Remote sensing involves collecting data about objects or areas on Earth through sensors on aircraft or satellites without physical contact. The document discusses the remote sensing process, which includes data acquisition through sensors that detect electromagnetic radiation reflected or emitted from surfaces. Different materials can be identified by analyzing their unique spectral signatures in images across wavelength bands. Resolution of sensors affects the quantity and nature of data collected. Popular satellite examples mentioned are Sentinel-2 and Landsat 8.
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1
remote sensing (RS) is the science or the
technique of deriving information about
objects, area or phenomenon at the Earth
surface through an analysis of the data
(electromagnetic radiations) acquired by a
device which is not in contact with the target
under investigation
RS data basically consists of wavelength
intensity information acquired by collecting
the electromagnetic radiation leaving
(reflected or emitted) the object at specific
wavelength
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sensors mounted on aircraft or satellite platforms
measure the amounts of energy reflected from or
emitted by the earth's surface
the sensors scan the ground below the satellite or
aircraft platform and as the platform moves forward,
an image of the earth's surface is built up
2D image data can be collected by means of two
types of imaging sensors, namely, nadir looking or
side looking sensor
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Muheeb Awawdeh
the nature and properties of the target materials
can be inferred from the recorded electromagnetic
energy that is reflected, scattered or emitted by
these materials on the earth's surface
materials in images are not detected directly
by remote sensing, but their nature inferred is from
the measurements made
Active: operate in the
microwave region of
electromagnetic spectrum (
>1 mm), e.g. (Synthetic
Aperture RADAR (SAR), LASER
Passive:
operates in the visible
and infrared regions of
electromagnetic
spectrum
two types of sensing systems
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The Remote Sensing Process
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The data acquisition process The data analysis process
the data acquisition process comprises 5 elements:
(i) energy sources, (ii) propagation of energy through
the atmosphere, (iii) energy interactions with earth's
surface features (iv) airborne/space borne sensors to
record the reflected energy (v) generation of sensor
data in the form of pictures or digital information.
8
the data analysis process involves examining the
data by (i) visual image interpretation techniques
and (ii) digital image processing techniques
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visual image interpretation involves: tone, texture,
pattern, size and shape, stereoscopic instruments
(3D),and photogrammetric instruments
digital image processing techniques involves
extracting statistical data, classification, edge
Detection, height extraction, band ratioing, etc
reference data (ground truth) is an essential part
of RS data processing to support data for the entire
RS data analysis
reference data is used to:
(i) analyse and interpret remotely sensed data
(ii) calibrate a sensor
(iii) verify information extracted from remote
sensing data
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radiant energy is the energy associated
with electromagnetic radiation (Joule)
radiant flux is the rate of transfer of radiant energy
i.e. energy/time (Joule/s or watt)
irradiance =radiant flux density: it implies
distribution of the radiant energy over a surface i.e.
energy/time/area (Joule/s/m2 or watt/m2)
radiant exitance or radiant emittance is the
amount of light (the radiant flux) emitted by an
area of surface of a radiating body (watt/m2)
radiance (L) is defined as the radiant flux density
transmitted from a small area on the earth's surface
and viewed through a unit solid angle
measured in watts per square meter per
steradian (watt/m2/S)
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a group of particles with different frequencies
travel in a wave form at the speed of light (3x108
m/s).
the EM wave consists of two fields:
the electric field (E) and magnetic field (M)
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Wavelength (): length of one wave cycle (nm, µm, cm,m)
Frequency (): number of cycles of a wave (wave peaks)
passing a fixed point/unit of time (Hertz, Hz). (Hz =one
cycle/s)
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1. Wave Theory
2. Particle Theory (Quantum Theory)
3. Stephan Boltzman Law
4. Wien’s Displacement Law
Radiation Laws
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1. Wave Theory
•EM energy travels in a harmonic, sinusoidal fashion
at the velocity of light (3x108 m/s)
C =
C: speed of light (3x108m/s),
: wavelength (nm, µm, cm, m)
: frequency (cycles/sec, Hz)
when light interacts with matter, it behaves as
though it is composed of many individual bodies
called photons (quanta).
