Final Exam Lecture Flashcards
Why use remote sensing?9
- a regional view (in general), even a local view now a
days. - repetitive looks at the same area
- “see” over a broader portion of the spectrum than the human eye
- Remote sensors often record signals electronically
and provide geo-referenced digital data - Sensors can use a very specific bandwidth for imaging
- They can also use a number of bandwidths
simultaneously - Some remote sensors operate in all seasons, at night,
and in bad weather - Images are permanent record (fixed in time)
- Often more accurate source of historical information
What elements are involved in remote sensing?General 5
• EM Energy • Atmosphere • Objects • Satellite system -Use of energy source -Use of energy bands -Data acquisition approach -Capture -Storage and archive -Distribution • Data processing and analysis methodology -Visual -Digital
___ radiation is the carrier of electro-magnetic energy by transmitting the
oscillation of the electric and magnetic fields through space or matter.
EM radiation is the carrier of electro-magnetic energy by transmitting the
oscillation of the electric and magnetic fields through space or matter.
The spectral sensitivity of the human eye(visible light) is from about . to _._which is termed as visible
wavelength of EM spectrum.
0.4-0.7
4 basic rules of wave theory
Ex:Assume the speed of light to be 3x10(8) m/s. If the
frequency of an electromagnetic wave is 500,000 GHz
(GHz = gigahertz = 109 m/s), what is the wavelength of
that radiation?
-give answer in micrometers,nanometers, and centimeters
1.. Electromagnetic radiation consists of
a. an electrical field (E), which
varies in magnitude in a direction
perpendicular to the direction in
which the radiation is traveling,
and
b. a magnetic field (M) oriented at
right angles to the electrical field.
Both these fields travel at the
speed of light (c).
2.The wavelength is the length of one wave cycle, which can be measured as the distance between successive wave crests -A wavelength is usually represented by the Greek letter lambda (λ). Wavelength is measured in metres (m) or some factor of metres such as nanometres (nm, 10-9 metres), micrometres (μm, 10-6 metres) or centimetres (cm, 10-2 metres).
- Frequency refers to the number of cycles of a wave passing a fixed point per unit of time.
-Frequency is normally measured
in hertz (Hz), equivalent to one
cycle per second, and various
multiples of hertz.
4. Wavelength and frequency are related by the following formula: λν=c where λ is the wavelength, ν is the frequency and c is the speed of light.
Ex:Assume the speed of light to be 3x10(8) m/s. If the
frequency of an electromagnetic wave is 500,000 GHz
(GHz = gigahertz = 109 m/s), what is the wavelength of
that radiation?
(3x108 m/s)/(500,000,000,000,000)
=6x10(7) meters
=6x10(13) micrometers
______ the wavelength the _____ the frequency
shorter,higher
______ the frequency the _____ the wavelength
lower,longer
_____ light is most easily absorbed by atmos
visible
-becomes innacurate after
Role of atmos in remote sensing: 4
The sunlight’s transmission through the atmosphere is affected by absorption and scattering of atmospheric
molecules and aerosols.
Similarly, the reflected and emitted energy that is
received by a satellite sensor are also modified by the
atmospheric molecules and aerosols.
3 types of Scattering of EM by the Atmospheric elements
- Rayleigh scattering: occurs when the particles (gas
molecule) causing the scattering are significantly smaller than the wavelengths being affected.
• Blue Sky & Red Evening light - Mie scattering: the particles (dust or smoke) causing the scattering are roughly the same diameter as the
wavelengths they’re scattering. - Nonselective scattering: what’s (water droplets)
causing the scattering is larger than the wavelengths
being scattered.
• all wavelengths equally; explains why we see clouds as white if it is not much thick
3 interactions of EM with Earth Surface objects
reflected (R),
absorbed (A) or
transmitted (T)
2 types of light that are reflected from vegetation
Infrared and Green
EM interaction with water
What is there is suspended sediment?
longer wavelengths-more absorption by water
blue-is the most reflected by water
-means higher reflectivity in all bands
4 Main Classes of visible wavelength and μm
• blue is about 0.4 to 0.5 μm
• green is about 0.5 to 0.6 μm
• red is about 0.6 to 0.7 μm
Near infrared: 0.8-0.9
Describe Wavelengths for each? Clear Lake Water: Turbid river Water: Vegetation: Dry Soil: Wet Soil:
Clear Lake Water:lower reflectance than turbid
Turbid river Water: higher reflectance than clear, lasts into longer wavlengths
Vegetation: minimal reflection up until around 0.5-0.6(green) then goes down and increases to maximum at near infrared and infrared (0.8 up)
Dry Soil:much higher reflectance than wet
Wet Soil:
Microwave wavelength: can be used at…
any time of day or night
Infrared energy is the heat coming out of a vegetation
-________ the vegetation, the more Heat Energy coming off of it
Infrared energy is the heat coming out of a vegetation
-HEALTHIER the vegetation, the more Heat Energy coming off of it
ultra blue band(lower than blue) is useful for
Two thermal bands 10 and
11 are useful iTwo thermal bands 10 and
11 are useful in ….
