GEOG 201
1. Discuss the following terms as applied to remote sensing
a. Electromagnetic Spectrum (EMS)
The electromagnetic spectrum is the complete range of all possible frequencies and wavelengths
of electromagnetic radiation. It extends from very short-wavelength, high-frequency gamma rays
to very long-wavelength, low-frequency radio waves. In remote sensing, the EMS is fundamental
because different features on the Earth's surface interact with specific wavelengths in different
ways, allowing sensors to identify and analyze them.
b. Electromagnetic Radiation (EMR)
Electromagnetic radiation refers to the energy that is propagated through space or a material
medium in the form of electromagnetic waves. This energy is the primary information carrier in
remote sensing, as sensors record the radiation reflected or emitted from the Earth's surface.
EMR can be described by its wavelength, frequency, and amplitude.
c. Frequency
Frequency (often denoted as *v* or *f*) is the number of wave crests that pass a fixed point in a
given period of time. It is typically measured in cycles per second, or Hertz (Hz). Frequency is
inversely proportional to wavelength, meaning that shorter wavelengths have higher frequencies
and vice versa.
d. Wavelength
Wavelength (λ) is the distance between successive wave crests or between any two
corresponding points on consecutive waves. It is usually measured in units such as micrometers
(μm) or nanometers (nm) in the optical range, and centimeters (cm) for microwave radiation. The
relationship between wavelength (λ), frequency (*v*), and the speed of light (*c*) is expressed
by the formula: c = λ * v.
2, Highlight classes of electromagnetic radiation. Indicating their wavelength ranges
i. Gamma rays have the shortest wavelengths, generally less than 0.03 nanometers (nm).
They carry very high energy and are completely absorbed by the Earth’s atmosphere.
Therefore, they are not used in remote sensing of the Earth’s surface.
, ii. X-rays occupy the region from about 0.03 nm to 30 nm. Like gamma rays, X-rays are
absorbed by the atmosphere and are not used for normal Earth remote sensing, although
they are important in astronomy and medical imaging.
iii. Ultraviolet (UV) radiation extends from about 0.03 micrometres (μm) to 0.4 μm. In
remote sensing, the portion below about 0.3 μm is absorbed by ozone in the upper
atmosphere. The useful UV window for remote sensing is therefore approximately 0.3–
0.4 μm. This region can be used to study certain atmospheric gases, pollutants, and some
geological materials, but it is less commonly used than visible and infrared bands.
iv. Visible radiation covers the wavelength range from about 0.4 μm to 0.7 μm. This is the
portion of the spectrum that the human eye can detect. It is commonly subdivided into
blue (about 0.4–0.5 μm), green (about 0.5–0.6 μm), and red (about 0.6–0.7 μm). Visible
wavelengths are widely used in remote sensing because they provide information similar
to what we see in photographs, including the colour, texture, and appearance of land
cover, water, and vegetation.
v. Infrared (IR) radiation lies between about 0.7 μm and 100 μm. It is usually divided
into smaller sub-regions. Reflected infrared covers approximately 0.7–3.0 μm, and
within it the near-infrared (NIR) region, about 0.7–1.3 μm, is especially important for
vegetation studies because healthy plants reflect strongly in NIR. Thermal infrared
covers roughly 3.0–14 μm and is used to measure emitted heat or temperature. Thermal
IR cannot be recorded by ordinary photographic film and requires special thermal
sensors.
vi. Microwave radiation covers approximately 0.1 cm to 100 cm, which is the same as 1
mm to 1 m. Microwaves are very useful in remote sensing because they can penetrate
clouds, fog, and light rain. They are used by both passive microwave sensors and active
radar systems. Microwave remote sensing is important for measuring soil moisture, ocean
winds, sea ice, and surface topography.
vii. Radio waves have wavelengths longer than about 100 cm (1 m). They are not normally
used for remote sensing of the Earth’s surface, although they are used in radio astronomy
and communication.
3. Discuss the significance of the Electromagnetic Spectrum in Remote Sensing
The electromagnetic spectrum is the cornerstone of remote sensing. Its significance can be
summarized as follows:
i. Information Carrier: Electromagnetic radiation acts as the primary carrier of
information from the target to the sensor, allowing data to be collected over distances of
tens to thousands of kilometers.
