Transcript No Slide Title

Definition: Remote Sensing is the ability to obtain
information about the Earth's surface without being in
contact with it. This is obtained by sensing and
recording reflected or emitted energy and processing,
analyzing, and applying this information.
http://www.ccrs.nrcan.gc.ca/
History of remote-sensing
 Gaspard Felix Tournachon in 1859, took the first air
photos from a hot air balloon
 Bavarian war in 1903, cameras were attached to pigeons
 First aerial photographs which were in 1908
 Infra Red film was used during the World War II to
distinguish camouflaged equipment from vegetation
 The first military satellite imagery was obtained in August
1960 by the Corona Satellite
 LANDSAT, originally launched in 1972 under the Earth
Resources Technology Satellite (ERTS-1) name
Electromagnetic Spectrum
“energy that is propagated through
space between electric and magnetic
fields. The electromagnetic spectrum is
the extent of that energy ranging from
cosmic rays, gamma rays, X-rays to
ultraviolet, visible and infrared radiation
including microwave energy”.
USGS definition
Electromagnetic Waves are classified with respect to
frequency and wavelengths since the velocity of all
electromagnetic waves travel at the speed of light.
Frequency – refers to the number of wave crests passing
a fixed point for a given period of time.
Wavelength – refers to the distance from one wave crest
to another.
Wavelength is
measured in :
 Nanometers (nm, 10-9
meters)
 Micrometers (m, 10-6
meters)
 Centimeters (cm, 10-2
meters)
These waves are
radiated through space,
and in the case of our
own planet and are
almost all sourced from
our own sun
From our own sensory apparatus the most
important part of the electromagnetic spectrum that
is that found within the visible ranges 0.4 to 0.7 m.
The visible wavelengths include
• Violet: 0.4 - 0.446 m
• Blue: 0.446 - 0.500 m
• Green: 0.500 - 0.578 m
• Yellow: 0.578 - 0.592 m
• Orange: 0.592 - 0.620 m
• Red: 0.620 - 0.7 m
Visible (IR) includes
wavelengths from
approximately 0.7m to
3.0 m. The thermal IR
region is quite different
than the visible and
reflected IR portions, as
this energy is essentially
the radiation that is
emitted from the Earth's
surface in the form of
heat.
As these Electromagnetic Radiation
(EMR) pass through the earth’s
atmosphere and they are subject to
three processes.
Scattering
Absorption
Refraction
a) Scattering
b) Absorption
c) Refraction
Electromagnetic radiation that passes through the
atmosphere interacts with the earth’s surface in three ways:
a) be reflected from the object - R
b) absorbed by the object - A
c) transmitted through the object - T
The total radiation (R + A + T) is also referred to as
incident radiation - I
There are two important
types of reflection:
1) Specular Reflection
(mirror reflection) occurs
from smooth surfaces and
causes light to be reflected
in a single direction at an
angle equal to the angle of
incidence.
2) Diffuse Reflection occurs
from rough surfaces and
causes light to be reflected
in several directions.
Each object or land use has different reflectances which
are termed albedos. This concept is encapsulated in the
concept of a Spectral Signature.
Spectral Signatures are the percentage of reflectance
across this electromagnetic spectrum and is quite
different between different objects and can be used
to distinguish features as subtle as difference species
of plants.
Although we know
plants reflect green
and absorb blue and
red light, it is important
to also include Infra
Red IR wave lengths.
In plants the near IR is
scattered in the
spongy mesophyll
tissue.
Using spectral
signatures we can
identify algal blooms at
sea
The spectral signature
for water differs from
that of vegetation
exhibits moderate
reflectance in the visible
portion of the
Electromagnetic
Spectrum, but absorbs
almost all Near IR.
Consequently in images
displaying NIR, water
appears to be very dark
(absorptive).
We can then compare the spectral signatures of
various features and use standardized signatures to
identify and map different features in the landscape.
The process can be divided into the following components
a) Energy Source
b) Radiation and the Atmosphere
c) Radiation and the Surface
d) Sensor recording Radiation
e)Transmitting Sensor Data
f) Data Analysis
g) Remote Sensing Application
The Nature of Images - Printed
Most of the images that we are familiar with are
based on representations of reflected light, this is
how a camera works.
