introduction to mapping sciences: lecture #7 (remote sensing) introduction to remote sensing...

Introduction to Mapping Sciences: Lecture #7 (Remote Sensing)

Introduction to Remote Sensing

Resolution

Digital Images

Image Interpretation

Satellites and Sensors


Remotes Sensing Technology

Remote Sensing Images can be obtained from:

Aerial Photographs• Contract a company to take the aerial photographs• Obtain from local Property Appraiser’s Office• Obtain from USGS

Satellite Images• There are a number of countries that operate satellites

that collect images of the Earth for commercial purposes• LANDSAT is operated by the United States


Digital Images

A digital image can be broken down layers (or CHANNELS or BANDS) representing different types of light • each layer is black and white, • combination of three channels result in a

color image

into a regular grid of PICTURE ELEMENTS or PIXELS


Digital Images

An aerial photograph or satellite image has three different resolutions

The SPATIAL resolution

The SPECTRAL resolution

The RADIOMETRIC resolution

The TEMPORAL resolution


Resolution & Remote Sensing Systems

4 major resolutions associated with each remote sensing system

Spectral resolutionSpatial resolutionTemporal resolutionRadiometric resolution

These resolutions should be understood by the scientist in order to extract meaningful biophysical or hybrid information from remotely sensed imagery.


Resolution

Resolving power

Measure of the ability of a sensor to distinguish between signals that are spatially near or spectrally similar


Spectral Resolution

Number and size of the bands which can be recorded by the sensor – nominal spectral resolution

Course – sensitive to large portion of ems contained in a small number of wide bandsFine – sensitive to same portion of ems but have many small bands

Goal – finer spectral sampling to distinguish between scene objects and features

More detailed information about how individual features reflect or emit em energy increase probability of finding unique characteristics that enable a feature to be distinguished from other features.


Spectral Resolution

Difficult to create detector that has extremely sharp bandpass boundaries such as describe in previous slide

More precise method of stating bandwidth is look at typical Gaussian-shape of the detector sensitivity

Describe bandwidth as Full Width at Half Maximum (FWHW)


Spectral Resolution

The SPECTRAL resolution defines the range of light stored in the image

A black and white photograph stores a visible light; it has one channel that stores the light for 0.4 to 0.7 micrometersA natural color image stores reflected red, blue and green light in different channels; e.g. 0.45 - 0.52 m for blue, 0.52 - 0.60 m for green and 0.63 - 0.69 m for redA LANDSAT image contains 7 channnels as described above that store reflected light other than visible light.A HYPERSPECTRAL image contains hundreds of channels. E.g. A hyperspectral image that collects visible light may divide the visible light range into 300 channels, each channel containing a narrow range of wavelengths.


Spatial Resolution

Measure of the smallest angular or linear separation between 2 objects that can be resolved by the sensorIn practice, sensor system’s nominal spatial resolution is the dimension in meters (or feet) on the ground projected instantaneous field of view (IFOV)Generally, smaller spatial resolution greater the resolving power of the sensor system


Spatial Resolution

The SPATIAL resolution defines that size of Earth’s surface that is stored in a pixel

In a LANDSAT image a pixel represents 30 m by 30 m of the Earth’s surface.

In an USGS orthophotograph a pixel repesents 1 m by 1 m of the Earth’s surface.


Graphic representation showing differences in spatial resolution among some well known sensors

(Source: Landsat 7 Science Data Users Handbook)


Spatial Resolution

Useful rule: To detect a feature, the spatial resolution of the sensor system should be less than ½ the size of the feature measured in its smallest dimension.


Temporal Resolution

How often the remote sensing system records imagery of a particular area.


Radiometric Resolution

Refers to the sensitivity of the sensor to incoming radiance.

How much change in radiance must there before a change in recorded brightness value takes place.

This sensitivity to different signal levels will determine the total number of values that can be generated by the sensor

26 = (0-63) 64

28 = (0-255) 256

210 = (0-1023) 1024

Examples:

GOES Imager – 10bit

Landsat 7 ETM+ - 8bit


Radiometric Resolution

The RADIOMETRIC resolution defines the range of values that an individual pixel can have

Typical digital images have a range of values from 0 – 255 (a total of 256 possible values).

An image that just shows black or white pixels would only store 0 (black) or 1 (white).


Summary of Resolution

• By increasing 1 or any combination of these resolutions, increase chance of obtaining remotely sensed data about a target that contains accurate, realistic, and useful information.

• Downside of increased resolution need for increased storage space, more powerful processing tools, more highly trained individuals.


