Iirs lecure notes for Remote sensing –An Overview of Decision Maker

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Iirs lecure notes for Remote sensing –An Overview of Decision Maker

  1. 1. CONTENTS. No. Topics Faculty Page No.1. Overview of Remote Sensing Ms. Shefali Agarwal 12. Terrain Analysis Ms. Shefali Agarwal 153. Geographic Information System Mr. P.L. N. Raju 274. Fundamental Concepts of GPS Mr. P. L. N. Raju 385. Geo informatics for Natural Dr. P.S. Roy 69 Resources Management Dean, IIRS6. Applications in Agriculture and Soils Dr. S.K. Saha 1047. Applications in Forest Management Dr. S. P.S. Kushwaha 1178. Applications in Geosciences Dr. P.K. Champtiray 1289. Applications in Human Settlement Dr. B.S. Sokhi 139 Studies and Management10. Applications in Marine Sciences Dr. D. Mitra 14311. Applications in Water Resources Dr. S.P. Aggarwal 154
  2. 2. 1 OVERVIEW OF REMOTE SENSING Shefali Agrawal Photogrammetry and Remote Sensing Division1. Introduction In recent times earth observation from aerospace media has gained significantimportance due to ever increasing demand for most authentic, timely and uniforminformation of earth surface features and processes involved. Due to rapid developmentand changing life style, the impact on environment and its effect on surface processesand features have under gone sea change. The impact of development on theenvironment is significant as the rapidly growing population; urbanization and otherdevelopment efforts have exerted tremendous pressure on natural resources and havecaused their depletion and degradation. Biodiversity is declining at an unprecedentedrate - as much as a thousand times what it would be without the impact of humanactivity. Half of the tropical rainforests have already been lost. Land degradation affectsas much as two thirds of the worlds agricultural land. As a result, agriculturalproductivity is declining sharply. The conservation measures are far from satisfactoryand as development processes and interventions still continue, natural resources will besubjected to greater damage in the future. Hence there is an urgent need to look foralternative strategies and approaches for better and more efficient management ofnatural resources in order to ensure their sustainable use. This is further compoundedby the ever increasing occurrences of natural hazards. Therefore, there is a greaterdemand for most authentic timely information on a suit of geophysical parameters andenvironmental indicators. Towards this space provides a vantage point where a largenumber of sensors have been deployed onboard satellites providing geo spatialinformation needed to understand the Earth system as a whole.1.1. Definition of Remote Sensing Remote sensing is the science of acquiring information about the Earths surfacewithout actually being in contact with it. This is done by sensing and recording reflected Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  3. 3. 2or emitted energy and processing, analyzing, and applying that information (Lillesandand Kiefer, 2004).Remote sensing, also called earth observation, refers to obtaininginformation about objects or areas at the Earth’s surface by using electromagneticradiation (light) without coming in physical contact with the object or area. The basicprocess involved in remote sensing is the interaction of the electromagnetic radiationwith the Earths surface and detection at some altitude above the ground. RemoteSensing Systems have four basic components to measure and record data about anarea from a distance, Fig1. These components include: • Emission of electromagnetic radiation (EMR) • Transmission of energy from the source to the surface of the earth, as well as absorption and scattering • Interaction of EMR with the earths surface: reflection and emission • Transmission of energy from the surface to the remote sensor • Sensor data acquisition • Data transmission, processing and analysis Fig.1 Remote sensing process With respect to the type of energy resources, the RS technology is defined aspassive or active, Fig 2. Passive Remote Sensing makes use of sensors that detect the Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  4. 4. 3 reflected or emitted electro-magnetic radiation from natural sources. Active remoteSensing makes use of sensors that detect reflected responses from objects that areirradiated by artificially generated energy sources, such as radar. Fig.2. Passive and active remote sensingWith respect to Wavelength Regions, the RS technology is classified as: • Visible and reflective infrared RS operating at a range of 0.4μm to 2.5μm. • Thermal infrared remote sensing operating at a range of 3μm to14μm. • Microwave remote sensing operating at a range of 1mm to1m. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  5. 5. 4 ‘Optical range’ Cosmic Gamma X- Radio Electric power U-V Infrared Micro-waves TV rays rays Rays Visible spectrum Ultraviolet Blue Green Red Infrared (IR) 0.3μ m 0.4 0.5μ m 0.6 0.7μ m 10.0 15.0 300nm 500nm 700nm Wavelength Fig.3. Electromagnetic spectrum 1.2 Interaction of EMR with the Earths Surface Radiation from the sun, when incident upon the earths surface, is either reflectedby the surface, transmitted into the surface or absorbed and emitted by the surface. TheEMR, on interaction, experiences a number of changes in magnitude, direction,wavelength, polarization and phase. These changes are detected by the remote sensorand enable the interpreter to obtain useful information about the object of interest. Theremotely sensed data contain both spatial information (size, shape and orientation) andspectral information (tone, color and spectral signature). In the visible and reflective Infrared remote sensing region, the radiation sensedby the sensor is that due to the sun, reflected by the earths surface. A graph of thespectral reflectance of an object as a function of wavelength is called a spectralreflectance curve. Figure shows the typical spectral reflectance curves for three basictypes of earth feature vegetation, soil, and water in the visible and reflective Infraredregion Fig.4.The band corresponding to the atmospheric window between 8 μm and 14μm is known as the thermal infrared band. The energy available in this band for remote Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  6. 6. 5sensing is due to thermal emission from the earths surface. Both reflection and self-emission are important in the intermediate band from 3 μm to 5.5 μm. In the microwave region of the spectrum, the sensor is radar, which is an activesensor, as it provides its own source of EMR. The EMR produced by the radar istransmitted to the earths surface and is reflected (back scattered) from the surface tobe recorded by the radar system again. The microwave region can also be monitoredwith passive sensors, called microwave radiometers, which record the radiation emittedby the terrain in the microwave region. Fig. 4. Typical spectral reflectance curves for vegetation, soil and water. In the microwave region of the spectrum, the sensor is radar, which is an activesensor, as it provides its own source of EMR. The EMR produced by the radar istransmitted to the earths surface and is reflected (back scattered) from the surface tobe recorded by the radar system again. The microwave region can also be monitoredwith passive sensors, called microwave radiometers, which record the radiation emittedby the terrain in the microwave region. 