MIDTERM Flashcards
the three major components of geospatial technologies
GIS
GPS
remote sensing
scientific method
systematic way of gathering information and answering questions
seven steps of the scientific method
identify the problem
form a hypothesis
make observations/perform experiments
do experiments and observations support hypothesis
organize and analyze data
draw conclusions
communicate results
in situ data collection
when a measurement is taken in the same place where the phenomenon is occurring
examples of in situ data collection
GPS unit
thermometer
spectral radiometer
the two distinct ways in which remotely sensed data must be calibrated
1) geometrically (x, y, z) and radiometrically (% reflectance) so that data obtained on different dates can be compared
2) calibrated with what is on the ground in terms of environmental, biophysical or cultural characteristics
three types of remote sensing
satellite
aerial photography
UAS (drones)
the two attributes of instantaneous field of view
solid angle (3 dimensional cone) - a measure of how large the object appears to a sensor looking from that point
altitude above ground - vertical distance between the object and the sensor
the two types of remote sensing platforms
orbital (satellite) and suborbital (aircraft/UAS)
the two types of remote sensing instruments
passive (external source of energy, such as reflected solar radiation) and active (sends a pulse of energy from the sensor to the object)
platform and instrument best for measuring 30 year change in amazon forest
orbital platform and passive instrument
platform and instrument best for monitoring environmental impact of construction site
suborbital platform and passive instrument
platform and instrument best for seeing backside of moon
orbital platform and active instrument
examples of passive sensors
landsat
terra
aster
examples of active sensors
lidar
sar
why is remote sensing a science
science is the broad field of human knowledge concerned with facts held together by rules
sciences include math and logic, physical sciences, biological sciences, social sciences and remote sensing is involved in all of these
what is remote sensing
the use of remote sensors to detect and measure the amount of electromagnetic radiation exiting an object or geographic area from a distance and then extracting valuable information from the data using math and stats based algorithms
what is as the core of geospatial technologies
GIScience
why is remote sensing an art and a science
it combines scientific knowledge with real world analyst experience
advantages of remote sensing
provides new scientific information
can be obtained systematically over very large areas (satellite only)
unobtrusive (but lidar can disturb environment because it sends out laser pulses)
limitations of remote sensing
not a panacea
human method-produced error may be introduced
some remote sensing systems can be intrusive
instruments may become uncalibrated
data can be very expensive to collect and analyze
camera obscura
a dark box with a small hole that lets in light to produce an upside down and backwards image on the opposing wall
year and inventor of the first photograph
1826 and Joseph Nicéphore Niépce
year, name, and inventor of first commercially successful camera
1839, daguerreotype, Louis Daguerre
year, name, and inventor of first consumer camera
1888, Kodak, George Eastman
how was Kodak camera different
affordable, roll film could be taken to be developed
first known surviving aerial photograph
Tournachon (Nadar) via tethered balloon
inventors of world’s first successful
motor operated airplane in 1903
Wright brothers
origins of using remote sensing
military photo reconnaissance during
WWI and WWII
U2 aerial reconnaissance
program
used during cold war
very difficult to fly
Lockheed SR 71 “Blackbird”
flew higher and faster than U2
NASA’s Earth Observing System (EOS)
series of polar orbiting and low inclination satellites for long term global observations of the land surface, biosphere, solid Earth, atmosphere, and oceans
Unmanned Aircraft System (UAS)
a reconnaissance aircraft that is piloted from the ground via remote control
false color composite
created by putting the near infrared band
image in the red channel, the red band image in the green channel, and the green band image in the blue channel
can highlight vegetation
what is energy
the ability to do work
the six basic forms of energy
Chemical
Electrical
Nuclear
Thermal
Radiant
Mechanical
the three forms of energy transfer
conduction
convection
radiation
conduction
requires DIRECT CONTACT
temperature difference - frying pan on burner
convection
the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat
radiation
transfer of heat without any physical contact between objects
which form of energy transfer is the fastest
radiation
how solar energy is transferred
electromagnetic radiation
why EMR is of interest in remote sensing
does not need a medium to occur
can propagate in a vacuum space such as the space between earth and sun at the speed of light
how EMR travels
waves
the two parameters that describe an EMR wave
wavelength
frequency
wavelength
the distance between two adjacent crests or troughs
measured in micrometers (µm) or nanometers (nm)
frequency
the number of wavelengths that pass a point per unit time
