Remote sensing is the science of acquiring data without being in contact with it. For this reason, a major part of
this event involves the processing of images and analyzing them to come to a conclusion.
INSTRUMENTS USED
RADAR: short for Radio Detection and Ranging. It transmits radio waves, which are scattered and reflected
when they come into contact with something. They can pass through water droplets and are generally used with
active remote sensing systems. Radar is good for locating objects and measuring elevation.
LIDAR: short for Light Detection and Ranging. It is similar to RADAR but uses laser pulses instead of radio
waves.
TM: stands for Thematic Mapper. It was introduced in the Landsat program and involves seven image data
bands that scan along a ground track.
ETM+: stands for Enhanced Thematic Mapper Plus. It replaced the TM sensor on Landsat 7. Unlike TM, it has
eight bands.
MSS: stands for Multispectral Scanner. It was introduced in the Landsat program also, and each band responds
to a different type of radiation, thus the name “multispectral”.
MODIS: stands for Moderate-resolution Imaging Spectroradiometer. It is on the Terra and Aqua satellites. It
measures cloud properties and radiative energy flux.
CERES: stands for Clouds and the Earth's Radiant Energy System. It is on the Terra and Aqua satellites. It
measures broadband radiative energy flux.
ALI: Advanced Land Imager
ASTER: Advanced Space Borne thermal Emission and Reflected Radiometer
ATSR: Along Track Scanning Radiometer
AVHRR: Advanced Very High Resolution Radiometer (used with NOAA)
AVIRIS: Airborne Visual/Infrared Imaging Spectrometer
CCD: Charge Coupled Devices
CZCS: Coastal Zone Color Scanner
GPS: Global Positioning System
HRV: High Resolution Visible sensor
LISS-III: Linear Imaging Self-Scanning Sensor
MESSR: Multispectral Electronic Self-Scanning Radiometer
MISR: Multi-angle Imaging Spectro Radiometer
MSR: Microwave Scanning Radiometer
RAR: Real Aperture Radar
VTIR: Visible and Thermal Infrared Radiometer
WiFS: Wide Field Sensor
SATELLITES
Notable Satellite Agencies: NASA (National Aeronautics and Space Association), NOAA (National Oceanic
Atmospheric Administration), and IRS (Indian Remote Sensing).
Earth Observation System: The EOS is a series of NASA satellites designed to observe the Earth's land,
atmosphere, biosphere, and hydrosphere. The first EOS satellite was launched in 1997.
A-Train: an EOS satellite constellation scheduled to be with seven satellites working together in Sun
synchronous (SS) orbit. Their compiled images have resulted in high-resolution images of the Earth's surface.
The A-Train was supposed to be a group of seven satellites operated by NASA. There are only four currently in
formation, due to failures, or change of orbit.
Active:
o Aqua: studies the water cycle, such as precipitation and evaporation
o CloudSat: studies the altitude and other properties of clouds
o CALIPSO: studies of clouds and air particles, and their effect on Earth's climate
o Aura: studies Earth's ozone layer, air quality, and climate
Past: Parasol: studies radiative and microphysical properties of clouds and air particles; moved to lower orbit
Failed:
o OCO(Orbiting Carbon Observatory): was intended to study atmospheric carbon dioxide
o Glory: was to study radiative and microphysical properties of air particles
o Both failures occurred because of launch vehicle failure.
Other EOS Satellites
Landsat: A series of 7 satellites using multiple spectral bands. Only two are operational today (Landsat 7 and
Landsat 5). These are generally the most commonly tested satellites, as well as those using the ASTER sensor. The name Landsat is a mixture of the two words "land" and "satellite".
SeaWiFS (Sea-viewing Wide-Field-of View Sensor): Eight spectral bands of very narrow wavelength ranges,
monitors ocean primary production and phytoplankton processes, ocean influences on climate processes (heat
storage and aerosol formation), and monitors the cycles of carbon, sulfur, and nitrogen.
Terra: Provides global data on the atmosphere, land, and water. Its scientific focus includes atmospheric
composition, biogeochemistry, climate change and variability, and the water and energy cycle.
Other Satellites
o GOES (Geostationary Operational Environmental Satellite) System: 2 weather satellites in
Geostationary orbit 36000 km. It is partially organized by NASA, in cooperation with NOAA.
o MOS: Marine Observation Satellite
o SEASAT: SEA SATellite
o SPOT: Système Pour l'Observation de la Terre
Image Interpretation
Terms
o Tone is the brightness or color of an object. It's the main way to distinguish targets from backgrounds.
o Shape is the shape of an object. Note that a straight-edged shape is usually man-made, such as
agricultural or urban structures. Irregular-edged shapes are usually formed naturally.
o Size, relative or absolute, can be determined by finding common objects in images, such as trees or roads.
