Download - Introduction to remote sensing
Introduction to Remote Sensing
What is REMOTE SENSING ?
REMOTE SENSING includes all methods and techniques used to gain qualitative and quantitative information about distant objects without coming into direct contact with these objects.
Look-Look, NO Touch
What is REMOTE SENSING ?
Remote Sensing (RS) methods try to answer four basic questions:
HOW MUCH of WHAT is WHERE? What is the SHAPE and EXTENT
of ... ? (Area, Boundaries, Lineaments, ...)
Has it CHANGED? What is the MIX of Objects
What is REMOTE SENSING ?
HOW MUCH of WHAT is WHERE? WHAT: Type, Characteristic and
Properties of Object. Eg. Water, Vegetation, Land; Temperature, Concentration, State of Development; Subtype, Species, Use of ... ; Includes determination of generic object type, character and property as well as it’s abstract meaning.
=> DATA INTERPRETATION
What is REMOTE SENSING ?
HOW MUCH of WHAT is WHERE? HOW MUCH: determine by simple
COUNTING, measuring AREA covered or percentage of total area coverage.
WHERE: Relate locations and area covered to either a standard map or to the actual location on the ‘ground’ where the object occurs.
NOTE: WHERE also refers to a moment in time
What is REMOTE SENSING ?
What is the SHAPE and EXTENT of ... ? (Area, Boundaries, Lineaments, ...)
This extends the ‘WHERE’ to be a completely GEOMETRIC problem. MAP PRODUCTION methods are to be applied to the analysis of RS information. These include:
Photogrammetric Methods:Identification and Delineation of Boundaries
and Lineaments (Roads, Rivers, Fault Lines)
What is REMOTE SENSING ?
Has it CHANGED?
CHANGE may occur with progress of TIME.Change may be detected through comparison
of observed states at different moments in time.
=> CHANGE DETECTION
What is REMOTE SENSING ?
What is the MIX of Objects?The surface of the Earth is covered by
objects like Soil, Water, Grass, Trees, Houses, Roads and so on. These are ‘GENERIC OBJECTS’. We know these well, but we also know objects like Open Forest, Residential and Industrial Estates, etc. Each of these ABSTRACT OBJECTS are made up of a typical collection of Generic Objects.
What is REMOTE SENSING ?
What is the MIX of Objects?One important task for Remote Sensing
is to identify GENERIC OBJECTS as well asABSTRACT OBJECTS within areas of
interest
The following lessons will be devoted to techniques and methods as well as to the logistic for finding answers to the four basic questions.
What is REMOTE SENSING ?
Remote Sensing (Look-Look, No Touch) is a much wider field than we will discuss in this lecture series. We will concentrate on that part of RS dealing with
EARTH LAND RESOURCES
Vision Medical Imaging
Sound and Radio Wave Detection
What is REMOTE SENSING ?
What makes it tick ???(1) RS requires a CARRIER of information,
which can bridge distances.(2) RS requires a SENSOR which can
detect changes in the carried Signal.(3) RS requires RECORDING, ANALYSIS,
INTERPRETATION and REPRESENTATION of the sensed information in a purposeful way.
What is REMOTE SENSING ?
(1) RS requires a CARRIER of information, which can bridge distances.
These Carriers of Information are FIELDS of FORCES:
* Pressure Wave Fields of Sound,* Gravity Force Fields,* Magnetic Force Fields and* Electro-magnetic Force Fields.The latter are of our main interest, since
they include visible and invisible LIGHT.
What is REMOTE SENSING ?
(2) RS requires a SENSOR which can detect changes in the carried Signal.
Apart from our own eyes and ears, technology has provided us with a multitude of sensors operating in the detection of force fields:
microphones, geophones,photographic film, video cameras and photo
detectors,radio wave receivers, gravimeters and
magnetometers.
What is REMOTE SENSING ?
(3) RS requires RECORDING, ANALYSIS, INTERPRETATION and REPRESENTATION of the sensed information in a purposeful way.
This is a technique based topic. It is essential for the success or failure of RS in respect of it’s anticipated purpose.
This topic will be dealt with in it’s main aspects (but not completely) in the following lessons.
What is REMOTE SENSING ?
Source of ForceField
Object (generic)
Reflection
Sensor System eg. Camera
Resulting RS Data Set
eg. Image
DATAACQUISITION
What is REMOTE SENSING ?