1 Hertz = 1 wavelength/second
wavelength and frequency have an _______ relationship
inverse
as frequency increases, wavelength decreases
the speed of an EM wave
the speed of light
quantum theory of EMR
energy is transferred in discrete packets of particles called quanta or photons
photoelectric effect
is the emission of electrons when EMR hits a material
Stefan Boltzmann Law
the amount of energy any object radiates per unit area is a function of its surface temp
the electromagnetic spectrum
used to examine the properties of EMR in relation to wavelength
EM spectrum in order of increasing wavelength
radio
microwave
infrared
visible
ultraviolet
x-rays
gamma rays
Raging Martians Invaded Venus Using X-ray Guns
band
the spectral region of EMR wavelengths measured by a remote sensing device
if wavelength increases, frequency decreases and energy _______
decreases
if wavelength decreases, frequency increases and energy _______
increases
TRUE/FALSE
there is no clear cut dividing line between one spectral region and the next
TRUE
Wien’s Displacement Law
states that the radiation emitted by a blackbody peaks at a wavelength that is inversely proportional to the temperature
blackbody
a theoretically idealized physical body that absorbs all incident EMR and does not reflect any
Re: blackbody peak radiation – as temperature increases, dominant wavelength shifts toward the ______ wavelength (_____ frequency)
short, high
As temperature increases, radiation increases in a ______ shape (Stefan Boltzmann Law)
exponential
four distinct layers of the atmosphere in order from bottom to top
troposphere
stratosphere
mesosphere
thermosphere
in the troposphere, temperature _____ as altitude increases
decreases
the most active zone of the atmosphere is the ______
troposphere
environmental lapse rate in troposphere
temperature decreases 6.5°C per kilometer of altitude increase
the stratosphere contains the _____, which filters UV radiation from the sun
ozone layer
commercial jets fly in the _______ because there is _______
stratosphere, calm air and fuel efficiency
the coldest layer of the atmosphere is the ________
mesosphere
ionization occurs in the ____ layer of the atmosphere
mesosphere
in the thermosphere, gas molecules are _______ therefore there is no ______
far apart, heat exchange
auroras occur in the ______ layer of the atmosphere
thermosphere
99% of the atmosphere is made up of ________
nitrogen
oxygen
argon
____ percent of total incoming solar radiation (direct and indirect) reaches the earth’s surface
45
the troposphere is heated by _____ radiation emitted from the earth
longwave
the sun emits _____ radiation while the earth emits _____ radiation
shortwave, longwave
radiation budget
the balance between incoming radiation (shortwave) from the sun and outgoing radiation (longwave) from the earth
for the radiation budget to be balanced, net radiation must be _____
zero
four ways in which solar radiation interacts with earth’s atmosphere
refraction
absorption
scattering
reflection
refraction is the ______ of light due to differing ______ and _______
bending, densities, speed of light
because of ______, when we look at the sun, the perceived position is ______ than its true position
refraction, higher
Snell’s law
used to calculate how much bending will take place based on the angle of incidence and the optical density of each substance
absorption
process by which EMR is absorbed by the atmospheric particles and converted into other forms of energy
absorption band
range of wavelengths in the spectrum within which radiant energy is absorbed by substances such as water (H2O), carbon dioxide (CO2), oxygen (O2)
atmospheric window
atmosphere essentially closes down in certain portions of the spectrum and thus remote sensing can operate
scattering
when EMR hits atmospheric particles and is redirected back out in random directions
when diameter of atmospheric particle is less than the EMR wavelength, ___________ scattering occurs
Rayleigh
when diameter of atmospheric particle is equal to the EMR wavelength, ___________ scattering occurs
Mie
when diameter of atmospheric particle is greater than the EMR wavelength, ___________ scattering occurs
non-selective
______ scattering is responsible for blue sky and orange/red sunrise/sunset
Rayleigh
The _____ band is scattered the most because it has the _____ wavelength
blue, shortest
_____ scattering causes a hazy/orangish look due to smoke and dust
Mie
___________ scattering is why clouds are white because all wavelengths being scattered equally
Non-selective
reflection
change in direction of EMR at an interface between two different media
reflection is different from scattering because the direction is _______
predictable
Specular reflection
angle of incidence = angle of exitance
(flat surface)
Diffuse reflection
EMR is reflected at many angles
(rough surface)
in remote sensing we are most interested in _______ reflection because it contains information about the color of the reflecting surface
diffuse
a ________ is the ideal diffuse reflector
lambertian surface
sunsets and sunrises appear red because sunlight is traveling a _____ distance and red light is scattered the _____
longer, least
radiant flux
radiant energy per unit time (Watts)
the total amount of incident radiant flux is called
insolation
irradiance