(see Finding Area section, below)
o Pattern refers to the arrangement of objects in an image, such as the spacing between buildings in an
urban setting.
o Texture is the arrangement of tone variation throughout the image.
o Shadow can help determine size and distinguish objects.
o Association refers to things that are associated with one another in photographs, which can assist
interpretation, i.e. boats on a lake, etc.
Electromagnetic Spectrum: In one sense light is particles of energy we call photons that move in caboosed rows from
one place to another at 182,000 miles per second. This particle model of light goes on to explain that not all photons are
created equal‐meaning that some have more energy than others do. The amount of energy content per photon is one of
the ways in which we can distinguish
characteristics of different ranges of light.
A substance will emit photons when its
energy level increases by chemical
reactions such as fire, nuclear reactions
such as solar radiation, the presence of
an electric current or an increase in
temperature such as in heating metal.
The best way to describe electromagnetic
radiation is by describing its most basic
component‐the electromagnetic wave.
Electromagnetic radiation (EMR) is the
most common energy source for remote
sensing. It consists of an electric and
magnetic field perpendicular to each
other and the direction of travel while
traveling at the speed of light. This is
important to remote sensing because
that's how sensors detect certain data about the objects a satellite is studying.
Radiation is an important part of remote sensing, since different materials respond to radiation in different ways, so this
can be used to identify objects. One example of this is scattering (or atmospheric scattering), where particles in the
atmosphere redirect radiation. There are three types: Raleigh, Mie, and non-selective. This scattering is used to identify
the presence and quantity of certain gases in the
atmosphere. Also, transmission is when radiation
passes through a target, indicating it is unaffected by
that particular wave.
o Gamma rays and x-rays cannot be used
for remote sensing because they are
absorbed by the Earth's atmosphere: in
general, the shorter the wavelength (and
the greater the frequency), the more
absorption occurs.
o Ultraviolet radiation is not useful either
because it is blocked by the ozone layer.
o Visible light allows satellites to detect
colors a human eye would see. Some of
these satellites are panchromatic, meaning they are sensitive to all wavelengths of visible light.
o Infrared (IR) is divided into categories: near infrared, reflected infrared and thermal infrared. Near
infrared (NIR) is useful for vegetation, and thermal infrared (TIR) is also known as heat and is emitted
passively, not actively.
o Microwaves are used in radar.
Ecology Aspect
Global Warming When human impact on the environment is mentioned, one of the main ideas it entails is
global warming. Global warming is defined as “the increase in the average temperature of Earth's near-surface
air and oceans since the mid-20th century and its projected continuation”. The causes of global warming are
debated, but the main consensus is that the main cause is the increase in concentrations of greenhouse gases.
Possible results of global warming include a rise in sea levels, a change in weather patterns, the retreat of
glaciers and sea ice, species extinctions, and an increased frequency of extreme weather.
The greenhouse effect is caused by certain greenhouse gases that trap heat in the Earth’s atmosphere. The main
gases, along with their percent contribution to the greenhouse effect, are water vapor (36-70%), carbon dioxide
(9-26%), methane (4-9%), and ozone (3-7%). Of these, carbon dioxide is perhaps the gas most focused on as a
potential human impact on the environment; thus, it is the most likely to appear on tests. Humans have
increased the amounts of these and other greenhouse gases in the atmosphere during industrialization periods
such as the Industrial Revolution. CFC’s and nitrous oxide are among the greenhouse gases now present in the
atmosphere that were not before.
Carbon Cycle The carbon cycle is the process through which carbon atoms are cycled through the environment.
It cycles through the atmosphere as carbon dioxide, and some carbon is dissolved into the hydrosphere. It is also
taken in by plants during photosynthesis and released when the plants die. When animals feed on plants, they
also take in carbon.
However, the burning of fossil fuels, which come from biomatter, releases excess carbon into the atmosphere,
increasing the concentration of carbon dioxide. Carbon can be stored for long periods of time in trees and soil in
forest biomes, so the altering of this balance affects the cycle of carbon and can help global warming and
climate change. The resulting global warming can then affect plant growth since slight changes in temperature
or other biotic factors can kill off certain species of plants. Since there would be less plants remaining alive,
more carbon dioxide stays in the atmosphere rather than being taken in by plants.
Hydrological Cycle The hydrologic cycle, more commonly known as the water cycle, describes the cycle
through which water travels. Its base is the more commonly known cycle of evaporation, condensation, and
precipitation. Among smaller parts of the water cycle, water is stored as ice and snow in cold climates. It also
enters the ground through infiltration, although some simply flows over it as surface runoff. The groundwater
flow then takes this water to the oceans where it reenters the main cycle.
