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Chapter 10 How Remote Sensing Works
portions of the visible light spectrum) aside from that shade of green, which
is then being reflected to your eyes.
Different surfaces across Earth have different properties that cause them
to absorb energy wavelengths in various ways. For instance, we see a clear
lake as a blue color—it could be dark blue, lighter blue, maybe even some
greenish blue, but it’s nonetheless a shade of blue. We see it this way because
water strongly absorbs all electromagnetic wavelengths aside from the range
of 0.4 to 0.5 micrometers (with a little lesser absorption past the edges of that
range), which corresponds to the blue portion of the spectrum. Thus, other
wavelengths of energy (such as the infrared portion) get absorbed and the
blue portion gets reflected.
What remote sensing devices are really measuring is the reflectance of
energy from a surface—the energy that rebounds from a target to be collected
by a sensor. Like absorption, different items on Earth’s surface reflect energy
differently. Thus, the total amount of energy that strikes a surface (the incident energy) can be computed by adding up the amounts of energy that was
transmitted, absorbed, and reflected per wavelength by a particular surface
as follows:
I ϭ R ϩ A ϩ T
where I is the incident energy (the total amount of energy of a particular
wavelength) that strikes a surface and is made up of the amount of R (reflection), A (absorption), and T (transmittance) of that particular wavelength.
Since remote sensing is focused on the reflection of energy per wavelength,
let’s change that equation to focus on calculating what fraction of the total
incident energy was reflected (and to turn this value into a percentage instead
of a fractional amount, we’ll multiply by 100):
ϭ (R/I) ϫ 100
where is the portion of the total amount of energy composed by reflection
(rather than absorption or transmittance) per wavelength. This final value is
incident energy the
total amount of energy
(per wavelength)
that interacts with an
object.
The remote sensing processes described in this chapter are systems that measure energy reflection (and
turn it into images) without interfering with what’s
happening below them. For instance, when an aircraft
flies overhead to take pictures or a satellite crosses
over your house (at more than 500 miles above it),
they collect their data and move on. The data collection process doesn’t physically affect you or
your property in the slightest, and all of this is done
without your explicit permission and likely without
your knowledge. If you can see your car in your
driveway on Google Earth, then it just happened to
be parked there when the airplane or satellite collected that image. Does this unobtrusive method of
data collection affect your privacy? Is the acquisition of images via remote sensing invasive to your
private life? In what ways could this use of geospatial technology intrude on someone’s life?
How Does Remote Sensing Affect Your Privacy?
Thinking Critically with Geospatial Technology 10.1
Chapter 10 How Remote Sensing Works
portions of the visible light spectrum) aside from that shade of green, which
is then being reflected to your eyes.
Different surfaces across Earth have different properties that cause them
to absorb energy wavelengths in various ways. For instance, we see a clear
lake as a blue color—it could be dark blue, lighter blue, maybe even some
greenish blue, but it’s nonetheless a shade of blue. We see it this way because
water strongly absorbs all electromagnetic wavelengths aside from the range
of 0.4 to 0.5 micrometers (with a little lesser absorption past the edges of that
range), which corresponds to the blue portion of the spectrum. Thus, other
wavelengths of energy (such as the infrared portion) get absorbed and the
blue portion gets reflected.
What remote sensing devices are really measuring is the reflectance of
energy from a surface—the energy that rebounds from a target to be collected
by a sensor. Like absorption, different items on Earth’s surface reflect energy
differently. Thus, the total amount of energy that strikes a surface (the incident energy) can be computed by adding up the amounts of energy that was
transmitted, absorbed, and reflected per wavelength by a particular surface
as follows:
I ϭ R ϩ A ϩ T
where I is the incident energy (the total amount of energy of a particular
wavelength) that strikes a surface and is made up of the amount of R (reflection), A (absorption), and T (transmittance) of that particular wavelength.
Since remote sensing is focused on the reflection of energy per wavelength,
let’s change that equation to focus on calculating what fraction of the total
incident energy was reflected (and to turn this value into a percentage instead
of a fractional amount, we’ll multiply by 100):
ϭ (R/I) ϫ 100
where is the portion of the total amount of energy composed by reflection
(rather than absorption or transmittance) per wavelength. This final value is
incident energy the
total amount of energy
(per wavelength)
that interacts with an
object.
The remote sensing processes described in this chapter are systems that measure energy reflection (and
turn it into images) without interfering with what’s
happening below them. For instance, when an aircraft
flies overhead to take pictures or a satellite crosses
over your house (at more than 500 miles above it),
they collect their data and move on. The data collection process doesn’t physically affect you or
your property in the slightest, and all of this is done
without your explicit permission and likely without
your knowledge. If you can see your car in your
driveway on Google Earth, then it just happened to
be parked there when the airplane or satellite collected that image. Does this unobtrusive method of
data collection affect your privacy? Is the acquisition of images via remote sensing invasive to your
private life? In what ways could this use of geospatial technology intrude on someone’s life?
How Does Remote Sensing Affect Your Privacy?
Thinking Critically with Geospatial Technology 10.1