Module 4 Assessment Flashcards
(34 cards)
Which of the following change detection approaches does not require the selection of a threshold value?
Comparison of two classified maps created for different time periods
An active microwave/radar sensor which uses the motion of the carrying aircraft of spacecraft to simulate a larger antenna is known as what?
a. Fully coherent radar system
b. dual or quad-pol system
c. Passive microwave radiometer
d. Synthetic Aperture Radar (SAR)
d. Synthetic Aperture Radar (SAR)
Yes, the spatial resolution of a microwave imaging system is controlled by the antenna size. Synthetic aperture radars simulate a large antenna using the motion of the carrying craft.
This is a form of SAR terrain distortion where the backscatter from sensor facing slopes is received at close to the same time, causing these slopes to appear steeper and brighter
a. Layover
b. Foreshortening
c. Shadow
d. Speckle
b. Foreshortening
Yes, foreshortening compresses the backscatter from a large area on the sensor facing slope into a shorter distance, causing it to appear steeper and brighter
This type of sensor makes hundreds to thousands of measurements in narrow portions of the EM spectrum
a. Hyperspectral sensor
b. Multispectral sensor
c. Full waveform lidar
d. Quad-pol SAR instrument
a. Hyperspectral sensor
Correct, most hyperspectral sensors make at least a few hundred measurements in wavelength windows not wider than about 10 nm
The analysis of the coherence between two SAR images taken of the same place but at different times, yielding information about the surface displacement is called what?
a. Two-date backscatter ratio
b. Cross polarized fraction
c. SAR altimetry
d. SAR Interferometry
Yes, SAR Interferometry analyzes changes in the phase of backscattered radiation in order to measure the displacement of the Earth’s surface. In this way, very small (ca. 1 cm or less) changes in the surface can be accurately measured.
d. SAR Interferometry
Yes, SAR Interferometry analyzes changes in the phase of backscattered radiation in order to measure the displacement of the Earth’s surface. In this way, very small (ca. 1 cm or less) changes in the surface can be accurately measured.
Question with image
Question with image
GEDI is an example of this type of lidar system that is capable of detailed measurement of the vertical distribution of vegetation, for example, on Earth’s surface.
a. Discrete return green wavelength lidar
b. Full waveform lidar
c. Quad-pol SAR system
d. Orbital hyperspectral radiometer
b. Full waveform lidar
Yes, by measuring the intensity of the entire returned lidar pulse, GEDI and other full waveform lidar systems can accurately measure the vertical distribution of biomass within the lidar footprint
Radar vegetation indices take advantage of which property of the interaction of microwaves with Earth’s surface?
a. Interferometric analysis of the phase coherence between images at different times
b. Strong double-bounce scattering within tree crowns
c. The tendency of vegetation crowns to depolarize microwave radiation
d. The tendency of healthy chloroplasts to strongly reflect NIR radiation
c. The tendency of vegetation crowns to depolarize microwave radiation
Yes, both the RVI and RFDI measure the relative amount of depolarized microwave radiation
Which of the following resolutions is most important in most marine remote sensing applications?
a. Spatial
b. Polarization
c. Spectral
d. Radiometric
d. Radiometric
Yes, because water is so dark having more values of brightness to distinguish is very helpful
Which of the following is not a reason that passive microwave sensors have been so useful in monitoring polar sea ice?
a. They have very high spatial resolution and so can monitor sea ice distributions on the scale of 10s of meters
b. The ability of microwaves to penetrate clouds in the atmosphere is useful because the poles are often cloudy
c. Microwave sensors measure emitted radiation which is critical because it is dark at least half the year at the poles and so reflected solar radiation is not very abundant.
d. Differences in emissivity across different microwave frequencies allows for the discrimination of different types of snow and ice (e.g. wet vs dry and old vs new)
a. They have very high spatial resolution and so can monitor sea ice distributions on the scale of 10s of meters
Correct. In fact, passive microwave sensors have very coarse spatial resolution, typically 10s of kilometers
Which of the following surfaces would create the strongest/highest backscatter value for an C-band system?
a. Soybean field after crops have emerged
b. Smooth open water
c. Soybean field before crops have emerged
d. Flat sand beach
a. Soybean field after crops have emerged
Yes, in comparison to the others, this would be the roughest surface and so would have a higher proportion of diffuse scattering. This results in the strongest backscattered portion and the stronges/highest measurement
Evaluate whether the following statement is true or false: “Classification-based change detection methods typically overmap change because each classification error is likely to result in a spurious change detection.”
