Remote Sensing,gis And Gps

THANTHAI PERIYAR GOVT INSTITUTE OF TECHNOLOGY REMOTE SENSING,GIS AND GPS TECHNOLOGY AND ITS APPLICATIONS

Submitted by A.Senthamilselvan([email protected])-IIIrd year T.S.Sharathkumar([email protected])-IIIrd year Address: Dept of Civil Engg,TPGIT,Vellore-2

RE MO TE SENS IN G TEC HN IQ UE: INTRODUCTION: “Remote sensing is the science (and to some extent, art) of acquiring information about the earth’s surface without actually being in contact with it. This is done by sensing and recording reflected or emitted energy and processing, analyzing and applying that information”

KINDS OF REMOTE SENSING 1.Passive sensor 2.Active sensor

PASSIVE SENSOR: Passive sensors detect natural radiation that is emitted or reflected by the object or surrounding area being observed. Reflected sunlight is the most common source of radiation measured by passive sensors EX: Film photography, Infrared, charge-coupled devices, and radiometers.

ACTIVE SENSOR: Active collection, on the other hand, emits energy in order to scan objects and areas whereupon a sensor then detects and measures the radiation that is reflected or backscattered from the target. EX: RADAR

Qual ity of remote sensing data: The quality of remote sensing data consists of its spatial, spectral, radiometric and temporal resolutions. Spatial resolution The size of a pixel that is recorded in a raster image - typically pixels may correspond to square areas ranging in side length from 1 to 1,000 metres (3.3 to 3,280 ft). Spectral resolution The wavelength width of the different frequency bands recorded - usually, this is related to the number of frequency bands recorded by the platform. Current Landsat collection is that of seven bands, including several in the infra-red spectrum, ranging from a spectral resolution of 0.07 to 2.1 μm. The Hyperion

sensor on Earth Observing-1 resolves 220 bands from 0.4 to 2.5 μm, with a spectral resolution of 0.10 to 0.11 μm per band. Radiometric resolution The number of different intensities of radiation the sensor is able to distinguish. Typically, this ranges from 8 to 14 bits, corresponding to 256 levels of the gray scale and up to 16,384 intensities or "shades" of colour, in each band. Temporal resolution The frequency of flyovers by the satellite or plane, and is only relevant in timeseries studies or those requiring an averaged or mosaic image as in deforesting monitoring. This was first used by the intelligence community where repeated coverage revealed changes in infrastructure, the deployment of units or the modification/introduction of equipment . Cloud cover over a given area or object makes it necessary to repeat the collection of said location.

GEO-REFERENCING: In order to create sensor-based maps, most remote sensing systems expect to extrapolate sensor data in relation to a reference point including distances between known points on the ground. This depends on the type of sensor used. For example, in conventional photographs, distances are accurate in the center of the image, with the distortion of measurements increasing the farther you get from the center. Another factor is that of the platen against which the film is pressed can cause severe errors when photographs are used to measure ground distances. The step in which this problem is resolved is called georeferencing, and involves computer-aided matching up of points in the image which is extrapolated with the use of an established benchmark, "warping" the image to produce accurate spatial data. As of the early 1990s, most satellite images are sold fully georeferenced. In addition, images may need to be radiometrically and atmospherically corrected

WORKING: Remote sensing works on the principle of the inverse problem. While the object or phenomenon of interest (the state) may not be directly measured, there exists some other variable that can be detected and measured (the observation), which may be related to the object of interest through the use of a data-derived computer model. The common analogy given to describe this is trying to determine the type of animal from its footprints. For example, while it is impossible to directly measure temperatures in the upper atmosphere, it is possible to measure the spectral emissions from a known chemical species (such as carbon dioxide) in that region. The frequency of the emission may then be related to the temperature in that region via various thermodynamic relations

Here is a generalized picture of a remote sensing system on an orbiting satellite, showing what it is looking at and how it gathers its data: Since the 1960s, most remote sensing has been conducted from satellites. Prior to that remote sensing is associated mainly with aerial photography, using cameras mounted in aircraft that fly at various altitudes (which affect image scale and area encompassed. Aircraft remote sensing continues through today but is usually directed towards specific tasks and missions. Sometimes a distinction is made between "Remote" and "Proximal" Sensing. The first involves making measurements and collecting data for (and from) objects, classes, and materials that are not in contact with the sensor (sensing device) whereas the second " " includes making direct contact with these targets. Thus, if the objective is to measure a person's bodily temperature, the proximate approach would be to place a thermometer in or on the body whereas the remote approach would be to hold a radiometer sensitive to thermal energy at some distance from the body. In both situations, the measuring device would need to be calibrated (see page I-5a), that is, its response as a sensor must be transformable into a good approximation of the actual temperature by determining the response using a target whose temperature range is specifically known.

