introduction to remote sensing

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Introduction to Remote Sensing

Dr. Mathias (Mat) Disney

UCL Geography

Office: 301, 3rd Floor, Chandler House

Tel: 7670 4290

Email: mdisney@ucl.geog.ac.uk

www.geog.ucl.ac.uk/~mdisney

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• Course outline– Lectures for first part of session, practicals second part

• Course mark 70% for exam, 30% for write-up of final practical, to be handed in by the end of term (Weds Mar 23rd?)

– First week familiarise ourselves with lab PCs and sources of image data on the web

– Next 3 practicals 2 weeks each (expect you to spend time on this outside Monday session)

– Final practical (Classification): 3 weeks, write-up

Format of the course

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• Books– Jensen, J. R. (2000) Remote Sensing of the Environment: An Earth

Resource Perspective, 2000, Prentice Hall, New Jersey. (Excellent on RS but no image processing, around £40 from Waterstones).

– Jensen, J. R. (2005, 3rd ed.) Introductory Digital Image Processing, Prentice Hall, New Jersey. (Companion to above, around £40 from Waterstones) BUT mostly available online at http://www.cla.sc.edu/geog/rslab/751/index.html

– Lillesand, T. M., Kiefer, R. W. and Chipman, J. W. (2004, 5th ed.) Remote Sensing and Image Interpretation, John Wiley, New York. (good all-round text-book around £35).

– Mather, P. M. (1999) Computer Processing of Remotely‑sensed Images, 2nd Edition. John Wiley and Sons, Chichester.

– Campbell, J. B. (1996) Introduction to Remote Sensing (2nd Ed), London:Taylor and Francis.

Course material

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• Web– Tutorials– http://rst.gsfc.nasa.gov/Front/tofc.html– http://mercator.upc.es/nicktutorial/TofC/table.html– http://earth.esa.int/applications/data_util/SARDOCS/spaceborne/

Radar_Courses/– http://www.crisp.nus.edu.sg/~research/tutorial/image.htm– http://www.ccrs.nrcan.gc.ca/ccrs/learn/tutorials/fundam/fundam_e.html– http://octopus.gma.org/surfing/satellites/index.html– Glossary of alphabet soup acronyms!

http://www.ccrs.nrcan.gc.ca/ccrs/learn/terms/glossary/glossary_e.html– Other resources– NASA www.nasa.gov– NASAs Visible Earth (source of data): http://visibleearth.nasa.gov/– European Space Agency www.esa.int– NOAA www.noaa.gov– Remote sensing and Photogrammetry Society UK www.rspsoc.org

Course material

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• Course outline– Lecture 1: Introduction to EO

– Lecture 2: Introduction to image processing (image display/enhancement) - practical 1

– Lecture 3: Introduction to electromagnetic spectrum

– Lecture 4: Image arithmetic: ratios and spectral indices - practical 2

– Lecture 5: EM spectrum and the atmosphere, plus angular info.

– Lecture 6: Information extraction: spatial filtering and classification - practical 3 (assessed practical)

– Lecture 7: Spatial, spectral, temporal resolution and tradeoffs

– Lecture 8: Orbits, swaths and coverage

– Lecture 9: Pre-processing stages and sensor scanning mechanisms

– Lecture 10: Applications plus recap

Format of the course

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• General introduction to remote sensing (RS), Earth Observation (EO).......– definitions of RS

– Why do we do it?• Applications and issues

– Who and where?

– Concepts and terms• remote sensing process, end-to-end

Lecture outline

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The Experts say "Remote Sensing is...”• ...techniques for collecting image or other forms of data

about an object from measurements made at a distance from the object, and the processing and analysis of the data (RESORS, CCRS).

• ”...the science (and to some extent, art) of acquiring information about the Earth's surface without actually being in contact with it. This is done by sensing and recording reflected or emitted energy and processing, analyzing, and applying that information.”

http://www.ccrs.nrcan.gc.ca/ccrs/learn/tutorials/fundam/chapter1/chapter1_1_e.html

What is remote sensing?

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The not so experts say "Remote Sensing is...”

• Advanced colouring-in.

• Seeing what can't be seen, then convincing someone that you're right.

• Being as far away from your object of study as possible and getting the computer to handle the numbers.

• Legitimised voyeurism(more of the same from http://www.ccrs.nrcan.gc.ca/ccrs/eduref/misc)

What is remote sensing (II)?

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Remote Sensing Examples•First aerial photo credited to Frenchman Felix Tournachon in Bievre Valley, 1858.

•Boston from balloon (oldest preserved aerial photo), 1860, by James Wallace Black.

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Remote Sensing Examples

•Kites (still used!) Panorama of San Francisco, 1906.

•Up to 9 large kites used to carry camera weighing 23kg.

