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/

Electromagnetic spectrum

•  A continuum of all possible energies that radiate through space •  In remote sensing, we mainly focus on visible, infrared and

microwave

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

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.

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

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.

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

Spatial resolution comparison among four data sources

LANDSAT (30m) ASTER (15m) SPOT (10m) Quickbird (60 cm)

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

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

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

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)

Imagery Sources

Orthoimagery

•  Truecolorimages(likeaphotograph)withanydistor8onscausedbythe8ltofthecameraortopographyofthelandremoved.

•  Comefrombothaerialphotographsandsatellitesources

•  GoogleEarth/Maps•  AvailableforallofthecountrythroughtheUSGSEarthExplorer

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

Panchromatic Panchromatic Imagery: SPOT Resolution 10m

Jebel Sinjar, Iraq - 1992

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)

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

LANDSAT Multispectral Scanner (MSS) Chicago, Illinois

Four bands (2 Visible & 2 IR) Resolution ~ 90m

Landsat egypt Multispectral Satellite Imagery: LANDSAT Thematic Mapper

Western Nile Delta, Egypt Band 4: Red Band 3: Green Band 2: Blue Resolution 30m

Global Land Survey

Treated and standardized Landsat Imagery from 1976, 1990, 2000 and 2005

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

ASTER Multispectral Imagery: ASTER Advanced Spaceborne Thermal Emission and Reflection Radiometer

Mexicali, California 19 May 2000 Resolution 15m

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

Moderate Resolution Imaging Spectroradiometer (MODIS)

Avhrr Advanced Very High Resolution Radiometer (AVHRR)

Resolution ca. 1km

High Resolution Imagery: CORONA

Resolution ca. 1.6m Assyrian Canal at Bandwai, Iraq Mission 1102 (11 Dec 1967)

Notre Dame Stadium: 2/28/2011 Resolution: 60 cm

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

Uses of Satellite Imagery

•  Classification of Landcover •  Vegetation Indices •  Geologic Indices •  Pan Sharpening

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

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).

NDVI

Example NDVI

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

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