Chapter 1 History and Scope of Remote Sensing

Report
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
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Lillesand and Kiefer
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.
Spectral Reflectance Curves
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Visible portion of EM
spectrum
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Lillesand and Kiefer
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.
Practical Experience with Remote
Sensing: Vision
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Your eyes are extraordinarily effective remote sensing
devices.
Each of you have 20+ years of experience using “data”
generated by your eyes to make inferences about the
world around you
Color, texture and context provide valuable clues
Your eyes gather data using only the visible part of the
EM spectrum
The field of remote sensing involves the use various
sensors to extend your ability to monitor the world
around you
Remote Sensing: Defined
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General: “..it is the art or science of telling
something about an object without being in
direct contact with it.” (Fisher et al. 1976;
from Table 1.1 of your text)
Remote Sensing: Defined
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More specific: “Remote sensing is the
practice of deriving information about the
earth’s land and water surface using images
acquired from an overhead perspective,
using electromagnetic radiation in one or
more regions of the electromagnetic
spectrum, reflected or emitted from the
earth’s surface.” (Campbell)
Remote Sensing: Defined
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More cynical? More fun? More accurate?
“Remote sensing is the art of dividing up
the world into multicolored squares and
then playing endless computer games with
them to release unbelievable potential that
is always just out of reach.”
Milestones in Remote Sensing
1920-30: routine use of aerial photos by
various government agencies
 1939-45: WWII and the development and
use of Infrared film. Unlike conventional
film, IR film is sensitive to EM energy in
the near Infrared portion of the EM
spectrum. Why might this be useful during
wartime?
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Spectral Reflectance Curves: What are the
unique features of vegetation?
Lillesand and Kiefer
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Vegetation is “dark” (low reflectance) in the visible
part of the spectrum and very bright in the near IR
Kodak advertisement circa 1943: two
photographs using conventional film
N. Short tutorial
The same site with Infrared film
N. Short tutorial
IR film is also referred to as
“Camouflage Detection” or CD film
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
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Post WWII: Extensive use of air photos (conventional and
IR) during war spilled over into extensive civilian
applications after the war.
1950s: extensive application of IR film to agricultural
monitoring
1950-60: Extensive R&D by military on use of RS for
intelligence gathering. This was done in secret but older
technology made its way into the civilian sector.
1960s: lots of developments, including First moves from
photographic to digital multispectral scanners. This
facilitates the move away from subjective
photointerpretation to more objective statistically based
image classification.
Milestones in Remote Sensing
1972: The launch of the Earth Resources
Technology Satellite (ERTS-A); later
renamed LANDSAT I. This was the first
satellite dedicated to civilian remote
sensing.
 A fork in the road: civilian and military RS
head in different directions.
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Milestones in Remote Sensing
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Launch of Landsat I represented a fork in
the road: civilian and military RS head in
different directions
 Civilian RS: moderate spatial resolution
sensors and a focus on “regional” studies.
A standard Landsat scene is 185 km X
185 km. Great for things like crop
monitoring.
 Military RS: focus on very high spatial
resolution. Imagery of planes, military
installations etc.
Milestones in Remote Sensing
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1970s: lots of basic research in RS and lots
of new applications for Landsat data.
Launch of Landsat 2 and 3 to keep up with
demand. Modest improvements with each
launch.
Milestones in Remote Sensing
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1980s: Two parallel lines of development:
 Improved sensor for Landsat 4; the
Thematic Mapper (TM) that was
optimized for vegetation RS based on
basic research done during the 1970s
 Delays in development of Landsat 4
suggested that there might be a window
during which there would be no
operational Landsat.
 This lead to “discovery” that operational
meteorological satellites could be used
for vegetation RS
Milestones in Remote Sensing
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1980s: (continued): NOAA
meteorological satellites have very low
spatial resolution (1-4km vs. 30-80m for
the sensors carried by Landsat) but this
also enables them to image much larger
areas (swath width of over 2000km vs.
185 km for Landsat). Data from these
sensors can be used to address different
questions, especially those related to
global climate change
Milestones in Remote Sensing
Mid-1980s: Hyperspectral data;
measurements in hundreds of very narrow
parts of the EM spectrum. All previous
sensors take measurements in 3-7 broad
portions of the spectrum. Hyperspectral
data are particularly useful for geological
applications. Airborne only at this time.
Some newer satellites now provide
measurements in about 30-40 bands.
 Privatization of Landsat: creation of
EOSAT, now called Space Imaging. 10X
increase in cost of imagery to users.
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Milestones in Remote Sensing:
Current status of Landsat
Landsat 4 and 5 launched in 1982 and 84
respectively; designed to operate for 3 years.
 EOSAT pledged to fund Landsat 6
 Landsat 6 finally launched in 1993: It crashed.
