Introduction to Remote Sensing

ESCI 435: Landscape Ecology

What color is my shirt?

What color is my shirt?

What does this really mean?

The Electromagnetic Spectrum

μm = micrometer = 10-6 meters

The micrometer is the most common unit used to quantify the wavelength of EM energy

Lillesand and Kiefer

Interactions of EM energy with earth surface features

λ the greek letter “lambda” is the symbol for wavelength

This figure is really a statement about the First Law of Thermodynamics. You will recall that this law deals with the conservation of energy.

All incident EM energy of a particular wavelength, λ, will be partitioned among reflection, transmission and absorption.

This basic principle hold for solids, liquids and gases.

Lillesand and Kiefer

Spectral Reflectance Curves The % of incident energy

that is reflected from an object usually varies as a function of wavelength.

This variation can be displayed in the form of a spectral reflectance curve.

This wavelength dependent variation in reflectance is the basis for making inferences about the properties of different earth surface features and distinguishing between different cover types.

Lillesand and Kiefer

Visible portion of EM spectrum

Practical Experience with Remote Sensing: Vision

Your eyes are extraordinarily effective remote sensing Your eyes are extraordinarily effective remote sensing devices.devices.

Each of you have 20+ years of experience using “data” Each of you have 20+ years of experience using “data” generated by your eyes to make inferences about the generated by your eyes to make inferences about the world around youworld around you

Color, textureColor, texture and and contextcontext provide valuable clues provide valuable clues Your eyes gather data using only the visible part of the Your eyes gather data using only the visible part of the

EM spectrumEM spectrum The field of remote sensing involves the use various The field of remote sensing involves the use various

sensors to extend your ability to monitor the world sensors to extend your ability to monitor the world around youaround you

Remote Sensing: Defined

General: General: “..it is the art or science of telling “..it is the art or science of telling something about an object without being in something about an object without being in direct contact with it.”direct contact with it.” (Fisher et al. 1976; (Fisher et al. 1976; from Table 1.1 of your text)from Table 1.1 of your text)

Remote Sensing: Defined

More specific: More specific: “Remote sensing is the “Remote sensing is the practice of deriving information about the practice of deriving information about the earth’s land and water surface using earth’s land and water surface using images acquired from an overhead images acquired from an overhead perspective, using electromagnetic perspective, using electromagnetic radiation in one or more regions of the radiation in one or more regions of the electromagnetic spectrum, reflected or electromagnetic spectrum, reflected or emitted from the earth’s surface.” emitted from the earth’s surface.” (Campbell)(Campbell)

Remote Sensing: Defined

More cynical? More fun? More More cynical? More fun? More accurate?accurate? “Remote sensing is the art of “Remote sensing is the art of dividing up the world into multicolored dividing up the world into multicolored squares and then playing endless computer squares and then playing endless computer games with them to release unbelievable games with them to release unbelievable potential that is always just out of reach.” potential that is always just out of reach.”

Milestones in Remote Sensing 1920-30: routine use of aerial photos by 1920-30: routine use of aerial photos by

various government agenciesvarious government agencies 1939-45: WWII and the development and 1939-45: WWII and the development and

use of use of Infrared Infrared film. Unlike conventional film. Unlike conventional film, IR film is sensitive to EM energy in film, IR film is sensitive to EM energy in the near Infrared portion of the EM the near Infrared portion of the EM spectrum. spectrum. Why might this be useful during Why might this be useful during wartime?wartime?

Spectral Reflectance Curves: What are the unique features of vegetation?

Vegetation is “dark” (low reflectance) in the visible part of the spectrum and very bright in the near IR

Lillesand and Kiefer

Kodak advertisement circa 1943: two photographs using conventional film

N. Short tutorial

The same site with Infrared film

IR film is also referred to as “Camouflage Detection” or CD film

N. Short tutorial

Another example of IR film

Standard color film

Color IR film

Do you see anything odd?

Lillesand & Kiefer Fig 2.27

Milestones in Remote Sensing Post WWII:Post WWII: Extensive use of air photos (conventional and Extensive use of air photos (conventional and

IR) during war spilled over into extensive civilian IR) during war spilled over into extensive civilian applications after the war.applications after the war.

