also wach my previous video for atmospheric windows
   • ATMOSPHERIC WINDOWS ✈  
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Spectral reflectance pattern
Different surface features reflect and absorb the
sun’s ​electromagnetic radiation in different ways.
The reflectance properties of an object depend on
the material and its physical and chemical state, the surface
roughness as well as the angle of the sunlight.
The reflectance of a material also varies with the
wavelength of the electromagnetic energy. The amount of reflectance
from a surface can be measured as a ​function of wavelength, this is
referred to as Spectral
Reflectance.
Spectral Reflectance is a measure of how much
energy (as a percent) a surface reflects at a specific wavelength.
Many surfaces reflect different amount of energy in different
portions of the spectrum. These differences in reflectance make it
possible to identify different earth surface features
​or
materials by analyzing their spectral reflectance signatures.
Spectral Reflectance of Earth Surface
Features
Vegetation
In general, healthy vegetation is a very good
absorber of
electromagnetic energy in the visible region.
Chlorophyll strongly absorbs light at wavelengths
around ​0.45 (blue) and 0.67 µm (red) and reflects strongly
in green light, therefore our eyes perceive healthy vegetation as
green.
Healthy plants have a high reflectance in the
nearinfrared between 0.7 and 1.3 µm. This is primarily due to
healthy internal structure of plant leaves.
As this internal structure varies amongst
different plant
​species, the near infrared wavelengths can be used
to discriminate between different plant species.
Water
In its liquid state, water has relatively low
reflectance, with clear water having the greatest reflectance in
the blue portion of the visible part of the spectrum.
​Water has high absorption and virtually no
reflectance in near infrared wavelengths range and beyond.
Turbid water has a higher reflectance in the
visible region than clear water.
This is also true for waters containing high
chlorophyll concentrations.
Ice and Snow
​Ice and snow generally have high reflectance
across all visible wavelengths, hence their bright white
appearance. Reflectance decreases in the near infrared portion and
there is very low reflectance in the SWIR (shortwave infrared). The
low reflection of ice and snow in the SWIR is related to their
microscopic liquid water content.
​Reflectance differs for snow and ice depending on
the actual composition of the material including impurities and
grain size
Soil
Bare soil generally has an increasing reflectance,
with greater reflectance in nearinfrared and shortwave infrared.
Some of the factors affecting soil reflectance are:
​Moisture
content
Soil texture (proportion of sand, silt, and
clay)
Surface roughness Presence of iron oxide Organic
matter content