Remote Sensing Review

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Remote Sensing Review

• Lecture 1
• January 21, 2005

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What is remote sensing

• Remote Sensing remote sensing is science of
• acquiring,
• processing, and
• interpreting
• images and related data that are obtained from
  ground-based, air-or space-borne instruments that
  record the interaction between matter (target)
  and electromagnetic radiation.
• Remote Sensing using electromagnetic spectrum to
  image the land, ocean, and atmosphere.

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Electromagnetic Spectrum
Source http//oea.larc.nasa.gov/PAIS/DIAL.html
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Ways of Energy Transfer
Energy is the ability to do work. In the process
of doing work, energy is often transferred from
one body to another or from one place to another.
The three basic ways in which energy can be
transferred include conduction, convection, and
radiation. Most people are familiar with
conduction which occurs when one body (molecule
or atom) transfers its kinetic energy to another
by colliding with it (physical contact). This is
how a pan gets heated on a stove. In
convection, the kinetic energy of bodies is
transferred from one place to another by
physically moving the bodies. A good example is
the convectional heating of air in the atmosphere
in the early afternoon (less dense air rises).
The transfer of energy by electromagnetic
radiation is of primary interest to remote
sensing because it is the only form of energy
transfer that can take place in a vacuum such as
the region between the Sun and the Earth.
Jensen, 2000
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Wave model of EMR

• Electromagnetic wave consists of an electrical
  field (E) which varies in magnitude in a
  direction perpendicular to the direction in which
  the radiation is traveling, and a magnetic field
  (M) oriented at right angles to the electrical
  field. Both these fields travel at the speed of
  light (c).

Jensen, 2000
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Three characteristics of electromagnetic wave

• Velocity is the speed of light, c3 x 108 m/s
• wavelength (?) is the length of one wave cycle,
  is measured in metres (m) or some factor of
  metres such as
• centimetres (cm) 10-2 m
• micrometres (µm) 10-6 m
• nanometres (nm) 10-9 m
• Frequency (v) refers to the number of cycles of a
  wave passing a fixed point per unit of time.
  Frequency is normally measured in hertz (Hz),
  equivalent to one cycle per second, and various
  multiples of hertz. unlike c and ? changing as
  propagated through media of different densities,
  v remains constant.
• Hertz (Hz) 1
• kilohertz (KHz) 103
• megahertz (MHz) 106
• gigahertz (GHz) 109

The amplitude of an electromagnetic wave is the
height of the wave crest above the undisturbed
position
Travel time from the Sun to Earth is 8 minutes
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Particle model of EMR

• Sir Isaac Newton (1704) was the first person
  stated that the light had not only wavelike
  characteristics but also light was a stream of
  particles, traveling in straight lines.
• Niels Bohr and Max Planck (20s) proposed the
  quantum theory of EMR
• Energy content Q (Joules) hv (h is the
  Planck constant 6.626 x 10 34 J s)
• ? c/vhc/Q or Qhc/ ?
• The longer the wavelength, the lower its energy
  content, which is important in remote sensing
  because it suggests it is more difficult to
  detect longer wavelength energy

Newtons experiment in 1966
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Energy of quanta (photons)
Jensen, 2000
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EMR details

• (mm)
• Red 0.620 - 0.7
• Orange 0.592 - 0.620
• Yellow 0.578 - 0.592
• Green 0.500 - 0.578
• Blue 0.446 - 0.500
• Violet 0.4 - 0.446

Bees and some other insects can see near UV. The
Sun is the source of UV, but only 0.3 mm (near
UV) can reach the Earth.
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EMR details (2)
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Source of EMR

• All objects above absolute zero emit
  electromagnetic energy, including water, soil,
  rock, vegetation, and the surface of the Sun. The
  Sun represents the initial source of most of the
  electromagnetic energy remote sensing systems
  (except radar and sonar)
• Total radiation emitted M (Wm2) sT4
  (Stefan-Boltzmann Law), where T is in degrees K
  and s is the Stefan-Boltzmann constant,
  5.67108 K4Wm2
• -- Energy at Sun enormous, 7.3107 Wm2,
  reduced to 459 Wm2 by Earth-Sun distance
• Wavelength ?max of peak radiation, in µm 2897/T
  (Wiens Displacement Law) Examples
• -- Peak of Suns radiation ?max 2897/6000
  0.48 µm
• -- Peak of Earths radiation ?max 2897/300
  9.7 µm

Jensen, 2000
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Jensen, 2000
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Paths and Interactions

• If the energy being remotely sensed comes from
  the Sun, the energy
• is radiated by atomic particles at the
  source (the Sun),
• propagates through the vacuum of space at
  the speed of light,
• interacts with the Earth's atmosphere (3A),
  
• interacts with the Earth's surface (3B),
• interacts with the Earth's atmosphere once
  again (3C),
• finally reaches the remote sensor where it
  interacts with various optical systems, filters,
  emulsions, or detectors (3D).

