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Remote Sensing Theory & Background. GEOG370 Instructor: Christine Erlien. Overview. What is remote sensing Brief remote sensing history Photography enables remote sensing Film, then digital; balloons  satellites Satellite remote sensing Resolutions Scanner types Platforms.

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Remote Sensing Theory & Background

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Remote Sensing Theory & Background

GEOG370

Instructor: Christine Erlien


Overview

  • What is remote sensing

  • Brief remote sensing history

    • Photography enables remote sensing

    • Film, then digital; balloons  satellites

  • Satellite remote sensing

    • Resolutions

    • Scanner types

    • Platforms


What is Remote Sensing?

Remote  far away

Sensing things from a distance

Remote sensing is the science and art of obtaining information about a target through the analysis of data acquired by a device that is not in contact with the target under investigation.

What we see & why

Eyes: Sunlight is reflected onto our nerve cells in the retina.

What we see: Visible spectrum (blue, green, red wavelengths)

Remote sensing equipment allows us to sense electromagnetic radiation beyond the visible spectrum


Silk Road, China

Waterless plains of southern Algeria

Grand Canyon

http://www.remotesensingart.com/


Types of Remote Sensing

  • Type  Based on source of the energy recorded by the sensor

  • Passive Remote Sensing: Energy collected by sensors is either reflected or emitted solar radiation.

    • Reflected – must be collected during daylight hours

    • Emitted – day or night as long as emissions large enough to record

  • Active Remote Sensing: Energy collected by sensors is actively generated by a man-made device.

  • Examples: Radar, LIDAR (Light Detection and Ranging)


Active and Passive Remote Sensing

AVHRR Thermal Image

http://www.coml.org/edu/tech/count/srs1.htm

QuikSCAT radar image

http://nsidc.org/seaice/study/active_remote_sensing.html


Particle=photon

Wavelength

Solar Radiation

Electromagnetic radiation energy: Wave-particle duality.

Light speed: c=f 

c = speed of light (186,000 miles/second)

f = light frequency: number of waves passing a reference per unit time (e.g., second).

The amount of energy carried by a photon:  = hf

h=Planck’s constant (6.62610-34 Js)

Note: The shorter the radiations’ wavelength, the higher its frequency  the more energy a photon carries


Atmospheric windows

Solar Electromagnetic Radiation


First Remote Sensing Image

Tree

Rooftop

1st permanent photograph (remotely sensed image), by Niepce in 1826.

http://www.artlex.com/ArtLex/p/images/photo_niepce.lg.jpg


Remote Sensing of Large Areas

Early remote sensing  limited by means available to put the sensor (i.e., camera) high above the target

The means:

1. Balloons

2. Pigeons

3. Gliders

4. Aircraft

5. Satellite

http://rst.gsfc.nasa.gov/Front/overview.html


Military Intelligence

Remote sensing  a critical source of military intelligence for WWI & WWII, Cold War

Remains a critical source of intelligence today

Examples:

WWI: British reconnaissance aerial photography revealed a major change in direction of the German forces advancing on Paris  allowed the Allied army to fortify its position and hold off the German advance to Paris

WWII: German barges identified in canals near the coast of France in summer of 1940. British launched an air attack on the invasion forces  Germany forced to postpone & eventually abandon invasion


Cold War: U-2 Aircraft

  • Balloons can be easily shot down  high altitude aircraft called the U-2 built to collect remotely sensed data

  • U-2 flies at 70,000 ft, putting it beyond the range of surface-to-air missiles & other aircraft (at that time)

  • Remains a valuable means of collecting remote sensing data today

    • President Bush used it during Gulf War in 1991

    • President Clinton used it in the war in Bosnia in 1998-99

Cuba, 1962


Military Intelligence & Image Resolution

1 meter

2.5 meter

5 meter

10 meter

10 cm

25 cm

50 cm

100 cm

http://rst.gsfc.nasa.gov/Intro/Part2_26e.html

http://www.fas.org/irp/imint/resolve3.htm


Satellite Remote Sensing

  • Resolutions

    • Spatial: Area visible to the sensor

    • Spectral: Ability of a sensor to define fine wavelength intervals

    • Temporal: Amount of time before site revisited

    • Radiometric: Ability to discriminate very slight differences in energy

  • Scanner types

    • Along-track

    • Across-track


Across-track scanning

  • Scan the Earth in a series of lines

    • Lines perpendicular to sensor motion

    • Each line is scanned from one side of the sensor to the other, using a rotating mirror (A).

