topic engi 3703 surveying and geomaticssitotaw/site/fall2007_files/lecture24.pdf · engi 3703...

ENGI 3703Surveying and Geomatics

TopicInstructor: Prof. Ken Snelgrove

Lect 24 - Nov 21/07 Slide 1 of 13Remote Sensing - Overview

Remote Sensing and Lidar: (Section 27.19-27.20) We have spent some time to understand

photogrammery and how to derive elevation data from it. However, there are limitations are limitations

to the measurement of parallax that relate to features that can be extracted from air photo and the

scale of the airphoto. Other means of determining elevation data have been determined though

LIDAR measurements and through radar remote sensing.

LIDAR: (Section 27.19) A play on the acronym RADAR (RADio Detection And Ranging), LIDAR (LIght

Detection and Ranging) combines: i) aircraft overflights, ii) relative GPS positioning, iii) inertial

navigation and iv) laser range finding to map ground targets to a very high accuracy. The GPS unit

determines the location of the aircraft (X,Y,Z), while the internal measures determine the rotation of the

aircraft (pitch, roll and yaw). The laser scanner can then determine the distance to ground targets and

because of the high sampling rate and narrow beam can penetrate tree cover to determine ground

elevation.

LIDAR SystemLIDAR Image of Ground Zero NYC Septemer 17, 2001




LIDAR Digital Elevation Model (DEM)

Airborne Radar Digital Elevation Model (DEM)

LIDAR system is better able to penetrate

the tree canopy to extract surface

elevation data. Road network and

stream channels are visible.

Airborne RADAR system captures the

gross features of elevation but is not

able to extract finer features. This is due

to wider beam width and lower look

angles with radar that prevents canopy

penetration.

http://www.cfr.washington.edu/research.pfc/research/jfsp/index.htm




Stephenville Flooding - 2005

How would you predict this event?

Land Cover Data

LandSat7

Digital Terrain Data

Shuttle Radar Topographic Mission

(SRTM)




LandSat 7 & SRMT View of Stephenville Google Earth View of Stephenville(LandSat foreground; Quickbird background)

Close-Up (next page)

Shuttle Radar Topographic Mission (SRTM) DEM provides 100m x 100m elevation

data over most of the globe (60N to 55S).




Close up view of the Stephenville area

shows that the high resolution

Quickbird imagery (0.7m x 0.7m) does

not match with the coarse resolution

SRTM DEM (100m x100m).




What is Remote Sensing?

Remote Sensing Process: (A) An energy source emits radiation, (B) this interacts with the

atmosphere, and (C) the target. The result is (D) recorded by a sensor, and (E) transmitted for (F)

processing and (G) application.

"Remote sensing is the science (and to some extent,

art) of acquiring information about the Earth's surface

without actually being in contact with it. This is done

by sensing and recording reflected or emitted energy

and processing, analyzing, and applying that

information."

From: http://ccrs.nrcan.gc.ca/resource/tutor/fundam/index_e.php




Satellite Orbits

Polar Orbit

Eg: Landsat

Geostationary Orbit

eg: GOES

Landsat ETM+

Sun Synchronous (10 am local) Polar Orbit

Altitude: 705 km

Repeat Cycle: 16 days (233 orbits)

Resolution: 30m x 30m

GOES -8

Geostationary Orbit

Altitude: 36,000 km

Repeat Cycle: Continuous

Resolution: 4km x 4km




Electromagnetic Radiation

Most remote sensing information is received in the

form of electromagnetic radiation. This radiation

travels at the speed of light (c) and two important

characteristics of this radiation are frequency (f) andits wavelength ( ). These are related by:

c = f

where: c = speed of light 3x108 m/s

f = frequency (Hz = cycles per sec)

= wavelength (m)

0.4 μm 0.7 μmLandSat

(7 channels)

RadarSat

(1 channel)




Active Radar Satellites - Unlike LandSat which reflects reflected solar energy from

the earth’s surface, radar satellites emit there own energy and then detect the

reflections. RadarSat is the only Canadian remote sensing satellite.

RADARSAT 1 - C-Band Radar (5.3 GHz / 5.7 cm)

Altitude - 800 km

Internal Energy Source

Resolution - 9 m (Fine Beam)

100 m (SCANSAT)

Polar Orbit




Winnipeg 1997

“Flood of the Century”

RADARSAT 1 - Active RadarCoverage day or night, rain or shine

Radar Remote Sensing Uses - Flooded area determination; radar

signals are absorbed by water which provides a contrast against

the land. It is also not affected by clouds and can operate day or

night since it is an “active” system.




Water is a polar molecule

Radar beams induce vibration

Vibration Resistance

(Di-Electric) increases in ice

and dry soil Wet Snow - Dark

Dry Snow and Urban - Light

RADARSAT - Ottawa

Radar Remote Sensing can “see” things that human senses cannot such as the properties of water.




Shuttle Radar Topographic Mission (SRTM)

195 ft

Data Resolution (1 m elevation)

USA: 1 arc sec (~30 m)

60N-60S: 3 arc sec (~100 m)

Generated Based on Stereoscopy




Google Earth Tour

-various image resolutions: LandSat (15m) from Terrametrics

Quickbird (0.7 m) from DigitalGlobe

High Resolution Air Photos (0.03 m) (Google Campus)

Special Projects (National Geographic)

-New high resolution DEM (10m x10m): Switzerland.

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