Aerial Photography

Types depend on: the altitude of the plane

the camera

the angle of view and

the type of film used


The angle of view

Vertical (directly over)shows the scale and distance

Oblique (at an angle)shows the object size


A Vertical Aerial Photograph


An oblique photograph


Photographic films

Black and White

Color

InfraRed

beyond the visible part of the spectrum


Monochrome(black and white)


Panchromatic (color)


Color Infrared(heat)

Used for vegetation studies

Green vegetation strongly reflects IR

Vigorously growing vegetation appears red



Size of objects relative to one another

Shape depends on the object outline

Image tone brightness - hue, colour

Patterns arrangement of features


Texture smooth or coarse

Shadow helps determine heights

Site location helps recognition

Association features that are normally found near others



Interpretation


Difficulties with Interpretation

unfamiliar prospective viewing from above

use of wavelengths outside visible light range

Images often display different types of infrared lightColors in image not that same as colors seen by us

• E.g. False infrared images displayed reflect near infrared light using red

unfamiliar scales and resolutionLandsat image’s pixels are 30 m by 30 mSPOT image’s pixels are 20 m by 20 mAerial photograph’s pixels can be smaller than 6inches


Characteristics of Objects

Shape

the general form of the object

stereo photographs also show height which further defines shape



Sizethis needs to be considered in reference to scaleWhat is the object in the image• The image covers

approx 1 square mile?



Pattern

this is the spatial arrangement of objects

e.g. Orchard vs. Forest

Man made objects vs. natural objects



Tone (Hue)

the relative brightness of an object or its color



Texture

frequency of tonal changes

e.g. grass appears ‘smoother’ than forest

depends on scale



Shadows are both useful and a nuisance

define the profile of the object

hide objects in the shadow area



Sitetopographical locatione.g. palm trees are not found in New England

Associationwhat objects are found togethere.g. a Ferris wheel


Strategies

Other information in addition to the image

e.g. for crop identification use information on typical planting dates, recent weather conditions etc


Strategies

There are two types of Interpretation keys.Selective keys provide a set ofexample images.

E.g. pictures of different trees from aboveElimination keys makes the interpreter make a series of decision.

Is the ‘crown’ of the tree large or small: small might suggest pine tree in a given location rather than oak trees.

better for man made objects rather than vegetation.


Strategies

Consider film / filter combinations (or sensor channels)

Would a false infra red image be better than a natural color image?

Consider the Arial extent of the photograph

Do you need to have great detail or large aerial coverage?


Approaching Classification

Define the classifications.What objects are you trying to identify in the imageWhat objects are considered the same

• Pine tree forest and oak tree forest considered as just forest?

‘fuzzy’ edges,• Try to give good definition of where boundaries lie

between natural objects– E.g. where desert ends and non-desert starts


What is a satellite?

The term Satellite simply refers to a body in orbit around another body. In 1957 the first artificial satellite SPUTNIK, was launched by the Soviet Union. Today there are hundreds of these spacecraft in orbit around the Earth. Satellites may serve many different purposes; they may be part of a television or telephone network or they can carry instruments to investigate the Earth’s surface or the Earth’s atmosphere. Other spacecraft point towards the Sun and monitor this star, or travel for many years carrying probes or landers which investigate the atmosphere, moons or surface features of distant planets. There are also manned spacecraft such as the US shuttle spacecraft and space stations such as MIR, the Soviet space station launched in 1986.


Satellite Orbits

Satellites generally have either polar orbits or geostationary orbits.


Meteosat

A program sponsored by 17 European weather services. It started with the successful launch of METEOSAT 1 in 1977 and has continued unabated. METEOSAT 7, the last in the current series was launched in early September 1997.

They are stationed above the equator at 0° longitude above the Gulf of Guinea and image this part of the globe every 30 minutes in three wavebands. These are:

the visible (0.4 to 1.1 micrometers),

the water vapour (5.7 to 7.1 micrometers) and

the thermal infrared (10.5 to 12.5 micrometers).

The first has a resolution of 2.5 km The first has a resolution of 2.5 km at the sub-satellite point (SSP) while the two infrared wavebands both have one of 5 km.


NOAA (National Oceanic & Atmospheric Administration) Polar Orbiters

The programme that started with the successful launch of TIROS-1 in 1960 continues today with the NOAA polar orbiters. The satellites' AVHRR instruments image the planet in five bands:

8 to 0.68 micrometres

0.725 to 1.10 micrometres





Geostationary Operational Environmental Satellites (GOES)

This NOAA series of geostationary weather satellites began in 1974 and continues today with the launch of a new ‘GOES-NEXT series of more advanced satellites in 1994.

The resolution varies from 4 to 8 km.

They have five wavebands: 0.55 to 0.75micrometres

3.80 to 4.00 ”

6.50 to 7.00 “

10.20 to 11.20 ”

11.50 to 12.50 "


The Space Shuttle

The space shuttle is a manned spacecraft mission, carrying astronauts and scientists as well as instruments.The most important sensors that have been carried on the Shuttle for Earth imaging are:

The Shuttle Imaging Radar The Metric Camera. The Large Format Camera (LFC) The Modular Optical-Electronic

Multispectral Scanner (MOMS).


