Upload
daniel-oon-wei-rhen
View
216
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Earth Observation
Citation preview
Man must rise above the Earth, to the top of the atmosphere and beyond, for only thus will he fully understand the world in which he lives
Earth Observation
In very simple terms, remote sensing means gaining knowledge about distant objects
A very simple example of this is human vision
Instruments can be used to aid vision
Instruments can be used to record visual images
Recording images as photographs represents a structured form of remote sensing
What is remote sensing?
Earth Observation
In the context of a technical discipline, remote sensing generally refers to Earth Observation
This involves acquiring and interpreting remotely-sensed photographs or images of the Earths surface
Numerous sources, types and scales of imagery are available
Remotely-sensed images
Remotely-sensed images represent the Earths surface
but how?
Remote sensing instruments measure the electromagnetic energy reflected from features on the Earths surface
What is electromagnetic energy!?
The most common example is blindingly obvious
solar radiation, or sunlight
How does remote sensing work?
Sun
Earths surface
Incoming solar radiation
Atmospheric distortion
Reflected radiation Scattered
radiation
Received radiation
Sensor
Data download
User
Data supply
Ground receiving station Absorbed/transmitted
radiation
Image acquisition
Satellite path
Field of view
59 88 132 128 134 135
12 14 56 124 118 128
5 8 15 25 78 112
5 7 7 12 18 45
Raster grid
Viewed numerically as Digital Numbers (DNs)
Viewed graphically as image
Picture element or pixel Image
data set
Ground track (imaged area)
Data format
A multispectral image comprises several bands or layers
Each band represents a certain part of the electromagnetic spectrum
Individually, each band contains a limited amount of information
In combination, the bands comprise a powerful data set
Multispectral imagery
Typical spectral reflectance curves
Water
Bare soil
Vegetation
Landsat Thematic Mapper 7 visible, near-, mid- and thermal -infrared bands
True colour composite Bands 3 (red), 2 (green), 1 (blue)
1
7
3
4
5
6
2 1 7 3 4 5 2 6
A false colour composite image includes an infrared band, providing a display that can appear unconventional (e.g. red vegetation, blue concrete)
False colour composite
Typical spectral reflectance curves
Water
Bare soil
Vegetation
False colour composite Bands 4 (NIR), 3 (red), 2 (green)
Band 4 near infrared
Band 3 - red
Band 2 - green
Series of remote sensing satellite missions, developed by NASA
First major civil remote sensing initiative, starting in 1972
Landsat-7 was launched in 1999, carrying the Enhanced Thematic Mapper Plus (ETM+) sensor
The ETM+ sensor provides various types of imagery:
Panchromatic imagery
Multispectral imagery
1. Blue 30 m 2. Green 30 m 3. Red 30 m 4. Near infrared 30 m 5. Mid infrared 30 m 6. Thermal infrared 60 m 7. Mid infrared 30 m
Spectral Spatial waveband resolution
Visible/near infrared 15 m
Sometimes orthorectified to 25 m
Often excluded from multispectral analysis
Landsat
How is remote sensing used?
In lots of different ways!
A few geographical examples
Illegal deforestation
Remote sensing helped prove the widely held suspicion that extensive illegal deforestation was taking place in the Amazon in the early 1990s
Forest canopy heighting
Airborne remote sensing using laser technology (Light Detection And Ranging or LiDAR) can measure elevation and height with great accuracy
LiDAR imagery can derive both a Digital Terrain Model of the ground surface and a Canopy Height Model of above-surface (forest) features
Wildlife habitat monitoring
Animal populations can be monitored using image-derived habitat data
Normalised Difference Vegetation Index images were used to assess structural vegetation change in Kruger National Park in relation to rapidly increasing elephant populations
Black rhino
White rhino
Elephant
1988 1999 1990
2000
Greenhouse gas flux modelling
Imagery can be used in tandem with ground and other physical data, enabling spatial characterisation of environmental processes
Gas flux measurements acquired in situ are mapped according to image-derived land cover categories
Month
Feb March April May June July August Sept Nov
CO
2 (
mg m
-2 h
-1)
0
100
200
300
400
500
Rain
fall
(cm
)
0
10
20
30
40
50
Palm
Hard wood
Sawgrass
Rainfall
1. Sawgrass bog plain 2. Stunted forest 3. Hardwood forest 4. Mixed forest 5. Palm swamp 6. Mixed swamp 7. Mangrove swamp Banana
Urban Water Other
Classes Vegetation gradient
CO
Human population analysis
Nightlights imagery shows global anthropogenic footprint
Social modelling and analysis conducted with US Defense Meteorological Satellites Program (DMSP) Operational Linescan System (OLS) imagery
Urban planning
Fine spatial resolution satellite sensor imagery enables detailed urban investigation
GeoEye-1 can acquire multispectral imagery with
Geohazards
A range of remote sensing data and techniques are used in various stages of geohazard prediction, prevention and response
Before and after images clearly show the extent and severity of tsunami inundation
El Nio Southern Oscillation
Synoptic view of remote sensing captures global events such as El Nino
Sea surface temperature anomalies were computed from images collected by the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR)
Antarctic ice depletion
Remotely-sensed imagery shows the scale and speed of ice cap breakup
Larsen B ice shelf collapse was monitored using NASAs Terra satellites Moderate Resolution Imaging Spectroradiometer (MODIS)
Ozone hole monitoring
Remote sensing helped discover the ozone hole in the stratosphere
Seasonal variation in ozone concentration is now monitored using satellite sensors such as the TIROS Operational Vertical Sounder (TOVS)
Man must rise above the Earth, to the top of the atmosphere and beyond, for only thus will he fully understand the world in which he lives
where we started
Socrates circa 399BC
When was Earth Observation first conceived?