1.3 Platforms and Sensors In order to enable sensors to collect and record energy reflected or emitted froma target or surface, they must reside on a stable platform away from the target orsurface being observed. As space provides one of the most vantage points for earth Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  7. 7. 6observation, two prominent orbits are considered for Earth observation: the geo-stationary orbit and the polar orbit. The geo-stationary orbit is such a position that itkeeps pace with the rotation of the Earth. These platforms are covering the same placeand give continuous near hemispheric coverage over the same area day and night.These are mainly used for communication and meteorological applications. This geo-stationary orbit is located at an altitude of 36,000 km above the equator Fig 5. Fig. 5 Geostationary and near polar orbits The second important remote sensing orbit is the polar orbit. Satellites in a polarorbit cycle the Earth from North Pole to South Pole. The polar orbits have an inclinationof approximately 99 degrees with the equator to maintain a sun synchronous overpassi.e. the satellite passes over all places on earth having the same latitude at the samelocal time. This ensures similar illumination conditions when acquiring images over aparticular area over a series of days. The altitude of the polar orbits varies from 600 to900 km, approximately.1.4. Resolutions In general resolution is defined as the ability of an entire remote-sensing system,including lens antennae, display, exposure, processing, and other factors, to render asharply defined image. It depends on large number of factors that can be groupedunder: Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  8. 8. 7a. Spectral resolution: The spectral band in which the data is collected.b. Radiometric resolution: It is the capability of the sensor to differentiate two objectsbased on the reflectance / emittance differences.c. Spatial resolution: It is the capability of the sensor to discriminate the smallestobject on the ground. Higher the spatial resolution smaller the object that can beidentified Spatial resolutions vary from few kilometers to half a meter.d. Temporal resolution: It is the capability to view the same target, under similarconditions at regular intervals. Today a large number of earth observation satellites provide imagery that can beused in various applications.2. Indian Remote Sensing Satellites India is one of the major providers of the earth observation data in the world in avariety of spatial, spectral and temporal resolutions. India has launched severalsatellites including earlier generation IRS 1A, IRS 1B, IRS 1C, IRS 1D, IRS P2,IRS P3,IRS P4 and latest P6 and Cartosat series for different applications, the details of theseare listed in Table 1.Table 1: Indian Earth Observation Satellites. Spectral Swath Satellite No. of Resolution Revisit Launch Sensors Types Range Width Name Bands (m) (days) (µ) (km) MarchCartosat-1 PAN 1 2.5 m 25 2005 0.52 - 0.59 17th 0.62 - 0.68IRS-P6 October LISS -III MSl 4 23 140 24 0.77 - 0.86 2003 1.55 - 1.70 Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  9. 9. 8 0.52 - 0.59 0.62 - 0.68 AWiFS MSl 4 56 740 0.77 - 0.86 1.55 - 1.70 0.52 - 0.59 0.62 - 0.68 LISS -IV MS 3 5.8 23.9 5 0.77 - 0.86 LISS -IV PAN 1 0.62 - 0.68 5.8 70 5 OCM MS 8 0.4 - 0.885 360 m 1420IRS-P4 May 26, 6.6,10.65, 120, 80, 2(Oceansat) 1999 MSMR RADAR 4 1360 18, 21 GHz 40 and 40 0.62-0.68 (red) WiFS MS 2 189 774 5 0.77-0.86 (NIR) 0.52-0.59 (green) SeptemberIRS-1D 0.62-0.68 - 1997 3 23 142 (red) LISS-III MS 0.77-0.86 24-25 (NIR) 1.55-1.70 1 70 148 (SWIR) PAN PAN 1 0.50-0.75 6 70 0.62-0.68IRS-1C 1995 (red) WiFS MS 2 189 810 5 0.77-0.86 (NIR) Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  10. 10. 9 0.52-0.59 (green) 0.62-0.68 3 23.6 142 (red) LISS-III MS 0.77-0.86 24-25 (NIR) 1.55-1.70 1 70.8 148 (SWIR) PAN PAN 1 0.50-0.75 5.8 70 450-520 0.52-0.59 LISS-I MS 4 0.62-0.68 72.5 148IRS-1B 1991 0.77-0.86 22 (NIR) (same as LISS-II MS 4 36.25 74 LISS I) Same as LISS-I MS 4 72.5 148 aboveIRS-1A 1988 22 Same as LISS-II MS 4 36.25 74 above3. Global Satellites Global remote sensing satellites include Landsat, SPOT, ASTER, MODIS, MOS,JERS, ESR, Radarsat, IKONOS, QuickBird etc (Table 2): Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  11. 11. 10 Table 2: Earth Observation satellites from other countries Spectral Swath Satellite No. of Resolution Revisit Launch Sensors Types Range Width Name Channels (m) (days) (µ) (km) 0.43-0.47 (blue) 0.61- 600 xSPOT -5 May 2002 VMI MS 4 0.68(red) 1000 1 120 0.78-0.89( NIR) 1.58- 1.75(SWIR) 0.5-0.59 (green) HRS 0.61-0.68 10 (red) 10 MS 4 60 26 0.79-0.89 10 HRG (NIR) 20 1.58-1.75 (SWIR) 5 m, combined to PAN 1 0.61-0.68 60 generate a 2.5-metre product. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  12. 12. 11 10 m (resampled 1 0.61-0.68 at every 60 PAN 5m along track) blue (0.45- 4 2.5 m 17 km 0.52) green (0.52-0.6) MSQuickBird- Oct. 18, red (0.63-2 2001 0.69) NIR.76- 0.89) PAN 1 0.45-0.9 0.61 m Dec. 5, 12.5EROS 1 PAN 1 0.5-0.9 1.8 m 1-4 2000 kmTerra VNIR - Dec. 18,(EOS AM- 3 stereo (0.5- 15 m 16 19991) 0.9) ASTER MS 60 km SWIR (1.6- 6 30 m 2.5) 5 TIR (8-12) 90 m SWIR, TIR, CERES MS 3 20 km Total 360 MISR MS 4 250-275 m km MODIS 2 0.4-14.4 250 m 2330 5 500 m km Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  13. 13. 12 29 1000 m 640 MOPITT MS 3 2.3 (CH4) 22 km km 0.45-0.52 (blue) 0.52-0.60 (green)IKONOS- September MS 4 IKONOS 0.63-0.69 112 24, 1999 (red) 0.76-0.90 (NIR) PAN 1 1M Landsat7 16TM As Landsat 4-5 30x30 185 705 km 15/04/1999 days Band 6: 10,40 - 60×60 12,50 Panchromatic: 15×15 0,50 - 0,90NOAA-K May - 1998 AVHRR MS 5 1100 0.5-0.59 VMI MS 4 1000 (green) 0.61-0.68 (red) March 24, 26SPOT-4 0.79-0.89 1998 MS 4 20 60 HRV (NIR) 1.58-1.75 (SWIR) PAN 1 0.61-0.68 10 60 Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  14. 14. 134. Image Analysis and Interpretation In order to take advantage of and make good use of remote sensing data, wemust be able to extract meaningful information from the imagery. Interpretation andanalysis of remote sensing imagery involves the identification and/or measurement ofvarious targets in an image in order to extract useful information about them. Muchinterpretation and identification of targets in remote sensing imagery is performedmanually or visually by a human interpreter. It is also possible to apply digitaltechniques for image analysis and information extraction.9. Comparison of RS to Traditional Observations RS data, with its ability for a synoptic view, repetitive coverage, observations atdifferent resolutions, provides a better alternative for natural resources management,environmental monitoring and disaster management as compared to traditionalmethods. It provides images of target areas in a fast and cost-efficient manner. Whileair photos and fieldwork remain critical sources of information, the cost and time to carryout these methods often make them unviable and the human ability of observation issubjective and individual dependant, thereby making it even more unviable. RSinstrumentation makes it possible to observe the environment with EM radiation outsidethe visible part of the EM spectrum; the invisible becomes visible. RS is flexible in thatthere is a variety of RS observation techniques and a diversity of digital imageprocessing algorithms for extracting information about the earths surface. The data canbe easily integrated into a Geographical Information System thus making it even moreeffective in terms of solution offering.6. Future Prospects In near future large number of new satellites will be launched by India and othercountries with capabilities of providing high spatial, spectral and radiometric resolutiondata for variety of applications like water security, disaster management, naturalresource management, food security, infrastructure development etc. The use ofgeosynchronous orbit for providing high spatial resolution data will be a major break- Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  15. 