Geography Reference
In-Depth Information
Fig. 2.1 Electromagnetic remote sensing of Earth resources (Source modified from Lillesand
et al.
2008
)
sensor collects information. Spectral density indicates to the number of spectral
bands in an exacting part of the EMS (e.g., the LANDSAT-MSS has only four bands,
while the TERRA-ASTER has 14 bands, etc.). Spatial coverage is the area enclosed
by the image, while spatial resolution indicates to the smallest pixel or picture
element recorded. Temporal coverage is the acquiring period over which the data is
obtainable (e.g., LANDSAT-Sensors have a temporal coverage of 41 years). Tem-
poral resolution relates to the time that the data is obtainable over. It is generally low
by most remote sensing systems. Temporal density refers to the repeat properties of
the satellite. A good repeating in gathering the data would, for some applications,
offer more availability of cloud free data (McVicar and Jupp
1998
). Radiometric
resolution indicates to the active range or number of potential data file values in each
spectral band (the number of bits into which the recorded energy/data is divided).
For example, the total intensity of the energy for 8-bit data is measured from 0 to the
maximum amount of 256 brightness values. Where 0 stands for no energy return,
255 is the maximum return of each pixel (ERDAS
1999
).
A multispectral sensor (e.g., MSS) acquires multiple images of the same target
Earth surface feature (e.g., water, soil, etc.) at different wavelengths (spectral
bands). Each band measures single spectral characteristics about the target (e.g.,
the fourth near infra-red band of MSS is responsible for detection and recoding the
spectral response of the natural vegetation). A spectral band is a data set recorded
by the sensor with information from separate parts of the electromagnetic spec-
trum. One foundation of remote sensing is that LULC-features have different
spectral properties and responses (McVicar and Jupp
1998
). Analysts generate
spectral signatures based upon the detected electromagnetic energy's measurement
and place in the electromagnetic spectrum. A spectral signature contains statistics
that define the spectral characteristic of a target feature or training samples. Image
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