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Remote Sensing Examples

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Remote Sensing: scales and platforms

•Not always big/expensive equipment

•Individual/small groups

•Calibration/validation campaigns

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Remote Sensing: scales and platforms

•Both taken via kite aerial photography•http://arch.ced.berkeley.edu/kap/kaptoc.html

•http://activetectonics.la.asu.edu/Fires_and_Floods/

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Remote Sensing: scales and platforms

•Platform depends on application

•What information do we want?

•How much detail?

•What type of detail?

upscale

http://www-imk.fzk.de:8080/imk2/mipas-b/mipas-b.htm

upscale upscale

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Remote Sensing: scales and platforms•E.g. aerial photography

•From multimap.com

•Most of UK

•Cost? Time?

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Remote Sensing: scales and platforms

•Many types of satellite

•Different orbits, instruments, applications

upscale

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Remote Sensing Examples

•Global maps of vegetation from MODIS instrument

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Remote Sensing Examples

•Global maps of sea surface temperature and land surface reflectance from MODIS instrument

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Remote sensing applications

•Environmental: climate, ecosystem, hazard mapping and monitoring, vegetation, carbon cycle, oceans, ice

•Commercial: telecomms, agriculture, geology and petroleum, mapping

•Military: reconnaissance, mapping, navigation (GPS)

•Weather monitoring and prediction

•Many, many more

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• Collection of data– Some type of remotely measured signal

– Electromagnetic radiation of some form

• Transformation of signal into something useful– Information extraction

– Use of information to answer a question or confirm/contradict a hypothesis

EO process in summary.....

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Remote sensing process: IStatement of problem

•What information do we want?

•Appropriate problem-solving approach?

Formulate hypothesis

Hypothesis testing

•In situ: field, lab, ancillary data (Meteorology? Historical? Other?)

•EO data: Type? Resolution? Cost? Availability?

•Pre/post processing?

Data collection

•Analog: visual, expert interp.

•Digital: spatial, photogrammetric, spectral etc.

•Modelling: prediction & understanding

•Information extraction

Data analysis

•Products: images, maps, thematic maps, databases etc.

•Models: parameters and predictions

•Quantify: error & uncertainty analysis

•Graphs and statistics

Presentation of information

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The Remote Sensing Process: II• Collection of information about an object without

coming into physical contact with that object

Passive: solar reflected/emitted

Active:RADAR (backscattered); LiDAR (reflected)

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The Remote Sensing Process: III

• What are we collecting?– Electromagnetic radiation (EMR)

• What is the source?– Solar radiation

• passive - reflected, emitted

– OR artificial source• active - RADAR, LiDAR

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Electromagnetic radiation?

•Electric field (E)

•Magnetic field (M)

•Perpendicular and travel at velocity, c (3x108 ms-1)

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• Energy radiated from sun (or active sensor)• Energy 1/wavelength (1/)

– shorter (higher f) == higher energy

– longer (lower f) == lower energyfrom http://rst.gsfc.nasa.gov/Intro/Part2_4.html

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Information

• What type of information are we trying to get at?

• What information is available from RS?– Spatial, spectral, temporal, angular,

polarization, etc.

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Spectral information: vegetation

Wavelength, nm

400 600 800 1000 1200

refle

ctan

ce(%

)

0.0

0.1

0.2

0.3

0.4

0.5

very high leaf area

very low leaf area

sunlit soil

NIR, high reflectance

Visible red, low reflectance

Visible green, higher than red

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Spectral information: vegetation

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Colour Composites: spectral‘Real Colour’

composite

Red band on red

Green band on green

Blue band on blue

Approximates “real” colour (RGB colour composite)

Landsat TM image of Swanley, 1988

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Rondonia 1975

Temporal information

Change detection

http://earth.jsc.nasa.gov/lores.cgi?PHOTO=STS046-078-026

http://www.yale.edu/ceo/DataArchive/brazil.html

Rondonia 1986

Rondonia 1992

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when we view an RS image, we see a 'picture’ BUT need to be aware of the 'image formation process' to:

– understand and use the information content of the image and factors operating on it

– spatially reference the data

Always bear in mind.....

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Remote Sensing:What is it and why do we use it?

• Many monitoring issues global or regional• Drawbacks of in situ measurement …..• Remote sensing can provide (not always!)

– Global coverage

• Range of spatial resolutions

– Temporal coverage (repeat viewing)

– Spectral information (wavelength)

– Angular information (different view angles)

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• source of spatial and temporal information (land surface, oceans, atmosphere, ice)

• monitor and develop understanding of environment (measurement and modelling)

• information can be accurate, timely, consistent • remote access • some historical data (1960s/70s+) • move to quantitative RS e.g. data for climate

– some commercial applications (growing?) e.g. weather– typically (geo)'physical' information but information widely used

(surrogate - tsetse fly mapping)

– derive data (raster) for input to GIS (land cover, temperature etc.)

Why do we study/use remote sensing?

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Caveats!

• Remote sensing has many problems– Can be expensive– Technically difficult– NOT direct

• measure surrogate variables

• e.g. reflectance (%), brightness temperature (Wm-2 oK), backscatter (dB)

• RELATE to other, more direct properties.