15. 14through to receive bio-geophysical parameters in real time basis. Remote sensingcoupled with geographical information systems where the data can be integrated withother information, will provide geo-spatial information that is critical for decision makingrelated to natural resource utilization, environmental monitoring and disastermanagement.ReferencesLillesand T.M. and Kiefer R. 2004: Remote Sensing and Image Interpretation (Third Edition). John Wiley, New York.Web Linkshttp://www.ccrs.nrcan.gc.ca/ccrs/learn/tutorials/fundam/chapter1/chapter1_2www.planetary.brown.edu/arc/sensor.htmlhttp://www.ersc.edu/resources/EOSC.htmlwww.isro.orgwww.spaceimage.comwww.eospso.gfc.nasa.govwww.landsat.orgwww.spotimage.fr/homewww.space.gc.cawww.esa.int/export/esasa/ESADTOMBAMC_earth_O.html Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  16. 16. 15 TERRAIN ANALYSIS Shefali Agrawal Photogrammetry and Remote Sensing Division1. Introduction Terrain components play an important role in natural resource survey,environmental monitoring and natural hazards survey and analysis. Terrain features arethe most common features that can be observed from EO systems. Most importantly the3-D attribute/nature of the terrain can also be mapped and monitored using presentgeneration of EO systems using stereo viewing capability of Cartosat-1, SPOT ALOSPrism etc. and InSAR (Interferometric SAR) capability of Envisat and Radarsat. Terrainfeatures such as elevation, slope, aspect, and curvature influence most of the surfaceprocess including soil erosion, slope failures and vegetation composition. One of themost important attributes of terrain, topography influences atmospheric, hydrologic andecologic processes, such as, microclimate, local wind circulations and precipitation-runoff processes. Soil formation is also a function of relief, slope and geomorphology.Topographical features such as drainage basins, stream networks and channels, peaksand pits, drainage divides (ridges) and valleys play an important role in hydrologicalmodeling related to flooding, locating areas contributing pollutants to a stream,estimating the effects of altering the landscape etc. Relief information is also requiredfor removal of terrain distortions in aerial and satellite images and for creation oforthorectified image maps. Terrain visualization has also an important place in militaryand civil engineering operations. Based on the above application requirements and EOopportunities, a lot of emphasis is given on extraction of terrain features from usingoptical, radar, and Lidar data sets.2. Digital Elevation Model (DEM) The most important aspect of the terrain is relief that can be represented as a Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  17. 17. 16continuous surface in the form of a Digital Elevation Model (DEM). In GIS, DEM is usedto refer specifically to a regular grid of spot heights. It is the simplest and most commonform of digital representation of topography. The term Digital Terrain Model (DTM) mayactually be a more generic term for any digital representation of a topographic surface.DEM, can be generated from the following basic relief information.a) Contour lines: Usually elevations on a topographic map are represented as a groupof contour lines with a discrete and constant contour interval.b) Grid data: For convenience of computer processing, a set of grid data with elevationare acquired from contour maps, aerial photographs or stereo satellite image data.Terrain data other than the grid data are interpolated from the surrounding grid data.c) Random point data: Terrain features are sometimes represented by a group ofrandomly located terrain data with three-dimensional coordinates. For computerprocessing, random point data are converted to triangulated irregular network (TIN). TINhas the advantage of easy control of point density according to the terrain feature,though it has the disadvantage of being time consuming in the random search for theterrain point.d) Surface function: Terrain surface can be expressed mathematically as a surfacefunction, for example, a Spline function3. Elevation Data Sources Elevation data can be obtained from the following sources • Survey data: including ground-based leveling and satellite-based GPS data; • Remotely sensed data: including radar altimeter data, laser altimeter data, optical and SAR stereoscopic image pairs, complex interferometric SAR data, and shade information in single images; and Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  18. 18. 17 • Cartographic data: including contours, spot height points and surface structural lines digitized from paper topographical map sheets. Each data source has its own inherent strengths and limitations in terms of theavailability, accuracy, sampling density and pattern, and the ground coverage.4. Elevation Data Acquisition Techniques At present a number of techniques are available for acquiring digital elevationdata. The ground survey and aerial photogrammetry represent the traditional elevationextraction and measurement techniques. Contour-based topographical maps have longbeen the primary storage media for terrain information throughout the world. GPS,satellite image based stereoscopic technique, SAR interferometry, radar altimetry, andlaser altimetry are relatively new techniques for digital elevation acquisition. The adventof new data capture technologies has increased the acquisition speed of elevation data,improved the position and height measurements, extended their ground coverage, andreduced the cost. Ground survey and satellite-based GPS technology tend to generatevery accurate positional and height measurements. Since both ground survey and GPStechniques require physical visit of ground sampling points, the resulting measurementsare usually sparse. Often, they are utilized as GCPs (Ground Control Points) forextracting more dense elevation data from stereo photogrammetric and InSARtechniques or used as checking points for the DEM accuracy assessment.5. Digitizing Topographic Maps Due to the relatively low cost and the widest availability, the digitization oftopographical maps represents the practical method for gathering digital elevation datafor a large area, particularly for national and continental scale projects. Cartographicdata are the second hand topographical information source, in the sense that they areoriginally derived from direct height measurements of some kind. The information Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  19. 