Remote Sensing Reference Material 2012-2013
TOPEX/Poseidon and Jason: The spacecrafts' radar
altimeters measure the precise distance between the
satellite and sea surface. The round-trip travel time of
microwave pulses bounced from the spacecraft to the
sea surface and back to the spacecraft provides data
indicating sea surface height and the topography of the
ocean surface. monitor large-scale features like Rossby
and Kelvin waves, track El Niño's like the large event of
1997-1998 and the subsequent La Niña events, and
explores long-term changes such as the Pacific Decadal
Oscillation
Landsat: unique resource for global change research and applications in
agriculture, cartography, geology, forestry, regional planning, surveillance and
education. Landsat 7 data has eight spectral bands with spatial resolutions ranging
from 15 to 60 meters; the temporal resolution is 16 days
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Landsat 1 (originally named Earth Resources Technology Satellite
1): launched July 23, 1972, terminated operations January 6, 1978
Landsat 2: launched January 22, 1975, terminated January 22, 1981
Landsat 3: launched March 5, 1978, terminated March 31, 1983
Landsat 4: launched July 16, 1982, terminated 1993
Landsat 5: launched March 1, 1984, still functioning,[7][8] but severe
problems since November 2011.[9] On December 26, 2012, USGS
announced that Landsat 5 will be decommissioned.[10]
Landsat 6: launched October 5, 1993, failed to reach orbit
Landsat 7: launched April 15, 1999, still functioning, but with faulty
scan line corrector (May 2003) [11]
Landsat Data Continuity Mission (Landsat 8): launched February 11,
2013.[12]
Landsat: The 30 m spatial resolution and 185 km swath of Landsat imagery fills an important scientific niche because the orbit swaths are wide
enough for global coverage every season of the year, yet the images are detailed enough to characterize human-scale processes such as urban
growth, agricultural irrigation, and deforestation
A-Train: The A-train (from Afternoon Train) is a satellite
constellation of four French and American Earth observation
satellites in sun-synchronous orbit at an altitude of 690
kilometers above the Earth.[1]The orbit, at an inclination of
98.14°, crosses the equator each day at around 1:30 pm solar
time, giving the constellation its name; the “A” stands for
“afternoon;”[2] and crosses the equator again on the night side
of the Earth, at around 1:30 am.
Their collective
observations may be used to build high-definition threedimensional images of the Earth’s atmosphere and surface.
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GCOM-W1 (SHIZUKU), lead spacecraft in
formation, launched by JAXA on May 18, 2012
Aqua, runs 4 minutes behind GCOM-W1, launched
by NASA on May 4, 2002
CloudSat, a cooperative effort between NASA and
the Canadian Space Agency, runs 2 minutes and 30
seconds behind Aqua, launched with CALIPSO on
April 28, 2006
CALIPSO, a joint effort of CNES and NASA,
follows CloudSat by no more than 15 seconds,
launched on April 28, 2006
Aura, a multi-national satellite, lags Aqua by 15
minutes, crossing the equator 8 minutes behind due
to different orbital track to allow for synergy with
Aqua, launched by NASA on July 15, 2004
Orbits
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Altitude classification
Low Earth orbit (LEO): Geocentric orbits ranging
in altitude from 0–2000 km (0–1240 miles)
Medium Earth orbit (MEO): Geocentric orbits
ranging in altitude from 2,000 km (1,200 mi) to just
below geosynchronous orbit at 35,786 km
(22,236 mi). Also known as an intermediate circular
orbit.
High Earth orbit (HEO): Geocentric orbits above
the altitude of geosynchronous orbit 35,786 km
(22,236 mi).
Image Resolution:The quality of remote sensing data consists
of its spatial, spectral, radiometric and temporal resolutions.
Spatial resolution The size of a pixel that is recorded in a
raster image – typically pixels may correspond to square areas
ranging in side length from 1 to 1,000 metres (3.3 to 3,300 ft).
Spectral resolution The wavelength width of the different
frequency bands recorded – usually, this is related to the
number of frequency bands recorded by the platform.
