Samenvatting
Remote Sensing GRS-20306 summary 21/22
- Instelling
- Wageningen University (WUR)
Summary of Remote Sensing 21/22
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Summary GRS20306L1 introduction remote sensing
Active = using radiation emitted by objects
Passive = using reflected solar radiation
Wave theory
Electric field and magnetic field created
C= wavelength (m) * frequency (Hz)
Particle theory
- Photons = electromagnetic radiation is described as
discrete particles
- Energy of photons: Q = h x v
The amount of emitted radiation by earth’s surface depends
on wavelength, temperature and emissivity.
MIR = water vapor which blocks solar radiation. Radio waves > 1mm atmosphere does not interfere. >1 cm, you
need radar remote sensing because of transparency.
L2 optical remote sensing
Reflected solar radiation 0.4 to 0.7
(reaches earth’s surface)
Emitted thermal radiation (radiation
emitted by objects)
RS solar radiation (infrared)
Imaging sensor systems
Camera: aerial image plane 2D image
Whiskbroom scanner: scanning earth’s
surface in which the sensor is horizontal.
Mirror could move to have an image from
left to right (1D). motion of forwards
created 2nd dimension image
Push broom: line array detector, line by
line
AD conversion
Number has to be converted to binary numbers 0 1.
8 bits (2^8): 256 digitalization levels. Start with 0 thus 255 digitalization level.
Noise caused by: sensor/imaging system, atmosphere, variability terrain objects.
Spectral resolution
- Band width in nm or hz
- Mid-value = where the sensitivity is half wat the peak ½.
, - Sensitivity curve: 50% width FWHM (full width at half maximum)
- The narrower the spectral band, less photons need to be detected.
Radiometric resolution
Smallest measureable step deltaQ where radiation is reflected
Noise level Qmin
Saturation level Qmax
The pixel size in terms of terrain size and angular aperture.
temporal resolution = recording frequency = time lapse
between two successive images of the same area.
Panchrometic = one wide band, lot of photons can be
detected which results in more resolution.
Pansharpening = use panchrometric image to sharpen the
resolution of a multispectral band. Adjacent pixel not
statistically dependent of each other.
LIDAR = pulses send to earth reflected and returned to the
sensor.
L3 Spectral signatures
Reflection = process of sending back EM
radiation by an object
Soil moisture creates a dip in reflection curve.
The higher the moisture content, the
reflectance decreases. Around 1.4 um and 1.9
um there is water absorption.
LEAF:
- VIS absorptance (In the green there is
more reflectance, therefore leaves
are green colored.
NIR = reflectance (there is not
absorption of infrared, how this
depends on leaf structure.)
- MIR water (absorptance)
Barley the reflectance changes over plant growth. There Is a peak in green, because it reflects relatively more
than blue and red.
Crop grow increase chlorophyll reflectance green and decrease of blue and red. In the NIR green material
increases thus more reflectance. Full grown there is more yellowing less chlorophyll, thus reflectance increases.
When there is yellowing and dying of the crop, the reflectance decreases.
L4 Remote sensing concepts I
Radar = transmits a pulse of EM energy and receives the redirected energy of an object.
Range = the distance that is determined by timing of the echo
, Side looking airborne radar vs down.
ground range resolution
- Ability to separate features on ground
range
- Incidence angle, pulse length
- It improves with increasing distance from
the sensor
Azimuth resolution = ability to separate features on
the ground in azimuth (along track direction)
- Defined by pulse, degrading linearly with
increasing distance between sensor and
ground
SAR = advanced radar system that uses image
processing techniques to synthesize a large
antenna to achieve a higher spatial resolution.
Satellite can have ascending from south to north or
descending.
There are different bands for radar, in which it has
different wavelengths. Polarization is the
orientation of the electrical field. In which there
can be HH, VV, HV, VH.
Optical vs. radar
Advantages radar
- All weather capability
- Day and night, not dependent on sun
- No effects of atmosphere
- Sensitivity to dielectric properties (water content)
- Accurate measurement distance (height, DEM
Disadvantage
- Difficult understanding
- Speckle effects
- Topographic effects
- Pre-processing needed.
L5 accessibility of Earth observation data
Earth observation = collection, processing, modeling and dissemination of data about the earth system.
Application = weather forecast, land cover, biodiversity, disaster monitoring
Developments
More bands and barrow
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