19. 18content of a topographical map depends on not only the quality of original source databut also map scale and contour interval. In addition to contours and spot heights,topographical maps may also contain, implicitly or explicitly, many important terrainfeatures such as surface break lines, ridges and drainage lines.6. Photogrammetry-Based Stereo Technique The photogrammetry-based stereo technique derives the digital elevation databased on parallax differences between a stereo image pair. The principle is simple; first,two images are acquired of the same area with slightly different viewing perspectives(stereo-overlap). These images are then aligned and geometrically matched so that amathematical (triangulation) model can be obtained. The analyst then has theopportunity to view the modeled stereo pair in 3D to manually extract the terraininformation or use automated stereo correlation tools to extract a new DTM. Theautomated process is typically used when the surface landscape needs to be extracted.“Above-the-landscape” features (e.g., buildings) are typically derived manually (usingstereo extraction tools) and then “placed” on the DTM. The accuracy of the elevationdata derived from stereo technique is often influenced by mismatch of conjugate imagepixels, and errors of the sensor position and attitude. The current and future high-resolution earth observation satellites (table 1) having a spatial resolution of 1m & lessand stereo capabilities will go a long way in the field of mapping in terms of cost, timeand accuracy.Table 1: High resolution sensors Sensor Launch Date Resolution IRS-1C 28-DEC-95 Panchromatic: 5.8 m IRS-1D 29-SEP-97 Panchromatic: 5.8 m IKONOS 24-SEP-1999 Panchromatic: 1 m Multispectral: 4 m Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  20. 20. 19QuickBird 18 October 2001 Panchromatic: .61 m Multispectral: 2.44 mEROS A1 05-DEC-2000 1.8mCBERS 3 2003 Panchromatic: 5 mEROS B1 2003 Panchromatic: .81 mEROS B2 2003 Panchromatic: .81 m Multispectral: 3.3 mSPOT- 5 1985 Panchromatic: 2.5m from 2 x 5m scenes Panchromatic: 5m (nadir)Terra-ASTER December 1999 Multispectral (B1-B3) 15mCartosat-1 May 2005 (Panchromatic): 2.5 mALOS - PRISM January 2006 Panchromatic: 2.5 mWorldView 1 September 2007 Panchromatic: 0.55 mGeoEye-1 August 2008 Panchromatic – 0.41m Multispectral : 1.65m Fig. 1. Photogrammetric technique (www.univcalagary) Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  21. 21. 207. Synthetic Aperture Radar (SAR) Interferometry Incidence Revisit Year of Ban Polarizatio Swath ResolutSAR sensor angle (days) launch d n (km) ion (m) (deg.) The interferometric SAR (InSAR) technique has emerged as a precise approachto the extraction of high-resolution elevation data and measurement of very smallsurface motion (displacement); InSAR technique is based on the phase informationderived from the complex radar images. SAR interferometry combines complex radarsignals (images) recorded by the antenna at slightly different locations to measure thephase differences between the complex radar images. Relating two complex SARimages of the same scene acquired at two orbital locations forms an interferogram. Asthe radar signal transmitted by the SAR sensor is coherent, the complex SAR imagepossesses both phase and magnitude (quantities) information. The constructive anddestructive interference of coherent SAR images respectively recorded at slightlydifferent locations produce an interferogram with a two-dimensional fringe pattern,which can be unwrapped into the absolute measurement of elevation. Fig. 2. Principle of SAR interferrometry (www.aerosensing.com) Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  22. 22. 21ERS-1 1991 C VV 23 100 30 35JERS-1 1992 L HH 35 75 18 44ERS-2 1995 C VV 23 100 30 35Radarsat-1 1995 C HH 10 to 50 40-500 8-100 24SRTM 2000 X, C VV Variable 30-350 20-30 HH/HV, 100- 30-Envisat-1 2002 C 14 to 45 35 VV/VH 400 1000 VV, HH,PALSAR 2004 L HH/HV, 18 to 55 70 10-100 44 VV/VHTerraSAR-X 2006 X Quad-pol 10 to 100 15-60 2-16 11Radarsat-2 2008 C Quad-pol 10 to 50 10-500 8-100 24 20 to 49 (qualified) 10 to 20RISAT 2008 C Quad-pol 10-240 3 - 50 13 and 49-54 (unqualifie d)Table 2: SAR satellites and sensors8. Radar Altimetry Spaceborne radar altimeters have been deployed on board of Geosat, Seasatand ERS-1 platforms for acquiring surface height measurements. A radar altimeter is anadir-pointing active microwave sensor designed to measure the surface height overocean and ice surfaces. The radar altimeter transmits a short duration Ku-band pulsevertically downwards, and then tracks the returned radar pulse. The information of theshape and timing of the returned signal is utilized to estimate the surface height. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  23. 23. 22 Radar altimeters can provide accurate elevation measurements regardless ofweather condition over ocean and relatively flat and low-slope ground surface, but areprone to errors over highly sloped and rugged lands due to the relatively large footprint.9. Laser Altimetry A laser altimeter can provide height measurements of submeter level accuracywith the aid of GPS and Inertial Navigation System (INS) in determining the position andattitude of aircraft or spacecraft, but the data collection is usually time consuming due toits narrow ground swath. Laser altimeter data may deteriorate in the condition of badweather, such as clouds and precipitation, it generally provides much more accuratemeasurements than the radar altimeter due to the small footprint of the laser beam. Fig. 3. Principle of laser scanning (www.terraimaging.com)10. Derivation of Surface Parameter10.1 Elevation If the point of interest is exactly at a point in the raster, the elevation can be takendirectly from the database If the point of interest is between nodes of DEM grid, weneed to interpolate from neighboring grid points, e.g. bilinear, cubic, or fit a plane to thenearby raster points. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  24. 24. 2310.2 Slope Measure the surface steepness; Slope is rise over reach (rise/reach), where riseis the change in elevation, and reach is the horizontal distance. It is expressed as: a ratio, a simple fraction, a percent, an angle in degrees.10.3 Aspect (azimuth orientation) Aspect is azimuthal direction of maximum surface slope with reference to truenorth. Aspect calculation is very sensitive to elevation errors, especially when thesurface slope is small. Without a slope, there is no topographic aspect. The aspect ateach location determines the direction of water flow over the terrain surface.10.4 Surface Curvature (convergence/ divergence) The surface curvature is the second derivative of the surface (i.e., the slope ofthe slope); the curvature of a surface can be calculated on a cell-by-cell basis. For eachcell, a fourth-order polynomial of the form is fit to a surface composed of a 3x3 window.10.5 Profile Curvature The curvature of surface in the direction of slope is referred to as the profilecurvature. Profile curvature indicates where the surface is concave or convex, resultingacceleration or deacceleration of flow. Where acceleration of flow occurs, the streamgains energy and its ability to transport particles increases. Therefore, areas of convexprofile curvature indicate areas of erosion. Conversely, in areas of concave profilecurvature, the flow rate decreases, the stream loses energy, and deposition occurs. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  25. 25. 2410.6 Planform Curvature The curvature of a surface perpendicular to the direction of slope is referred to asthe planform curvature. Planform curvature indicates where the surface is concave orconvex, resulting in convergence or divergence of flow respectively; Convergent flowindicates a concentration of runoff and would indicate a valley. Alternatively, divergentflow would indicate a ridge.10.7 Cut and Fill Calculation Estimation of the volume of material related to cutting and filling. By subtractingthe upper (top) surface height values from the lower surface height, a variable thickness(depth) value can be obtained. The thickness values over the entire area can beintegrated to obtain the volume. Engineers need to establish road or railroad routes andgradients that minimize the movement of earth. It is generally most economical tobalance the amount of material removed from the high areas (cut) with the amount ofmaterial required to fill low areas (fill). Also used in Reservoir capacity estimation, icevolume, etc.11. Viewshed Analysis A viewshed is the region that is visible from a given vantage point in the terrain. Itassembles all the areas where the line of sight is rising as the rays move outwards. Theyes/no values can be summed to give a cumulative sense of how many times a place isseen. Inter-visibility (what can be seen from where) can be computed based on a set ofrays radiating outwards from a vantage point. In a complex 3D situation, there are manyeffects to calculate, but on a surface the surface can only obstruct a view by risingabove the line of sight. Applications of viewshed analysis include GPS signalavailability, scenic beauty evaluation, sitting television, radio, and cellular telephonetransmitter and receiver towers, locating towers for observing forest fires or enemymovement. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  26. 26. 2512. Watershed Analysis The shape of a terrain determines the movement of water across the terrainsurface; Water will flow from higher locations downwards. A raster DEM containssufficient information to determine pattern and characteristics of a drainage basin, suchas, the upstream area contributing to a specific location and the downstream path waterwould follow, the boundary of catchment area, flow line, ridges, the hierarchical streamsystem, etc. The topology of terrain surface (skeleton of surface): peaks, pits, ridges,courses (valleys), hills and dales, etc. The area upon which water falls, and the networkthrough which it travels to an outlet is referred to as a drainage system. The flow ofwater through a drainage system is only a subset of the hydrologic cycle, which alsoincludes precipitation, evaporation, and groundwater; Watersheds tend to functionecologically as single, uniform regions. Ecologists, hydrologists, engineers, pollutionand flood control experts need to be able to define these areas precisely.13. Dem Visualization There are number of techniques to enhance and display DEM data. Shaded reliefis also one of the techniques, which is considered to be one of the most effectivetechniques for representing topography.13.1 ShadingThe gradation from dark to light in a single color according to specific principals for thepurpose of creating a three dimensional effect is called shading. In contrast to the metricaccuracy of contour lines, hill shading is primarily used for its visual effects. Slopeshading operates on the principal that the steeper the slope - the darker the shade.Oblique shading or hill shading is based upon the effect of an oblique light source on aterrain surface. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  27. 27. 2613.2 Slope ShadingSlope shading, operates basically on the principal of the steeper - the darker.13.3 Hill Shading Hill shading is also known as a shaded relief or simply shading, it attempts tosimulate how the terrain looks with the interaction between sunlight and surfacefeatures. It Helps viewers recognize the shape of landform features on a map.14. Conclusions Terrain analysis typically encompasses numerical methods of describinglandscape attributes such as terrain roughness, vegetation, urban features, 3D modelsetc. To fully model the continuous terrain surface, a large number of points are requiredand DEM and TIN are two commonly used models of representing the continuoustopographic surface in digital form with a finite number of sample points. Most of thecommercial GIS systems provide both raster DEM and TIN model that can be used inspatial analysis and surface modeling. However, it is important to note that the mostcritical aspect of any terrain analysis is the accuracy of the terrain model it uses or howclose the data model either DEM/TIN represents the actual surface with all attributes.Web Linkswww.isprs.orgwww.terraimaging.comwww.aerosensing.com Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  28. 28. 27 GEOGRAPHIC INFORMATION SYSTEM P.L.N. Raju Geoinformatics Division1. Significance of GIS in the Present Day Scenario Geographic Information System plays an important role in creation ofgeospatial information from vast sources such as analogue and digital domains, andaid the decision makers at various junctures of resource identification, assessmentand management. It can answer many simple questions like what, where, how aswell as complex situations of using models for estimation, prediction and dynamicallyrecreate real world situation to visualise and fly though the area for effective planningand management. GIS is becoming quite popular in the recent past among thegeneral public with the introduction of Google earth (http://earth.google.com),Microsoft Virtual earth (http://www.microsoft.com/virtualEarth/) and NASA’sWorldwind (http://worldwind.arc.nasa.gov) for viewing rich Geographic content in theform of satellite pictures/maps in 2D/3D, explore, locate, navigate etc. With the helpof these resources people can find their location, assess the present situation andfind them the route to reach the destination, overlay the new surveyed routes andother information. World wide web has also become the source for viewingGeographic information in the form of maps and location information like Maps ofIndia (http://mapsofIndia.com). All types of tools used to carry out these tasks arepart of GIS with the background of satellite image. The 3d view and animation thatwe carry out on the images are carried out using GIS tools. Third Generation mobiledevices are integrated with (GPS) receiving capability are loaded with Geographicinformation (i.e. GIS data) and used to find where you are located and givingdirections to reach the desired destination (i.e. house/office/tourist destination etc). This summary note outlines status of GIS that includes importance of GIS andits role for different application studies, journey of GIS from a mere a tool to science,how important it is to create a geospatial database and its critical nature,transformation of GIS from commercial nature to the present potential of havingmany open source and free software for the user community, progress of GIS and its Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  29. 