Object(s)
RS Data Seteg. Image
DATAPROCESSING
Interpretation (secondary) Measurements
Data Processing & Mapping (geometric)Presentation of Processing Results
Explaining deduced OBJECT INFORMATION
ER, the Physical Basis of RS Fraunhofer, Joseph (1877-1826), German optician and
physicist, Spectroscopy Wien, Wilhelm (1864-1928), German physicist, 1911
Nobel Prize in Physics, Wien’s Displacement Law Planck, Max Karl Ernst Ludwig (1858-1947), German
physicist, 1918 Nobel Prize in Physics, laid basis to Quantum Physics, developed Planck’s Law
Einstein, Albert (18779-1955), German(?) physicist, 1921 Nobel Prize in Physics, General Theory of Relativity, and E = m c^2
Serious, Jahoo (still alive), son of Tasmanian apple grower,, How to put bubbles into beer: E = m c^2
ER, the Physical Basis of RS
Fraunhofer discovered ‘black lines’ in the spectrum of light emitted by various superheated chemical elements. These lines were as typical for each of the elements as fingerprints for humans.
Chemical Composition of objects effects emitted ER in a unique way for each element.
Fraunhofer Lines
(found empirically by observation)
ER, the Physical Basis of RSIn Einstein's formula
E = mc^2 E = Energy m = mass (of matter/object) c = propagation velocity of
lightWhat does that tell us ? There is a well defined
relationship between MATTER, ENERGY and ELECTROMAGNETIC RADIATION (eg. light)
Fraunhofer Lines
E = mc2
ER, the Physical Basis of RS
The basic building blocks of all matter are ATOMS
The basic building blocks of Atoms are the NUCLEUS (Neutrons and Protons) and several ELECTRONS.
Electrons are thought to be spinning around the Nucleus at orbits of different, but well pre-defined discrete sequential radii.
ER, the Physical Basis of RSNeutrons are thought to carry NO
Energy charge.Protons are thought to carry a
charge of energy defined as being positive.
Electrons are thought to carry a charge of energy defined as being negative.
Because of the dual polarity (positive <=> negative) an energy potential exists between Nucleus and Electrons
ER, the Physical Basis of RS
An equal number of Electrons and Protons exist in all atoms (isotopes excluded).
A balance exists quasi mechanical between the attraction forces of opposite charges and centrifugal forces of the spinning Electrons.
This balance is an intricate compromise of these forces and the actual energy level inherent to each atom.
ER, the Physical Basis of RS
The energy level contained in an atom can be changed (eg. by heating or cooling).
The balance of forces inside the atom will automatically adept to energy level changes by moving electrons to higher or lower orbits.
ER, the Physical Basis of RS
To have an electron move from it’s current orbit to the next outer orbit, an energy amount equal to one Planck’s Quantum has to be added to the atom (eg. by heating).
To have an electron drop back from an outer orbit to the next inner one, the same amount of energy has to be extracted from the atom.
ER, the Physical Basis of RS
It is this EXTRACTION of energy from an atom when electrons drop back to lower orbits which is of interest to us.
One widely accepted theory says, that atoms lose energy in form of
Electromagnetic Radiation
Energy differential = 1 Planck’s Quantum
ER, the Physical Basis of RSElectromagnetic RadiationOne theory explains ER as a
WAVE field,another as a field of a stream of
PHOTONS, particles so small that they have no mass.
Both are said to propagate at light speed.
Energy differential = 1 Planck’s Quantum E = mc^2
Photon
Wave
ER, the Physical Basis of RS
Electromagnetic Radiation Some atoms may have been
charged to a higher energy level; pushing electrons further than one orbital level. In turn they can drop back over more than one orbit level: more energy than one Quantum
Energy differential = 1 Planck’s Quantum E = mc^2
Photon
Wave
c = const ~ 300000 km/sec
ER, the Physical Basis of RS
Electromagnetic RadiationGerd’s interpretation:
Since c is constant, all photons travel about 300,000 km/sec
Those with a higher energy charge will use a ‘more
wiggly’ (thus, longer) wave path than those with lesser
charge.
Energy differential = 1 Planck’s Quantum E = mc^2
Photon
Wave
c = const ~ 300000 km/sec2 Quantum charge
ER, the Physical Basis of RS
Electromagnetic RadiationWave characteristics:
= Wave length = distance between consecutive wave
peaks (measured in m)f = frequency = number of wave
peaks (wiggles) in the wave train propagating for 1 sec
(measured in Hz) = c / f
c = const ~ 300000 km/sec
ER, the Physical Basis of RS
Electromagnetic RadiationSumming up: High Energy Radiation
proceeds at higher frequencies (shorter wavelength compared to low energy radiation.
