Remote Sensing Lecture Midterm

Problems Associated with In Situ Data Collection

method produced errors introduced by

-sampling design does not capture the spatial variability

-improper operation

-uncalibrated in situ measurement instruments

Remote sensing definition

"the measurement or acquisition of information of some property of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object or phenomenon under study" (Colwell, 1997).

combined formal definition of photogrammetry and remote sensing

"the art, science, and technology of obtaining reliable information about physical objects and the environment, through the process of recording, measuring and interpreting imagery and digital representations of energy patterns derived from noncontact sensor systems".

IFOV

Instantaneous field of view

EMR

electromagnetic radiation

Remote Sensing scientific activity

Using sensors to measure the amount of electromagnetic radiation (EMR) exiting an object or geographic area from a distance and then extracting valuable information from the data using mathematically and statistically based algorithms

Interaction Model Depicting the Relationships of the Mapping Sciences as they relate to Mathematics and Logic, and the Physical, Biological, and Social Sciences

A superior image analyst is able to...

1) understand the scientific principles better

2) are more widely traveled and have seen many landscape objects and geographic areas, and/or

3) have the ability to synthesize scientific principles and real-world knowledge to reach logical and correct conclusions

The EMR reflected, emitted, or backscattered from an object or geographic area is used as a _________ for the actual property under investigation

surrogate

passive remote sensing

-unobtrusive

-sensor passively records the EMR reflected or emitted by the object of interest

-does not disturb the object or area of interest

Remote sensing can provide biophysical information such as...

-x,y location

-z elevation or depth

-biomass

-temperature

-moisture content

Remote sensing devices can be programmed to collect data systematically to remove ________ ____

sampling bias

Remote sensing can be used to model natural processes such as...

-water-supply estimation

-eutrophication studies

-nonpoint source pollution

Remote sensing can be used to model cultural processes such as...

-land-use conversion at the urban fringe

-water-demand estimation

-population estimation

Limitations of Remote Sensing

-Often oversold

-Human method-produced error

-active remote sensor systems can emit intrusive electromagnetic radiation

-uncalibrated instruments

-expensive to collect and analyze

Remote sensing process definition

The remote sensing data-collection and analysis procedures used for Earth resource applications are often implemented in a systematic fashion

Remote sensing process steps

1. Statement of the problem

2. Data Collection

3. Data-to-information conversion

4. Information Presentation

Remote sensing process- Statement of the Problem steps

1. Formulate Hypothesis

2. Select Appropriate Logic

3. Select Appropriate Model

Remote sensing process- Data Collection steps

1. In Situ Measurements

2. Collateral Data

3. Remote Sensing

Remote sensing process- Data-to-Information Conversion steps

1. Analog (visual) image processing

2. Digital Image Processing

3. Hypothesis testing

Remote sensing process- Information Presentation steps

1. Image Metadata

2. Accuracy Assessment

3. Analog and Digital

4. Statistics

5. Graphs

Spatial resolution

the size of the field-of-view

Spectral resolution

the number and size of spectral regions the sensor records data in

Temporal resolution

how often the sensor acquires data

Radiometric resolution

the sensitivity of detectors to small differences in electromagnetic energy.

angle of incidence

the angle of the incoming energy that illuminates the terrain

angle of exitance

angle of energy from the terrain to the sensor system

angular characteristics are a function of

-location in a three-dimensional sphere of the illumination source

-orientation of the terrain facet

-location of the suborbital or orbital remote sensing system

In situ and remotely sensed data are processed using...

a) analog image processing

b) digital image processing

c) modeling

d) n-dimensional visualization.

Information that may be useful for modeling includes

• the global carbon cycle

• biology and biochemistry of ecosystems

• aspects of the global water and energy cycle

• climate variability and prediction

• atmospheric chemistry

• characteristics of the solid Earth

• population estimation

• monitoring land-use change and natural hazards

Examples of shorter wavelengths on the electromagnetic spectrum

gamma and x rays

Examples of longer wavelengths on the electromagnetic spectrum

microwaves and broadcast radio waves

Energy conduction

conducted from one object to another by being in direct physical contact

Energy Convection

Sun heats Earth with radiant energy, heating up the air near the surface, hot air rises creating convectional currents in the atmosphere

Radiation

The transfer of energy by electromagnetic waves (as in from the sun through the vacuum of space)

Wave Model

-Concept of electromagnetic radiation

Wave model- the electromagnetic wave consists of two fluctuating fields at right angles, these fields are ________ and ________

electric, and magnetic

The wavelength of electromagnetic radiation depends upon the length of ____that the charged particle is accelerated

time

frequency of electromagnetic radiation (v) depends on the number of _____________ ___ ______

accelerations per second

Wavelength Definition

the mean distance between maximums (or minimums) of a roughly periodic pattern and is normally measured in micrometers or nanometers (nm).

Frequency definition

the number of wavelengths that pass a point per unit time. A wave that sends one crest by every second (completing one cycle) is said to have a frequency of one cycle per second or one hertz, abbreviated 1 Hz

The longer the wavelength the _____ the frequency

lower

The amplitude of an electromagnetic wave is the ______ of the wave crest above the undisturbed position.

height

The electromagnetic energy from the Sun travels in _ minutes across the intervening __ million miles (150 million km) of space to the Earth.

