explain four types of revolutions
Answers
The resolution of remote sensed raster data can be characterized in several different ways. There are four primary types of "resolution" for rasters:
Spatial
Spectral
Radiometric
Temporal
Spatial
Spatial resolution is the type of resolution most people are familiar with. Spatial resolution is usually reported as the length of one side of a single pixel. For example Landsat 8 has 30 meter spatial resolution. In other words, a image with 30 meter spatial resolution meas that a single pixel represents an area on the ground that is 30 meters across.In analog imagery (film), the dimension (or width) of the smallest object on the ground that can be distinguished in the imagery defines the spatial resolution. The spatial resolution of a raster is determined by sensor characteristics for digital imagery and film characteristics including field of view, altitude for analog photography.
Spectral
Spectral resolution refers to how many spectral “bands” an instrument records. Spectral resolution is also defined by how “wide” each band is or the range of wavelengths covered by a single band. Black and white photos contain only 1 band that covers the visible wavelengths, color (RGB ) images contain 3 bands and Landsat 8 has a total of 11 bands. For example MODIS has a greater spectral resolution than Landsat 8 because it has 36 relatively narrow bands that cover wavelengths from 0.4 to 14 micrometers. Landsat 8 on the other hand has a total of 11 bands that cover less wavelengths.
Radiometric
Radiometric resolution is how finely a satellite or sensor divides up the radiance it receives in each band. The greater the radiometric resolution the greater the range of intensities of radiation the sensor is able to distinguish and record. Radiometric resolution is typically expressed as the number of bits for each band. Traditionally 8-bit data was common in remote sensed data, newer sensors (like Landsat 8) have 16-bit data products. 8 bits = 28 = 256 levels (usually 0 to 255) 16 bits = 216 = 65,536 levels (0 to 65,535).
Temporal
Remote sensed data represents a snap shot in time. Temporal resolution is the time between two subsequent data acquisitions for an area. This is also known as the “return time” or "revist time". The temporal resolution depends primarily on the platform, for example satellites usually have set return times and while sensors mounted on aircrafts or unmanned aircraft systems ( UAS ), have more varied return times. For satellites the return time depends on the orbital characteristics (low vs high orbit), the swath width and whether or not there is an ability to point the sensor. For example Landsat has a return time of approximately 16 days, while other sensor like MODIS have nearly daily return times.
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