Sources of Geographic Information

Transcription

1 Sources of Geographic Information Data properties: Spatial data, i.e. data that are associated with geographic locations Data format: digital (analog data for traditional paper maps) Data Inputs: sampled from the real world digitizing from paper maps produced by government agencies, e.g. census bureau, USGS, USFS, state government, etc. space or airborne remote sensing (NASA, NOAA, commercial, etc.) Approximately 80% of the duration of many large scale GIS projects is concerned with data input and management

2 What is Remote Sensing? 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 We routinely use remote sensing when we see things: Our eyes can see thing around us, and sometimes even far away from us We can identify what we see as objects (e.g. blackboard, door, desks, etc.) Why can we see? Because of the sunlight (or light from light bulbs) reflected off objects to the nerve cells in our retinae. However, our eyes can only see a narrow range of solar radiation within a large spectrum

3 Two Types of Remote Sensing In remote sensing, the medium that usually carries the information is electromagnetic radiation. Using various sensors, we can collect the electromagnetic radiation in any portion of the spectrum. Based on the source of the energy, remote sensing can be broken into two categories: Passive remote sensing: The source of energy collected by sensors is either reflected solar radiation (e.g. cameras) or emitted by the targets (thermal imaging). Active remote sensing: The source of energy collected by sensors is actively generated by a man-made device. Examples include radar (which uses microwave energy) and LIDAR (LIght Detection Imagery And Ranging, which uses a laser).

4 Solar Radiation Electromagnetic radiation energy: Wave-particle duality Wavelength (λ) particle EMR energy moves at the speed of light (c): c = f λ f = frequency: The number of waves passing through a point within a unit time (usually expressed per second) Energy carried by a photon: ε = h f [h=planck constant ( Js)] The shorter the wavelength, the higher the frequency, and the more energy a photon carries. Therefore, short wave ultraviolet solar radiation is very destructive (sunburns)

5 Light and Color Our visual system not only allows us to identify objects; we also see things in color; this provides us additional information about the objects we see For example: We can distinguish between a banana that is green (not ripe nor ready to eat) from a banana that is yellow (that is ripe and ready to eat) The natural light we see can be described using seven colors, which can be remembered using the acronym ROYGBIV: R = Red, O = Orange, Y = Yellow, G = Green, B = Blue, I = Indigo, V = Violet These colors were identified by Sir Isaac Newton with a prism in 1672: His research helped launch the era of modern optics

6 Solar Electromagnetic Radiation The sun emits EMR across a broad spectrum of wavelengths: But the atmosphere blocks much of the energy before it reaches the surface Atmospheric windows

7 Early Remotely Sensed Images Beyond what we see with our eyes, we need remotely sensed images that we can record and show to others: Pear tree Barn roof M. Joseph Nicephore Niepce produced the very first permanent photograph (remotely sensed image) in He used a camera obscura and a metal plate coated with asphalt. The exposure lasted eight hours, taken through an open window at his courtyard

8 Obtaining Remotely Sensed Images for Large Areas Geographic applications of remote sensing require that the camera be suspended high above the target to obtain remotely sensed images for large areas Doing so required the means to suspend cameras in the air Progress in aviation and remote sensing platforms: 1. Pigeons 2. Balloons 3. Gliders 4. Aircraft 5. Satellites

9 Remote Sensing - A Critical Source of Intelligence Like many technologies, remote sensing was initially developed for military applications. It became a critical source of military intelligence for the two World Wars and the Cold War, and it remains a critical source of intelligence Knowing where enemy forces are deployed ahead of time is crucial intelligence to help win a battle World War I: On August 22, 1914, British reconnaissance aerial photography revealed a major change in direction of the German forces advancing on Paris. This timely information allowed the Allied army to fortify its position on the Marne River and hold off the German advance to Paris

10 Remote Sensing During WW II Remote sensing played a significant role in WW II. In 1938, Werner von Fritsch, Chief of the German General Staff, predicted that the nation with the best photo-reconnaissance will win the next war Photo identification of German invasion barges in canals near France in the summer of 1940 constituted the major evidence that an invasion of England would take place in less than 48 hours. The British launched such an effective air attack on the invasion forces that Germany was forced to postpone the invasion, and finally to abandon it

11 Cold War Photo Reconnaissance During the Cold War, both the United States and the Soviet Union wanted to know about missile deployment in the other country (the number of missiles and their locations) Early photo reconnaissance planes were defenseless and could not fly long distances. Balloons played a major role in collecting photos at that time Between Jan. 10 and Feb. 6, 1956, the US launched 448 balloons from Scotland, Norway, West Germany and Turkey. The jet stream carried the balloons over the airspace of the Soviet Union and took pictures Soviet air defense responded quickly and destroyed many of the balloons. Only 44 of 448 balloons were recovered A significant nuclear refining facility at Dononovo in Siberia was identified from the photos recovered from the balloons

12 High Altitude Reconnaissance Aircraft Since balloons could be easily shot down by air defense weapons, a high altitude aircraft (U-2) was developed to collect information over Soviet territory The U-2 can fly at 70,000 ft., beyond the range of surface-to-air missiles and aircraft at that time. These aircraft provided a tremendous amount of information about the Soviet Union during the 1950 s and 1960 s The U-2 remains a valuable means of collecting military intelligence today (it is still operational), and it also used as a platform for a civilian research sensor - the AVIRIS (Airborne Visible InfraRed Imaging Spectrometer) hyperspectral sensor is flown aboard a modified U-2

13 AVIRIS ER-2 Imagery

14 The Cuban Missile Crisis On October 14, 1962, President Kennedy ordered high altitude U-2 reconnaissance flights over western Cuba which identified the deployment of Soviet missiles only 90 miles from the US mainland. President Kennedy then initiated a naval blockade of Cuba This photograph was shown to President Kennedy on Oct. 16, 1962 by the United States top photo interpreter, A.C. Lundahl

15 Satellite Remote Sensing The continuing advancement of missile technology made aircraft reconnaissance less feasible. Both the US and the Soviet Union initiated development of space reconnaissance systems in In 1967, President Johnson had this to say about US space intelligence in response to critics that he spent too much on the space program and not enough on poverty: We ve spent $35-40 billion on the space program. And if nothing else had come out of it except the knowledge we ve gained from space photography, it would be worth ten times what the whole program has cost. Without satellites, I d be operating by guess. But tonight we know how many missiles the enemy has, and it turned out our guesses were way off. We were doing things we didn t need to do. We were building things we didn t need to build. We were harboring fears we didn t need to harbor.

