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63 Cards in this Set

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  • Back
Where/when was the world's first ?GIS
Canada, 1967
What are 4 things that computers can be used for in terms of digital spacial data?
collection, storage, manipulation, analysis
What are the 6 components of a GIS?
Network, People, software, hardware, data, procedures
Definition of GIS
Gis is a system of hardware, software, people, data and networks for collecting, storing and analysing information about the Earth's surface.
What is latitude?
Circles parallel to the equator. The equator is 0degrees and the poles are 90degrees.
In miles, how big is one degree of latitude?
What is longitude?
Meridians that are not parallel to each other that are east or west of the prime meridian at greenwich uk.
What is a map projection?
A way of drawing a round earth on a flat map.
Features of the Mercator projection system
Globe is projected onto a cylinder
low distortion at equator
unusable distortion at poles (>70 degs)
conformal - constant true direction
maritime uses
Features of the Robinson projection
-pseudo cylindrical
-flat top and bottom
-lattitude lines are straight, longitude lines are curved
-area looks correct
-distances and compass directions are incorrect
-areas near north and south pole appear flattened
What do coordinate systems use?
Projections and datums
What are datums?
A set of reference points on the Earth's surface based on the elliptical shape of the earth in conjunction with local/regional control points.
What is UTM and who invented it?
Universal transverse mercator invented by Lambert
Features of the UTM
-cylindrical with tangent circle N-S instead of along the equator
-globe divided up into a rectangular grid
-60 N-S zoneseach spanning 6degs of longitude from 84N to 80S
How big is each UTM zone?
10,000,000m long by 500,000m wide
What do UTM coordinates consist of?
The zone (Melb is in 55) then 6 figure eastings and 7 figure northings
What is Australia's current map grid called?
Map Grid of Australia 1994 (MGA94) uses GDA94 as local datum
What was Australia's old map grid called?
AMG66 which used AGD 66
What does a GPS calculate?
Latitude and Longitude, altitude and velocity
What is remote sensing?
The technology of aquiring information about the Earth's surface from airborne platforms (balloon, aircraft) or spaceborn platforms (satellites)
What are the advantages and disadvantages of airborn remote sensing?
Adv - Higher spatial resolution images then spaceborne
Disadv - Low coverage area, high cost per unit area
Types of airborne remote sensing are...
digital photography, analogue photography, videography, some optical remote sensing, few cases use microwave remote sensing
What are the imaging capabilities of remote sensing satellites?
-Large area coverage
-frequent/repetitive coverage
-quantitative measures of features
-semi automated computer analysis
-low cost per unit area
4 Types of spaceborne remote sensing satellites/sensors are
-remote sensing staellites
-microwave remote sensing satellites
-space shuttle imaging radar
-meteorological satellites
What is optical remote sensing?
ORS forms images of the Earth's surface by detecting solar radiation reflected from objects on the ground.
Which parts of the electromagnetic spectrum are detected by optical remote sensing?
Infrared, near infrared and visible wavelengths.
How can different materials/objects be differentiated in ORS data?
Because objects/land surfacces reflect and absorb different amounts of solar radiation at different wavelengths, objects can be differentiated by their spectral reflectance signatures.
What are the three kinds of optical remote sensing images?
Panchromatic, multispectral and Hyperspectral.
What is the panchromatic imaging system?
- single channel detector sensitive to radiation in a broad wavelength
-resembles a black and white photo taken from space
What is the multispectral imaging system?
-multichannel detector, each channel sensitive to a different wavelength
-multi layer image containing both the brightness and spectral (colour) information
-colour composite images (primary colours assigned separate bands)
What are the most common multispectoral images?
How is a true colour composite image created?
When the 3 spectral bands measured are in the red, blue and green visible wavelengths and each is assigned the corresponding primary colour. (if given different colours its a fals colour composite)
What is a natural colour composite image?
When the spectral bands measured are not in the RGB wavelengths but each wavelength is assigned a primary colour to give the image a natural look.
What is microwave remote sensing?
Electromagnetic radiation in microwave wavelength transmitted by a synthetic aperture radar (SAR) device to generate high resolution images.
How does SAR imaging work?
Microwave pulses are transmitted by an antenna to the Earth's surface. The microwave energy that is scattered back is measured by the spacecraft. An image is formed by utilising the time delay of the backscattered signals.
