lecture9 remote sensing

8/10/2019 Lecture9 Remote Sensing

1/29

Remote Sensing

Geog 170

Lecture 9

January 21, 2003


2/29

Remote Sensing

Practice of gathering information via asensor that is not in direct contact with the

object being observed Such as using our eyes (the sensors) to

observe the world

Observations are based on how objects

reflect energy Energy source may be the sun (light) or may

be generated by the sensor


3/29

Remote Sensing and Maps

Remote sensing data is becoming a

primary source of cartographic information

As raw data

Data products derived from remote sensing

imagery


4/29

Projections of future

urban development in

northern Virginia given

three different policy

scenarios.

Background image: Landsat 7

ETM+, bands 4, 3, 7, acquired

August 2000.

Source: Mid-Atlantic RESAC


5/29

The Electromagnetic (EM)

Spectrum

The EM spectrum describes the range ofwavelengths that make up electromagneticradiation (energy) Some things, like the sun or radioactive objects, emit

electromagnetic radiation

Everything reflects or absorbselectromagneticradiation

Patterns of reflection and/or emission are calledsignatures, and can be unique for differentobjects


6/29

The EM Spectrum


7/29

EM Reflectance Signatures

0.4 0.7Visible spectrum


8/29

EM Reflectance Signatures


9/29

Classification

Remote sensing imagery is usually classifiedbefore it is put on a map

Computer algorithms are developed that canrecognize specific reflectance patterns acrossthe EM spectrum Those patterns are translated into categories, such as

land use or land cover categories

Aerial photographs are often classified manually(photo-interpretation), an extremely timeconsuming task


10/29

Terminology

Pixel: picture element Rectangular area on the ground for which a remote

sensing instruments record information

Remotely sensed images are made of many pixels The minimum mappingunit for a remotely sensed

image

Related to the resolutionof the image

Resolution: the size of the area on the groundthat is captured A high resolution image is made up of pixels that are

very small; low resolution image is made up of pixelsthat are very large.


11/29

Types of Remote Sensing

Instruments

Many, many types of instruments

Differentiated by:

Spectral range Broad-band (panchromatic), narrow-band, multispectral

Signal source

Active vs. passive

Detector location On, under, or above the earths surface

Airborne, satellite


12/29

Passive Remote Sensing

Detects naturally generated energy that is

either emitted or absorbed by objects

The sun is typically the energy source, andthe signal results when light is either reflected

or absorbed.

Example: Our eyes are passive remote sensors

Aerial photographs, most satellite imagery


13/29

Color-infrared

aerial photograph

This image of Herndon, VA

was taken in Dec. 1988.

Because green vegetation

reflects strongly in the near-

infrared wavelengths, itappears redin this image.

Deciduous trees are evident,

but have lost their leaves and

are a greenishcolor. Waterabsorbs most wavelengths

and will appearblackin most

cases. Concrete and bare

ground are highly reflective

and appear white.


14/29

Wilkes-Barre, PA

Industrial Corridor


15/29

Washington, DC


16/29

Richmond, VA


17/29

Active Remote Sensing

The instrument transmits a signal that is

reflected off a surface

The reflected signal is recorded by thesensor


18/29

Radar

Wavelengths of radar signals can penetrate

clouds that may obscure the earths surface

Since radar is an active remote sensor, it canoperate day or night

Sensitive to how moisture changes reflective

properties of soil or clouds

Sensitive to texture (smoothness or roughness)

of the earths surface


19/29

Soil Moisture (wetlands)These images are for a section of the Patuxent River on two different dates. The

soil in the November image has less moisture, while the soil in the April image is

wetter, resulting in a brighter image.

Source: Megan Weiner, UMD Geography


20/29

LIDAR

Light Detection and Ranging

LIDAR sensors emit laser energy and

record how fast that energy returns to thesensor

Can be used to detect distance, speed, or

rotation of objects on earth


21/29

Source: University

of Maryland VCL


22/29

Source: University of Maryland VCL


23/29

Mission to Planet Earth

Earth observation from space

The National Aeronautical and Space Administration

(NASA) made earth observation and earth science a

top priority in the early 1990s.

A proliferation of earth observing satellites have been

launched to monitor the land, water and atmospheric

systems on earth.

Over 25 satellites are part of the Mission to Planet

Earth initiative; satellites usually carry several

different remote sensing instruments


24/29

ADEOS-MIDORI/TOMS Objectives: Take

remote sensing

measurements of

Earths

atmosphere, land

surface and the

oceans in order

to facilitate the

study of ozone

depletion,

greenhousegasses and the

El Nino

phenomenon.


25/29

GOES

A polar orbiting

weather

satellite. A

GOES satellitehas been in

operation since

1968.


26/29

The Landsat Program

Began

observing

the earth in

1972. First satellite

launched to

specifically

map the land

instead of

the water or

atmosphere.

Mozambique coastline

on August 22, 1999

and on March 1,

2000 after heavy rains

caused severe

flooding.


27/29

The Terra Satellite

NASAs Earth Observing System (EOS)

flagship satellite, launched December

1999. Determine how life on earth affects, and

is affected by, changes within the climate

system (http://terra.nasa.gov/)


28/29

Fires in Venezuela and

Columbia. This image

was captured Dec. 14,

2002 by the MODISsensor, one of the many

sensors aboard the

Terra satellite.

Computer algorithmshave been developed to

identify active fires,

shown here in red.


29/29

These are the first

global measurements

of carbon monoxide

(CO). Note theconcentration of CO

in the northern

hemisphere in April

2000, attributable to

the burning of fossil

fuels in industrialized

nations. In the

October images, fires

near the equatorexplain the high CO

measurements.

lecture9 remote sensing

Documents