1950s: extensive application of IR film to agricultural 1950s: extensive application of IR film to agricultural monitoringmonitoring

1950-60: Extensive R&D by military on use of RS for 1950-60: Extensive R&D by military on use of RS for intelligence gathering. This was done in secret but older intelligence gathering. This was done in secret but older technology made its way into the civilian sector.technology made its way into the civilian sector.

1960s: lots of developments, including First moves from 1960s: lots of developments, including First moves from photographic to photographic to digital multispectral scanners. digital multispectral scanners. This This facilitates the move away from subjective facilitates the move away from subjective photointerpretation to more objective statistically based photointerpretation to more objective statistically based image classification. image classification.

Milestones in Remote Sensing 1972: The launch of the 1972: The launch of the Earth Resources Earth Resources

Technology Satellite (ERTS-A); Technology Satellite (ERTS-A); later later renamed renamed LANDSAT I. LANDSAT I. This was the first This was the first satellite dedicated to civilian remote satellite dedicated to civilian remote sensing.sensing.

A fork in the road: civilian and military RS A fork in the road: civilian and military RS head in different directions. head in different directions.

Milestones in Remote Sensing Launch of Landsat I represented a fork in Launch of Landsat I represented a fork in

the road: civilian and military RS head in the road: civilian and military RS head in different directionsdifferent directions Civilian RS: moderate spatial resolution Civilian RS: moderate spatial resolution

sensors and a focus on “regional” studies. sensors and a focus on “regional” studies. A standard Landsat scene is 185 km X A standard Landsat scene is 185 km X 185 km. Great for things like crop 185 km. Great for things like crop monitoring.monitoring.

Military RS: focus on very high spatial Military RS: focus on very high spatial resolution. Imagery of planes, military resolution. Imagery of planes, military installations etc. installations etc.

Milestones in Remote Sensing 1970s: lots of basic research in RS and lots 1970s: lots of basic research in RS and lots

of new applications for Landsat data. of new applications for Landsat data. Launch of Landsat 2 and 3 to keep up with Launch of Landsat 2 and 3 to keep up with demand. Modest improvements with each demand. Modest improvements with each launch.launch.

Milestones in Remote Sensing 1980s: Two parallel lines of development:1980s: Two parallel lines of development:

Improved sensor for Landsat 4; the Improved sensor for Landsat 4; the Thematic Mapper (TM) that was Thematic Mapper (TM) that was optimized for vegetation RS based on optimized for vegetation RS based on basic research done during the 1970sbasic research done during the 1970s

Delays in development of Landsat 4 Delays in development of Landsat 4 suggested that there might be a window suggested that there might be a window during which there would be no during which there would be no operational Landsat.operational Landsat.

This lead to “discovery” that operational This lead to “discovery” that operational meteorological satellites could be used meteorological satellites could be used for vegetation RSfor vegetation RS

Milestones in Remote Sensing 1980s: (continued): NOAA 1980s: (continued): NOAA

meteorological satellites have very low meteorological satellites have very low spatial resolution (1-4km vs. 30-80m for spatial resolution (1-4km vs. 30-80m for the sensors carried by Landsat) but this the sensors carried by Landsat) but this also enables them to image much larger also enables them to image much larger areas (swath width of over 2000km vs. areas (swath width of over 2000km vs. 185 km for Landsat). Data from these 185 km for Landsat). Data from these sensors can be used to address different sensors can be used to address different questions, especially those related to questions, especially those related to global climate changeglobal climate change

Milestones in Remote Sensing Mid-1980s: Mid-1980s: Hyperspectral dataHyperspectral data; ;

measurements in hundreds of very narrow measurements in hundreds of very narrow parts of the EM spectrum. All previous parts of the EM spectrum. All previous sensors take measurements in 3-7 broad sensors take measurements in 3-7 broad portions of the spectrum. Hyperspectral portions of the spectrum. Hyperspectral data are particularly useful for data are particularly useful for geological geological applications. applications. Airborne only at this time. Airborne only at this time. Some newer satellites now provide Some newer satellites now provide measurements in about 30-40 bands.measurements in about 30-40 bands.

Privatization of Landsat: creation of Privatization of Landsat: creation of EOSAT, now called Space Imaging. 10X EOSAT, now called Space Imaging. 10X increase in cost of imagery to users.increase in cost of imagery to users.

Milestones in Remote Sensing: Current status of Landsat

Landsat 4 and 5 launched in 1982 and 84 Landsat 4 and 5 launched in 1982 and 84 respectively; designed to operate for 3 years.respectively; designed to operate for 3 years.