16 Civil Remote Sensing While early applications of remote sensing were developed for military use, those technologies are now of benefit to society in many other applications, including environmental research In 1972, the first remote sensing satellite designed solely for peaceful purposes -- the Earth Resource Satellite -- was launched. This satellite was later renamed Landsat. The Landsat series of satellites continues to be used today (now up to Landsat 7) Numerous meteorological satellites have been launched to monitor weather conditions as well. Since the launch of these satellites, we have not missed having some prior warning of every land-falling hurricane. Accurate prediction of disastrous weather conditions beforehand provides precious time for making better preparations, thus significantly reducing the loss of life and material damage

17 GOES Hurricane Imagery

18 The Limitations of Film The traditional method of remote sensing used cameras to record images on film. This has many disadvantages: 1. It is very difficult to send the remotely sensed data to the ground in a timely fashion. Early remote sensing approaches delivered film to the ground using a parachute:

19 The Limitations of Film 2. The speed of information delivery is limited - Because the film had to be recovered and then developed, it was impossible to acquire timely intelligence of high value E.g. The Soviet invasion of Czechoslovakia in 1968 ended before the United States could obtain imagery of the region. Because remotely sensed images from satellites recorded on film could only be sent back to Earth using parachutes it sometimes took some time to find the film, which delayed the speedy delivery of critical information

20 The Limitations of Film 3. Visual interpretation of remotely collected photographs was the only way to obtain information, which required years of experience for accurate interpretation, and this could not be done for large areas quickly Only the very best interpreters could see the missiles in this U-2 photograph. This was identified by then top US photo interpreter A. C. Lundahl

21 Digital Remote Sensing The advent of digital remote sensing for geographic information purposes has a great deal in common with the availability of digital cameras for consumers, that provide the following advantages: 1. You can take as many pictures as you d like 2. You can process the images with computers to produce special effects 3. The color information will not fade with time 4. You can make as many copies as you d like to give to your friends

22 What is Digital Remote Sensing? Digital remote sensing literally means that the remotely sensed information is stored as digits or numbers rather than on film Information recorded on film (in a satellite photograph) is essentially the amount of sunlight reflected back into space from the Earth s surface. Different ground object reflect different amounts of energy in certain wavelengths, leading to a different extents of exposure on the film. The developed photo is a printed representation of the sunlight reflected from the target. The interpreter has to extract information from a print based on the shape, size, tone, and texture to identify target objects

23 Analog-to-Digital Conversion As long as we can record the amount of energy (in a certain wavelength range) received from the ground surface, we do not have to record it on film Later technology has replaced the film with a device that generates electric current when exposed to sunlight. The level of voltage is linearly related to the amount of sunlight received (these are not really very different from the charge coupled devices [CCD] that you d find in a consumer digital camera) Through a analog-to-digital converter, digital remote sensing produces numbers 1, 2, 3, instead of the exposure of negatives. Each of the numbers indicates the intensity of sunlight received for a certain target area

24 Digital Images sensor The area is covered with a grid of cells 2. Each cell has a digital number indicating the amount of energy received from the cell (in a certain wavelength range) 3. The cell is called a pixel (a picture element) 4. The size of the pixel is the spatial resolution

25 Multispectral Remote Sensing Spectral Bands of Landsat Thematic Mapper Sensors

26 Multispectral Remote Sensing Multispectral remotely sensed data Each band will generate a layer of remotely sensed data, usually with the same cell (pixel) size. For Landsat satellites, we will have 6 layers of data corresponding to the 6 bands

27 How Do We Display Multispectral Image Data? 1. We put the digital numbers into the color guns of computer display so that the level of intensity for the color corresponds to the size of the number (i.e. brightness values are equal) 2. If we put the same digital numbers into all three color guns on a computer, we will get a black and white picture. We call this an image 3. If we put the digital number for red light in red gun, and the digital numbers for blue light in blue gun, and the digital numbers for green light in green gun, we will have a true color image. Otherwise mappings we call false color images

28 Color Arithmetic red + green = yellow green + blue = cyan red + blue = magenta R B G

29 Image Display - Single Band Assume that the In and Out Brightness Values are equal For a single band, the resultant color will be grayscale Band 1 Band 1 Band 1 BV out BV out BV out BV in BV in BV in All three colors display the same value, so the colors are shades of gray

30 Image Display - Single Band Band 1 - Blue Band 2 - Green Band 3 - Red Band 4 - NIR

31 Image Display - Single Band Band 5 - IR Band 6 - TIR Band 7 - FIR

32 Image Display - Multi-Band For a multi-band image, the resultant color will depend on which bands are assigned to which color guns True Color Composite (321) BV out Red (3) Green (2) Blue (1) BV out BV out BV in BV in BV in False Color Composite (432) BV out Near Infrared (4) Red (3) Green (2) BV out BV out BV in BV in BV in

33 Image Display - Multi-Band