Mapping & Monitoring|
The Global Positioning System (GPS)
GPS is a worldwide radio-navigation system formed
from a constellation of 24 satellites and their ground stations. GPS uses these satellites as reference points to calculate positions accurate to a matter of meters. In fact, advanced forms of GPS can make measurements to better than a centimeter.
It's like giving every square meter on the planet a unique address.
GPS receivers have been miniaturized to just a few integrated circuits and so are becoming very economical, making the technology accessible to virtually everyone.
Today, GPS is found in cars, boats, planes, construction equipment, farm machinery, even laptop computers. Soon it will be almost as basic as the telephone.
How GPS Works:
- The basis of GPS is "triangulation" from satellites.
- To "triangulate," a GPS receiver measures distance using the travel time of radio signals.
- To measure travel time, GPS needs very accurate timing which it achieves through complex mathematical calculations.
- Along with distance, you need to know exactly where the satellites are in space. High orbits and careful monitoring are the key.
- Finally, you must correct for any delays the signal experiences as it travels through the atmosphere.
Because of its accuracy, GPS mapping is an indispensable tool where sensitive areas in silviculture need to be exactly measured.
Many forest operations such as vegetation resources inventory, silviculture, timber harvesting, range and recreation, and others involve mapping natural and man-made features. These features include points such as sample plots, reference markers and map ties; lines such as roads, streams and fences; and areas such as cut-blocks, burn or infested areas, and vegetation polygons. These features have been surveyed or mapped using conventional survey techniques such as aerial photography or compass and tight chain traverses. GPS has recently become an important survey and mapping tool to supplement and, in many cases, replace conventional techniques because of its advantage of accuracy, efficiency and cost effectiveness.
Standards and procedures are needed to ensure the quality of GPS survey work and the consistency and compatibility of GPS survey data in the forest inventory database. With this in mind, the Public Sector GPS Users Committee (PSGUC) has developed the Standards, Specifications and Guidelines with respect to GPS surveys in support of mapping in the resource-sector.
The Geographic Information System (GIS)
GIS is a compterized information system that records, stores, and analyzes information about the physical features of the earth's surface. A GIS can generate two- or three-dimensional images of an area, showing natural features like forests, hills and rivers, as well as artificial features such as roads bridges and power lines. Researchers use GIS images as models, making precise measurements, gathering data, and testing ideas with the aid of a computer.
Many GIS databases usually made up of sets of information called "layers". Each one represents a specific type of geographic data. As an example, one layer may include information on waterways in an area, while another may contain information on the soil in that area, and another might record the elevation. The GIS can combine these layers into one image, showing how features relate to one another. Foresters might use this image to predict erosion. A GIS database can include as many as 100 layers.
A GIS is designed to accept geographic data from many sources, including maps, satellite photographs, and printed text and statistics. GIS sensors can scan some of this data directly - for example, a computer operator may feed a map or photograph into the scanner for a computer to "read" the information the scan contains. All geographical data is then converted into a digital code, which the computer program arranges in a database to produce the images or information researchers need.
The uses for Geographic information Systems are vast and continue to grow. By using a GIS, foresters can plan and predict forest growth, scientists can research changes in the environment; engineers can design road systems; electrical companies can manage complex networks of power lines; governments can track the uses of land; and emergency departments can plan routes.
The first GIS, the Canada Geographic Information System, was built by the Canadian government during the 1960s. It's purpose was to to analyze data collected by the Canada Land Inventory. Other governments and university laboratories soon built similar systems, but GIS systems did not find wide use until the late 1970s, when technological improvements and lower costs made computers widely available. By the early 1990s, about 100,000 GIS systems were in operation around the globe.
Synthetic Aperture Radar (SAR)
SAR is an airborne system developed for use by the remote sensing research and development community, natural resource managers, and the exploration, maritime, and mapping industries.
SAR can provide imagery of all classes of terrain - forests, mountains, ocean, or ice scenes - which can be easily compared with previous mapped information. It is possible to monitor natural resources, temporal variations, and disasters, such as oil spills, floods and forest fires.
Since the commissioning of SAR, systems have undergone several upgrades, including improvements in real-time processing, more flexible imaging geometries, navigation, motion compensation processing, and a data recording unit. The system is highly versatile when used in its basic configuration. In addition, the C-band radar now has two advanced research capabilities, providing interferometric and polarimetric modes.
SAR is carried on an aircraft, complemented by the latest in navigation equipment and a suite of other sensors. This advanced system provides reliable, accurate products, and is used worldwide, from polar ice caps to equatorial rain forests.
Satellite-based Systems (SAR)
Canada's premier remote sensing satellite, RADARSAT, has been imaging the earth since November 1995 for a wide variety of applications made possible with spaceborne radar, including monitoring the natural environment and human activity.
Data from RADARSAT and other international satellites is received and distributed to other agencies by the Canada Centre for Remote Sensing (CCRS) satellite stations.
Similar satellites and systems around the world include: LANDSAT, NOAA and SEASAT (USA), SPOT (France), ERS (Europe), and MOS and JERS (Japan.)
Satellite-based Forest Fire Monitoring
Forest fires have a significant impact on vegetation dynamics. They are a major disturbance to the boreal ecosystem and contribute to the increase in trace gases that cause variations in climate. Fires also deplete timber resources so that monitoring forest fires is a critical aspect of sustainable forest management. However, conventional ground-based fire detection techniques are severely limited because they can only cover small areas.
Using satellite images, researchers have developed algorithms to detect forest fires. These are used to provide daily satellite-based fire monitoring worldwide. The algorithms take advantage of information from multi-channel AVHRR measurements to determine the locations of active fires on satellite images under clear sky or thin cloud conditions. Typically, an image of a forest fire will display smoke plumes and burning areas (red spots), which are detected by the computer algorithm. Zoom-in images are available for closer study.
Algorithms can be applied to a data set containing daily mosaics, over a number of fire seasons, to provide a history of forest fires in any given region, or across a country as a whole.
Satellite monitoring can also provide advance weather information or data on the evolution of fires as they develop. These are valuable tools for fire bosses and agencies in a fire-suppression strategy.
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