EOSAT pledged to fund Landsat 6EOSAT pledged to fund Landsat 6 Landsat 6 finally launched in 1993: It crashed.Landsat 6 finally launched in 1993: It crashed. Privatization of Landsat widely viewed as a Privatization of Landsat widely viewed as a

failurefailure Mid-1990s: NASA takes back Landsat; Space Mid-1990s: NASA takes back Landsat; Space

Imaging continues to market older imagery; Imaging continues to market older imagery; NASA launches Landsat 7 in 1999. NASA launches Landsat 7 in 1999.

Milestones in Remote Sensing: Current status of Landsat Mid-1990s: NASA takes back Landsat; Space Mid-1990s: NASA takes back Landsat; Space

Imaging continues to market older imagery; Imaging continues to market older imagery; NASA launches Landsat 7 in 1999. NASA launches Landsat 7 in 1999.

Landsat 5 continued to operate until Landsat 7 Landsat 5 continued to operate until Landsat 7 became operational. It worked for 15 years! 12 became operational. It worked for 15 years! 12 years beyond its designed lifespan!years beyond its designed lifespan!

Landsat 7: Modest improvements over Landsat Landsat 7: Modest improvements over Landsat 5. Fed govt manages; committed to maintaining 5. Fed govt manages; committed to maintaining system for decades system for decades

The Future of Remote Sensing?

The Earth Observing System (EOS) era: The Earth Observing System (EOS) era: lots of new sensors (15m-5km spatial lots of new sensors (15m-5km spatial resolution)resolution)

Commercial Remote Sensing finds a niche: Commercial Remote Sensing finds a niche: high spatial resolution data (0.6-4m); high spatial resolution data (0.6-4m); IKONOS, Quickbird, othersIKONOS, Quickbird, others

LIDARLIDAR

The metamorphosis of a Remote Sensing Scientist Up until the 1980s, the field of RS was dominated Up until the 1980s, the field of RS was dominated

by engineers and physicistsby engineers and physicists 1970s: RS scientists began to talk to agronomy 1970s: RS scientists began to talk to agronomy

departments; first practical applications of RS departments; first practical applications of RS were in agriculture. Crops are an ideal “target” were in agriculture. Crops are an ideal “target” (single species, uniform spacing, etc.)(single species, uniform spacing, etc.)

1980s: RS scientists began to talk to ecologists; 1980s: RS scientists began to talk to ecologists; application of RS to “natural” plant communites; application of RS to “natural” plant communites; no more single species stands, no more single species stands, much more much more difficult!difficult! First real “ground truth” First real “ground truth”

The metamorphosis of a Remote Sensing Scientist: Costs melt away 1980s: It took at least a half million dollars worth 1980s: It took at least a half million dollars worth

of hardware, customized software and several full-of hardware, customized software and several full-time programmers to do RStime programmers to do RS

By the early 1990s: $5000-10,000 worth of By the early 1990s: $5000-10,000 worth of hardware (UNIX or PCs) and commercially hardware (UNIX or PCs) and commercially available software made it possible for a much available software made it possible for a much wider array of scientists from a wider array of scientists from a much widermuch wider array array of fields to get involved with RS.of fields to get involved with RS.

2000: lots of free imagery, cheap computers and 2000: lots of free imagery, cheap computers and softwaresoftware

Wide use of RS in archeology, agriculture, Wide use of RS in archeology, agriculture, forestry, geography, environmental science, forestry, geography, environmental science, ecology, oceanography, geology and many others.ecology, oceanography, geology and many others.

Where are we now? Good news and bad news. Wide use of RS in archeology, agriculture, forestry, Wide use of RS in archeology, agriculture, forestry,

geography, environmental science, ecology, geography, environmental science, ecology, oceanography, geology and many others.oceanography, geology and many others.

Low cost and high availability of RS imagery Low cost and high availability of RS imagery means that many people are using these data means that many people are using these data without any understanding of what they are doing. without any understanding of what they are doing. Lots of misuse! Lots of misuse!

RS is more than eyeballing pretty pictures!RS is more than eyeballing pretty pictures! Training is needed to insure proper use of these Training is needed to insure proper use of these

data. data.

Elements of Resolution Spatial resolutionSpatial resolution: smallest entity on the ground : smallest entity on the ground

that can be examined by the sensor; the “pixel that can be examined by the sensor; the “pixel size” or grid cell size.size” or grid cell size.