New band 1 (ultra-blue) is useful for coastal and aerosol studies
Two thermal bands 10 and
11 are useful in providing
more accurate surface
temperatures.
Spatial resolution of:
___ meters (visible, NIR, SWIR);
___ meters (thermal);
and ___ meters (panchromatic).
30,100,15
Principal Applications of Blue, Greeen, Red, Near Infrared
- 0.45-0.52. Blue. Water body penetration makes this band useful for coastal water mapping. Also useful for soil/vegetation discrimination, forest type mapping, and cultural feature identification.
- 0.52-0.60. Green. Suitable for measuring the green reflectance peak of vegetation for vegetation discrimination and vigor assessment. Also useful for cultural feature identification.
- 0.63-0.69. Red. A chlorophyll absorption region aids in plant species differentiation. Also useful for cultural feature identification.
- 0.76-0.90. Near-infrared. Useful for determining vegetation types, vigor, and biomass content, for delineating water bodies, and for soil moisture discrimination.
________ data: when you have many bands within your study
Hyperspectral
______ clouds: interceptor of all the signals in and out
cirrus
to delineate between water/moisture level what is the best em to use?
infrared
If you wanted to map the deciduous (e.g. maple, birch) and the coniferous (e.g. pine, fir, spruce) trees in a forest in summer using remote sensing data, what would be the best way to go about this and why?
- Infrared-because there is the biggest deviation
- deciduous trees reflect alot more then coniferous
_______ trees reflect less than ________ trees in infrared
coniferous
deciduous
Image Pixel value:grayscale
Black=
gray=
White=
0
127
255
need to ______ pixels if using data from different satellite types
coregister
. Remote sensing uses _______ colour system
. when printing a map it is ______ colour system
. Remote sensing uses Additive colour system
-when printing a map it is Subtractive colour system
False colour composite
Blue Gun:
Green Gun:
Red Gun:
Blue Gun:Green
Green Gun:Red
Red Gun:near-Infrared
Normalized Difference Vegetation Index
Normalized Difference Vegetation Index
(NDVI) = (NIR - Red)/
(NIR + Red)
ex:
(0.50-0.08)/(0.50+0.08)
=0.72
ex:
(0.40-0.30)/(0.40+0.30)
=0.14
Image Classification
Digital Classification
Image classification is the process of categorization of all image pixels into land cover classes to produce a thematic representation of the image.
Digital classification is a the process of recognising patterns in the image pixel values in one or multiple bands and assign them to one of the land cover classes.
Patterns in an Image:
Spectral Pattern ( pixel values in different bands - 110, 49, 70……..)
Spatial pattern (contextual information)
Temporal information (e.g. agriculture)
Classification can be done on single or multiple bands of image as well as adding other raster GIS layers, various methods
Training Pixels/Samples
- are typical representative pixels’ values from each class of interest to be supplied to the computer or classifier to be used for the classification.
Analyst identifies the groups of pixels with similar spectral pattern
Each of the patterns represents a category of land cover class
The statistical properties of the patterns are used for categorizing all pixels of the image set
Describe 4 resolution types
1.Spectral resolution:
Panchromatic-brightness
Multispectral-multiple wavelengths
Hyperspectral-loads of different wavelengths
2.Spatial resolution: pixel size->pixel output
smaller pixels mean more clear view
- Radiometric resolution:“how many different
intensity levels can be discriminated by the remote sensor within a specific band
Number of digital levels that a sensor can use to express variability of brightness within the data. It
determines the information content.
The more digital levels, the more detail can be expressed
Most remote sensing imagery recorded with
quantized levels in the 0 – 255 (8-bit) range - Temporal resolution:
Refers to the frequency of data acquisition over
an area.
• Important :
– infrequent observational opportunities (e.g., when
clouds often obscure the surface)
– short-lived phenomenon (floods, oil spills, etc.)
– rapid-response (fires, hurricanes)
– detecting changing properties of a feature to
distinguish it from otherwise similar feature
More bits means more ____
clarity
Swath
the Image extent:
.Refers to the “Swath” with of image acquisition by a
satellite image
-length and width of what the sattelite actually captures
Number of images to cover study area
Generally, higher spatial resolution = smaller
area coverage per frame = more scenes
Data sources for terrain mapping(2)
Direct Measurement -survey -GPS -Contours points from a topographic map Remote Sensing -Aerial photos - Satellite data - LiDAR
point cloud data
Data collected by lider system