True - Classification errors are typically random and they may differ in location in two different classified maps. This means that each place could be incorrectly mapped as change. Overall, this leads to more change being mapped than occurred in reality. Therefore this is a true statement
The measurement made by an active microwave sensor that quantifies the portion of EM energy returned in the direction of the sensor is known as?
a. Backscatter
b. Interferometry
c. Coherence
d. Dielectric constant
a. Backscatter
Yes, backscatter is very similar in concept to surface reflectance in the optical wavelengths
Select all of the characteristics associated with microwave remote sensing
a. All orbital microwave sensors are active sensors
b. Microwaves have much longer wavelengths relative to optical bands
c. Microwaves are relatively unaffected by the atmosphere and so can “see” through clouds
d. Microwave remote sensing is useful for mapping ocean color (e.g. for chlorophyll)
e. Microwave backscatter is sensitive to both structural and electrical properties of the surfaces with which they interact
b. Microwaves have much longer wavelengths relative to optical bands
Yes, microwaves have longer wavelengths than optical sensors. Also, the backscatter varies with the structural properties of a surface as well as its dielectric properties, and measurements are relatively unaffected by clouds.
c. Microwaves are relatively unaffected by the atmosphere and so can “see” through clouds
Yes, measurements are relatively unaffected by clouds. Also, the backscatter varies with the structural properties of a surface as well as its dielectric properties, and microwaves have longer wavelengths than optical sensors
e. Microwave backscatter is sensitive to both structural and electrical properties of the surfaces with which they interact
Yes, backscatter varies with the structural properties of a surface as well as its dielectric properties. Also, microwaves have longer wavelengths and are relatively unaffected by clouds.
Which of the following are image-to-image differences that must be controlled for in a change detection analysis?
a. Sun-sensor geometry
b. Atmospheric differences
c. Spatial registration
d. Plant phenology
e. All of these
e. All of these
Indeed, all of these are typically considered incidental changes which we would not want to map as change
Which of the following measurements would most likely only be possible with a hyperspectral instrument?
a. Surface displacement following an earthquake
b. Vertical distribution of foliage
c. Leaf nitrogen concentration
d. Land cover/use change
c. Leaf nitrogen concentration
Yes, detailed biochemical measurements like this are usually only able to be done using very narrow wavelength measurements.
SAR instruments used for Earth observation are always side-looking, meaning they transmit and receive at an oblique angle rather than straight down. Why?
a. In order to measure the sides of objects
b. To increase the path distance through the atmosphere
c. To eliminate left-right ambiguity
d. To not interfere with the return signal
c. To eliminate left-right ambiguity
Yes, if transmitting straight down, there’d be no way to distinguish a return that came from the same distance on either the left or right of the sensor.
This type of SAR terrain distortion increases with look angle and causes entire portions of the image to be missing data
a. Foreshortening
b. Layover
c. Speckle
d. Radar shadow
d. Radar shadow
Yes, slopes facing away from the sensor may be shadowed by the sensor-facing slope and not receive any transmitted radiation. Thus, no measurements can be made in these areas.
Evaluate whether the following statement is true or false: “A lidar altimeter, or laser profiler, is a sensor that sweeps a laser from side-to-side across the angle of travel so as to create a dense, wall-to-wall set of height measurements suitable for mapping”
False
Correct, these are characteristics of a lidar scanner NOT a profiler/altimeter. Laser altimeters do not sweep the laser from side to to side, but instead measure only one or a few transects directly below the aircraft
A lidar system that measures one or more individual heights for each pulse of emitted laser energy is known as this type of system
a. Full waveform lidar
b. Bathymetric lidar
c. NIR laser system
d. Discrete return lidar
Yes, discrete return lidars only provide one or a few measurements of height for each pulse. This is in contrast to waveform lidars which measure the entire returned signal.
d. Discrete return lidar
Yes, discrete return lidars only provide one or a few measurements of height for each pulse. This is in contrast to waveform lidars which measure the entire returned signal.
This type of instrument would be best suited for mapping the terrain below water, which is called bathymetric mapping.
a. Very High Spatial Resolution visible-NIR multispectral instrument
b. NIR wavelength lidar
c. Green wavelength lidar
d. Full coherent SAR system
c. Green wavelength lidar
Yes, a green wavelength lidar system can penetrate much more deeply into the water than an NIR system
A radar/microwave system that can transmit and receive in vertical and horizontal polarizations is known as what?
a. A quad-pol system
b. Fully coherent sensor system
c. Passive radar scanner
d. Radar altimeter
a. A quad-pol system
Yes, there are 4 possible polarization combinations with this system: VV, VH, HH, and HV.
This phenomenon is often seen in remotely sensed imagery of the oceans where variations in surface water roughness can create brighter spots due to preferential reflection in the direction of the satellite sensor
a. Sunglint
b. Diffraction
c. Polarization
d. Eutrophication
a. Sunglint
Correct, sunglint (or “specular” reflections) are caused by illumination-view geometry and the sea state.