Radiation wave length mix depends on amount of (heat) energy contain in an atom
PLANCK’s LAW c = const ~ 300000 km/sec
ER, the Physical Basis of RS
PLANCK’s LAW
c = const ~ 300000 km/sec
Wave Length
Total RadiationEnergy emitted
Radiation Energy Curve foran object (BLACK BODY)at constant temperature.
short long
peak
ER, the Physical Basis of RS
WIEN’s DISPLACEMENT LAW
0K = -273 degree Celsius300K = 27 degree Celsius
Wave Length
Total RadiationEnergy emitted
Radiation Energy Curves foran object (BLACK BODY)at various constant temperatures.
short long
300K1000K
3000k6000K
ER, the Physical Basis of RSUsing Fraunhofer’s Observations
A Black Body is a theoretical, not a real object.
Real Objects will produce somewhat different radiation output pattern.
c = const ~ 300000 km/sec
Wave Length
Radiation Energy Curve foran object at constant temperature.
short long
Gerd’s realobject
ER, the Physical Basis of RSUsing Fraunhofer’s Observations The variation in Radiation output from a REAL OBJECT
depends on it’s chemical composition. Water has a different SPECTRAL SIGNATURE than soil or chlorophyll containing leaf matter, etc.
Wave Length
Radiation Energy Curve foran object at constant temperature.
short long
Gerd’s realobject
QUESTIONS:• Can we use these facts to measure object temperatures?• Can we use these facts to identify the chemical composition of objects and• can we use the latter to identify the object itself?
ER, the Physical Basis of RS
WIEN’s DISPLACEMENT LAW
Wave Length
Total RadiationEnergy emitted
Radiation Energy Curves foran object (BLACK BODY)at constant temperatures.
short long
300K1000K
3000k6000K
The Average Temperature of Earth’s Surface rarely
exceeds 300 K, an object temperature to low to
provide for EMITTED RADIATION of sufficient
strength to register on most of the available sensors (except in thermal IR).
(Even warm nights can be pitch black)
ER, the Physical Basis of RS
WIEN’s DISPLACEMENT LAW
Wave Length
Total RadiationEnergy emitted
Radiation Energy Curves foran object (BLACK BODY)at constant temperatures.
short long
300K1000K
3000k6000K
The surface of the Sun’s outer atmosphere (photosphere) has a temperature of about
5800K, hot enough to provide adequate radiation
energy. (Peak output in GREEN of visible light).
Most RS systems utilise reflected sun light.
ER, the Physical Basis of RS
WIEN’s DISPLACEMENT LAW
Wave Length
Total RadiationEnergy emitted
Radiation Energy Curves foran object (BLACK BODY)at constant temperatures.
short long
300K1000K
3000k6000K
QUESTION: Does incident sun light interact in a similar way with matter as described is the case for emitted radiation?
ANSWER: YES! ER (including light) is a form of energy (as is heat). Matter (atoms) can absorb as well as emit energy.
ER, the Physical Basis of RS
WIEN’s DISPLACEMENT
Wave Length
Total RadiationEnergy emitted
Radiation Energy Curves foran object (BLACK BODY)at constant temperatures.
short long
300K1000K
3000k6000K
Objects under illumination by sun light will partially absorb radiation.
Absorption level varies with wave length depending on chemical composition of the object
Radiation not absorbed is mostly reflected and available for RS.
Spectral Signatures
ER, the Physical Basis of RS
Examples of Spectral Signatures(not to exact scale; see Textbook)
50
0.4 (blue) 0.80.6 (red)0.5 (green) 0.7 (IR=>) 1.0m
Reflectance
(of Sun Light)
0
Bare Soil (Grey/Brown)
Vegetation (green)
Water (clear)
(<= UV)
ER, the Physical Basis of RS
The Electromagnetic Spectrum(not to exact scale; see Textbook)
10^-6 10^-3 1 1000.1 10^5 10^8
-Rays
Sound
X-Ray UV
Visible
0.4 0.5 0.6 0.7 m
m
TV/RadioMicro-Wave
Thermal Infrared
Near & Mid Infrared
Wave Length
not part of ER)
Note: outsidethe visible Range,no colours orshades will be perceived.Blue Green Red
ER, the Physical Basis of RS
The General Remote Sensing Model
I
R
AT
A
Sensor
RadiationSource
I = R + A + T
SimplifiedRadiation-Balance
R = I - A - T
I = Incident ERR = ReflectedA = AbsorbedT = TransmittedS = Scattering
S
ER, the Physical Basis of RS
A bright Idea for RS
50
0.4 (blue) 0.80.6 (red)0.5 (green) 0.7 (IR=>) 1.0m
Reflectance
(of Sun Light)
0
Bare Soil (Grey/Brown)
Vegetation (green)
(<= UV)
G R IR
Veg. SoilG med medR low highIR high+ high
Truth Table
ER, the Physical Basis of RS
A bright Idea for RS
G R IR
Truth Table
Veg. SoilG med medR low highIR high+ high
Landsat 7