The idea of remote sensing carries with it a number of objectives and ancillary operations, each with its own "buzz word". Here is a diagram that connotes this concept, as it applies to the services offered by a specific remote sensing commercial company (IIRMR):

App li ca tions o f r emote sensing da ta: •

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Conventional radar is mostly associated with aerial traffic control, early warning, and certain large scale meteorological data. Doppler radar is used by local law enforcements' monitoring of speed limits and in enhanced meteorological collection such as wind speed and direction within weather systems. Other types of active collection includes plasmas in the ionosphere). Interferometric synthetic aperture radar is used to produce precise digital elevation models of large scale terrain (See RADARSAT, TerraSAR-X, Magellan). Laser and radar altimeters on satellites have provided a wide range of data. By measuring the bulges of water caused by gravity, they map features on the seafloor to a resolution of a mile or so. By measuring the height and wave-length of ocean waves, the altimeters measure wind speeds and direction, and surface ocean currents and directions. Light detection and ranging (LIDAR) is well known in the examples of weapon ranging, laser illuminated homing of projectiles. LIDAR is used to detect and measure the concentration of various chemicals in the atmosphere, while airborne LIDAR can be used to measure heights of objects and features on the ground more accurately than with radar technology. Vegetation remote sensing is a principle application of LIDAR. Radiometers and photometers are the most common instrument in use, collecting reflected and emitted radiation in a wide range of frequencies. The most common are visible and infrared sensors, followed by microwave, gamma ray and rarely, ultraviolet. They may also be used to detect the emission spectra of various chemicals, providing data on chemical concentrations in the atmosphere. Stereographic pairs of aerial photographs have often been used to make topographic maps by imagery and terrain analysts in trafficability and highway departments for potential routes. Simultaneous multi-spectral platforms such as Landsat have been in use since the 70's. These thematic mappers take images in multiple wavelengths of electromagnetic radiation (multi-spectral) and are usually found on earth observation satellites, including (for example) the Landsat program or the IKONOS satellite. Maps of land cover and land use from thematic mapping can be used to prospect for minerals, detect or monitor land usage, deforestation, and examine the health of indigenous plants and crops, including entire farming regions or forests.

Within the scope of the combat against desertification, remote sensing allows to followup and monitor risk areas in the long term, to determine desertification factors, to support decision-makers in defining relevant measures of environmental management, and to assess their impacts.

GEOGRAPHIC INFORMA SY STE MS(GI S):

TION

A geographic information system (GIS) is a computer-based tool for mapping and analyzing spatial data. GIS technology integrates common database operations such as query and statistical analysis with the unique visualization and geographic analysis benefits offered by maps. These abilities distinguish GIS from other information systems and make it valuable to a wide range of public and private enterprises for explaining events, predicting outcomes, and planning strategies. GIS is considered to be one of the most important new technologies, with the potential to revolutionize many aspects of society through increased ability to make decisions and solve problems.

COMPONENTS SYST EM

OF

GEOGRAPHI C

INF ORMATION

A working Geographic Information System seamlessly integrates five key components: • • • • •

Hardware Software Data People Methods.

WORKING OF GIS: A GIS stores information about the world as a collection of thematic layers that can be linked together by geography.This simple but extremely powerful and versatile concept has proven invaluable for solving many real-world problems from modeling global atmospheric circulation, to predicting rural land use, and monitoring changes in rainforest ecosystems. Geographic information contains either an explicit geographic reference such as a latitude and longitude or national grid coordinate, or an implicit reference such as an address, postal code, census tract name, forest stand identifier, or road name. An automated process called geocoding is used to create explicit geographic references (multiple locations) from implicit references (descriptions such as addresses). These geographic references can then be used to locate features, such as a business or forest stand, and events, such as an earthquake, on the Earth's surface for analysis.

General purpose GIS’s perform seven tasks: • • • • • •

Input of data Map making Manipulation of data File management Query and analysis Visualization of results

Input of Data : Before geographic data can be used in a GIS, the data must be converted into a suitable digital format. The process of converting data from paper maps or aerial photographs into computer files is called digitizing. Modern GIS technology can automate this process fully for large projects using scanning technology; smaller jobs may require some manual digitizing which requires the use of a digitizing table. Today many types of geographic data already exist in GIS-compatible formats. These data can be loaded directly into a GIS. Map Making : Maps have a special place in GIS. The process of making maps with GIS is much more flexible than are traditional manual or automated cartography approaches. It begins with database creation.Existing paper maps can be digitized and computer-compatible information can be translated into the GIS. The GIS-based cartographic database can be both continuous and scale free. Map products can then be created centered on any location, at any scale, and showing selected information symbolized effectively to highlight specific characteristics.

