Remote sensing [compatibility mode]

Introduction to
Remote Sensing
Prof. Sumanta Das
Dept. of civil Engg.
Engg.
MEFGI, Rajkot

Image: NASA 2005

Outline
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Remote Sensing Defined
Resolution
Electromagnetic Energy (EMR)
Types
Interpretation
Applications

ND GIS Users Workshop
Bismarck, ND October 24-26,
242005

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Remote Sensing is:
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“The art and science of obtaining information
about an object without being in direct contact
with the object” (Jensen 2000).

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There is a medium of transmission involved.

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Environmental Remote Sensing:
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… the collection of information about Earth surfaces
and phenomena using sensors not in physical contact
with the surfaces and phenomena of interest.

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We will focus on data collected from an overhead
perspective via transmission of electromagnetic
radiation.

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Source: Jensen (2000)

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Remote Sensing Includes:
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A) The mission plan and choice of sensors;

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B) The reception, recording, and processing of the
signal data; and

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C) The analysis of the resultant data.

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 Types of Remote Sensing:Sensing:Based on Range of Electromagnetic
Spectrum:Spectrum:1. Optical Remote Sensing.
2. Thermal Remote Sensing.
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3.

Microwave Remote Sensing.

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Based on the source of the energy:energy:Active remote sensing.
Passive remote sensing.

1.
2.

 Based on Range of Electro
magnetic Spectrum:Spectrum:
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Optical Remote Sensing:Sensing:The optical remote sensing devices
operate in the visible, near infrared,
middle infrared and short wave
infrared portion of the electromagnetic
spectrum.
These devices are sensitive to the
wavelengths ranging from 300 nm to
3000 nm.

 Thermal Remote Sensing:Sensing:

The sensors, which operate in
thermal range of electromagnetic
spectrum record, the energy
emitted from the earth features in
the wavelength range of 3000 nm to
5000 nm and 8000 nm to 14000 nm.

 Microwave Remote Sensing:Sensing:

A microwave remote sensor records the
backscattered microwaves in the
wavelength range of 1 mm to 1 m of
electromagnetic spectrum.

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Most of the microwave sensors are active
sensors, having there own sources of
energy.

Depending on the source of the
energy:energy:
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Active remote sensing:sensing:Active remote sensing uses an artificial source for
energy.
For example the satellite itself can send a pulse of
energy which can interact with the target.
In active remote sensing, humans can control the
nature (wavelength, power, duration) of the source
energy.
Active remote sensing can be carried out during
day and night and in all weather conditions.
ExampleExample- RADAR

 Passive remote sensing:sensing:

Passive remote sensing depends on a natural
source to provide energy.

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The sun is the most powerful and commonly
used source of energy for passive remote
sensing.

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The satellite sensor in this case records primarily
the radiation that is reflected from the target.

Fig. active & passive remote sensing.

Remote Sensing Process Components

Energy Source or Illumination (A)
Radiation and the Atmosphere (B)
Interaction with the Target (C)
Recording of Energy by the Sensor (D)
Transmission, Reception, and
Processing (E)
Interpretation and Analysis (F)
Source: Canadian Centre for Remote Sensing

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Application (G)

EM energy interaction of earth surface:

 Advantages of remote sensing:sensing:
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Provides a regional view (large areas).
Provides repetitive looks at the same area.
Remote sensors "see" over a broader.
portion of the spectrum than the human
eye.
Provides geo-referenced, digital, data.
geoSome remote sensors operate in all
seasons, at night, and in bad weather.
Give information of inaccessible area.

 DISADVANTAGE OF REMOTE
SENSING:SENSING:• Expensive to build and operate.
• Measurement uncertainty can be
large.
• Data interpretation can be difficult.

 Applications of Remote
Sensing:Sensing:

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Agriculture:Agriculture:Crop type classification.
Crop condition assessment.
Crop yield estimation.
Mapping of soil characteristic.
Soil moisture estimation.

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Geology:Geology:Lithological mapping.
Mineral exploration.
Environmental geology.
Sedimentation mapping and monitoring.
GeoGeo-hazard mapping.
Glacier mapping.
Hydrocarbon exploration and mine
exploration

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Urban Planning:Planning:Land parcel mapping.
Infrastructure mapping.
Land use change detection.
Future urban expansion planning.

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Hydrology:Hydrology:Watershed mapping and management.
Flood delineation and mapping.
Ground water targeting.

Land Use/Land Cover
mapping:mapping:Natural resource management.
Wildlife protection.
Encroachment.
LULC change detection & analysis

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Ocean applications:applications:Storm forecasting.
Water quality monitoring.
Aquaculture inventory and monitoring.
Navigation routing.
Coastal vegetation mapping.
Oil spill.
Coastal hazard monitoring &
assessment.

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Civil Engineering:Engineering:Building construction(ICONOS,LIDAR)
City and Town planning & development
Surveying
Ground water exploration and mapping
Site investigation
Land information system(LIS)

Resolution
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All remote sensing systems have four types of
resolution:
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Spatial

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Spectral

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Temporal

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Radiometric

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Spatial Resolution

High vs. Low?