Radiometric resolution The number of different intensities of
radiation the sensor is able to distinguish. Typically, this
ranges from 8 to 14 bits, corresponding to 256 levels of the
gray scale and up to 16,384 intensities or “shades” of colour, in
each band.
Temporal resolution The frequency of flyovers by the
satellite or plane, and is only relevant in time-series studies or
those requiring an averaged or mosaic image as in deforesting
monitoring.
Inclined orbit: An orbit whose inclination in reference to the equatorial
plane is not zero degrees.
o Polar orbit: An orbit that passes above or nearly above both poles
of the planet on each revolution. Therefore it has an inclination of
(or very close to) 90 degrees.
o Polar sun synchronous orbit: A nearly polar orbit that passes the
equator at the same local time on every pass. Useful for image
taking satellites because shadows will be nearly the same on every
pass.
Circular orbit: An orbit that has an eccentricity of 0 and whose path traces
a circle.
o Hohmann transfer orbit: An orbital maneuver that moves a
spacecraft from one circular orbit to another using two engine
impulses. This maneuver was named after Walter Hohmann.
Elliptic orbit: An orbit with an eccentricity greater than 0 and less than 1
whose orbit traces the path of an ellipse.
o Geosynchronous transfer orbit: An elliptic orbit where the
perigee is at the altitude of a Low Earth orbit (LEO) and the
apogee at the altitude of a geosynchronous orbit.
o Geostationary transfer orbit: An elliptic orbit where the perigee
is at the altitude of a Low Earth orbit (LEO) and the apogee at the
altitude of a geostationary orbit.
o Geostationary orbit (GEO): A geosynchronous orbit with an
inclination of zero. To an observer on the ground this satellite
would appear as a fixed point in the sky.[15]
Tundra orbit: A highly elliptic orbit with inclination of 63.4° and orbital
period of one sidereal day (roughly 24 hours). Such a satellite spends most
of its time over a single designated area of the planet.
Sun-synchronous orbit: An orbit which combines altitude and inclination
in such a way that the satellite passes over any given point of the planets’s
surface at the same local solar time. Such an orbit can place a satellite in
constant sunlight and is useful for imaging, spy, and weather satellites.
o
Corrections:
Atmospheric correction eliminates atmospheric haze by rescaling each frequency band
so that its minimum value (usually realised in water bodies) corresponds to a pixel
value of 0.
Topographic correction In the rugged mountains, as a result of terrain, each pixel
which receives the effective illumination varies considerably different. In remote
sensing image, the pixel on the shady slope receives weak illumination and has a low
radiance value, in contrast, the pixel on the sunny slope receives strong illumination
and has a high radiance value
Radiometric correction Gives a scale to the pixel values, e. g. the monochromatic
scale of 0 to 255 will be converted to actual radiance values.
Data processing levels
Level Description
Reconstructed, unprocessed instrument and payload data at full
resolution, with any and all communications artifacts
1a
Reconstructed, unprocessed instrument data at full
resolution, time-referenced, and annotated with ancillary
information, including radiometric and geometric calibration
coefficients and georeferencing parameters
1b
Level 1a data that have been processed to sensor units
(e. g., radar backscatter cross section, brightness temperature,
etc
2
Derived geophysical variables (e. g., ocean wave
height, soil moisture, ice concentration) at the same resolution
and location as Level 1 source data.
3
Variables mapped on uniform spacetime grid scales,
usually with some completeness and consistency (e. g.,
missing points interpolated, complete regions mosaicked
together from multiple orbits, etc.).
4
Model output or results from analyses of lower level
data (i. e., variables that were not measured by the instruments
but instead are derived from these measurements).
Mathematics of sensing:
NDVI (normalized difference vegetative index) computes
health of vegetation by comparing the Red band (VIS) and
Near Infrared (NIR): (answers -1to +1)
NDVI = (NIR — VIS)/(NIR + VIS)
EVI (enhanced vegetation index) more accurate: filters out
‘noise’ of canopy and haze and is from MODIS with better
resolution. Where blue is ‘1’, red is ‘3’ and near infrared is ‘4’.
