Remote Sensing: an introduction

29/01/1441
muheeb awawdeh, Yarmouk University-Fall
2018/20191
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

29/01/1441
2018/20192
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

29/01/1441
2018/20193
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

29/01/1441
2018/20194
The Remote Sensing Process
9/28/2019
7
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

29/01/1441
2018/20195
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

29/01/1441
2018/20196
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)

29/01/1441
2018/20197
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)

29/01/1441
2018/20198
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)
9/28/2019 15
1. Wave Theory
2. Particle Theory (Quantum Theory)
3. Stephan Boltzman Law
4. Wien’s Displacement Law
Radiation Laws

29/01/1441
2018/20199
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)

29/01/1441
2018/201910
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

29/01/1441
2018/201911
1) Visible (0.4-0.7m)
-blue (0.4-0.5 m), green (0.5-0.6 m)
and red (0.6-0.7 m) bands
2) Infrared (IR) (0.7-300m)
-reflected IR (0.7-3µm) and thermal IR (3-15m)
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

29/01/1441
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

29/01/1441
2018/201913
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

29/01/1441
2018/201914
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

29/01/1441
2018/201915
every object on the surface of the earth has its
unique spectral reflectance curve (also called spectral
signature)

29/01/1441
2018/201916
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

29/01/1441
2018/201917
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

29/01/1441
2018/201918
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

29/01/1441
2018/201919
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
38
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
energy reflected or emitted from the phenomena of
interest for each spectra band 9/28/2019

29/01/1441
2018/201920
9/28/2019 39
Scanning Systems
the detected energy is recorded as an electrical
signal, which is then converted to a digital value
scanners produce digital images

29/01/1441
2018/201921
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

29/01/1441
2018/201922
Source: Canadian Centre of Remote
Sensing
Matrix of digital numbers in a satellite
image
9/28/2019 44
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)

29/01/1441
2018/201923
9/28/2019 46
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)

29/01/1441
2018/201924
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

29/01/1441
2018/201925
 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)
9/28/2019 49
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

29/01/1441
2018/201926
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

29/01/1441
2018/201927
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

29/01/1441
2018/201928
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

29/01/1441
2018/201929
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

29/01/1441
2018/201930
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

29/01/1441
2018/201931

29/01/1441
2018/201932
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

Remote Sensing: an introduction

More Related Content

What's hot (20)

Similar to Remote Sensing: an introduction (20)

Recently uploaded (20)

Remote Sensing: an introduction