29. 28market potential as on today, where to look and find different GIS resources in WorldWide Web and finally summarising the technological trends and future of GIS.2. GIS Application Potential The strength of GIS depends upon how good is the geospatial database. Itcan be used for natural resource application (i.e. forestry, agriculture and waterresources etc.) in combination with remote sensing and earth observation. Inaddition it is used for infrastructure development (i.e. highways, railways etc.); utilityservices like water supply distribution network, telephone network management, gassupply distribution etc.; business application such as real estate, establishment ofnew retailer shops; heath services; investigation services like crime incidences andtheir distribution etc and geospatial information kiosks like Bhoomi project(http://www.kar.nic.in/bhoomi.html) of Karnataka State. In addition GIS can be usedfor research and scientific investigations, particularly for water budgeting,atmospheric modelling, climatic studies and global warming.3. GIS: Tool to Science GIS has evolved from a mere tool into a spatial science covering broadspectrum of fields starting from surveying, mapping, modelling, and management todecision theory. A discussion forum was launched on “GIS is a tool or science?” wasinitiated in 1993 brought out many views about GIS (Wright et al., 1997): somestrongly feel that it is considered merely a tool as it helps only in manipulation ofspatial data, combines elements of computer science, geography and enablingtechnology in problem solving environment (Skelly, 1993); Petican,1990);Groom,1993); Feldman,1993). At the same time, many others argue that it is notonly a tool but also it is definitely a science as it addresses vast issues such asunderstanding of modelling spatial phenomena (Carlson, 1993), study of spatial datauncertainty and error, data lineage and how GIS is adopted by agencies (Wright1993 et al.,), spatial data representation and developing algorithms to solve aproblem and apply it to test a theory (Sandhu, 1993). According to some, GIS isconsidered as part of a broader information science (Wright et al., 1993), anenvironment as well as a method used to discover, explore, and test spatial theory Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  30. 30. 29(Laffey, 1993) and concepts that the tools seek facilitate, automate, and develop arestrongly rooted in science (Bartlett, 1993). Amidst diverse views, growth of GIS isphenomenal and expanded to many areas like Environmental and Earth Sciences,Urban Planning & Infrastructure Development, Socio- Economic outreach, businessenterprise and technological domains, covering them under geoinformatics umbrellaand making itself an inevitable scientific field.4. Critical Part of GIS Hardware, Software, Data and trained Manpower makes it to total GIS.Though each component is important, the most critical part of GIS is data, i.e.creation of data needs three forth of cost involved to develop the total GISapplication project, highly trained professional are required to be part of geospatialdatabase creation and three fourth’s time is spend to accomplish the task of creatingthe geospatial database. All the users require the basic framework data like commondatum and projection, administrative, roads, topographical and land use / land coverlayer information. The issue is creation of the same by one and use it by many. Allcountries are in the process of creating it and it takes lot of time. India is also in theprocess of developing at national level (i.e. National Resource Repository (NRR)under ISRO /NNRMS and National Spatial Data Infrastructure (NSDI) under DSTand many others are in the process of development which in turn helps for overalldevelopment and progress of India.5. GIS Software: Commercial vs. Open/Free GIS software is one of the bottlenecks in GIS industry as the major junkmoney (~50 per cent or so) is invested towards its procurement and maintenanceannually. Because of it many users have apprehensions to change fromconventional methods to GIS. In the recent past there is a paradigm shift in usage ofGIS software. There are many new and open/free software are launched into themarket. The free software where it is freely available and mostly through www butthe user do not have access to program coding, so not possible to modify or updateit. In case of open source, it is free as well as available with full access to program Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  31. 31. 30coding so user can modify/update it according to his requirements. Table 1 belowprovides list of some of commercial, open and free GIS software.Table 1: List of GIS software available commercially/as a open source/freely to the user.S.No. Software Functionality /RemarksCommercial Software1. ArcGIS Core modules,market leader but high cost, many more to be bought for other applications2. Geomedia Core modules of GIS, supports education and research institutions3. MapInfo Moderate cost4. AutoCAD Map Better input and database creation facility5. JTMaps Quite economical and works in vector model (India)Open Source6. GRASS GIS Satellite data analysis & GIS (http://grass.itc.it/)7. Quantum GIS Desktop GIS, supports all OS (http://qgis.org/)8. ILWIS Satellite data analysis & GIS (www.itc.nl)9. JUMP Read shp and gml format, display facility and support for wms and wfs, limitations of working with large data files (http://jump-project.org/)10. PostGIS With spatial extensions for the open source. PostgreSQL database, allowing geospatial queries (http://postgis.refractions.net/)11. Mapserver Web server GIS S/W (http://mapserver.gis.umn.edu/)Free Software12. ArcView Limited analysis functionality, old version13. TNTMIPS Satellite data analysis and GIS but limited to window size6. Indian Geospatial Market Indian Geospatial market has matured well and growing at much higher ratethan normal growth. Geospatial market can divide into three categories such as: Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  32. 32. 31spatial data producing agencies, user organizations (government, private, andresearch and academic setup) and industry (private entrepreneurs). As per themarket survey and compilation work done by GIS development (Indian GeospatialHandbook 2008, published by GIS Development Pvt. Ltd.) the growth for the lastthree years (i.e. 2005 to 2008) is phenomenal and it is more 45 per cent increasefrom the previous years. The annual turnover increased from Rs. 760 crores in 2005that includes GIS (540), photogrammetry (120) and Image Processing (100) to Rs.1128 crores in 2006, i.e. an increase of 48 per cent. It is further increased to morethan double i.e. Rs. 1780 crores. The details of overall Geospatial Industry includingsoftware, hardware and Services, are shown in Table 2.Table 2: Status of GIS revenue during 2005-08 period (Crores of rupees) (source: GIS 540 800 1250 Photogrammetry 120 188 350 Image Processing 100 140 180 Total 760 1128 1780 Increase (%) - 48 58 Indian Geospatial Handbook, 2008). There are many institutions / organizations which generate Remote Sensingand Geo-Information products