Energy of quantum (Q) = h
where,
h= Planck’s constant (6.626x10-34 Js)
= frequency
2. Particle Theory (Quantum Theory)
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Wavelength
(nm)
Cosmic
Rays
Gamma
Rays
XRays Microwaves
(Radar)
Radio &Television
WavesUV
105
106 107 108 109 1010 1011 1012101
1010‐110‐210‐310‐410‐5
Shorter Wavelengths
HighEnergy
Longer Wavelengths
Low Energy
V / NIR / SWIR /
MWIR / LWIR
OpticalRegion
400 14000
400
0.4
14000
14.0
15003000
1.5 3.0
5000
5.0
700
0.7
SWIR MWIR LWIRB G R NIR LWIR
Wavelength
(nm)
(m)
Reflected Emitted
Energy Energy
the continuum of energy that ranges from meters to nano-
meters in , travels at the speed of light, and propagates
through a vacuum like the outer space (Sabins, 986)
Regions of the EM spectrum
a wavelength interval in the electromagnetic
spectrum is called a band, channel or region
1 m= 1010 Angstrom (Å), 1 m = 109 Nanometer, 1 m =1000 nm
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1) Visible (0.4-0.7m)
-blue (0.4-0.5 m), green (0.5-0.6 m)
and red (0.6-0.7 m) bands
2) Infrared (IR) (0.7-300m)
-reflected IR (0.7-3µm) and thermal IR (3-15m)
3) Microwave or radar (1-300cm)
-most used in the range 5 - 500mm
the wave lengths of greatest interest in RS
gamma rays, X-rays,
and UV-rays are not
used in satellite remote
sensing, because of the
effect of scattering and
absorption
all objects whose
temperature is
greater than an
absolute zero
(273°k), emit radiation
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2018/201912
all electromagnetic radiation detected by a remote
sensor has to pass through the atmosphere twice,
before and after its interaction with earth's
atmosphere
this passage alters the speed, frequency, intensity,
spectral distribution, and direction of the radiation
as a result atmospheric scattering and
absorption occur
most severe in visible and infrared wavelengths
during the transmission of energy through the
atmosphere, light interacts with gases and
particulate matter in a process called atmospheric
scattering:
selective scattering (Rayleigh, Mie and Raman
scattering)
non-selective scattering (independent of
wavelength)
scattering causes a reduction in the image contrast
and introduces radiometric errors
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an absorption band is a range of wavelengths in the
EM spectrum within which radiant energy is absorbed by
a substance
atmospheric windows: areas of the spectrum which
are not severely influenced by atmospheric absorption
and thus, are useful to remote sensors
RS data acquisition is limited to the unblocked spectral
regions
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when EMR from the sun strikes an object, the
energy may be transmitted, absorbed, re-emitted,
reflected or scattered
remote sensors observe earth features mainly by
detecting EMR reflected or emitted from them
different objects reflect, absorb, transmit or emit
EMR in different proportions
Spectral Reflectance Curves
spectral reflectance: the portion of the incoming
radiation that is reflected (0 and 100%)
measured as a function of wavelength
the spectral reflectance curves describe the
spectral response of a target as a function of
wavelength, that depends upon certain factors,
among which nature of the target
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every object on the surface of the earth has its
unique spectral reflectance curve (also called spectral
signature)
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1) Aerial photographs
2) Multispectral and hyperspectral images
3) Thermal IR images
4) Radar images
5) LiDAR point clouds
captured using cameras
mounted on aircraft
detect electromagnetic
radiation in the UV (0.3-0.4
m), visible and near IR (0.7-
0.9 m) regions
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photos or images produced from cameras that
are sensitive to the entire visible band are called
panchromatic
cameras can produce true (normal) color aerial
photographs or false color images (infrared
images)
B&W panchromatic photo
B&W IR photo
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Oblique Aerial
Photographs
Vertical Aerial Photography
20 – 30%
sidelap
oblique photography may be
acquired at the end of a
flightline as the aircraft
banks to turn
Flightline #3
Flightline #2
Block of Aerial Photography
Flightline #1
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aerial photographs are most useful when fine
spatial detail is more important than spectral
information
traditionally, aerial photographs are interpreted
visually, and these results are then digitized into a
GIS
digital aerial photographs can now be processed
directly in a GIS, which makes full use of the
spectral detail contained in the photographs for
feature enhancement and extraction
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multispectral images are usually referred to as the
image data captured by multispectral scanners in
multiple spectral bands of the electromagnetic
spectrum
a multispectral scanner is a scanning system that
uses a set of electronic detectors, each sensitive to
a specific spectral band
the electronic detectors detect and measure the
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interest for each spectra band 9/28/2019
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Scanning Systems
the detected energy is recorded as an electrical
signal, which is then converted to a digital value
scanners produce digital images
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a digital image is actually a raster dataset
each cell in the raster is called a pixel and has a
brightness value, also called a digital number (DN)
DN represents the detected and measured
energy in a given wavelength band, which is
quantized to an 8-bit or l0-bit or a higher-bit
digital number
the higher the reflected or emitted energy a
pixel records, the brighter the pixel is in the image
Matrix of digital numbers in a satellite image
255
200
50
0
150
100
Pixel
values
Gray levels
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Source: Canadian Centre of Remote
Sensing
Matrix of digital numbers in a satellite
image
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0
127
255
Brightness value
range
(typically 8 bit)
Associated
gray-scale
10 15 17 20
15 16 18 21
17 18
20
22
18
20
22 24
1
2
3
4
1 5432
Columns ( j)
Bands (k)
1
2
3
4
X axis Picture element (pixel) at location
Line 4, Column 4, in Band 1 has a
Brightness Value of 24, i.e., BV4,4,1 = 24 .