LANDSAT Satellite Series

First LANDSAT satellite launched in 1972

Lasted until 1978

Six Landsat satellites to dateLANDSAT-4 and -5 still operational

LANDSAT -6 experienced launch failure


Landsat 4 (launched 16.07.82) Landsat 5 (launched 01.03.84) Orbit

near polar sun-synchronous complete orbit every 99 mins

Altitude - 705 km, 438 miles Re-visit - 16 days

Technical Information


Landsat 1, 2 and 3

Landsat was the first satellite to be designed specifically for observing the Earth’s surface.Landsat 1, 2 and 3 carried a multispectral scanner (MSS) system which records reflected energy from the Earth’s surface or atmosphere across four wavebands; three visible channels and one near infrared. The MSS has a pixel resolution of 80 metres.


Landsats 4 & 5 - Thematic Mapper

LANDSATs 4 and 5 have a more refined multispectral scanner, the Thematic Mapper (TM), instrument on board.

TM is a multispectral sensor since it detects energy across seven wavelength bands.

The pixel resolution of six of the wavelength bands is 30 metres but the thermal infrared band has a pixel resolution of 120 metres.

On this Landsat TM true colour image of west and central London


Landsat 7

After a successful launch on April 15 1999, Landsat 7 is up and running. Visit http://www.eurimage.com/ to see "Quick Looks" of some of the first acquired images..LANDSAT 7 carries a TM sensor developed from that on Landsat 5. Key differences are: (1) extra 15m panchromatic band co-registered with the multi-spectral, and (2) band 6 resolution at 60m.

The fires of Dili, east Timor

The Turkish earthquake


1. 0.45 - 0.52 m blue R 2. 0.52 - 0.60 m green R 3. 0.63 - 0.69 m red R 4. 0.76 - 0.90 m near IR R 5. 1.55 - 1.75 m mid IR R 6. 10.4 - 12.5 m thermal IR E 7. 2.08 - 2.35 m mid IR R and

E

B G R Near IR Mid IR Thermal IR

1 2 3 4 5 7 6

LANDSAT’s Thematic Mapper Sensor

Collect 7 different types of light


Payload MSS (4 channels) TM (7 channels)

Resolution MSS 80 m

Resolution TM 30 m (band 6, 120 m)

Swath 185 km x 185 km

Technical Information


Applications of LandSat Imagery

Geology surveys for oil and mineral exploration

Agriculture crop monitoring / yield forecast

Cartography large area maps, to 1:50,000

Environment environmental audits and pollution monitoring

Forestry woodland mapping / species identification


Planning land use analysis and change detection

Utilities highway / power / resource management

Commerce insurance damage assessment, civil engineering and commodities forecasting

Marine coastal zone management and bathymetric mapping

Applications of LANDSAT Imagery


SPOT (Systeme Probatoire de l’Observation de la Terre)

•SPOT satellites are placed in near-polar, sun-synchronous orbits at an altitude of 832 km. •The satellites have a pushbroom scanner system which can view the surface immediately below them (nadir view), or can be directed so that they view the surface to the side. This is important because it means that two views of the same area can be collected within a short time of each other, by two adjacent over-passes. Because the system can take two images of the same area with different look angles, it is possible to create stereoscopic (3-D) images. This is similar to having two eyes, enabling us to view in three dimensions because each eye views the same scene from a slightly different position, the brain then creates a 3-D picture.

A computer can create a Digital Elevation Model (DEM) from two

stereoscopic images, which means the shape of the land can be measured.


Images with two different spatial resolutions can be produced from SPOT data. The first is a panchromatic (black and white) image with a spatial resolution of 10 m. The second is an image from the multi-spectral sensor (SPOT XS) which collects 3 bands of data, with a resolution of 20 m.

SPOT


Active Sensors: ERS-1 and ERS-2

In July 1991, the first European Remote Sensing Satellite (ERS-1) was launched by the European Space Agency (ESA). It had a sun-synchronous circular orbit (near polar) at 770 km. Its purpose was to collect information on areas of the world that are difficult to observe from the surface, such as oceans and ice-covered areas. It also produces images of the land surface in all weather conditions, 24 hours a day.

ERS-1 was so successful that the ERS-2 was launched in April 1995, carrying additional equipment called Global Ozone Monitoring Experiment (GOME).


Active Sensors: Radarsat

RADARSAT-1 spacecraft was launched in November 1995, by the Canadian Space Agency. The satellite carries a Synthetic Aperture Radar system providing all-weather, day and night observations of land and sea surfaces.The satellite’s SAR system has been designed to make it useful for a range of applications including:crop investigations coastal zone mapping ship detection hydrological applications geological applications ice monitoring oil spill detection ocean applications

e.g. mapping the ocean depths/shape of the sea floor)

introduction to mapping sciences: lecture #7 (remote sensing) introduction to remote sensing...

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