Postby salsinawi » Wed Aug 16, 2006 10:12 pm

Introduction to Remote Sensing #1:
The Geographic Information System (GIS)

A computer-based system designed to input, store, manipulate, and output geographically referenced data.

A geographic information system is an integrated set of hardware and software designed to input, store, manipulate, and output, geographically referenced data (i.e. geographic information) . Any data referenced to a location on the Earth can be considered geographic information. All geographic information has three components: the attribute of interest (i.e. a measurement or class such as temperature or forest type), the location to which the attribute refers, and time (i.e. the moment or period of time when the attribute was observed). There is a vast amount of geographic information available, much of it in digital form suitable for input to a GIS. Topographic data, remote sensing imagery and analysis results, digital and paper maps, field measurements, survey data, photographs, anecdotal information and even sound can all be input to a GIS . Conceptually, each data set can be thought of as a data layer co-registered so that corresponding locations are superimposed. In performing an integrated analysis, multiple data sets are simultaneously examined, in effect “drilling down” through the multiple data layers at each location. A GIS generally includes one or more input devices, some form of database software to store the data, software tools to manipulate the data, and one or more output devices. Costly input and output devices such as large format scanners, digitizing tables and printers, and specialized analytical tools such as stereoplotters for analyzing stereo images, are commonly set up as separate workstations. Geographic information systems are used in fields ranging from natural resource management to municipal and regional planning. For any inquiry pertaining to geographic location, there are geographic information systems that can be used to carryout the analysis. The power of a GIS is in the analysis capabilities it provides. GIS analyses can be broadly grouped into three categories. Descriptive analyses integrate the data from one or more sources and present conclusions about conditions at some point in time, as represented by the data. A vegetation map or municipal zoning plan are examples. Predictive analyses assess current information and apply knowledge of processes to develop one or more future scenarios of the way conditions could become at some point in the future. Examples include the modeling of forest growth, emergency planning for a flood event, or projecting the location of future urban development. Prescriptive analyses incorporate a knowledge of processes, as well as multiple scenarios that may include value choices expressing the wants and needs of one or more stakeholders in a decision-making process. Prescriptive analyses seek to define courses of action that optimize several often conflicting trade-offs. Examples include regional development planning and forest management planning. The capability to rapidly process large geographic data sets makes it cost effective to perform repeated analyses to update information as new data become available or to develop solutions involving complex compromises using iterative procedures that progressively refine a solution. In the pre-GIS era, the presentation and integration of geographic data depended on manual drafting of maps and map overlays, making the production an updating of maps or performing iterative analyses prohibitively expensive or completely impractical. A GIS cannot produce anything without digital geographic data. The development of GIS has depended as much upon the creation and storage of vast quantities of geographic data as on the development of the hardware and software to analyze them. Remote sensing is the major source of geographic data used in geographic information systems and for this reason has played a major role in the widespread adoption of GIS. Most digital geographic information pertaining to land topography, ocean floor topography, natural resources, and cultural features such as roads and urban infrastructure are generated using remotely sensed data. Virtually all data derived from remote sensing are now made available in GIS-readable digital formats. Digital image data can be rectified and displayed as image maps or in combination with other GIS data such as road networks and administrative boundaries, or boundaries and annotations (Graphic 4). Data provided with three-dimensional geographic coordinates, such as surface topography, can be used to generate perspective views that simulate a three-dimensional surface over which other geographic information can be superimposed. The data may be a colour composite satellite image (Graphic 5) or GIS-generated data such as a vegetation classification displayed over the topography. The closer integration of digital image analysis and GIS software has facilitated the use of GIS data to improve remote sensing analysis procedures. For example, an analyst can use the field data stored in a GIS to improve the accuracy of a digital image classification. The classification results can then be stored in the GIS as a data source for other analyses. While a GIS has the capability to integrate multiple sources of any geographic data, a number of conditions must be satisfied. The data sets must be registered to the same geographic coordinate system, termed geocoding or georeferencing. The level of detail of the different data sets must be appropriate for the analysis. The spatial accuracy of small scale data is usually insufficient for large scale analyses. The quality of the attribute data must also suit the application. Data that are too old, defined using categories that are too broad, or were not collected with sufficient consistency may produce results with insufficient accuracy for the application. Finally, the analysis procedures chosen must be appropriate to generate the required information from the available data.



