gis: geographic information systems module 5: …...launched in 1999 as a joint usa japan project...
TRANSCRIPT
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GIS: Geographic Information Systems
Module 5: Satellite Imagery
Matthew L. Sisk Center for Digital Scholarship
Hesburgh Library, University of Notre Dame
library.nd.edu/cds/
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Electromagnetic spectrum
• A continuum of all possible energies that radiate through space • In remote sensing, we mainly focus on visible, infrared and
microwave
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Reflectivity
• The color of an object is controlled by how much light it reflects in each wavelength in the visible spectrum – Objects reflect some wavelengths – Objects absorb some wavelengths
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Remote Sensing
• Remote sensors are devices that sense energy from a remote location (i.e., a device not in physical contact with what it is sensing)
• Remote sensing is the science of acquiring, processing and interpreting information/data collected by remote sensors.
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Panchromatic ● Single band image. ● Usually like a black and white photograph ● Sampling reflectivity in the visible spectrum
Multi-spectral
● Multi-band imagery ● Like a digital photograph ● Each band represents reflectivity in a certain
wavelength ● Each band can be visualized in GIS software as a
particular color “gun.”
Key Terms:
Satellite Imagery
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Satellite Imagery
Described by different types of resolution – Spatial resolution: area on ground represented by each
pixel – Temporal resolution: how often a satellite obtains imagery
of a particular area – Spectral resolution: specific wavelength intervals in the
electromagnetic spectrum captured by each sensor – Radiometric Resolution: number of possible data values
reportable by each sensor (how sensitive the sensor is to changes in brightness of objects that it views)
– Others: • View angle resolution: the number of angles at which the ground
objects are recorded by the sensor.
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10 m
10 m
Spatial Resolution
• The length, in real world measurements, of one side of each square pixel
100 m2
10 m
10 m
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Spatial resolution comparison among four data sources
LANDSAT (30m) ASTER (15m) SPOT (10m) Quickbird (60 cm)
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Remote Sensor Data Acquisition
June 1, 2004 June 17, 2004 July 3, 2004
16 days
Temporal Resolution
• Number of days between overhead passes at the same location – Roughly, the amount of time taken to orbit the Earth
• Landsat - 16 days • AVHRR - daily • IKONOS - 1 to 3 days
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Spectral Resolution
• Number, spacing and width of sampled wavelength bands
• Higher resolution results in more precision in representation of spectral signatures
1 2 3 4 5 7 6
8
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Landsat Bands
Band 1 Band 2 Band 3
Band 4
Band 5 Band 7 Band 6
BLUE GREEN RED
NEAR IR
SHORT WAVE IR
MID- WAVE IR
LONGWAVE IR
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Radiometric Resolution
• Number of possible data values reported by the sensor – Range is expressed as a power (2n) – 8-bit resolution has 28 values, or 256 values
Range is 0-255 – 16-bit resolution has 216 values, or 65,536 values
Range is 0-65535 • The value in each pixel is called the
– Digital Number (DN) – Brightness Value (BV)
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Imagery Sources
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Orthoimagery
• Truecolorimages(likeaphotograph)withanydistor8onscausedbythe8ltofthecameraortopographyofthelandremoved.
• Comefrombothaerialphotographsandsatellitesources
• GoogleEarth/Maps• AvailableforallofthecountrythroughtheUSGSEarthExplorer
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SPOT: Satellite Pour l'Observation de la Terre
Spectral sampling: Panchromatic Band 1 : Green (0,50 - 0,59 µm) Band 2 : Red (0,61 - 0,68 µm) Band 3 : Near Infrared (0,78 - 0,89 µm) Band 4 : Middle Infrared (MIR) (1,58 - 1,75 µm) Temporal Resolution: 1 - 4 days Resolution: Panchromatic / Multispectral SPOT 1-4 (1986 – 2010 ) 10 m / 20 m SPOT 5 (2002 – present) 2.5 m / 10 m SPOT 6-7 (Launch 2012) 1.5 m / 6 m
Recent SPOT imagery is privately distributed and somewhat expensive. Older (pre-1999) SPOT imagery is licensed within USGS Earth Explorer
4 3 2 1
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Panchromatic Panchromatic Imagery: SPOT Resolution 10m
Jebel Sinjar, Iraq - 1992
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Landsat
Longest running earth observing satellite Three phases of sensors over 7 satellites Multi-spectral scanner (MSS) Landsat 1 - 3 4 bands Thematic Mapper (TM) Landsat 4 - 5 7 bands Enhanced Thematic Mapper (ETM+) Landsat 7 8 bands
Data Continuity Mission (LDCM) Landsat 8 10 bands Temporal Resolution: ~16 days Nearly all Landsat data is free for academic uses through the United States Geological Survey (USGS)
