Podcast
Questions and Answers
Which characteristic is NOT an element of image interpretation?
Which characteristic is NOT an element of image interpretation?
- Shadow
- Shape
- Color
- Density (correct)
Spatial resolution refers to the largest possible feature that a sensor can detect.
Spatial resolution refers to the largest possible feature that a sensor can detect.
False (B)
Name one factor that increases challenges for remote sensing imagery interpretation.
Name one factor that increases challenges for remote sensing imagery interpretation.
Unfamiliar aerial perspective
The spatial resolution of a sensor is limited by its ______ size.
The spatial resolution of a sensor is limited by its ______ size.
Match the following terms with their definitions:
Match the following terms with their definitions:
What is a key requirement for supervised classification?
What is a key requirement for supervised classification?
Unsupervised classification allows for the analyst to have complete control over class definitions.
Unsupervised classification allows for the analyst to have complete control over class definitions.
What is the primary advantage of using supervised classification?
What is the primary advantage of using supervised classification?
In supervised classification, the purpose of using __________ is to recognize spectrally similar areas for each class.
In supervised classification, the purpose of using __________ is to recognize spectrally similar areas for each class.
Which of the following is a disadvantage of supervised classification?
Which of the following is a disadvantage of supervised classification?
Match the following aspects with their classification types:
Match the following aspects with their classification types:
What is the main goal of accuracy assessment in classification?
What is the main goal of accuracy assessment in classification?
Supervised classification typically requires field work to verify class identification.
Supervised classification typically requires field work to verify class identification.
Which of the following satellite sensors has a 10-meter resolution?
Which of the following satellite sensors has a 10-meter resolution?
Stressed plants reflect more in the NIR compared to healthy plants.
Stressed plants reflect more in the NIR compared to healthy plants.
What is the revisit cycle for the Landsat satellite?
What is the revisit cycle for the Landsat satellite?
___ classification involves grouping similar pixels together based on their attributes.
___ classification involves grouping similar pixels together based on their attributes.
Match the following satellite sensors with their respective properties:
Match the following satellite sensors with their respective properties:
Which factor does NOT influence NDVI readings?
Which factor does NOT influence NDVI readings?
Derivatives of NDVI such as LAI are physical quantities that can be used reliably.
Derivatives of NDVI such as LAI are physical quantities that can be used reliably.
What is the primary function of image classification in remote sensing?
What is the primary function of image classification in remote sensing?
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Study Notes
Supervised Classification
- Analyst defines and selects samples to classify image based on chosen samples
- Training data is used to 'train' the algorithm to recognize spectrally similar areas for each class
- Algorithm determines numerical ‘signatures’ for each training class
- Each pixel is compared to class signatures and labelled as the class it most closely resembles
- Requires ancillary data (maps, photos, etc)
- Field work is often needed to verify
- Analyst has control over the selected classes, tailored to the purpose
- Disadvantage: Analyst imposes a classification that may not be natural.
Unsupervised Classification
- Requires no prior knowledge of the region
- Human error is minimized
- Unique classes are recognized as distinct units
- Disadvantage: Classes may not necessarily match informational categories of interest
Accuracy Assessment
- Measure of how well a classification worked
- Determination of class types at specific locations
- Compare reference to classified map
- Indicators must be sufficiently representative and easy to understand and measure on a routine basis
Vegetation Spectral Reflectance Curves
- Healthy plants reflect highly in the NIR
- Stressed plants reflect less in NIR
- Healthy plants absorb well in the SWIR regions
- Stressed plants absorb less in the SWIR
Spectral Indices
- NDVI is an example of a spectral index
- NDVI saturates over dense vegetation
- Any factor that unevenly influence the red and NIR reflectance will influence the NDVI
Satellite Sensors and their properties
- Landsat images are free of charge and have a 16-day revisit cycle
- Sentinel images are free of charge with a 12-day revisit cycle
- MODIS images have a 1-2 day revisit cycle and are free of charge
- Worldview-2, IKONOS, and Quickbird are all charge-based services
Image Classification
- Science of turning remotely sensed data into meaningful categories representing surface features or classes
- Assigning pixels to classes
- Group similar pixels together
- Classifications are divided into two: Terrestrial and Non-Terrestrial
Visual Image Interpretation
- We make sense of what we see by interpreting a large variety of elements in visual scenes
- Remote sensing imagery has increased challenges due to an unfamiliar perspective, the use of wavelengths outside the visual spectrum, unfamiliar scales and resolutions
- Elements include: Shape, size, pattern, shadow, and texture
Sensor Characteristics
- The ability of the sensor to identify features depends on 4 types of resolutions: spatial, spectral, temporal, and radiometric
- Spatial resolution refers to the size of the smallest possible feature that can be detected.
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