  • Internal detectors (B) detect & measure energy for each spectral band, convert to digital data

  • IFOV or Instantaneous Field of View (C) of the sensor and the altitude of the platform determine the ground resolution cell viewed (D), and thus the spatial resolution.

  • The angular field of view (E) is the sweep of the mirror, measured in degrees, used to record a scan line, and determines the width of the imaged swath (F).

http://ccrs.nrcan.gc.ca/resource/tutor/fundam/chapter2/08_e.php


Along-track scanning

  • Uses forward motion to record successive scan lines perpendicular to the flight direction

    • Linear array of detectors (A) used; located at the focal plane of the image (B) formed by lens systems (C)

      • Separate array for each spectral band

    • Each individual detector measures the energy for a single ground resolution cell (D)

      • May be several thousand detectors

      • Each is a CCD

      • Energy detected and converted to digital data

    • “Pushed" along in the flight track direction (i.e. along track).

    • “Pushbroom scanners”

http://ccrs.nrcan.gc.ca/resource/tutor/fundam/chapter2/08_e.php


Civil Remote Sensing

Earth Resources Technology Satellite (ERTS-1; renamed Landsat 1)

1st satellite launched for peaceful purposes (1972)

Satellite Launched Decom RBV MSS TM Orbit

Landsat-1 23 Jul 1972 6 Jan 1978 1-3 4-7 none 18d/900km

Landsat-2 22 Jan 1975 25 Feb 1982 1-3 4-7 none 18d/900km

Landsat-3 5 Mar 1978 31 Mar 1983 A-D 4-8 none 18d/900km

Landsat-4 16 Jul 1982 -- none 1-4 1-7 16d/705km

Landsat-5 2 Mar 1984 -- none 1-4 1-7 16d/705km

Landsat-6 5 Oct 1993 Launch Failure none none ETM 16d/705km

Landsat-7 15 Apr 1999 -- none none ETM+ 16d/705km

RBV: Return Beam Vidicon MSS: Multispectral Scanner TM: Thematic Mapper

Decom: decommissioned


Landsat

Data transmission to the ground, allows fast & efficient data delivery


Landsat Orbit

Sun-synchronous orbit: Satellite always crosses the equator at precisely the same local time


Landsat Temporal Resolution

Temporal Resolution: The shortest time needed to repeat the ground track


Landsat Swath Width & Field of View

Landsat

Field of View

705km

Satellite ground track

scene

Spatial Resolution

175km

185 km

Pixel size=

(30x30m)


Landsat 7 ETM+ Spectral Bands

Spectral resolution: The number of bands and the width of spectrum that each sensor covers


255

Digital numbers (DN)

0

Radiance intensity

Maximum

Radiance

Minimum

Radiance

RadiometricResolution

The number of levels of DN values is determined by the radiometric

resolution of the instrument. For example, 8-bit system can differentiate

256 (0-255) levels of radiance


Landsat Images

Alaska’s Aleutian Islands

Mississippi River Delta

http://earthasart.gsfc.nasa.gov


SPOT (Systeme Pour l’Observation de la Terre)

  • Along track scanning system (Pushbroom System)

  • Sensors are pointable

    • Allows repeat coverage from different angles

    • Increases potential frequency of coverage of areas where cloud cover is a problem

    • Ability to collect stereoscopic imagery

Temporal resolution=26 days

Radiometric resolution=8-bit


SPOT Imagery

http://www.spotimage.fr/automne_modules_files/gal/edited/r444_santiago3D_800x600.jpg


Ikonos

Owner: Space Imaging

Temporal resolution: 11 days

Radiometric resolution: 11-bit

Spectral bands spatial resolution

Blue (0.45-0.52 4m

Green (0.51-0.60) 4m

Red (0.63-0.70) 4m

NIR (0.76-0.85) 4m

Panchromatic (0.45-0.90) 1m

Swath width: 11km

Orbit: Sun-synchronous; equatorial crossing time of 10:30am


IKONOS


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