60 miles or 100km
Jensen, 2000
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Several concepts

• Plancks equation
• - if a blackbody transforms heat into radiant
  energy, then the radiation received at a sensor
  is given by Plancks equation.
• Spectral Emissivity

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• Spectral reflectivity is the percentage of EMR
  reflected by the object in a each wavelength or
  spectral bands
• Albedo is ratio of the amount of EMR reflected by
  a surface to the amount of incident radiation on
  the surface. Fresh Snow has high albedo of
  0.8-0.95, old snow 0.5-0.6, forest 0.1-0.2, Earth
  system 0.35

EMR
EMR
EMR
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Remote sensing platforms
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Ground and Aircraft Based

• Ground
• repeat or continuous sampling
• regional or local coverage
• example NEXRAD for precipitation
• Aircraft
• repeat sampling , any sampling interval
• regional or local coverage
• examples AVIRIS for minerals exploration
• LIDAR for ozone and aerosols

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Space Based

• Sun-synchronous polar orbits
• global coverage, fixed crossing, repeat sampling
• typical altitude 500-1,500 km
• example MODIS, Landsat
• Low-inclination, non-Sun-synchronous orbits
• tropics and mid-latitudes coverage, varying
  sampling
• typical altitude 200-2,000 km
• example TRMM
• Geostationary orbits
• regional coverage, continuous sampling
• over equator only, altitude 35,000 km
• example GOES

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Types of remote sensing

• Passive source of energy is either the Sun,
  Earth, or atmosphere
• Sun
• - wavelengths 0.4-5 µm
• Earth or its atmosphere
• - wavelengths 3 µm -30 cm

• Active source of energy is part of the remote
  sensor system
• Radar
• - wavelengths mm-m
• Lidar
• - wavelengths UV, Visible, and near infrared

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Measurement scales constrained by physics and
technology

• Spatial resolution (IFOV/GSD) and coverage (FOV)
• Optical diffraction sets minimum aperture size
• Spectral resolution (Dl ) and coverage (lmin to
  lmax)
• Narrow bands need bigger aperture, more
  detectors, longer integration time
• Radiometric resolution (S/N, NEDr, NEDT ) and
  coverage (dynamic range)
• Aperture size, detector size, number of
  detectors, and integration time
• Temporal resolution (site revisit) and coverage
  (global repeat)
• Pointing agility, period for full coverage

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Basics of Bit

• Computer store everything in 0 or 1

(2bits)
Bit no.
0
256
8 bits as an example
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The size of a cell we call image resolution,
depending on Such as 1 m, 30 m, 1 km, or 4 km
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Digital Image Data Formats

• Each band of image is stored as a matrix (array)
  format
• To efficiently handle the multi-bands (and
  hyperspectral) imagery in an image processing
  software, BSQ (band sequential), BIL (band
  interleaved by line), BIP (band interleaved by
  pixel) are common image data format (see an
  example in p103 of the text book) .

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Procedures of image processing

• Preprocessing
• Radiometric correction is concerned with
  improving the accuracy of surface spectral
  reflectance, emittance, or back-scattered
  measurements obtained using a remote sensing
  system. Atmospheric and topographic corrections
• Geometric correction is concerned with placing
  the above measurements or derivativeproducts in
  their proper locations.
• Information enhancement
• Point operations change the value of each
  individual pixel independent of all other pixels
• Local operations change the value of individual
  pixels in the context of the values of
  neighboring pixels.
• They are image reduction, image magnification,
  transect extraction, contrast adjustments (linear
  and non-linear), band ratioing, spatial
  filtering, fourier transformations, principle
  components analysis, and texture transformations
• Information extraction
• Post-classification
• Information output
• Image or enhanced image itself, thematic map,
  vector map, spatail database, summary statistics
  and graphs

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Remote Sensing Applications

• Land
• rocks, minerals, faults, land use and land
  cover, vegetation, DEM, snow and ice, urban
  growth, environmental studies,
• Ocean
• ocean color, sea surface temperature, ocean
  winds,
• Atmosphere
• temperature, precipitation, clouds, ozone,
  aerosols,

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Applications driving remote sensing
Jensen, 2000
Jensen, 2000
Various application demands as driving forces for
the resolution improvements of remote sensing
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Trend and Future of Remote Sensing (1)

• High spatial resolution
• - IKONOS launched in 1999 by Space Imaging
• (4 m multi-spectral and 1 m panchromatic)
• - QuickBird launched in 2001 by DIGITALGLOBE
• (2.44 m multi-spectral and 61 cm panchromatic)
• High spectral resolution
• - AVIRIS, 10nm and 20 m, 224 bands
• - Hyperion launched in 2000, 10nm and 30m, 220
  bands
• High radiometric resolution
• - 8 bits to 12 bits
• High temporal resolution
• - GOES 15-30 minutes
• - NEXRAD 6 or 10 minutes

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Trend and Future of Remote Sensing (2)

• Globe coverage, high repeatability (or improved
  temporal resolution)
• - AVHRR, 1100m, morning or afternoon
• - MODIS, 250-1000m, morning or afternoon
• - NPOESS Preparatory Program (NPP) (to be
  launched 2007) 4 sensors
• - NPOESS (to be launched in 2009), 370-740m, 4
  hours 14 sensors
• Real-time or near real-time availability
• - MODIS available online in the second day ?
• - NEXRAD available online in 6 minutes
• - NPOESS available online in 15 minutes
• Cost free or affordable
• - Most of the federal collected images are free
  available or lower
• cost, while commercial high resolution images
  are affordable.
• Integrated remote sensing and GIS
• - Remote sensing applications with the support
  of GIS
• - Remote sensing data as a major GIS data
  source

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Major image processing software

• ENVI/IDL http//www.rsinc.com/
• ERDAS Imagine http//www.gis.leica-geosystems.com
  /Products/Imagine/
• PCI Geomatics http//www.pci.on.ca/
• ER Mapper http//www.ermapper.com/
• INTEGRAPH http//imgs.intergraph.com/gimage/
• IDRIS
• Ecognition http//www.definiens-imaging.com/ecogn
  ition/pro/40.htm
• See5 and decision tree

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Earth in a New Light by NASA Earth Science
Watch Movies (about half a hour)