In black and white film dots are applied and the
intensity from high saturation of pigment to low
saturation creates the grades from black to white.
Colour pictures are created in the same way except
that three layers of colour saturation are applied,
the three printing colours are cyan, magenta and
yellow.
Nature of Images Displayed
Dsiplayed images
such on a monitor
are digitally
generated. The
implications of this
are that the intensity
of each colour band
is stored in discrete
values, usually
ranging from 0 to
255.
Difference between aerial photographs and digital
satellite images?
Aerial photographs
Satellite Images e.g. LANDSAT
Scanned for processing
Collected digitally
High resolution <1m
Low resolution >15 m
Small footprints 1-3 kms
Large footprints 185 kms
Limited spectral bands,
black and white, colour
or Infra Red
8 spectral bands, including
black and white, colour, nearand mid-Infra Red and thermal
High radial distortion difficult to mosaic
Relatively low distortion fairly
easy to mosaic
As remote sensing
platforms (satellites and
airplanes) travel, they
record reflected
electomagnetic radiation
from the Earth’s surface.
The quality of images the
collect are subject to
cloud cover both low level
light conditions such as
dust storms. Since
satellites are put into
orbits which are
synchronized with the sun
they almost always
sample during daytime.
As a satellite revolves
around the Earth, the
sensor "sees" a certain
portion of the Earth's
surface. The area imaged
on the surface, is referred
to as the swath.
There are two types of
sensors, namely
passive sensors which
records reflected light
(LANDSAT, SPOT,
IKONOS) and active
sensors (RADAR and
SONAR) which provide
their own energy source
and record the reflected
response as it interacts
with various objects.
Landsat MSS (Multispectral Scanner) - 1972
Spatial Resolution: 56m x 79m
Spectral Resolution: 4 Bands
Temporal Resolution: 16 days
Swath: 185 km
Landsat TM (Thematic Mapper) - 1982
Spatial Resolution: 30m x 30m
Spectral Resolution: 7 Bands
Temporal Resolution: 16 days
Swath: 185 km
SPOT Panchromatic - 1986
Spatial Resolution: 10m x 10m
Spectral Resolution: 1 Band
Temporal Resolution: 26 days
Swath: 60 km
SPOT XS (Multispectral) - 1986
Spatial Resolution: 20m x 20m
Spectral Resolution: 3 Bands
Temporal Resolution: 26 days
Swath: 60 km
IKONOS Panchromatic - 1999
Spatial Resolution: 1m x 1m
Spectral Resolution: 1 Band
Temporal Resolution: 3 days
Swath: 11 km
IKONOS Multispectral - 1999
Spatial Resolution: 4m x 4m
Spectral Resolution: 4 Bands
Temporal Resolution: 3 days
Swath: 11
km
SeaWifs
Is an ocean water colour satellite launched on August 1, 1997. It is a
multispectral satellite that contains bands which are specified for detecting
biological activity in the oceans. The colour imagery can be processed to
produce a natural colour "portrait" of the entire globe in which vegetation-rich
areas are in green, vegetation-poor (including deserts) areas are in various
shades of yellow and brown, and ice is displayed in white.
Active Sensors
Radar data are produced when
a radar transmitter emits a beam
of micro or millimeter waves, the
waves reflect from the surfaces
they strike, and the
backscattered radiation is
detected by the radar’s system’s
receiving antenna, which is
tuned to the frequency of the
transmitted waves. Radar
microwaves have the advantage
that they can penetrate the
atmosphere day or night under
virtually all weather conditions.
Radar Imagery is
particularly important
for marine pollution
since it clearly detects
and oil spill through
greater back scattering
of radiation.
References
Fundamentals of Remote Sensing, Canada Centre for Remote
Sensing, Natural Resources Canada, http://www.ccrs.nrcan.gc.ca
TutorOnline - Introduction to Remote Sensing, ERDAS Inc,
http://www.erdas.com
Copyright for pictures used
ERDAS Inc
Canada Centre for Remote Sensing