Geomatics for Engineers

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Geomatics for Engineers

• Remote Sensing Component
• Michael McGoldrick
• (Office in Instrument Room)

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Lecture 1Data Sources
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EMR

• EM-Radiation
• 3 RS wavelength regions
• vis reflective IR
• microwave
• thermal IR

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EM Spectrum
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Visible Reflective IR

• Reflectance
• ratio of incident to reflected flux
• range 0 to 1
• Basic Assumption of RS
• unique spectral reflectances

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Visible Reflective IR
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Visible Reflective IR
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Microwave
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Microwave

• Active Passive
• airborne Some Sats
• radar

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Thermal

• Black Body
• theoretical object
• E l dependent on T
• same input Energy freq for different objects
• diff T
• Water is a grey body
• Emissivity

Radiant E of object at T1 Radiant E of BB at T1
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Sensor Types
Passive Satellites Cameras Videos
Active Radar Laser Sonar

• Sensor type is determined by project needs

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Satellite Data Acquisition

• More data or bands gives better discrimination
  ability
• Overview of process needed to turn RS data into
  information

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Satellite Data Acquisition

• Multispectral imaging discrete detectors
  scanning mirrors
• Landsat MSS
• Landsat TM
• NOAA AVHRR
• Multispectral imaging linear arrays
• SPOT

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Satellite Data Acquisition

• Imaging spectrometry linear area arrays
• CASI
• MEIS
• Radar satellites
• Radarsat
• Seasat
• J/ERS

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Landsat

• First launched in 1973
• Multi Spectral Scanner (MSS)
• 4 bands (G, R, NIR x2)
• 80m gd resolution
• 185Km swath
• First Series - Landsats 1,2 and 3
• Landsat 4 Launched 1983

• Upgraded instrument - Landsat Thematic Mapper
  (TM)
• Seven bands (B,G,R,NIR,SWIR x 2, TIR)
• 30m gd resolution
• 185Km swath
• Landsat 5 still operating
• Landsat 7 launching Dec this year (hopefully)

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Landsat
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AVHRR

• Primary operators - NOAA
• Launched as a weather satellite series in 1978
• 5 bands at a 1.1Km resolution
• 2700 Km swath
• Cheap satellite for global or continental scale
  monitoring

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AVHRR
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SPOT

• French satellite launched in 1986
• Two modes of operation
• MS - 3 bands at twenty meters resolution
• PAN - 1 band at 10m resolution
• Off nadir look capability
• Stereo capability

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SPOT
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IRS

• IRS 1C
• 4 bands
• 25 to 70m resolution
• 141 Km swath
• Launched 1996
• Also PAN
• 5m resolution
• 70 Km swath
• WIFS -
• 1 band at 188m res.
• 774 Km swath

• IRS 1A
• 4 bands
• 72m resolution
• 148 Km swath
• Launched in 1988
• IRS 1B
• 36m resolution
• Launched 1991

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IRS
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Radar Satellites

• SEASAT
• SIR series
• ERS series
• JERS-1
• Radarsat

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Lecture 2Image Display
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Image Display

• Image display (mainly this)
• Arithmetic manipulation
• Filtering
• Classification
• Principal component analysis

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Overview of Image Display

• Satellite band definition
• Image histograms
• Image contrast enhancement
• Band combinations

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Satellite Bands

• What are Bands?
• Filtered information from spectrum
• Chosen to highlight potential features of
  interest coincide with atmospheric windows

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Satellite Bands
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Satellite Bands

• Band information for major satellite sensors
• Landsat TM
• B G R NIR SWIRx2 TIR
• Landsat MSS
• G R NIR1 NIR2
• SPOT HVR
• G R NIR Pan(GR)
• AVHRR
• R NIR TIRx3

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Image Histograms

• What is an image histogram?
• Each pixel has 8 bit colour range containing
  brightness information
• 256 colour computer display
• frequency vs brightness

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Image Histograms
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Histogram Properties

• Describing Histograms
• mode, median, mean
• range, variance, standard deviation
• skew, unimodal / bimodal
• Image properties alter the display therefore,
  interpretation of an image

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Image Contrast

• Sensors designed to image all objects on planet
• rarely (if ever) cover full range in single image
• Expand original brightness input to full range of
  output device
• increasing contrast

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Image Stretching

• Basic stretches include
• linear - standard clip (most common)
• logarithmic exponential
• piecewise sawtooth
• equalise normalise

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(No Transcript)
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Image Display RGB
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Image Display Pseudo
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Image Display Pseudo
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Band Combination

• True colour false colour
• Commonly assign the RGB colour-guns to the
  following bands
• true colour (R G B)
• NIR (G R NIR)
• IR (NIR SWIR SWIR)
• Highlighting bimodal features

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Bimodal Histogram
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Summary

• Band information displayed in histograms showing
  the frequency of different brightnesses
• Histogram contrast enhancement used to aid image
  interpretation
• Contrast stretch used depends on image histogram
  shape desired information
• Band combinations display mode used to
  highlight features of interest

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Ratios
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Ratios
Any operation can be applied to an image band

• Addition
• Subtraction
• Division - Ratios
• Multiplication

Using an arithmetic operation creates a new band
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Ratios
Most commonly used operation Applications
include shadow removal thematic mapping
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Ratios

• Basic ratio form for target
• Common thematic ratios
• vegetation
• water
• iron oxide
• clay

highly reflective band highly absorbing band
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Ratios - Vegetation

• Simple vegetation ratio
• NDVI
• normalised difference vegetation index
• used in long term global monitoring
• used in Multi-temporal comparisons

NIR band R band
NIR - R NIR R
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Common Ratios

• Water ratios
• Clay
• Iron Oxide

G band SWIR band
B band SWIR band
OR
NIR SWIR
R B
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Displaying Results

• Displayed either as single bands or colour
  composites
• All bands created by arithmetic operations must
  be enhanced
• histograms stretched LUTs (Look Up Tables)
  applied

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Applications - NDVI

• NDVI used extensively
• improvement on simple ratio as it is not as
  affected by changing insolation
• Combination of NDVI Tasseled Cap used for plant
  health
• important to agriculture
• Data source depends on temporal, spatial
  spectral requirements
• AVHRR better temporal resolution than Landsat,
  but poorer spatial

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Applications - Oceanography

• Arithmetic operations can be utilised for optical
  oceanography
• Use ground truthing, determine relationship
  between
• depth / turbidity / bottom reflectance spectral
  characteristics

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Applications - Water Quality

• Ratios can be used to highlight colour changes in
  the water column
• extensively used with AVHRR imagery SeaWifs
• can highlight Phytoplankton (via chlorophyll)
• can highlight terrigenous material (via clay
  iron oxide)

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Summary

• Arithmetic operations used to extract information
• Ratios are the most common form of operation -
  covered in practical
• For each target identify one band which is highly
  reflective one which absorbs information
• Arithmetic operations used for many environmental
  applications

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Summary
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Summary