Finally, some evaporation occurs as evapotraspiration in plants. Fewer plants would result in less carbon taken
in, and thus more carbon dioxide in the atmosphere contributing to the greenhouse effect.
Albedo: Albedo is a very important way remote sensing is used to detect climate changes. Albedo is how much
a substance reflects light from the sun. This is useful when determining Earth's energy balance and how much
energy and heat the ground absorbs. Since ice and snow are very reflective and have high albedos, the presence
of them is important since it keeps the Earth from getting too warm. As albedo decreases, the Earth absorbs
more energy and warms up.
Satellite Imaging
Image Processing: Satellite data is sent from the satellite to the ground in a raw digital format. The smallest unit
of data is represented by a binary number. This data will be strung together into a digital stream and applied to a
single dot, or pixel (short for "picture element") which gets a value known as a Digital Number (DN). Each DN
corresponds to a particular shade of gray that was detected by the satellite. These pixels, when arranged together
in the correct order, form an image of the target where the varying shades of gray represent the varying energy
levels detected on the target. The human eye can only distinguish between about 16 shades of gray in an image,
but it is able to distinguish between millions of colors. Thus, a common image enhancement technique is to
assign specific DN values to specific colors, increasing the contrast. A true color image is one for which the
colors have been assigned to DN values that represent the actual spectral range of the colors used in the image.
A photograph is an example of a true color image. False color (FC) is a technique by which colors are assigned
to spectral bands that do not equate to the spectral range of the selected color. This allows an analyst to
highlight particular features of interest using a color scheme that makes the features stand out.
Composites are images where multiple individual satellite images have been combined to produce a new image.
This process is used to create more detailed images that take multiple factors into account, as well as to find
patterns that would not have been revealed in a single image. It also helps to create larger images than the
satellite itself can make. This is because each satellite covers a specific swath, or area imaged by a satellite with
a fixed width. When these swaths are put together into a composite, a larger area is imaged.
Not all composites have to have natural colors. If you have an infrared band as one of the transparencies and
shine it through the red filter, you can make something called a "False Color Composite." (FCC) You may have
seen false color composites in competition. Often, they are used to show healthy vegetation compared to
vegetation poor in health. They may appear the same naturally, but false color displays healthy vegetation in a
much brighter tone. For example, false color composites may show a football field made up of healthy grass as
a strong red color, but a football field composed of Astroturf or other artificial substances will show up as a
duller red.
Common composites:
o True-color composite- useful for interpreting man-made objects. Simply assign the red, green, and blue
bands to the respective color for the image.
o Blue-near IR-mid IR, where blue channel uses visible blue, green uses near-infrared (so vegetation stays
green), and mid-infrared is shown as red. Such images allow seeing the water depth, vegetation coverage,
soil moisture content, and presence of fires, all in a single image.
o Near IR is usually assigned to red on the image; thus, vegetation often appears bright red in false color
images, rather than green, because healthy vegetation reflects a lot of near IR radiation.
Contrast refers to the difference in relative brightness between an item and its surroundings as seen in the image.
A particular feature is easily detected in an image when contrast between an item and its background are high.
However, when the contrast is low, an item might go undetected in an image.
Satellite Images
Satellite Images are acquired in black and white. Computers are used to assign ‘false colors’ to each of the
bands. Images created in each of the different bands have different areas of contrast‐light and dark areas. The
computer displays an image in three different bands at a time assigning one of the three primary colors of light
(red, green, blue).
o Visible satellite images are photographs of the earth that provide information about cloud cover. Areas
of white indicate clouds while shades of gray indicate generally clear skies. Visible images represent the
amount of sunlight being scattered back into space by the clouds, aerosols, atmospheric gases, and the
Earth's surface. Thicker clouds have a higher reflectivity (or albedo) and appear brighter than thinner
clouds on a visible image. However, it is difficult to distinguish among low, middle, and high level
clouds in a visible satellite image, since they can all have a similar albedo and for this distinction,
infrared satellite images are useful.
o Infrared satellite measurements are related to the brightness temperature. For an infrared picture, warmer
objects appear darker than colder objects. Since temperature in the troposphere decreases with height,
high level clouds are colder than low level clouds. Therefore, low clouds appear darker on an infrared
image and higher clouds appear brighter.
o Visible vs.
Infared:
The picture on the
left is a visible
light image while
the one on the
right is infrared
because the
intensity of the
color.
o Color
enhancement is a
procedure where specified levels of energy are given a
specific color. This makes locations with the desired energies easier to locate.
o Water vapor images are useful for pointing out regions of moist and dry air, which also provides
information about the swirling middle tropospheric wind patterns and jet streams. Darker colors indicate
drier air while the brighter the shade of white, the more moisture in the air.