8, 93

The earth approximates a ___ K (__ degrees C) blackbody

300k (27 deg C)

The earth has a dominant wavelength at

9.7

The sun has a ____ K blackbody

6,000

the amount of energy emitted by an object such as the Sun or the Earth is a function of its ___________

temperature

The formula used to determine dominant wavelength

Wein's Displacement law

The sun produces __% of its energy in the visible region (.4-.7)

41%

Quantum Theory of electromagnetic radiation

energy is transferred in discrete packets called quanta or photons

Thus, the energy of a quantum is _________ proportional to its wavelength

inversely

Electrons

the tiny negatively charged particles that move around the positively charged nucleus of an atom.

radiation is produced by changes in the energy levels of the ____ ______ _________

outer, valence electrons

Every time an electron jumps from a higher to a lower energy level, a ______ moves away at the speed of light.

photon

quantum leap

Somehow an electron might disappear from its original orbit and reappear in its destination orbit without ever having to traverse any of the positions in between

________ scattering causes the atmosphere to appear blue

Rayleigh

Atmospheric Scattering is a function of

wavelength and size of gas molecule

Mie scattering takes place when...

there are essentially spherical particles present in the atmosphere with diameters approximately equal to the wavelength of radiation being considered

Atmospheric Layers and Constituents (image)

Rayleigh scattering occurs when...

the diameter of the matter (usually air molecules) are many times smaller than the wavelength of the incident electromagnetic radiation.

All scattering is accomplished through absorption and re-emission of _________ by atoms or molecules

radiation

The amount of scattering is _________related to the fourth power of the radiation's wavelength.

inversely

Non-selective scattering is produced when...

there are particles in the atmosphere several times the diameter of the radiation being transmitted.

Absorption....

the process by which radiant energy is absorbed and converted into other forms of energy

absorption band

a range of wavelengths (or frequencies) in the electromagnetic spectrum within which radiant energy is absorbed by substances such as water (H2O), carbon dioxide (CO2 ), oxygen (O2 ), ozone (O3 ), and nitrous oxide (N2O).

The cumulative effect of the absorption by the various constituents can cause the atmosphere to _____ ____ in certain regions of the spectrum

close down

atmospheric windows

Parts of the spectrum that transmit energy effectively

Absorption occurs when...

-energy of the same frequency as the resonant frequency of an atom or molecule is absorbed, producing an excited state

-the energy is transformed into heat motion and is reradiated at a longer wavelength,

When dealing with a medium like air, absorption and scattering are frequently combined into an __________ ___________

extinction coefficient

Simplified definition of reflectance

Reflectance is the process whereby radiation "bounces off" an object like a cloud or the terrain

Process of Reflectance

re-radiation of photons in unison by atoms or molecules in a layer one-half wavelength deep.

Specular reflection occurs when

the surface from which the radiation is reflected is essentially smooth (i.e. the average surface profile is several times smaller than the wavelength of radiation striking the surface).

diffused radiation

when the reflecting surface is rough, the reflected rays go in many directions, depending on the orientation of the smaller reflecting surfaces.

- white paper

-white powder

a perfectly diffuse surface (Lambertian surface)

-the radiant flux leaving the surface is constant for any angle of reflectance to the surface normal.

-the surface is so rough that there are no individual reflecting surfaces

Radiation Budget Equation

the total amount of radiant flux in specific wavelengths (l) incident to the terrain ( ) must be accounted for by evaluating the amount of radiant flux reflected from the surface ( ), the amount of radiant flux absorbed by the surface ( ), and the amount of radiant flux transmitted through the surface ( ):

radiant flux

The time rate of flow of energy onto, off of, or through a surface. Measured in watts

Hemispherical Reflectance

the dimensionless ratio of the radiant flux reflected from a surface to the radiant flux incident to it

Hemispherical transmittance

the dimensionless ratio of the radiant flux transmitted through a surface to the radiant flux incident to it

hemispherical absorptance

dimensionless relationship

Irradiance

The amount of radiant flux incident upon a surface per unit area of that surface

Exitance

The amount of radiant flux leaving per unit area of the plane surface

Radiance

s the radiant flux per unit solid angle leaving an extended source in a given direction per unit projected source area in that direction and is measured in watts per meter squared per steradian

Radiance from paths 1, 3, and 5 contains....

intrinsic valuable spectral information about the target of interest.

path radiance (Lp ) from paths 2 and 4 includes

diffuse sky irradiance or radiance from neighboring areas on the ground.

index of refraction (n)

a measure of the optical density of a substance. This index is the ratio of the speed of light in a vacuum, c, to the speed of light in a substance such as the atmosphere or water, cn

The speed of light in a substance can never reach the speed of light in a vacuum. Therefore, its index of refraction must always be greater than....

1

Anytime energy is propagated through the atmosphere for any appreciable distance at any angle other than vertical, __________occurs.

refraction

The amount of refraction is a function of the

angle made with the vertical , the distance involved (in the atmosphere the greater the distance, the more changes in density), and the density of the air involved

Serious errors in location due to refraction can occur in images formed from energy detected at high altitudes or at acute angles. ______ ___ can predict this and be removed

Snells Law

Types of aerial cameras:

1. single-lens mapping (metric) camera

2. multiple-lens (multiple-band) camera

3. digital camera

4. miscellaneous cameras

The ability of a portion of a developed film to pass light is called its

transmittance

RS Data must be calibrated in two ways:

1. geometrically and radiometrically

2. calibrated to characteristics on the ground

Remote Sensing process:

1. statement of the problem

2. data collection

3. data-to-information conversion

4. information presentation

Types of resolution:

1. spatial

2. spectral

3. temporal

4. radiometric

5. thematic

Angular characteristics associated with each pixel are a function of:

1. location of the source of illumination (sun if passive, sensor if active)

2. orientation of the terrain

3. location of the sensor

Data processing types:

1. analog image processing

2. digital image processing

3. modeling

4. n-dimensional visualization (2D or 3D?)

GPS devices can be accurate to

10 cm

Aim for __% accuracy

80

Types of reflection:

1. specular reflectance (smooth)

2. diffused reflectance (rough)

3. Lambertian reflectance (perfectly rough)