and provide services such as (SOI, NRSA, NATMO,GSI, FSI, CGWB, CWC, IMD, Census & ANTRIX etc.) and the products and servicesare used by many user organizations like Highways, Railways, Airways, Waterways,Telecom, Power, Water resources & Irrigation, Health, Education, Environment &Forest, Agriculture, Urban Development and Land Resources and RuralDevelopment etc. Geospatial entrepreneurs mainly owned by private provide valueadded services to the above said user organizations. There are around 120companies are involved in Geospatial industry, majority of contribution i.e. 85 percent of the revenue is generated by 15 per cent of companies. The top fourcompanies are Infotech Geospatial India (30 per cent), RMSI (4 per cent ), WapmerrIndia (0.6 per cent) and Pixel Group (0.6 per cent). The manpower required forgeospatial industry is met with many who had acquired their higher education /professional qualifications from more than forty programs in geospatial education,range from P.G. Diploma, and graduate in engineering to Masters in Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  33. 33. 32Engineering/Technology/Science, are presently being run across the country atuniversity/ institutions level.7. GIS Web Resources World Wide Web has become an important source for accessing resources ofremote sensing, GIS and GPS in which one can even download the satellite data,GIS metadata, GIS themes, access to reading material, latest developments in theform of articles from newsletters, journals. One can access to online resources onpayment basis and many cases freely as well. Table 3 provide summary of few GISresources, emphasizing more in Indian context.Table 3: GIS web resources S.No. Hosted by and Website link Nature of resources Web access to Geospatial Information in India 1. National Natural Resources Natural Resource Repository (NRR) Information System generated under NNRMS, ISRO/DOS http://www.nnrms.gov.in National Remote Sensing Centre Browsing Indian Remote Sensing 2 http://www.nrsc.gov.in (IRS) data and buying for anywhere in India National Informatics Centre RS & GIS basic reading material 3. http://gis.nic.in/ National level spatial information search facility Indian National Centre for Ocean Provide ocean information and 4. Information Service (INCOIS) advisory services to the society, http://www.incois.gov.in/ industry, government, and scientific community Meteorological and Oceanographic Meteorological and Oceanographic 5. Satellite Data Archival Centre geophysical data products http://www.mosdac.gov.in/ Web Access to Geospatial Information World over Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  34. 34. 33 1. USGS Education material Common place to refer for education http://education.usgs.gov/ material on RS, GIS and GPS CGIAR consortium for spatial Site for downloading SRTM DEM 2. information data at 90 m resolution http://srtm.csi.cgiar.org/ GIS Reading Material 1. GIS Development monthly GIS reading material and published magazine articles in the magazine for more than http://gisdevelopment.net ten years My Coordinates monthly magazine GPS, GIS and RS reading material 2. http://www.mycoordinates.org/ with more emphasis on positioning technology 3. Indian Society of Geomatics Newsletter (quarterly) on RS, GIS http://www.isgindia.org/ and GPS NNRMS Bulletin Biannual technical publication from 4. ISRO/NNRMS bringing out RS & GIS application project outputs Geospatial Today Monthly magazine on Geospatial 5. http://www.geospatialtoday.com/ technologies Geo Place Website of multiple GIS and business 6. http://www.geoplace.com/ related publications8. Technological Trends and Future of GIS Information and Communication Technology (ICT) has revolutionized andhelped GIS to great extend. According to Peter Croswell (2005) five important trendshave exerted profound influence on geo-technology industry and user community: • Pervasive high-performance computing • Digital connectivity • Geographic data capture and compilation • Geographic data management and visualization • Standards and open system Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  35. 35. 34 Moore (Moore’s law) has predicted more than 25 years back that theprocessing power of computers doubles every 18 months for the same cost and thisis true even today. Increase in processing speed, availability of computers ataffordable cost, increase of analysis functionalities, and availability of web resourcesmade it possible in expanding the scope of GIS. In the last five years, hardwareadvances have offered GIS users a growing array of realistic and effective solutionsfor field and mobile computing needs as well. The Internet has been a driver foroverall IT development, and it forced the trend in digital connectivity. It has lead tothe development of Internet GIS (also called web GIS), that has played a major rolein expanding the GIS usage, helping the users to access the geoinformation at lowcost in client-server environment and it will continue to further with standards andbetter services. GIS technology has always been a tool for data visualization-portraying complex spatial data and patterns through the use of 2-D and 3-D mapsand displays. Technology for the visualization of geographic information has takensignificant leaps in the last 25 years. During this time, GIS users have seentremendous advances in graphic display and large-format plotting. Realistic 3-D citymodels as well as 3-D environment data; atmosphere and ocean in individualhorizontal layers can be investigated. Open standards and specifications hasbecome an issue due to the diverse formats and structures from different softwarehave complicated the integration efforts. Over the last ten years major developmentshave taken place for the open standards and specifications. OCC (Open GeospatialConsortium), ISO-TC 211, GSDI and many others at worldwide and country levelplayed a key role in development of these standards and it is continuing to expandalong with the ICT technological trends. As indicated above, the technological trendscan be categorized into five and summarized in the following Table 4 ( Dadhwal andRaju, 2006). Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  36. 36. 35Table 4: Technological trendsS.No. Category Technological Trends1. Data • Multispectral to Hyper-spectral • Low Spatial resolution to High Spatial resolution • Mono imaging to Stereo Imaging • Workstation to PC based2. Hardware • Workstation to PC based • PCs to Mobile / pocket PCs3. Software • Desktop level to web based GIS/Image • analysis to Mobile GIS4. Internet • Low bandwidth – Broad brand based • Web services (Google Earth / Wekemepia etc.)5. Standards • Proprietary based standards to Open • Standards As a whole the technological developments in geoinformatics lead to branch outto many areas. They are: • spatial multimedia • open GIS/ Free GIS • GIS Customization • spatial Modelling • geo-Visualization • data Warehouse and large database handling • knowledge discovery and Data mining • geo-Computation • mobile GIS /Fleet Management / Location Based Services • web GIS /Distributed GIS • spatial Data Infrastructure and Geo-Information Management • sensor Web enablement • metadata and clearing houses Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  37. 37. 