Basics of Remote Sensing

( contd…)
 SUMMARY OF LECTURE 1
Remote Sensing Definition

Component of Remote sensing

Planck’s Law

Peak wavelength from sun and earth

Available radiation for RS from sun

OR
Wavelength or EM waves absorbed by atmosphere

https://www.nrcan.gc.ca/maps-tools-publications/satellite-imagery-air-photos/tutorial-
fundamentals-remote-sensing/9309
WHAT are different type of remote sensing?

Classification of Remote sensing:

Based on spectral region:
Optical/IR remote sensing ( 0.4 to 8.0 micometer)
Thermal remote sensing ( 8 to 12 micrometer)
Microwave remote sensing ( .3 to 100 GHz)

The micrometre ( μm) also commonly known as a micron, is

unit of length equalling 1×10−6 metre
REMOTE SENING DATA COLLECTION METHODS

OPTICAL/IR REMOTE SENSING

PANCHROMATIC

COLOR

MULTISPECTRAL

HYPERSPECTRAL
Panchromatic

Multispectral

Hyperspectral
 Electromagnetic spectrum

Visible (400 nm - 1000 nm, VIS)

Infrared (~ 10,000 nm, IR)
Microwave (MW)
active (0.3-30 GHz)

Links:
http://www.biogeorecon.com/remote.htm 7
http://www.eeb.ucla.edu/test/faculty/nezlin/SatellitesAndSensors.htm
Comparison:

Micron= mm/1000

Wavelength ( Microwave) >>> Wavelength ( optical region)

In meters
Active remote sensing
Passive remote sensing
 A Systems View of Remote Sensing
Remote Sensing Instruments

Passive Active

Reflected Thermal Passive Visible/IR Active

light emission Microwave Microwave

Laser
Panchromatic Altimetry,
Thermal Passive Profiling
microwave Scatterometry
Visible/near imaging and Lidar
IR/SWIR radiometry Synthetic
imaging Microwave Aperture Radar
sounding
 What are Type of Remote sensing: PASSIVE & ACTIVE

Advantage: Ability of seeing object beyond human eyes limit

Advantage of Remote Sensing
i) Provide data of large region- Synoptic view

ii) Provide data of remote and inaccessible terrain

iii) Ability to obtain data of any region for repeated period of time.

iv) Ability to acquire data at any time of day

v) Ability to acquire data in cludy condition

vi) relatively less cost as compared to human intensive mapping.

v) Easy and rapid method of mapping

vi) No human bias.

vii) Can acquire data beyond human vision.

viii)Quick information

ix) Multispectral view

INTERACTION OF LIGHT WITH SURFACE MATERIAL

HOW WE SEE COLORS- HUMAN AND INSTRUMENT

SIMILIARITY

LIGHT ABSORPTION, SCATTERING AND TRANSMISSION

HOW MUCH ADVANTAGE:SPECTRAL VIEW

SIGNATURE: A KEY OF REMOTE SENSING DATA

INTERPRETATION

WHAT ARE PANCHROMATIC, MULTISPECTRAL AND

HYPERSPECTRAL OBSERVATIONS
 blue light, with a higher refractive index, will
be bent more strongly than red light, resulting
in the well-known rainbow pattern.

Color Wavelength

Violet 4000 Å to 4240 Å

Blue 4240 Å – 4912 Å

Green 4912 Å – 5750 Å

Yellow 5750 Å – 5850 Å

Orange 5850 Å – 6470 Å

Red 6470 Å – 7000 Å

Reflection is the process by which electromagnetic radiation is returned
either at the boundary between two media (surface reflection) or at the
interior of a medium (volume reflection)

transmission is the passage of electromagnetic radiation through a

medium.

Both processes can be accompanied by diffusion (also called scattering),

which is the process of deflecting a unidirectional beam into many
directions. In this case, we speak about diffuse reflection and diffuse
transmission
INTERACTION OF RADIATION SURFACE MAtERIAL

There are three forms of interaction that can take place when energy
strikes, or is incident (I) upon the surface. These are: absorption (A);
transmission (T); and reflection (R)
Φλ = ρλ + αλ +τλ [where Φλ is radiative flux; ρλ is the amount of
reflected energy; αλ is the amount of absorbed energy; and τλ is the
amount of transmitted energy]

https://www2.geog.soton.ac.uk/users/trevesr/obs/rseo/energy_interactions_with
_the_earths_surface.html
Where Does Color Come From?
The color of an object is not actually within the object itself.
Rather, the color is in the light that shines upon it and is ultimately
reflected
visible light spectrum consists of a range of frequencies, each of
which corresponds to a specific color
Darker colored objects heat up faster in the sun than light
colored ones, which is why running across asphalt in bare feet
can feel much hotter than walking across light-colored
concrete
Color Frequency Wavelength