In microwave remote sensing, what is the image's resolution limited by?
The size of the microwave beam sent out by the antenna illuminates an area on the ground (the footprint).
In MRS what is specular reflection?
Where a smooth surface acts like a mirror; most of the radar is reflected away so very little energy is scattered back to the sensor.
What is diffused reflection?
Where a rough surface reflects the radar pulse in all directions, part of which is scattered back to the satellite.
What is corner reflection?
When two smooth surfaces form a right angle facing the radar beam. Most of the beam is reflected back to the sensor as it bounces twice off the surfaces.
In MRS images, does soil appear bright or dark?
Depends on roughness and moisture content. Rough soil appears bright, the surface with the higher soil moisture content will appear brightest.
Flooded soil will appear dark as is reflected like a mirror.
What is a multi-temporal image?
They are colour composites of images gathered at different times. This is achieved by assigning different colour shades to images acquired at different times.
What is spatial resolution?
The size of the smallest object that can be resolved on the ground, limited by pixel size.
Eg. 10metre resolution = 10 metre pixel size.
What is radiometric resolution?
The smallest change in intensity level that can be detected by the system.
What determines the radiometric resolution?
The number of bits (binary digits). As a pixel is recorded with a digital number and due to finite storage capacity, the number is stored with a finite number of bits.
What is hyperspectral remote sensing?
The names is from instruments called hypserspectral sensors that aquire images in many (200+) very narrow spectral bands throughout the visible and infared spectrum and record the fine absorption detail.
What can hyperspectral systems do that multispectral systems cannot?
Discriminate amongst earth surface features that have diagnostic absorbtion/reflection characteristics over narrow wavelength intervals.
What is electronic absorption?
A natural process where surface materials absorb photons with specific wavelengths that cause a higher energy arrangement of subatomic particles in target earth surface materials.
What is a benefit of microwave over optical RS?
Microwaves can penetrate any kind of atmospheric condition eg smog, haze, clouds, smoke, snow.
What are active and passive microwave remote sensing systems?
Active MRSS supply their own radiation; radar.
Passive respond to extremely low levels of microwave energy that are naturally emitted or reflected from ambient sources (such as the sun) by terrain features.
what is radar an acronym for?
radio detection and ranging
how does radar work?
Transmission of short bursts of microwave energy in the direction of interest and recording the "echoes" received from objects within the systems field of view so the distance can be calculated based on the time it takes to reflect.
Why does side lighting occur in MRS?
Variation in the terrain results in strong radar signals from terrain facing the sensor; flatter areas and slopes facing away from the sensor come back weaker.
What is image parallax and what can it be used for?
Image parallax is caused by relief displacement when two images of the same object are taken from two different flight lines. This allows the image to be viewed with a stereoscope and the hight of the object can be calculated. Digital elevation maps can also be created.
In aerial photography, what is the principle point/nadir?
The point where the camera is directly over the object being photographed, ie where there is no relief displacement.
What is needed to determine the height of an object in an aerial photo?
-The PP/nadir position
-the flight altitude
-the base and the top of the object being clearly visible
What formula can be used to calculate object
Object height = d/r(H)
d=length of displaced image
r=radial distance between nadir to the top of displaced image
H = aircraft flying height
What are some pre processing procedures that can be carried out on raw data?
-Radiometric correction (correct for uneven sensor responses)
-Geometric correction (correct geometric distortion due to Earth's rotation)
-transformed to fit certain map projections
-ground control points can be added if accurate geographic locations are required (georeferencing)
What is a type of image enhancement?
Linear Grey level stretching to improve contrast and spatial filtering to enhance edges (eg if there is smog/light cloud cover)
What are the two different types of image classification algorithms?
Supervised and unsupervised classification
What is supervised classification?
Spectral features of some known land types are extracted from the image. These areas are known as "training areas". Every pixel is then matched to the training areas based on how similar its spectral features are to those of the training areas.
What is unsupervised classification?
A computer program automatically groups pixels according to their spectral features. An analysist must then go and label each as a specific landcover type.
What are themes and thematic maps?
A theme is a class of land cover. A thematic map is a map that has been classified into themes
How do you calculate the scale of an aerial photo?
dividing the focal length by the (flying height minus the avg. elevation above sea level) and then dividing the resulting figure by 1