A few Sensors:
ASTER: The Advanced Spaceborne Thermal Emission and Reflection
Radiometer. create detailed maps of land surface temperature, reflectance,
and elevation
MISR: multi-angle Imaging Spectroradiometer. 9 angles at once:
provide accurate measures of the brightness, contrast, and color of reflected
sunlight. Spatial resolution of climate parameters. distinguish different
types of atmospheric particles (aerosols), cloud forms, and land surface
covers. Combined with stereoscopic techniques, this enables construction of
3-D models
MODIS : Moderate Resolution Imaging Spectroradiometer. entire Earth's surface
every 1 to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths.
our understanding of global dynamics and processes occurring on the land, in the
oceans, and in the lower atmosphere
MOPITT: Measurements Of Pollution In The Troposphere (CANADIAN) measuring
carbon monoxide: intercepting the infra-red radiation coming from the planet
CERES Clouds and the Earth’s Radiant Energy System: measure of outgoing
longwave radiation (heat). most heat are nearly red, while cooler areas are white
TMI: Microwave Imager: passive microwave sensor: quantitative rainfall
information over a wide swath under the TRMM satellite: quantify the water
vapor, the cloud water, and the rainfall intensity in the atmosphere
VIRS: Visible and Infrared Scanner : senses radiation coming up from the
Earth in five spectral regions, ranging from visible to infrared, or 0.63 to 12
micrometers.
PR: Precipitation Radar . provide three-dimensional maps of storm structure.
intensity and distribution of the rain, on the rain type, on the storm depth and
on the height at which the snow. can be used to improve models of the global
atmospheric circulation. provide vertical profiles of the rain and snow from the
surface up to a height of about 12 miles
AIRS: The Atmospheric Infrared Sounder: an advanced sounder containing
2378 infrared channels and four visible/near-infrared channels, aimed at
obtaining highly accurate temperature profiles within the atmosphere.
AMSU-: The Advanced Microwave Sounding Unit, a 15-channel microwave
sounder designed primarily to obtain temperature profiles in the upper
atmosphere (especially the stratosphere) and to provide a cloud-filtering
capability for tropospheric temperature observations
AMSR-E: The Advanced Microwave Scanning Radiometer for EOS):
measures brightness temperatures at 6.925, 10.65, 18.7, 23.8, 36.5, and 89.0
GHz. Vertically and horizontally polarized measurements. Measures
precipitation rate, cloud water, water vapor, sea surface winds, sea surface
temperature, ice, snow, and soil moisture
ETM: The Landsat Enhanced Thematic Mapper Plus . consist of eight spectral bands,
with a spatial resolution of 30 meters for bands 1 to 5 and band 7.
Passive sensors can only be used to detect energy when the naturally
occurring energy is available. For all reflected energy, this can only take
place during the time when the sun is illuminating the Earth. There is no
reflected energy available from the sun at night. Energy that is naturally
emitted (such as thermal infrared) can be detected day or night, as long as
the amount of energy is large enough to be recorded.
Active sensors, on the other hand, provide their own energy source for
illumination. The sensor emits radiation which is directed toward the target
to be investigated. The radiation reflected from that target is detected and
measured by the sensor. Advantages for active sensors include the ability to
obtain measurements anytime, regardless of the time of day or season.
Active sensors can be used for examining wavelengths that are not
sufficiently provided by the sun, such as microwaves, or to better control the
way a target is illuminated. However, active systems require the generation
of a fairly large amount of energy to adequately illuminate targets. Some
examples of active sensors are a laser fluorosensor and a synthetic aperture
radar (SAR).
A photograph refers specifically to images that have been
detected as well as recorded on photographic film. Photos
are normally recorded over the wavelength range from 0.3
µm to 0.9 µm - the visible and reflected infrared. A
photograph could also be represented and displayed in a
digital format bypixels, and representing the brightness of
each area with a numeric value or digital number.
The information from a narrow wavelength range is
gathered and stored in a channel, also sometimes referred
to as a band. We can combine and display channels of
information digitally using the three primary colours (blue,
green, and red). The data from each channel is represented
as one of the primary colours and, depending on the relative
brightness (i.e. the digital value) of each pixel in each
channel, the primary colours combine in different
proportions to represent different colours.