Module 2 Assessment Flashcards
(27 cards)
The region of electromagnetic radiation from 400-700 nm is typically called what?
Visible range
By definition, a “black body” has an emissivity of:
a. pi
b. 0
c. 1
d. 100
c. 1
That’s correct, an emissivity of 1 indicates a perfect radiator
As the temperature of an object increases, the wavelength of peak radiation does what?
a. decreases
b. stays constant
c. increases
a. decreases
Exactly, as the temperature increases the wavelength of peak radiation gets shorter
The surface of the sun has an average temperature of 5,778 K. The Wien constant is 2900 um K. What is the wavelength of peak radiation from the sun?
a. 2 um
b. 500 um
c. 6.3x107 um
d. 0.5 um
d. 0.5 um
Yes, this corresponds to green light
The total radiation emitted from a black body is controlled by what?
a. Temperature and wavelength of peak radiation
b. It’s distance from the sun
c. The amount of atmospheric scattering
d. Only it’s temperature
d. Only it’s temperature
Indeed, the total emitted radiation increases proportional to the fourth power of the temperature
Which of the following is true?
a. Compared to Earth, the sun emits more overall radiation and has a shorter wavelength of peak radiation
b. Compared to Earth, the sun will emit less overall radiation and will have a longer wavelength of peak radiation
c. Compared to Earth, the sun will emit less overall radiation and will have a shorter wavelength of peak radiation
d. Compared to Earth, the sun will emit more overall radiation and has a longer wavelength of peak radiation
a. Compared to Earth, the sun emits more overall radiation and has a shorter wavelength of peak radiation
Yes, since the sun is much hotter than Earth, Wien’s Law and the Stefan-Boltzmann law tell us that it will emit more radiation and the peak radiation will have a shorter wavelength
why do most satellite Earth observing sensors not make measurements of radiance at wavelengths smaller than 0.3 um?
a. Absorption at these wavelengths, primarily from ozone, makes the atmosphere mostly opaque
b. Because the sun is so hot, very little radiation is emitted at these fine wavelengths
c. There is little value for Earth applications in measuring these wavelengths
d. Consistently manufacturing detectors that are sensitive to these wavelengths has proven very challenging and expensive
a.
Absorption at these wavelengths, primarily from ozone, makes the atmosphere mostly opaque
Exactly, very little UV and finer wavelengths of radiation make their way through the atmosphere, thankfully
The digital numbers (DNs) that are transmitted from the satellite can be converted to which quantity using sensor-specific calibration equations?
a. surface reflectance
b. radiance
c. TOA reflectance
d. emissivity
b. radiance
Yes, the DNs are proportional to radiance and we can obtain that using simple linear calibration equations
True or false: A TOA reflectance image will typically be brighter than the same image converted to surface reflectance
True - Because of path radiance, the sensor will typically record more radiation than has actually reflected off of the target, particularly at shorter wavelengths
The correct answer is ‘True’.
When EM radiation interacts with particles that are much smaller than the wavelengths of the EM radiation, what process can occur?
a. Mie scattering
b. Rayleigh scattering
c. Anisotropic scattering
d. Chlorophyll fluorescence
b. Rayleigh scattering
Correct, Rayleigh scattering is the process whereby particles that are much smaller than the wavelengths of the EM radiation absorb and reemit the radiation
Which atmospheric scattering process is isotropic and wavelength dependent?
a. Mie scattering
b. Rayleigh scattering
b. Rayleigh scattering
Exactly. Rayleigh scattering reemits absorbed photons in every direction with equal probability (isotropy) and affects shorter wavelengths much more than longer wavelengths (wavelength dependence)
True of false: One atmospheric process is responsible for clear skies appearing blue, and a different one is responsible for sunsets appearing orange and red.
False. In fact, it is the same process: Rayleigh scattering
? measures the amount of EM energy that is incident on a surface and has units of Wm-2. ? measures the amount of EM energy that is leaving a surface and has units of Wm-2sr-1.
[irradiance] measures the amount of EM energy that is incident on a surface and has units of Wm-2. [radiance] measures the amount of EM energy that is leaving a surface and has units of Wm-2sr-1.
The biggest difference between TOA reflectance and surface reflectance is that the latter corrects for which process?
a. View and illumination angle
b. Path radiance
c. Non-Lambertian surface reflectance
d. Earth-sun distance
b. Path radiance
Exactly, though path radiance is not the only thing that is corrected, it is the dominant one
A surface that reflects EM energy equally in every direction, or isotropically, is known as what?
a. A Lambertian surface
b. A BRDF
c. A black body
d. Stefan-Boltzmann material
a. A Lambertian surface
Correct, we often assume that Earth surfaces are Lambertian in order to make atmospheric correction easier
An important quantity that describes how much light can be transmitted through the atmosphere, and is necessary for atmospheric correction procedures is called what?
a. path radiance
b. Wien’s constant
c. aerosol optical depth (AOD)
d. coefficient of refraction
c. aerosol optical depth (AOD)
Yes, the AOD describes the transmittance of the atmosphere and is an indicator of how much “stuff” there is in the atmosphere.
Often, Earth surfaces have differing reflectance properties depending on their view and illumination angle. The function that describes this anisotropy in surface reflectance is called what?
a. TOA reflectance
b. The Bidirectional Reflectance Distribution Function (BRDF)
c. Multiple scattering coefficient
d. Wien’s Law
b. The Bidirectional Reflectance Distribution Function (BRDF)
Yes, the BRDF is a mathematical expression of the anisotropy of reflectance depending on view and illumination conditions.
The line or function that describes how different materials uniquely reflect different wavelengths of EM radiation is called what?
a. Bidirectional Reflectance Distribution Function (BRDF)
b. Coefficient of refraction
c. Spectral signature
d. Emissivity
c. Spectral signature
Yes, spectral signatures describes how reflective materials are in different wavelength regions. They are often plotted as a line and can help us distinguish between different surface conditions.
Chart question
Chart question
Chart question
In the RGB additive color model, adding equal amounts of red and green light creates which color?
a. Yellow
b. Brown
c. Cyan
d. Magenta
a. Yellow
Photo comparisons
Considering the process of georegistering a satellite image, which of the following are exclusively internal errors?
a. Terrain distortion, spacecraft altitude changes
b. Atmospheric haze, morphological changes caused by earthquakes
c. Sensor detector degradation, variations in earth-sun distance
d. Sensor optical distortion, rotation of the Earth
d. Sensor optical distortion, rotation of the Earth