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Spectral
Resolution

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Temporal Resolution

July 2

July 18

August 3

16 days

Time
11 days

July 1

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July 12

July 23

August 3

Radiometric Resolution

6-bit range

0

63

8-bit range

0

255

10-bit range

0

1023

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Electromagnetic Radiation

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Electromagnetic Spectrum

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Signature Spectra

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RS Data- AVHRR (Advanced Very
DataHigh Resolution Radiometer) NASA

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GOES (Geostationary Operational
Environmental Satellites) IR 4

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MODIS (250 m)

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Landsat TM
(False Color Composite)

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SPOT (2.5 m)

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QUICKBIRD (0.6 m)

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IKONOS (4 m Multispectral)

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IKONOS (1 m Panchromatic)

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RADAR
(Radio Detection and Ranging)

Image: NASA 2005

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LIDAR
(Light Detection and Ranging)

Image: Bainbridge Island,
WA courtesy Pudget Sound
LIDAR Consortium, 2005

Elements of Image Interpretation
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Shape:
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Many natural and human-made features have
humanunique shapes.

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Often used are adjectives like linear,
curvilinear, circular, elliptical, radial, square,
rectangular, triangular, hexagonal, star,
elongated, and amorphous.

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Shape

Jensen (2000)

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Shadow:
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Shadow reduction is of concern in remote sensing
because shadows tend to obscure objects that
might otherwise be detected.

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However, the shadow cast by an object may be
the only real clue to its identity.

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Shadows can also provide information on the
height of an object either qualitatively or
quantitatively.

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Shadow

Jensen (2000)

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Tone and Color:
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A band of EMR recorded by a remote sensing
instrument can be displayed on an image in
shades of gray ranging from black to white.

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These shades are called “tones”, and can be
qualitatively referred to as dark, light, or
intermediate (humans can see 40-50 tones).
40-

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Tone is related to the amount of light reflected
from the scene in a specific wavelength interval
(band).

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Tone and Color

Jensen (2000)

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Texture:
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Texture refers to the arrangement of tone or color
in an image.

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Useful because Earth features that exhibit similar
tones often exhibit different textures.

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Adjectives include smooth (uniform,
homogeneous), intermediate, and rough (coarse,
heterogeneous).

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Texture

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Jensen (2000)

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Pattern:
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Pattern is the spatial arrangement of objects on
the landscape.

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General descriptions include random and
systematic; natural and human-made.
human-

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More specific descriptions include circular, oval,
curvilinear, linear, radiating, rectangular, etc.

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Pattern

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Jensen (2000)

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Height and Depth:
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As discussed, shadows can often offer clues to the
height of objects.

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In turn, relative heights can be used to interpret
objects.

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In a similar fashion, relative depths can often be
interpreted.

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Descriptions include tall, intermediate, and short;
deep, intermediate, and shallow.

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Height and Depth

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Association:
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This is very important when trying to
interpret an object or activity.
Association refers to the fact that certain
features and activities are almost always
related to the presence of certain other
features and activities.

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Association

Jensen (2000)

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Digital Image processing
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1.
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Correction of data
Digital enhancement for the purpose of better visual
interpretation.
It involves three basic steps:
Image preprocessing
Image processing
Post processing & transformation

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Why do we need image
processing?
o

o

o

Improvement of pictorial information for
human perception
Image processing for autonomous
machine application
Efficient storage and transmission

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Color Image
Processing

Wavelet &
multiresolution
processing

Compression

Image
Restoration

Image Filtering
& Enhancement

Image
Acquisition

Morphological
Processing

Segmentation

Knowledge base

Representation
& Description

Object
Recognition

Image preprocessing
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Geometric correction
Radiometric correction

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Geometric correction
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Geometric corrections are made to correct the
inaccuracy between the location coordinates of the
picture elements in the image data, and the actual
location coordinates on the ground. Several types of
ground.
geometric corrections include system, precision, and
terrain corrections.
corrections.

Radiometric correction
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Radiometric corrections are made to the raw digital
image data to correct for brightness values, of the object
on the ground, that have been distorted because of
sensor calibration or sensor malfunction problems. The
problems.
distortion of images is caused by the scattering of
reflected electromagnetic light energy due to a
constantly changing atmosphere. This is one source of
atmosphere.
sensor calibration error.
error.

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Image processing
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Enhancing an image or extracting
information or features from an image
Computerized routines for information
extraction (eg, pattern recognition,
(eg,
classification) from remotely sensed
images to obtain categories of information
about specific features.

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Spatial filtering

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Image quality and statistical evaluation
Image contrast enhancement and sharpening
Image classification

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Pixel based
ObjectObject-oriented based

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Post processing & transformation
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Accuracy assessment of classification
PostPost-classification and GIS
Change detection

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Striping Noise and Removal

CPCA
Combined Principle
Component Analysis

Xie et al. 2004

Speckle Noise and
Removal
Blurred objects
and boundary

G-MAP
Gamma Maximum
A Posteriori Filter

Remote sensing [compatibility mode]

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