The characteristics of atlases and map series can be encoded in computer programs and compared with the database at final production time. Digital products for use in other GIS’s can also be derived by simply copying data from the database.In a large organization, topographic databases can be used as reference frameworks by other departments. Manipulation of Data: It is likely that data types required for a particular GIS project will need to be transformed or manipulated in some way to make them compatible with your system.For example, geographic information is available at different scales (street centerline files might be available at a scale of 1:100,000; census boundaries at 1:50,000; and postal codes at 1:10,000). Before this information can be integrated, it must be transformed to the same scale. This could be a temporary transformation for display purposes or a permanent one required for analysis. GIS technology offers many tools for manipulating spatial data and for weeding out unnecessary data. File Management : For small GIS projects it may be sufficient to store geographic information as simple files. There comes a point, however, when data volumes become large and the number of data users becomes more than a few, that it is best to use a database management system (DBMS) to help store, organize, and manage data. A DBMS is nothing more than computer software for managing a database--an integrated collection of data. There are many different designs of DBMS’s, but in GIS the relational design has been the most useful. In the relational design, data are stored conceptually as a collection

of tables. Common fields in different tables are used to link them together. This simple design has been widely used, primarily because of its flexibility and very wide deployment in applications both within and without GIS Query Analysis:

and

Once you have a functioning GIS containing your geographic information, you can begin to ask simple questions such as • How far is it between two places? • How is this particular parcel of land being used? • What is the dominant soil type for oak forest? • Where are all the sites suitable for relocating an endangered species? • Where are all of the sites possessing certain characteristics? • If I build a new highway here, how will animals in the area be affected? GIS provides both simple point-and-click query capabilities and sophisticated analysis tools to provide timely information to managers and analysts alike. GIS technology reallycomes into its own when used to analyze geographic data to look for patterns and trends, and to undertake "what if" scenarios. Modern GIS’s have many powerful analytical tools, but two are especially important. Proximity Analysis is used to examine spatial relationships by determining the proximity relationship between features.

Overlay Analysis integrates different data layers to look for patterns and relationships. At its simplest, this could be a visual operation, but analytical operations require one or more data layers to be joined physically. For example, to analyze the impact of urbanization on ecological characteristics of an area, an overlay could integrate data on soils, hydrology, slope, vegetation, and land use. Queries could be used to identify sources of pollution, to delineate potentially sensitive areas, or to plan for increased population growth in the area Visualization : For many types of geographic operations, the end result is best visualized as a map orgraph. Maps are very efficient at storing and communicating geographic information. While cartographers have created maps for millennia, GIS provides new and exciting tools to extend the art and science of cartography. Map displays can be integrated with reports, three-dimensional views, photographic images, and with multimedia.

THE IMP ORTANCE INF ORMATION SYSTE MS:

OF

GEOGRAPHIC

The ability of GIS to search databases and perform geographic queries has revolutionized many areas of science and business. It can be invaluable during a decisionmaking process. The information can be presented succinctly and clearly in the form of a map and accompanying report, allowing

decision makers to focus on the real issues rather than trying to understand the data. Because GIS products can be produced quickly, multiple scenarios can be evaluated efficiently and effectively. For this reason, in today’s world, the ability to use GIS is increasingly important.

GIS Applications: • • • • • • • •

Health and Anemities planning Market Research Operations Management - Distribution and Retail Services Spatial Information Services - Tourist & Tour Operators Spatial Services Management – Defense and Disaster Management Spatial Services Management - Land & Utilities Planning & Management& Many Others With the availability of real-time positioning systems, it is possible to develop GIS that monitor, transmit, record and analyse the movement of mobile agents such as vehicles, people or animals and hazards (telegeomonitoring). Virtual Reality GIS supports creation, manipulation and exploration of georeferenced virtual environment.

GLOBAL POSITIONING SYSTEM(GPS): INTRODUCTION: The Global Positioning System (GPS) is a U.S. space-based global navigation satellite system. It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis in all weather, day and night, anywhere on or near the Earth.

GPS is made up of three parts: between 24 and 32 satellites orbiting the Earth, four control and monitoring stations on Earth, and the GPS receivers owned by users. GPS satellites broadcast signals from space that are used by GPS receivers to provide three-dimensional location (latitude, longitude, and altitude) plus the time.

Basic concept of GPS: A GPS receiver calculates its position by precisely timing the signals sent by the GPS satellites high above the Earth. Each satellite continually transmits messages which include • • •

the time the message was sent precise orbital information (the ephemeris) the general system health and rough orbits of all GPS satellites (the almanac).