The following is a list remote sensing sites compiled for your benefit. It is continually being updated. If you would like your Web site (or any others) to be listed here, please notify us by e-mailing

Aerial photography and remote sensing info Provides images and detailed descriptions of the theory and applications in the areas of Remote Sensing, Aerial Photography, Digital Image Processing, Satellite Imaging, MSS, Thermal and Hyperspectral Scanning Radar Scanning, Remote Sensing and GIS.
Alaska SAR Facility Homepage
ASD: Welcome to Analytical Spectral Devices, Inc. Manufacturers of field portable spectroradiometers. These instruments allow the collection of ground truth spectra used in the development and validation of remote sensing data analysis models.
Atlantic Center for Remote Sensing of the Oceans Home Page.
Australian Environmental Resources Information Network A project of the Australian Department of the Environment and associated agencies
Canada Center for Inland Waters, Burlington Water research, generating environmental information and knowledge about the Great Lakes.
CCRS Cover Page / CCT page couverture. Responsible for the acquisition of remotely sensed data and for the development of remote sensing applications and related methodologies and systems.
CCRS Digital Browse Facility Spot/Landsat 5 Scene Browser
Center For Advanced Spatial Technologies (Main). University of Arkansas, Fayetteville. Applications in GIS, remote sensing, digital photogrammetry and interoperability.
Center For Remote Sensing and Spatial Analysis.
Centre d'applications et de recherches en télédétection (CARTEL)
CEOS: Committee on Earth Observations Satellites (from ESA)
EOL Welcome (Earth-Observations Laboratory, University of Waterloo) -- Part of the Institute for Space and Terrestrial Science, the EOL contributes towards the overall goal of providing leadership in key areas of multi-disciplinary space and terrestrial science, engineering and education.
Earth Observing System Home Page Provides convenient access to program information for those involved or interested in the EOS program.
ERIM Home Page The Environmental Research Institute of Michigan
EOS Project Science Office Retrieve and display documents and data about the Earth Observing System from all over the Internet
Remote Sensing Servers ERIN remote sensing server list from Australia
ESA listing of Earth Observation sites from the European Space Agency
ESRIN: European Space Agency site
ESA's Experimental AVHRR Preview Service
GCNet Cover Page - CCRS Global Change.
Geomatics International Home Page
GeoWeb - On-Line Resource for GIS/GPS/RS
GIS and Remote Sensing for Archaeology
GIS Software
GRASS Home Page.
IGARSS `94: Conference Electronic Digest
IMAGRS-L mailing list archive.
ISTS: Earth Observation Lab at the Institute for Space and Terrestrial Studies, York University
IUE Data Analysis Center Home page
JPL Picture Gallery
Downloadable Landdata from ESA
Lawrence Livermore National Laboratory
MODIS Home Page
MTPE: NASA's Mission to Planet Earth - 1 of dozens of NASA sites
MultiSpec Home Page.
NASA Global Change Directory
NASA/Goddard Space Flight Center
NASA Information Services via World Wide Web
NASA Jet Propulsion Laboratory
The NASA/JPL Imaging Radar Home Page
NASDA - Japanese Earth Observation Center.
NOAA's home page
National Atlas Information Service - Geomatics Canada.
Pathfinderassorted data sets (e.g., AVHRR, SSM/I, etc) from NASA for Global Change monitoring
Pictures of the World
Pre-Flight SIR-C Education CD-ROM
Queen's University listing of gis/rs sources
Remote Sensing Group at U. of Miami. A division of the Rosenstiel School of Marine and Atmospheric Science, the RSG processes NOAA AVHRR LAC and GAC data in several areas. Daily images and composites for the past seven days are available. Sea Surface Temperatures are available for the JGOFS Arabian Sea Expedition.
Remote Sensing Meta-Home Page (by S. Carl at the Technical University of Munich).
Seaspace Makers of the Terascan Receiving System which runs on Sun Workstations.
SeaWiFS Global Ocean Color Monitoring Mission
SIR-C/X-SAR: Space Shuttle radar images of Earth
SIR-C Education
Space Science and Engineering Center at U. of Wisconsin Specializing in geostationary satellite data. It provides real time images of GOES-7, GOES-8, Global Sea Surface Temperature updated weekly, and CRAS model runs every 12 hours.
Stennis Space R. S. Center
Sylva (Forestry) resource page at the University of Laval.
TAMU annotated list of GIS/RS/GPS/geoscience sites from Texas A&M
Terrestrial Remote Sensing at ERSL
University of MiamiRemote Sensing Lab
University of Minnesota R. S. Lab
Vegetation FAQ: Frequently Asked Questions about remote sensing of vegetation (from Terrill Ray)
Videos and animations
Weather images from geostationary weather satellites - inc. MPEG movie loops
Welcome to C.E.N.'s Web Client server technologies, offers digital satellite imagery.
WWW Remote Sensing Index
WWW Virtual Library: Remote Sensing.
Source: ... _geophsics