Temporal resolutionTemporal resolution: how frequently can the : how frequently can the sensor obtain repeat coverage of a given location? sensor obtain repeat coverage of a given location? (e.g., daily, monthly)(e.g., daily, monthly)

Spectral resolutionSpectral resolution: the number of different : the number of different portions of the EM spectrum that can be portions of the EM spectrum that can be simultaneously monitored by the sensorsimultaneously monitored by the sensor

Radiometric resolutionRadiometric resolution: the number of “shades : the number of “shades of gray” a sensor can recognize of gray” a sensor can recognize

Tucker et al. 1985

Lillesand & Kiefer

1100m

80m

30m

15m

20m

10m

WRS Overlay for NW Washington

High Spatial Resolution Satellites: a Niche for Commercial Remote Sensing

IKONOS (Space Imaging)IKONOS (Space Imaging) Launched Sept. 1999Launched Sept. 1999 1m Panchromatic: 0.45 – 0.90 1m Panchromatic: 0.45 – 0.90 µmµm 4m multispectral: 0.45-0.52, 0.52-0.60, 0.63-0.69, 4m multispectral: 0.45-0.52, 0.52-0.60, 0.63-0.69,

0.76-0.90 µm (same as TM bands #1-4)0.76-0.90 µm (same as TM bands #1-4) Swath width 13kmSwath width 13km Revisit freq: 2.9 days with off-nadir pointing (up Revisit freq: 2.9 days with off-nadir pointing (up

to 26 degreesto 26 degrees Cost of about $80/square mileCost of about $80/square mile

The cost of high spatial resolution: very high data volumes! Sometimes less is more. Sometimes less is more. How How

many pixels does it take to many pixels does it take to cover a hypothetical study cover a hypothetical study area of 100km by 100km?area of 100km by 100km?

This is the minimum number This is the minimum number of individual data values that of individual data values that would be would be required for required for each each band!band!

High data volume incurs a High data volume incurs a high cost for both storage and high cost for both storage and processingprocessing

Low spatial resolution makes Low spatial resolution makes it practical to study larger it practical to study larger spatial extents; e.g. global spatial extents; e.g. global rather than regional rather than regional

SensorSensor # pixels/band# pixels/band

IKONOS 1mIKONOS 1m 10 billion10 billion

IKONOS 4mIKONOS 4m 625 million625 million

SPOT 10mSPOT 10m 100 million100 million

SPOT 20mSPOT 20m 25 million25 million

TM 30mTM 30m 11 million11 million

MSS 80mMSS 80m 1.6 million1.6 million

AVHRR 1kmAVHRR 1km ~8200~8200

AVHRR 4kmAVHRR 4km ~550~550

Other Coarse-resolution Sensors

Moderate Resolution Imaging Spectrometer Moderate Resolution Imaging Spectrometer (MODIS): a key instrument on TERRA, part of (MODIS): a key instrument on TERRA, part of the Earth Observing System (EOS)the Earth Observing System (EOS)

MODIS

Two in operation (on EOS-AM and EOS-PM) Two in operation (on EOS-AM and EOS-PM) launched in 1999 and 2002, respectivelylaunched in 1999 and 2002, respectively

36 spectral bands from 0.4-14.4 36 spectral bands from 0.4-14.4 µmµm 2 bands at 250m resolution2 bands at 250m resolution 5 bands at 500m resolution5 bands at 500m resolution 29 bands at 1km resolution29 bands at 1km resolution

Radiometric resolution: 12-bitRadiometric resolution: 12-bit 2300km swath width2300km swath width 1-2 day repeat cycle1-2 day repeat cycle

http://modis.gsfc.nasa.gov/about/design.html

Summary: 3 broad categories of spatial resolution available High resolution (0.6-4m)High resolution (0.6-4m)

IKONOS, Quickbird, OrbviewIKONOS, Quickbird, Orbview expensive!expensive!

Moderate (10-80m)Moderate (10-80m) MSS, TM, SPOT, AsterMSS, TM, SPOT, Aster Free to cheapFree to cheap

Low (250m – 4km)Low (250m – 4km) AVHRR, MODISAVHRR, MODIS Free to cheapFree to cheap

End

The Electromagnetic Spectrum

μm = micrometer = 10-6 meters

The micrometer is the most common unit used to quantify the wavelength of EM energy