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
· 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]
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 three-dimensional images of the Earth’s atmosphere and surface.
· 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
· Altitude classification
· Low Earth orbit (LEO): Geocentric orbits ranging in altitude from 0–2000km (0–1240 miles)
· Medium Earth orbit (MEO): Geocentric orbits ranging in altitude from 2,000km (1,200mi) to just below geosynchronous orbit at 35,786km (22,236mi). Also known as an intermediate circular orbit.
· High Earth orbit (HEO): Geocentric orbits above the altitude of geosynchronous orbit 35,786km (22,236mi). / Orbits
· 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
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. / 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). / 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.
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’.
/ 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).