black
gray
white
21
23
22
25
Lines or
rows (i)
The data set may consist of several
multispectral bands (k)
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types of resolution that affect the quantity and
nature of the data a sensor collects:
1. Radiometric (range of DN values)
2. Spatial (pixel size)
3. Spectral (# of bands)
4. Temporal (return period of sensor)
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Sentinel-2 is a fleet of satellites belongs to the
European Commission’s Copernicus program of
the ESA
13 spectral bands: four bands at 10 metres, six
bands at 20 metres and three bands at 60 metres
spatial resolution
swath width of 290 km and frequent revisit times
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Launch Date: Feb. 11, 2013
Carry 2 sensors:
the Operational Land Imager (OLI) is a push-
broom sensor that has a five-year design life
the Thermal Infrared Sensor (TIRS)
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Landsat 8
Band Number Wave length range (µm) Spatial Resolution
1 0.433–0.453 30 m
2 0.450–0.515 30 m
3 0.525–0.600 30 m
4 0.630–0.680 30 m
5 0.845–0.885 30 m
6 1.560–1.660 30 m
7 2.100–2.300 30 m
8 0.500–0.680 15 m
9 1.360–1.390 30 m
10 10.6-11.2 100 m
11 11.5-12.5 100 m
B1-8: shortwave, B8: panchromatic, B10-11: thermal
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acquire images in hundreds of very narrow,
contiguous spectral bands throughout the visible
and infrared portions of the electromagnetic
spectrum
can be used to distinguish many surface features
not identified using broadband remote sensing
systems e.g. Landsat OLI
AVIRIS (Advanced Visible/Infrared Imaging
Spectrometer), HyMap (the hyperspectral
mapper) and MODIS (Moderate Resolution
Imaging Spectroradiometer)
Hyperspectral Remote Sensing (HSRS)
Hyperspectral
scanners
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3. Thermal lR images
restricted to the regions: 3- 5 µm and 8-14 µm
the spatial resolution of thermal images is usually
coarse compared to those of the visible and reflected
IR bands, why?
as the thermal radiation is emitted, not reflected,
thermal imagery can be acquired during the day or
night
applications: e.g. mapping forest fires, identifying
surface and subsurface hydrothermal features, and
monitoring water pollution
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many sources of remote sensing data are available
online to download for free or purchase:
1) The USGS Global visualization (GloVis):
Landsat, ASTER, Aerial, EO-1, MODIS
2) The European Copernicus Programme-Copernicus:
-Sentinel-1 (SAR), Sentinel-2 (10m Multispectral)
3) The Geo Airbus Defense System:
-paid
-give sample of SPOT, Pleiades, RapidEye and
TerraSAR data
4. Radar and LiDAR data
Radar (radio detection and ranging) and LiDAR
(light detection and ranging) are active remote
sensing systems
Radar systems transmit microwave energy at a
particular wavelength (1-30 cm) for a particular
duration of time, then measure the energy
backscattered from the ground
most imaging radar systems used for Earth's
resources and environment use side-looking airborne
radar (SLAR), which produces radar imagery on one
side of the aircraft's flight line
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a major advantage of radar is its all weather, day
and night operation capability, which allows
data to be collected at any time
different from radar, LiDAR is a vertical- or nadir
looking instrument, and uses electromagnetic
radiation in the visible and eye-safe near IR regions
the system emits laser pulses and measures their
travel time from the
transmitter to the
target on the terrain
surface and back to
the receiver
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as the velocity of the laser pulse (light) is known,
the distance or range between the sensor and the
ground can be calculated when the sensor location
can be determined with a high precision GPS, the
range can be converted to absolute coordinates (x,
y,z)
the range measurement process produces a
collection of elevation data points, commonly
referred to as mass points (point cloud data)
therefore, LiDAR records information at discrete
points which is not composed of contiguous
pixels
LiDAR elevation masspoints
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multiple returns can be used to detect the
elevations of several objects within a laser foot print
first returns are mainly used to create digital
surface models that include features above the
ground surface (such as buildings, bridges and trees)
the first return can also represent the ground,
in case only one return is detected by the LiDAR
sensor
intermediate re turns, in general, are used for
vegetation structure or for separating vegetation from
solid objects among the above ground features
last returns are used to build DEMs of the bare
ground surface