The earliest known examples of remote sensing involved taking photographs from (un-manned) balloons tethered above the area of interest
Boston
13 October 1860
Photographed by James
Wallace Black
Historical remote sensing
Photography emerged in the early 1800s
Early pioneers included Joseph Nicphore Nipce...
...and later Louis Daguerre
First came photography...
View from the Window at Le Gras Credited to Nicphore Nipce c1826
Boulevard du Temple Credited to Daguerre c1838/39
The potential of photography for aerial survey was identified very quickly
Argo, Director of the Paris Observatory, advocated the use of photography for topographic survey in 1840
By the 1950s, tethered balloons were used successfully for aerial photography
Gaspard-Flix Tournachon, known as Nadar, photographed Paris in 1958
The earliest existing image is of Boston, dating from 1860 and taken by James Wallace Black
Boston, as the eagle and the wild goose see it, is a very different object from the same place as the solid citizen looks up at its eaves and chimneys, Oliver Wendell Holmes, Atlantic Monthly, July 1863
Aerial photography followed swiftly
Manned aeroplane travel dates from the Wright brothers first flight in 1903
Wilbur Wright piloted an aeroplane in France and Italy in 1980/09 from which motion pictures were taken
This is considered the first example of aerial photography from an aeroplane
Aeroplanes brought great potential
The International Society for Photogrammetry was founded by Eduard Dolezal in Vienna in 1910
Photogrammetry is concerned with geometric measurement from photographic images The principal application of photogrammetry over
the last century has been the compilation of maps from aerial photographs
The expanded International Society for Photogrammetry and Remote Sensing celebrated its Centenary in 2010 Unveiled a commemorative plaque for Dolezal
International Society for Photogrammetry
Aerial photography became used routinely for military reconnaissance in World War I
Specialised aerial cameras were developed, though their housing within the aeroplane was rudimentary
Considerable infrastructure and manpower was committed to image processing
Example aerial photo shows Allied and German trenches, separated by no-mans land
Rapid development during World War I
[Images courtesy Prof Mike Heffernans Part 2 Geographies of Violence module]
Passchendaele, Third Battle of Ypres, 1917
Before
After
Stereoscopic imaging techniques were developed as early as WWI to enable terrain mapping
Overlapping stereo pairs of photos are used to generate a 3D image
Stereoscopic 3D mapping
Aerial survey technology developed to a point where it could be applied on a mass-production basis
Private firms became involved in the market
In the 1930s the US Geological Society and the Tennessee Valley Authority mapped the Tennessee River Basin, an area of 40,000 square miles
In Europe the emphasis was on making large scale maps of relatively small areas
Inter-war commercialisation
The war years saw breakthroughs in the use of the infrared and microwave parts of the electromagnetic spectrum
The scope of image analysis in WWII extended towards synoptic and strategic monitoring of enemy activity
There was also greater interest in general thematic mapping
World War II
US army aerial photos of Normandy beaches on the eve of D-Day, 1944
Throughout the Cold War, both the USA and the USSR engaged heavily in aerial surveillance, i.e. spying
Perhaps the most famous example is aerial reconnaissance during the Cuban missile crisis in 1962
Spy satellites were then used
extensively for several decades
Cold War
U-2 spy plane
Cuban missile sites
US Corona spy satellite and imagery
By the 1980s, a series of remote sensors were providing image data for civilian, but image analysis was constrained by limitations in computer technology
Effectively there was a data bottleneck
Computational image analysis technology developed rapidly at this time
Developments in computing
After the Cold War ended, both the USA and Russia declassified military remote sensing technology
In the 1990s, spy satellite image archives became publicly available
Restrictions on the technological sophistication of civilian remote sensing were loosened
E.g., fine spatial resolution satellite sensors became available
A strong commercial industry in satellite sensing emerged, predominantly in relation to fine spatial resolution imagery
Post-Cold War