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


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


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


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 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)


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 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 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.


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 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.


(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.


(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.


(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.


Source of ForceField

Object (generic)

Reflection

Sensor System eg. Camera

Resulting RS Data Set

eg. Image

DATAACQUISITION


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


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


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.


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.


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.


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


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


Photon

Wave

c = const ~ 300000 km/sec


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.


Photon

Wave

c = const ~ 300000 km/sec2 Quantum charge


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



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


PLANCK’s LAW


Wave Length

Total RadiationEnergy emitted

Radiation Energy Curve foran object (BLACK BODY)at constant temperature.

short long

peak


WIEN’s DISPLACEMENT LAW

0K = -273 degree Celsius300K = 27 degree Celsius

Wave Length


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.


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?



Wave Length


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)



Wave Length



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.



Wave Length



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.


WIEN’s DISPLACEMENT

Wave Length



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


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)


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


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


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


A bright Idea for RS

G R IR

Truth Table

Veg. SoilG med medR low highIR high+ high

Landsat 7

Introduction to remote sensing

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