Violet 668 THz to 789 THz 400 to 440

440 to 460
Indigo 600 THz to 700 THz

Blue 606 THz to 668 THz 460 to 500

Green 526 THz to 606 THz 500 to 570

Yellow 508 THz to 526 THz 570 t0 590

Orange 484THz to 508 THz 590 to 620

Red 400 THz to 484 THz 620 to 720

 Radiation Interactions with Matter
• Emission – release of electromagnetic
waves ( Planck’s Law of radiation)
• Absorption – receiving of electromagnetic
waves
• Scattering – deflection of electromagnetic
waves in all directions ( Surface roughness
relative to wavelength)
• Reflection – deflection of electromagnetic
waves into the backwards direction (
Smooth surface)
Amplitude

G
 Amplitude

B G R

Leaf Fall
 Tree with leave

Amplitude
Tree without leave

B G R

LOCATION
 Tree with leave

Amplitude
Tree without leave

B G R

LOCATION1
LOCATION 2
 Green
Amplitude

LOCATION1

LOCATION 2
 Introduction to GIS

Reflectance Curve

High
Reflectance

•The
wavelengths
in which it is
reflected
determine
the color of
the object Low
0.4mm 0.5mm 0.6mm 0.7mm
Blue Green Red

Source: Jarlath O’Neil-Dunne

©2007 Austin Troy
 Object recognition : SIGNATURE
Reflectance Curve

High
Reflectance

•The
wavelengths
in which it is
reflected G
determine R
the color of
the object Low
0.4mm 0.5mm 0.6mm 0.7mm
Blue Green Red

Source: Jarlath O’Neil-Dunne

©2007 Austin Troy
Spectral “Signatures”
https://ugc.berkeley.edu/background-content/reflection-absorption-sunlight/
Distribution
Greening of China and India
NASA

NASA has some good news, the world is a greener place today than it was 20 years ago.

https://www.forbes.com/sites/trevornace/2019/02/28/nasa-says-earth-is-greener-today-than-20-
years-ago-thanks-to-china-india/?sh=4dfd8c6f6e13
REMOTE SENING DATA COLLECTION METHODS
OPTICAL/IR REMOTE SENSING

• PANCHROMATIC

• MULTISPECTRAL

• HYPERSPECTRAL
Panchromatic

Multispectral

Hyperspectral
A panchromatic band (black and white band) is one band that usually contains a
couple of hundred nanometers bandwidth. The bandwidth enables it to hold a high
signal-noise, making the panchromatic data available at a high spatial resolution.
This images can be gathered with a higher resolution since the spectral range give
the smaller detectors allowance to be utilized while sustaining the high signal-noise
ratio.
Advantage:
High SNR
High resolution

Cartosat-3 has a ground

resolution of 0.25 m with
16 km swath
Doha

Cartosat-3

https://eos.com/panchromatic/
 Display of Multispectral Image
• NATURAL color composite
Bands Applied to color Resulting Image

Red

Green

Blue

©2007 Austin Troy

WHAT IS REMOTE SENSING DATA

A TWO DIMENSIONAL DISTRIBUTION

OF REFLECTED ENERGY
 Brightnes s value
range Associated
Columns ( j) (typically 8 bit) gray-scale
1 2 3 4 5
Lines or 1 255 white
rows (i) 1 10 15 17 20 21
2
15 16 18 21 23 2
3 Bands (k )
17 18 20 22 22
4 3 127 gray
18 20 22 24 25

0 black

X axis Picture element (pixel) at location

Line 4, Column 4, in Band 1 has a
Brightness Value of 24, i.e., BV 4,4,1 = 24 .
WHAT IS SPECTRAL SIGNATURE
Different surface types such as water, bare
ground and vegetation reflect radiation
differently in various channels. The radiation
reflected as a function of the wavelength is
called the spectral signature of the surface.
QUESTION BANK

EXPLAIN :

PACHROMAIC , COLOR , MULTISPECTRAL AND HYPERSPECTRAL REMOTE SENSING

What do you mean by SPECTRAL SIGNAURE