radiant flux per unit area (W/m^2)
radiation budget equation
total irradiance = radiant flux (reflected) + radiant flux (absorbed) + radiant flux (transmitted)
reflectance
ratio of radiant flux reflected and total irradiance
radiance
radiant flux per solid angle and per projected unit
___________ is the most important measurement in remote sensing
radiance
spectral signature plot
wavelength on x axis and reflectance on y axis
spectral signature is a ________ for an object
unique identifier
natural grass and artificial turf have the same reflectance in the ____ spectrum but natural grass has much higher reflectance in the ______ portion of the spectrum
visible, NIR
why can blue band images appear hazy
scattering due to shorter wavelength (Rayleigh)
four types of remote sensing resolution
spatial
temporal
spectral
radiometric
A ______ is the smallest unit of a digital image
pixel
spatial resolution
a measure of the smallest ground object that can be detected by the remote sensor
temporal resolution
how often sensor acquires data of the same location
spectral resolution
the number of bands and size of specific wavelength intervals
the more bands you have, the narrower they are
radiometric resolution
the sensitivity of remote sensing detectors to small differences in electromagnetic energy
also called pixel depth
the higher the spatial resolution, the _____ the temporal resolution
lower (less frequent re-visit)
if you want to see high spatial resolution, you need to fly very low, which means there is a longer revisit period
how to compensate for the spatial/temporal tradeoff
more satellites
how many bits can the human eye see
about 4
Full Width at Half Maximum
a more precise way of stating bandwidth
we care about peak intensity even if bandwidth covers some wavelengths we don’t want
______ is the brightest pixel value
255
A ______ sensor has several, wide spectral bands
multispectral
A ______ sensor has a lot of narrow bands (hundreds of spectral bands)
hyperspectral
spectral resolution of human eye
400-700 nm (visible light)
geostationary orbit
does not move at all relative to the ground
rotates at the same direction and speed as Earth
always directly over the same place on the Earth’s surface
near polar orbit
north to south path wherein the satellite moves close to the North and South Poles as it makes several passes a day about Earth
swath width
measurement of the width of ground the satellite can image during one pass
the closer a satellite is to Earth, the _____ it orbits
faster
geostationary (____ altitude) and sun-synchronous (____ altitude)
high, low
ndvi formula
nir - red / nir + red
a sun synchronous orbit always __________________
crosses the same area at the same local time
the longest running enterprise for acquisition of satellite imagery of Earth
Landsat
the two Landsat 8 sensors on board
OLI (Operational Land Imager)
TIRS (Thermal Infrared Sensor)
Landsat uses the ________________, which divides the
entire globe into a series of paths (columns) and rows
Worldwide Reference System (WRS)
which satellites carries modis sensor
terra and aqua
when was terra launched
1999
when was aqua launched
2002
The temporal resolution for MODIS is
1 to 2 days
which satellite carries aster sensor
terra
the three steps of image preparation
layer stacking
image mosaicking
image subsetting
layer stacking
stacking multiple bands into a single image file
for example for ndvi, we need red and nir stacked
steps of layer stacking
make sure all image layers are acquired by same sensor at the same time
check all image layers have same spatial extent
check all layers are georectified using the same spatial reference
image mosaicking
combing multiple scenes to cover entire study area
True/False - To perform mosaicking, there must be image overlap
True
different types of mosaic operators
minimum, maximum, mean, first/overlay, last, sum (not recommended), blend/feather (very common - uses a distance-weighted/averaging algorithm)
image subsetting
getting rid of any areas that are not in study area
requires a pre-defined area of interest, such as in a shapefile
8 elements in image interpretation
Tone/Color
Shape
Size/Scale
Texture
Pattern
Shadow
Site/Association
Expert/local knowledge
The higher the satellite’s orbit, the _____ the swath width and the ______ the spatial resolution
wider, lower
the narrower the swath width, the ______ the spatial resolution
better
a narrow swath width leads to _____ temporal resolution
lower (longer revisit)
sun-synchronous orbit is a type of ______ orbit
near-polar orbit
Polar orbits are a type of _____ Earth orbit
low
GPS uses a ______ earth orbit
medium
when was first landsat launched
1972
Watts are are equivalent to
Joules/second
Radiation occurs from all objects at temperature ______
> 0 K
The electromagnetic wave consists of _____ fluctuating fields
two
Before quanta/photon theory, light was thought of as
a smooth and continuous wave
altitude of troposphere
sea level –12 km
altitude of stratosphere
12 –50 km
altitude of mesosphere
50 –80 km
meteors burn up in the _____ layer
mesosphere
altitude of thermosphere
80 –480 km
The greater the amount of smoke and dust particles in
the atmosphere, the more ________light will be
scattered away, and only the _______ light will finally reach our eyes
violet and blue, longer orange and red
wavelength