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1: Blue (0.45-0.515 µm) 2: Green (0.525-0.605 µm) 3: Red (0.63-0.69 µm) 4: Near Infrared (0.75-0.90 µm) 5: Shortwave Infrared (SWIR) (1.55-1.75 µm) 6: Thermal Infrared (TIR) (10.4-12.5 µm) 7: Shortwave Infrared (SWIR) (2.09-2.35 µm) 8: Panchromatic (0.52-0.9 µm): ETM+ only
1 2 3 4 12 3 4 5 7 6
8
Landsat MSS Landsat TM and ETM +
Spatial Resolution MSS: 90 m TM: 30 m / 120 m thermal (band 6) ETM+: 30 m / 60 m thermal (band 6) / 15 m panchromatic (band 8)
1: Green (0.5 – 0.6) 2: Red (0.6 – 0.7) 3: Near Infrared (0.7 – 0.8) 4: Near Infrared (0.8 – 1.1)
Spectral Bands Spectral Bands
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LANDSAT Multispectral Scanner (MSS) Chicago, Illinois
Four bands (2 Visible & 2 IR) Resolution ~ 90m
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Landsat egypt Multispectral Satellite Imagery: LANDSAT Thematic Mapper
Western Nile Delta, Egypt Band 4: Red Band 3: Green Band 2: Blue Resolution 30m
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Global Land Survey
Treated and standardized Landsat Imagery from 1976, 1990, 2000 and 2005
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Launched in 1999 as a joint USA Japan Project Temporal Resolution: ~16 days Three Sensors VNIR: 15 m resolution Band 1: 0.52 - 0.60 µm Band 2: 0.63 - 0.69 µm Band 3N: 0.76 - 0.86 µm Band 3B: 0.76 - 0.86 µm SWIR: 30 m resolution Band 4: 1.600 - 1.700 µm Band 5: 2.145 - 2.185 µm Band 6: 2.185 - 2.225 µm Band 7: 2.235 - 2.285 µm Band 8: 2.295 - 2.365 µm Band 9: 2.360 - 2.430 µm TIR: 90 m resolution Band 10: 8.125 - 8.475 µm Band 11: 8.475 - 8.825 µm Band 12: 8.925 - 9.275 µm Band 13: 10.25 - 10.95 µm Band 14: 10.95 - 11.65 µm
ASTER Advanced Spaceborne Thermal Emission and Reflection Radiometer
1 2 3 4 5 76 8 9
10 - 14
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ASTER Multispectral Imagery: ASTER Advanced Spaceborne Thermal Emission and Reflection Radiometer
Mexicali, California 19 May 2000 Resolution 15m
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Other Satellite Imagery
• Modis – Medium resolution (250-1 km) – But has 36 bands covering a broad range of spectra.
• Advanced Very High Resolution Radiometer (AVHRR) – 1 km resolution – Relatively coarse spectral resolution – Orbits twice daily
• Declassified Spy Satellites – Corona: 1959 - 1972 – Gambit: 1963 - 1967
• Very high resolution (0.6 – 2 m) • Limited coverage
• Modern Commercial Satellites – Quickbird / Digital Globe – 1.6 meter multispectral / 0.6 cm panchromatic
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Moderate Resolution Imaging Spectroradiometer (MODIS)
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Avhrr Advanced Very High Resolution Radiometer (AVHRR)
Resolution ca. 1km
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High Resolution Imagery: CORONA
Resolution ca. 1.6m Assyrian Canal at Bandwai, Iraq Mission 1102 (11 Dec 1967)
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Notre Dame Stadium: 2/28/2011 Resolution: 60 cm
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Sources of Satellite Imagery
• There are lots of questionable companies that will offer commercial processing and download of satellite imagery.
• Almost all of the imagery discussed here can be downloaded freely for academic purposes – Quickbird (and other high resolution imagery is a
notable exception • The USGS EarthExplorer is a very useful tool for
finding imagery – http://earthexplorer.usgs.gov
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Uses of Satellite Imagery
• Classification of Landcover • Vegetation Indices • Geologic Indices • Pan Sharpening
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Vegetation Indices
• A Vegetation Index (VI) is a “synthetic image layer” created from the existing bands of a multispectral image
• This new layer often provides unique and valuable information not found in any of the other individual bands. For example: – Can quantify or predict vegetation biomass, productivity,
leaf area, and vegetative ground cover
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Vegetation Indices
• There are several different Vegetation Indices – Most are functionally equivalent and most use a combination of
the red and near infrared (NIR) bands • Most common is the Normalized Difference Vegetation Index
(NDVI): – NDVI = (NIR - Red)/(NIR + Red) – Resulting values are real numbers ranging from -1 to 1, – Well vegetated areas have higher values (NIR >> red reflectance) – Water (and sometimes shadow) have negative values (red
reflectance > NIR reflectance) – Rock, dry soil, and sparse vegetation have values near zero (red
reflectance = NIR reflectance).
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NDVI
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Example NDVI
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Geology Indices
• Some minerals reflect differently in higher wavelengths
• Depends on the satellite • Examples for Landsat TM
– Iron Oxides = Band 3 / Band 1 – Clay Minerals = Band 5 / Band 7 – Ferrous Minerals = Band 5 / Band 4
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Landsat TM bands 4,2,1 30 m resolution
Landsat TM band 8 15 m resolution
Sharpened bands 4,2,1 15 m resolution
Resolution Merge / Pan-sharpening • Using a high resolution panchromatic image to artificially sharpen a lower
resolution multispectral image
• Best if they are from the same, or similar, times