 Privatization of Landsat widely viewed as a
failure
 Mid-1990s: NASA takes back Landsat; Space
Imaging continues to market older imagery;
NASA launches Landsat 7 in 1999.
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Milestones in Remote Sensing: Current
status of Landsat
Mid-1990s: NASA takes back Landsat; Space
Imaging continues to market older imagery;
NASA launches Landsat 7 in 1999.
 Landsat 5 continued to operate until Landsat 7
became operational. It worked for 15 years! 12
years beyond its designed lifespan!
 Landsat 7: Modest improvements over Landsat
5. Fed govt manages; committed to maintaining
system for decades
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The Future of Remote Sensing?
The Earth Observing System (EOS) era: lots
of new sensors (15m-5km spatial
resolution)
 Commercial Remote Sensing finds a niche:
high spatial resolution data (0.6-4m);
IKONOS, Quickbird, others
 LIDAR
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The metamorphosis of a Remote
Sensing Scientist
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Up until the 1980s, the field of RS was dominated
by engineers and physicists
1970s: RS scientists began to talk to agronomy
departments; first practical applications of RS
were in agriculture. Crops are an ideal “target”
(single species, uniform spacing, etc.)
1980s: RS scientists began to talk to ecologists;
application of RS to “natural” plant communites;
no more single species stands, much more
difficult! First real “ground truth”
The metamorphosis of a Remote
Sensing Scientist: Costs melt away
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1980s: It took at least a half million dollars worth
of hardware, customized software and several fulltime programmers to do RS
By the early 1990s: $5000-10,000 worth of
hardware (UNIX or PCs) and commercially
available software made it possible for a much
wider array of scientists from a much wider array
of fields to get involved with RS.
2000: lots of free imagery, cheap computers and
software
Wide use of RS in archeology, agriculture,
forestry, geography, environmental science,
ecology, oceanography, geology and many others.
Where are we now? Good news and
bad news.
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Wide use of RS in archeology, agriculture, forestry,
geography, environmental science, ecology,
oceanography, geology and many others.
Low cost and high availability of RS imagery
means that many people are using these data
without any understanding of what they are doing.
Lots of misuse!
RS is more than eyeballing pretty pictures!
Training is needed to insure proper use of these
data.
Elements of Resolution
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Spatial resolution: smallest entity on the ground
that can be examined by the sensor; the “pixel
size” or grid cell size.
Temporal resolution: how frequently can the
sensor obtain repeat coverage of a given location?
(e.g., daily, monthly)
Spectral resolution: the number of different
portions of the EM spectrum that can be
simultaneously monitored by the sensor
Radiometric resolution: the number of “shades
of gray” a sensor can recognize
Tucker et
al. 1985
1100m
80m
30m
15m
20m
10m
Lillesand & Kiefer
WRS Overlay for NW Washington
High Spatial Resolution Satellites: a
Niche for Commercial Remote Sensing
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IKONOS (Space Imaging)
 Launched Sept. 1999
 1m Panchromatic: 0.45 – 0.90 µm
 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)
 Swath width 13km
 Revisit freq: 2.9 days with off-nadir pointing (up
to 26 degrees
 Cost of about $80/square mile
The cost of high spatial resolution:
very high data volumes!
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Sometimes less is more.
How many pixels does it
take to cover a
hypothetical study area of
100km by 100km?
This is the minimum
number of individual data
values that would be
required for each band!
High data volume incurs a
high cost for both storage
and processing
Low spatial resolution
makes it practical to study
larger spatial extents; e.g.
global rather than regional
Sensor
# pixels/band
IKONOS 1m
10 billion
IKONOS 4m
625 million
SPOT 10m
100 million
SPOT 20m
25 million
TM 30m
11 million
MSS 80m
1.6 million
AVHRR 1km
~8200
AVHRR 4km
~550
Other Coarse-resolution Sensors
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Moderate Resolution Imaging Spectrometer
(MODIS): a key instrument on TERRA, part of
the Earth Observing System (EOS)
MODIS
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Two in operation (on EOS-AM and EOS-PM)
launched in 1999 and 2002, respectively
36 spectral bands from 0.4-14.4 µm
 2 bands at 250m resolution
 5 bands at 500m resolution
 29 bands at 1km resolution
Radiometric resolution: 12-bit
2300km swath width
1-2 day repeat cycle
http://modis.gsfc.nasa.gov/about/design.html
Summary: 3 broad categories of
spatial resolution available
High resolution (0.6-4m)
 IKONOS, Quickbird, Orbview
 expensive!
 Moderate (10-80m)
 MSS, TM, SPOT, Aster
 Free to cheap
 Low (250m – 4km)
 AVHRR, MODIS
 Free to cheap
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End
The Electromagnetic Spectrum
μm = micrometer = 10-6 meters
The micrometer is the most common unit used to quantify the
wavelength of EM energy

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