1. Discuss the following terms as applied to remote sensing
a. Electromagnetic Spectrum (EMS)
The electromagnetic spectrum is the complete range of all possible frequencies and wavelengths
of electromagnetic radiation. It extends from very short-wavelength, high-frequency gamma rays
to very long-wavelength, low-frequency radio waves. In remote sensing, the EMS is fundamental
because different features on the Earth's surface interact with specific wavelengths in different
ways, allowing sensors to identify and analyze them.
b. Electromagnetic Radiation (EMR)
Electromagnetic radiation refers to the energy that is propagated through space or a material
medium in the form of electromagnetic waves. This energy is the primary information carrier in
remote sensing, as sensors record the radiation reflected or emitted from the Earth's surface.
EMR can be described by its wavelength, frequency, and amplitude.
c. Frequency
Frequency (often denoted as *v* or *f*) is the number of wave crests that pass a fixed point in a
given period of time. It is typically measured in cycles per second, or Hertz (Hz). Frequency is
inversely proportional to wavelength, meaning that shorter wavelengths have higher frequencies
and vice versa.
d. Wavelength
Wavelength (λ) is the distance between successive wave crests or between any two
corresponding points on consecutive waves. It is usually measured in units such as micrometers
(μm) or nanometers (nm) in the optical range, and centimeters (cm) for microwave radiation. The
relationship between wavelength (λ), frequency (*v*), and the speed of light (*c*) is expressed
by the formula: c = λ * v.
2, Highlight classes of electromagnetic radiation. Indicating their wavelength ranges
i. Gamma rays have the shortest wavelengths, generally less than 0.03 nanometers (nm).
They carry very high energy and are completely absorbed by the Earth’s atmosphere.
Therefore, they are not used in remote sensing of the Earth’s surface.
, ii. X-rays occupy the region from about 0.03 nm to 30 nm. Like gamma rays, X-rays are
absorbed by the atmosphere and are not used for normal Earth remote sensing, although
they are important in astronomy and medical imaging.
iii. Ultraviolet (UV) radiation extends from about 0.03 micrometres (μm) to 0.4 μm. In
remote sensing, the portion below about 0.3 μm is absorbed by ozone in the upper
atmosphere. The useful UV window for remote sensing is therefore approximately 0.3–
0.4 μm. This region can be used to study certain atmospheric gases, pollutants, and some
geological materials, but it is less commonly used than visible and infrared bands.
iv. Visible radiation covers the wavelength range from about 0.4 μm to 0.7 μm. This is the
portion of the spectrum that the human eye can detect. It is commonly subdivided into
blue (about 0.4–0.5 μm), green (about 0.5–0.6 μm), and red (about 0.6–0.7 μm). Visible
wavelengths are widely used in remote sensing because they provide information similar
to what we see in photographs, including the colour, texture, and appearance of land
cover, water, and vegetation.
v. Infrared (IR) radiation lies between about 0.7 μm and 100 μm. It is usually divided
into smaller sub-regions. Reflected infrared covers approximately 0.7–3.0 μm, and
within it the near-infrared (NIR) region, about 0.7–1.3 μm, is especially important for
vegetation studies because healthy plants reflect strongly in NIR. Thermal infrared
covers roughly 3.0–14 μm and is used to measure emitted heat or temperature. Thermal
IR cannot be recorded by ordinary photographic film and requires special thermal
sensors.
vi. Microwave radiation covers approximately 0.1 cm to 100 cm, which is the same as 1
mm to 1 m. Microwaves are very useful in remote sensing because they can penetrate
clouds, fog, and light rain. They are used by both passive microwave sensors and active
radar systems. Microwave remote sensing is important for measuring soil moisture, ocean
winds, sea ice, and surface topography.
vii. Radio waves have wavelengths longer than about 100 cm (1 m). They are not normally
used for remote sensing of the Earth’s surface, although they are used in radio astronomy
and communication.
3. Discuss the significance of the Electromagnetic Spectrum in Remote Sensing
The electromagnetic spectrum is the cornerstone of remote sensing. Its significance can be
summarized as follows:
i. Information Carrier: Electromagnetic radiation acts as the primary carrier of
information from the target to the sensor, allowing data to be collected over distances of
tens to thousands of kilometers.
