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Transcript
Remote Sensing
Outline:

definition of remote sensing

components of system

electromagnetic radiation

nature of an image

light interaction with atmosphere and surface

types of remote sensors
Remote Sensing


science and art of obtaining information about
something from a distance.
analysis of collected data to obtain information about
the objects, areas or phenomenon under
investigation.
Components of System
propagation through
the atmosphere
energy interactions with
earth surface features
transmission through
the atmosphere
Components of System
Data Analysis:

examining the data using various viewing and
interpretation devices to analyze pictorial data
and/or a computer to analyze digital sensor data
(i.e. GIS).
Electromagnetic
Radiation
Energy Sources:

energy available from sun is described by electromagnetic
spectrum
Electromagnetic
Radiation
Wavelength - distance from one wave crest to another.
Frequency - number of wave crests passing a fixed point
in a given period of time. Measured in hertz (1 cycle per
second)
Electromagnetic
Radiation
Amplitude - height of each peak. Measured as spectral
irradiance
Electromagnetic
Radiation
Ultraviolet Radiation - 0.4 micrometers
 not much is done with UV for remote sensing
since these shorter wavelengths are easily
scattered by the atmosphere
Electromagnetic
Radiation
Visible Radiation
BLUE (.4-.5 micrometers)
GREEN (.5-.6 micrometers)
RED (.6-.73 micrometers)
Electromagnetic
Radiation
Infrared Radiation - .72 - 15 micrometers
1.
Near Infrared - reflected, can be recorded on film
2.
Mid Infrared - reflected,
can be detected using
electro-optical sensors.
3.
Thermal Infrared emitted, can only be
detected using electrooptical sensors
Electromagnetic
Radiation
Microwave Radiation - radar sensors, wavelengths range
from 1mm to 1m
Electromagnetic
Radiation


most systems rely on the sun to generate all the EM
energy needed to image terrestrial surfaces - passive
sensors.
other sensors generate their own energy, called
active sensors, transmits that energy in a certain
direction and records the portion reflected back by
features within the signal path
Light Interaction with
Atmosphere

atmospheric modification of incoming and outgoing
EM radiation includes scattering, refraction and
absorption
Scattering

redirection of light by particles

can be in any direction
Light Interaction with
Atmosphere
General Effects of Scattering




causes skylight (allows us to see in shadow)
forces image to record the brightness of the atmosphere
in addition to the target.
directs reflected light away from the sensor, decreasing
spatial detail (fuzzy images)
tends to make dark objects lighter and light objects
darker (reduces contrast)
Light Interaction with
Atmosphere
Refraction


bending of light when it passes
through two media
degrades spectral signatures on
hot- humid days
Light Interaction with
Atmosphere
Absorption

mostly caused by three atmospheric gases: ozone,
carbon dioxide and water vapour
no attenuation
attenuation
Light Interaction with
Surface
Reflection


the bouncing of electromagnetic energy from a
surface
type of reflection is dependent on the size of the
surface irregularities relative to the incident
wavelength.
Light Interaction with
Surface
1.


Specular Reflectance
light is reflected in a single direction - 'mirror'
reflection
specular reflectance helps and hinders remote sensing
Light Interaction with
Surface
2.
Diffuse/Lambertian Reflectance

energy is reflected equally in all directions

many natural surfaces act as a diffuse reflector to
some extent.
Nature of the Image



image – model target features described through
the use of spectral reflectance
software and hardware specially designed to analyze
these images give us the ability to see a pictorial
rendition of targets.
images that we see on a computer screen are made
up of picture elements called pixels.
Nature of the image
Pixel - picture element having both
spatial and spectral properties.


the spatial property defines the "on
ground" height and width.
the spectral property defines the
intensity of spectral response for a
cell in a particular band
Nature of the Image
Nature of the Image

when only one band of
the EM spectrum is
sensed, the output
device (colour monitor)
renders the pixels in
shades of grey
Nature of the Image


multispectral sensors detect light reflectance in
more than one or two bands of the EM spectrum.
these bands represent
different data - when
combined into the red,
green, blue guns of a
color monitor, they
form different colors
Nature of the Image

multispectral image is composed of 'n' rows and 'n'
columns of pixels in each of three or more spectral
bands
Aerial
Photography/Airphoto

most common, versatile and economic form of
remote sensing

spectral range 0.3 to 0.9 mm (visible portion of
spectrum).

photogrammetry is the science, art and technology
of obtaining reliable measurements, maps, other
derived products from photographs.
ADVANTAGES OF AERIAL
PHOTOGRAPHY
Five Basic Advantages