The receiver measures the transit time of each message and computes the distance to each satellite. Geometric trilateration is used to combine these distances with the satellites' locations to obtain the position of the receiver. This position is then displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included. Many GPS units also show derived information such as direction and speed, calculated from position changes. Three satellites might seem enough to solve for position, since space has three dimensions. However, even a very small clock error multiplied by the very large speed of light—the speed at which satellite signals propagate—results in a large positional error. Therefore receivers use four or more satellites to solve for the receiver's location and time. The very accurately computed time is effectively hidden by most GPS applications, which use only the location. A few specialized GPS applications do however use the time; these include time transfer, traffic signal timing, and synchronization of cell phone base stations. Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. (For example, a ship or plane may have known elevation.) Some GPS receivers may use additional clues or assumptions (such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer) to give a degraded position when fewer than four satellites are visible.

WORKING OF GPS TECHNOLOGY: Position calculation introduction:

To provide an introductory description of how a GPS receiver works, errors will be ignored in this section. Using messages received from a minimum of four visible satellites, a GPS receiver is able to determine the times sent and then the satellite

positions corresponding to these times sent. The x, y, and z components of position, and the time sent, are designated as where the subscript i is the satellite number and has the value 1, 2, 3, or 4. Knowing the indicated time the message was received , the GPS receiver can compute the transit time of the message as . Assuming the message traveled at the speed of light, c, the distance traveled, can be computed as . A satellite's position and distance from the receiver define a spherical surface, centered on the satellite. The position of the receiver is somewhere on this surface. Thus with four satellites, the indicated position of the GPS receiver is at or near the intersection of the surfaces of four spheres. (In the ideal case of no errors, the GPS receiver would be at a precise intersection of the four surfaces.)

Correcting a GPS receiver's clock The method of calculating position for the case of no errors has been explained. One of the most significant error sources is the GPS receiver's clock. Because of the very large value of the speed of light, c, the estimated distances from the GPS receiver to the satellites, the pseudoranges, are very sensitive to errors in the GPS receiver clock. This suggests that an extremely accurate and expensive clock is required for the GPS receiver to work. On the other hand, manufacturers prefer to build inexpensive GPS receivers for mass markets. The solution for this dilemma is based on the way sphere surfaces intersect in the GPS problem. It is likely that the surfaces of the three spheres intersect, since the circle of intersection of the first two spheres is normally quite large, and thus the third sphere surface is likely to intersect this large circle. It is very unlikely that the surface of the sphere corresponding to the fourth satellite will intersect either of the two points of intersection of the first three, since any clock error could cause it to miss intersecting a point. However, the distance from the valid estimate of GPS receiver position to the surface of the sphere corresponding to the fourth satellite can be used to compute a clock correction. Let denote the distance from the valid estimate of GPS receiver position to the fourth satellite and let denote the pseudorange of the fourth satellite. Let . Note that is the distance from the computed GPS receiver position to the surface of the sphere corresponding to the fourth satellite. Thus the quotient, , provides an estimate of(correct time) - (time indicated by the receiver's on-board clock),and the GPS receiver clock can be advanced if is positive or delayed if is negative.

GPS APPLICATIONS: •

Environment

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Boosting the gold-mining industries

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Forestry and agriculture

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Natural disasters

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Maritime and Waterways

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Tele-communications

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Infrastructure development

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Archeology and Educational research

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Public health and safety

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Traffic management

SOFTWARES USED: REMOTE SENSING: Remote Sensing data is processed and analyzed with computer software, known as a remote sensing application. A large number of proprietary and open source applications exist to process remote sensing data. According to an NOAA Sponsored Research by Global Marketing Insights, Inc. the most used applications among Asian academic groups involved in remote sensing are as follows: ESRI 30%; ERDAS IMAGINE 25%; ITT Visual Information Solutions ENVI 17%; MapInfo 17%; ERMapper 11%. Among Western Academic respondents as follows: ESRI 39%, ERDAS IMAGINE 27%, MapInfo 9%, AutoDesk 7%, ITT Visual Information Solutions ENVI 17%. Another important Remote Sensing Software packages is PCI Geomatics who makes PCI Geomatica, the leading remote sensing software package in Canada. Open source remote sensing software includes GRASS GIS, QGIS, OSSIM, and Orfeo toolbox.

GIS: Geographic information can be accessed, transferred, transformed, overlaid, processed and displayed using numerous software applications. Within industry, commercial offerings from companies such as Autodesk, Bentley Systems, ESRI, Intergraph, Manifold System, Mapinfo and Smallworld dominate, offering an entire suite of tools. Government and military departments often use custom software, open source products such as GRASS or uDig, or more specialized products that meet a well defined need. Although free tools exist to view GIS datasets, public access to geographic information is dominated by online resources such as Google Earth and interactive web mapping.

GPS: Commercial navigation software with embedded maps • • • • • • • • •

Nav N Go (iGO) ROUTE 66 TomTom Navigator TomTom Mobile Destinator Garmin nRoute Garmin BaseCamp (to be released by the end of March 2009) [1] GPS Tuner (Version 6.0 to be released beginning 2nd Q 2009) [2] Microsoft Streets and Trips 2009