Long history of spacecraft airborne sensors
  • Landsat, TIMS, ASTER, SPOT, AVIRIS, AHI, SEBASS,
    SeaSat, SIR-A,-B,-C, TOPEX/Poseidon

4
Energy Detection and Physics of EM Waves
  • Interaction of EM energy (light) with material
    changes the energy
  • Five basic types of interactions between light
    sources and materials, such that the light is
  • Reflected illuminating energy is returned from a
    surface with an angle of reflection equal and
    opposite to the incidence angle characteristic
    of smooth (at scale of wavelength) surfaces
  • Scattered illuminating energy is deflected in
    multiple directions characteristic of rough (at
    scale of wavelength) surfaces

5
Incident light
Reflected
Scattered
Material
6
5 basic types of interactions, cont.
  • Transmitted (refracted) illuminating energy is
    passed through the material changes in spectrum
    are caused by change in density (velocity of
    incident wave) between material and surroundings
    (index of refraction)
  • Absorbed energy is transformed (usually into
    longer wavelength heat)
  • Emitted energy is released from the material
    (it's now the source)

7
Incident light
Reflected
Scattered
Emitted
Material
Absorbed
Transmitted
8
Energy Detection and Physics of EM Waves
  • Energy recorded vs. wavelength controlled by
  • Optical properties of the material
  • n, index of refraction
  • k, absorption coefficient R (n-1)2k2 /
    (n1)2 k2
  • Physical properties of the material surface
  • ratio of particle size to l (? grain size!)
  • Geometric optics (r gtgt l), specular
  • Rayleigh scattering (r ltlt l) intensity
    proportional to l-4
  • Mie scattering (r l)
  • roughness

r
9
EM Spectrum
  • EM waves vary in wavelength and frequency by
    c ln
  • c speed of light (3 x 108 m/sec)? wavelength
    (so, if ????10 µm)? frequency (then ? 3 x
    1013 s-1)
  • Relate the frequency (?) to energy by E hn
  • h Planck constant (6.626 x 10-34 Jsec)

Long l
Short l
Low Frequency Low Energy
High Frequency High Energy
Note Frequency refers to of wave crests of
same l that pass by a point in 1 second
10
(No Transcript)
11
Wavelength Ranges
  • Gamma rays (lt 0.0001 µm), change in energy state
    of neutrons/protons information on elements
  • X-rays (lt 0.01 µm) photons absorbed by the
    inner shell of electrons
  • Ultraviolet (UV, lt 0.4 µm) photons
    emitted/absorbed by the outer shell of
    electrons information on transition metals
    (Fe2, Fe3, Cu2), chlorophyll

12
Wavelength Ranges, cont.
  • Visible (VIS, lt 0.67 µm) similar to UV, also
    sensitive to H2O, OH- information on
    mineralogy, vegetation
  • Near infrared (NIR, lt 1.5 µm) similar to VIS
    information on mineralogy, vegetation
  • Thermal infrared (TIR, lt 100 µm) photons
    interact with molecular vibrations (controlled by
    bond length, strength) information on
    mineralogy, surface T
  • Microwave (0.1 cm 10 m) radar information
    on particle size, macro-roughness

13
Interpreting Spectral Information
  • Data can be complex function of composition,
    texture, wavelength
  • Information content also affected by the
    collection device (sensor) e.g., sensitivity,
    /width of wavelength bands, spatial resolution
  • Multispectral Several (usually few - dozen)
    broad, but discrete wavelengths in spectral
    region of interest
  • Hyperspectral Many (usually gt100) narrow,
    discrete wavelengths in same spectral region of
    interest

14
(No Transcript)
15
Interpreting Spectral Information
  • Atmospheric gases also interact with light
  • Can inhibit use of certain wavelength ranges
  • Atmospheric windows are regions not blocked by
    atm. gases/dust - have high transmission and low
    absorption
  • H2O, CO2, and O3 are primary VIS-TIR absorbers on
    Earth CO2 is primary at Mars (silicate dust too)
  • Transmissivity measure of the fraction of
    radiation that passes through the atmosphere
    unattenuated (varies between 0 and 1)

16
Atmospheric Windows
Absorptions primarily due to H2O, CO2, O3
Mostly Opaque due To H2O
Transmittance
Wavelength (µm)
17
Interpreting Spectral Information
  • Atmospheric influence, cont.
  • Path length Distance traveled through the
    atmosphere by a photon
  • Function of location of energy source, sensor
    type, wavelength
  • Path radiance Energy contributed by interactions
    with atmosphere prior to detection at sensor
  • Energy at sensor Esensor Rpath Rground
  • Atmospheric correction (separation) algorithms
    remove/lessen contribution of Rpath to get at
    Rground

18
Imaging Systems - Overview
  • Images are made of up rows and columns of picture
    elements, or pixels
  • Values recorded as digital numbers (DN)
  • 8-bit (28) data ranges from DN 0 - 255
  • 16-bit (216) data ranges from DN 0 - 65,535
  • Value chosen (8- or 16-bit) depends on the
    precision required for parameter you are storing
  • Display single wavelength data in grayscale
    (human eye only sees 30 levels of gray)
  • Display three wavelengths in color, with
    wavelengths represented in red, green, and blue
    (RGB)

19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
Color Imaging
24
Color Imaging
25
Color Imaging
THEMIS VIS
Band 1 0.654 µm
Band 2 0. 540 µm
Band 3 0.425 µm
Bands 1,2,3 RGB
26
Imaging Systems - Overview
  • Spatial resolution
  • Defined one of two ways
  • Pixel size (area viewed on ground)
  • Size of smallest resolvable feature (generally
    larger than pixel size)
  • Determined by two parameters
  • Height of sensor above ground
  • Instantaneous field of view (IFOV) of sensor
  • Pixel size H x IFOV
  • If H 2 km, and IFOV 2.5 mrad, then pixel 5 m
Write a Comment
User Comments (0)
About PowerShow.com