Improved vantage point

Capability to stop action

Permanent recording

Broadened spectral sensitivity

Increased spatial resolution and geometric fidelity
Aerial
Photography/Airphoto

camera produces a large-format 23x23cm photo

contain high precision/well calibrated lenses that
minimize spatial distortions

motor-driven film advances – 60% overlap between
successive exposures

panchromatic,
black-and-white,
true-colour film
Aerial
Photography/Airphoto

Grey scale step wedge

Notes

Altimeter

Fiducial marks

Clock

Lens serial number

Focal length

Frame number

Mission name and date
Aerial
Photography/Airphoto
Airphoto – Saudi Arabia
Aerial
Photography/Airphoto

advantages: improves vantage point, capability to
stop action, permanent recording, broadened spectral
sensitivity, increased spatial resolution.

disadvantages: can’t get at elevation, not appropriate
for urban areas (tall buildings block information)

applications: land use/land cover mapping, geologic
and soil mapping, agricultural application, forest
applications, wildlife ecology, etc.
Satellite Remote Sensors

currently there are 2777 satellites orbiting the earth
(US – 878)

multi-purpose:
 scientific
 defense
 communications
 global
positioning system (GPS)
Satellite Remote Sensors

geostationary orbiting satellites are those that remain
stationary relative to a point on the surface of the earth
i.e. communications and meteorological satellites
Satellite Remote Sensors

polar-orbiting satellites are those in which the position
of the satellite’s orbital plane is kept constant relative
to the sun.
i.e. Landsat satellite series
ACTIVE VS PASSIVE REMOTE SENSING
Passive Remote Sensing

measure natural radiation emitted by target or/and radiation
energy from other sources reflected from the target

examples: passive microwave radiometers, LandSat, SPOT
ACTIVE VS PASSIVE REMOTE SENSING
Active Remote Sensing

transmit their own signal and measure
the energy that is reflected or
scattered back from the target

advantages: ability to “see” regardless
of time of day or season; use
wavelengths not part of solar
spectrum; better control of the way
target is illuminated
Microwave Sensors

sensors that operate in the microwave portion of the
spectrum

advantages: capable of penetrating atmosphere under

disadvantage: radar instruments have a hard time

applications: sea ice and snow, geologic features, ocean
virtually all conditions, different view of the
environment.
identifying water bodies because the wavelength is
much longer than the general character of the surface
roughness
bottom contours, other planets.
Microwave Sensors
Microwave radiometer – narrow-beam antenna
attached to a scanning device

soil moisture, water content of snow, geologic strata
Synthetic Aperture Radar – shorter antenna that emits
and receives returned energy from ground objects

day/night, clouds/cloud free operation
Microwave
Sensors
RADARSAT

launched in November 1995

developed by Canada to monitor environmental change
and the planet’s natural resources

heart is synthetic aperture radar (SAR) – microwave
instrument that sends pulsed signals to earth and
processes the received reflected pulses.
Microwave
Sensors
First RADARSAT Image
Microwave
Sensors
European SAR
ERS-2 Vancouver Island
Optical Sensors

sensors that operate in the optical portion of
spectrum, which extends from approximately 0.3 to
14 mm.

can do more with these data because it is numbers.


look at differences in colors

look at differences over time
applications: meteorological, ocean monitoring (i.e.
chlorophyll absorption).
Optical Sensors

show how much energy from the sun was being
reflected or emitted off the Earth's surface when the
image was taken.




clear water reflects little radiation, so it looks black.
pavement and bare ground reflect a lot of radiation,
so they look bright.
urban areas usually look light blue-grey.
vegetation absorbs visible light but reflects infrared,
so it looks red
Optical image of Montreal area during ice storm of 1998. Ice
snow and clouds appear as various colors of white, vegetation
is green.
Optical Sensors
GOES - Geostationary Operational Environmental
Satellite (Visible to NIR, Thermal)
DMSP - Defense Meterological Satellite Program 600 m
resolution (Visible to NIR, Thermal), urban heat
island studies
Nimbus - CZCS - coastal zone color scanner, 825 m
spatial resolution
AVHRR - Advanced Very High Resolution Radiometer –
meteorological satellite (visible, NIR, thermal)
AVHRR - Advanced Very
High Resolution
Radiometer –
meteorological satellite
(visible, NIR, thermal)
AVHRR Channels
Channel
1
2
Wavelength
0.58 - 0.68
0.725 - 1.10
3A
3
1.58 - 1.64
3.55 - 3.93
4
10.30 - 11.30
5
11.50 - 12.50
Primary Use
Daytime cloud/surface mapping
Surface water delineation, ice and snow
melt
Snow / ice discrimination (NOAA K,L,M)
Sea surface temperature, nighttime cloud
mapping
Sea surface temperature, day and night
cloud mapping
Sea surface temperature, day and night
cloud mapping
Optical Sensors
LANDSAT - visible, NIR spectral bands (Landsats
1,2,3), and MIR and Thermal (Landsats 4 and 5)

Multispectral scanner - 4 spectral bands – Green,
Red, and 2 NIR

Thematic mapper - 7 spectral bands –
Blue/Green, Green, Red, NIR, MIR, MIR, Thermal
LANDSAT MSS
image - Grand
Canyon
LANDSAT TM image - southwestern Utah and Southern
Nevada
SPOT Image of the WTC Fires