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