Introduction to Remote Sensing #2
The Global Positioning System (GPS)


Introduction to Remote Sensing _THE GPS

A satellite-based radio-navigation system comprised of a constellation of twenty-four satellites and their supporting ground stations, used to obtain precise positions of targets on, or near, the surface of the Earth.

NAVSTAR GPS (NAVigation Signal Timing and Ranging Global Position System), commonly known as GPS, was developed by the United States Department of Defense to provide all-weather, around-the-clock navigation capabilities for ground, sea, and air military forces. The full satellite complement became available in 1995. The system consists of a constellation of twenty-four satellites, each of which orbits the Earth every twenty-four hours at an altitude of about 20,000 km. in six evenly distributed orbital planes around the Earth This configuration was chosen so that at least four GPS satellites can be visible to users from any point on the Earth’s surface at any time. The position of each satellite is known precisely at all times.

By providing the capability to accurately determine latitude, longitude, and elevation using portable receivers, GPS has revolutionized surveying, navigation, and the collection of geospatial data. GPS units can be small, lightweight, and relatively inexpensive and have been installed in aircraft, ships, trucks, and cars for navigation, as well as vehicle tracking. Using GPS and wireless communication technology, the location of any vehicle with GPS technology can be plotted on an electronic map and updated in real-time.Personnel in the field can collect data using GPS equipped laptop computers, which automatically input the location data with every field record. Traditional surveying techniques can be complemented or replaced by GPS survey methods; thereby, improving the efficiency of the map making process. GPS units are also used in construction equipment, farm machinery, pleasure boats and movie making equipment to provide precise positioning information.

Using very accurate distance measurements from several GPS satellites, the location of the GPS receiver on Earth can be calculated using a procedure termed triangulation. The GPS receiver calculates the time lag of the unique signal from each visible GPS satellite to reach it. Since the signal travels at the speed of light (3 X 108 m/sec), the distance is calculated by multiplying the time lag by the speed of light. The position of each satellite in view is determined from the orbital data of each satellite.

Simultaneous reception of data from a minimum of three satellites is needed to determine latitude and longitude, and from at least four satellites to determine elevation as well. Five satellites are needed to achieve real-time accuracy on the order of a few centimetres

Horizontal accuracy of about 20 m is possible using a single GPS receiver. Vertical accuracy is generally about 1.5 to 2 times worse than horizontal accuracy. GPS measurements are subject to errors from several sources including error in the synchronization of the atomic clocks in the different GPS satellites, uncertainties in the orbital data of each satellite, atmospheric conditions affecting signal velocity, and multipath errors caused by signal reflection. Differential correction can compensate for most of these errors.

Remote sensing benefits from GPS technology in geometric correction procedures as well as in field work for ground verification and in situ measurements.

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