36 • interoperability/Open standards and specificationsReferencesBartlett, D. 1993. Geography Department, Cork University, Ireland. Re: GIS as a Science [Discussion]. GeographicInformation Systems Discussion List [Online]Carlson, C. L. 1993. Northern Illinois University. Re: Value of Peer Review [Discussion]. Geographic Information Systems Discussion List [Online]Feldman, M. 1993. Community Planning, University of Rhode Island. Re: GIS as a Science & Value of Peer Review [Discussion]. Geographic Information Systems Discussion List [Online].Groom, A. 1993. Christchurch City Council, New Zealand. Re: Tool or Science? [Discussion]. Geographic Information SystemsDiscussion List [Online].Laffey, S. C. 1993. Department of Geography, Northern Illinois University. Re: GIS as a Science [Discussion]. GeographicInformation Systems Discussion List [Online].Petican, D. J. 1993. University of Waterloo, Canada. Re: GIS as a Science [Discussion]. Geographic Information SystemsDiscussion List [Online].Sandhu, J. 1993. Environmental Systems Research Institute, Redlands. Re: GIS as a Science [Discussion]. Geographic Information Systems Discussion List [Online].Skelly, C. W. 1993. James Cook University, Australia. GIS & Remote Sensing Research [Discussion]. Geographic Information Systems Discussion List [Online] Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  38. 38. 37Dadhwal,V.K and Raju,P.L.N. 2006. Geoinformatics technological trends –expanding to diversified application areas, National Conference on Geo Informatics,V.P.M’s Polytechnic, Thane, Maharastra, December 8-10, 2006.Wright, D. J. 1993a. Department of Geography, UC-Santa Barbara. Re: Value of Peer Review [Discussion]. Geographic InformationSystems Discussion List [Online]Wright, Dawn J., Goodchild, Michael F and Proctor, James D. 1997. “Demystifying the Persistent Ambiguity of GIS as “Tool” Versus “Science””Annals of the Association of American Geographers, 87(2): 346-362, 1997. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  39. 39. 38 Fundamental Concepts of GPS P.L.N. Raju Geoinformatics DivisionIntroduction: Traditional methods of surveying and navigation resort to tedious field andastronomical observation for deriving positional and directional information. Diverse fieldconditions, seasonal variation and many unavoidable circumstances always bias thetraditional field approach. However, due to rapid advancement in electronic systems,every aspect of human life is affected to a great deal. Field of surveying and navigation istremendously benefited through electronic devices. Many of the critical situations insurveying/navigation are now easily and precisely solved in short time. Astronomical observation of celestial bodies was one of the standard methods ofobtaining coordinates of a position. This method is prone to visibility and weather conditionand demands expertise handling. Attempts have been made by USA since early 1960`s touse space based artificial satellites. System TRANSIT was widely used for establishingnetwork of control points over large regions. Establishment of modern geocentric datumand its relation to local datum was successfully achieved through TRANSIT. Rapidimprovements in higher frequently transmission and precise clock signals along withadvanced stable satellite technology have been instrumental for the development of globalpositioning system. The NAVSTAR GPS (Navigation System with Time and Ranging Global PositioningSystem) is a satellite based radio navigation system providing precise three- dimensionalposition, course and time information to suitably equipped user. GPS has been underdevelopment in the USA since 1973. The US Department of Defence as a worldwidenavigation and positioning resource for military as well as civilian use for 24 hours and allweather conditions primarily develops it. In its final configuration, NAVSTAR GPS consists of 21 satellites (plus 3 activespares) at an altitude of 20200 km above the earth’s surface (Fig.1). These satellites are Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  40. 40. 39so arranged in orbits to have at least four satellites visible above the horizon anywhere onthe earth, at any time of the day. GPS Satellites transmit at frequencies L1=1575.42 MHzand L2=1227.6 MHz modulated with two types of code viz. P-code and C/A code and withnavigation message. Mainly two types of observable are of interest to the user. In pseudoranging the distance between the satellite and the GPS receiver plus a small correctiveterm for receiver clock error is observed for positioning whereas in carrier phasetechniques, the difference between the phase of the carrier signal transmitted by thesatellite and the phase of the receiver oscillator at the epoch is observed to derive theprecise information. The GPS satellites act as reference points from which receivers on the groundresect their position. The fundamental navigation principle is based on the measurementof pseudoranges between the user and four satellites (Fig.2). Ground stations preciselymonitor the orbit of every satellite and by measuring the travel time of the signalstransmitted from the satellite four distances between receiver and satellites will yieldaccurate position, direction and speed. Though three-range measurements are sufficientbut fourth observation is essential for solving clock synchronization error between receiverand satellite. Thus, the term "pseudoranges" is derived. The secret of GPS measurementis due to the ability of measuring carrier phases to about 1/100 of a cycle equaling to 2 to3 mm in linear distance. Moreover the high frequencies L1 and L2 carrier signal caneasily penetrate the ionosphere to reduce its effect. Dual frequency observations areimportant for large station separation and for eliminating most of the error parameters. There has been significant progress in the design and miniaturization of stableclock. GPS satellite orbits are stable because of the high altitudes and no atmospheredrag. However, the impact of the sun and moon on GPS orbit though significant can becomputed completely and effect of solar radiation pressure on the orbit and troposphericdelay of the signal have been now modeled to a great extent from past experience toobtain precise information for various applications. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  41. 41. 40 Comparison of main characteristics of TRANSIT AND GPS reveal technologicaladvancement in the field of space based positioning system (Table 1) Details TRANSIT GPS Orbit Altitude 1000 Km 20,200 Km Orbital Period 105 Min 12 Hours Frequencies 150 MHz 1575 MHz 400 MHz 1228 MHz Navigation data 2D : 4D : X,Y,Z, t velocity Availability 15-20 minute per pass Continuously Accuracy ñ 30-40 meters ñ15m (Pcode/No. SA (Depending on velocity 0.1 Knots error) Repeatability ------- ñ1.3 meters relative Satellite Constellation 4-6 21-24 Geometry Variable Repeating Satellite Clock Quartz Rubidium, Cesium GPS has been designed to provide navigational accuracy of ±10m to ±15 m.However, sub meter accuracy in differential mode has been achieved and it has beenproved that broad varieties of problems in geodesy and geodynamics can be tackledthrough GPS. Versatile use of GPS for a civilian need in following fields have been successfullypracticed viz. navigation on land, sea, air, space, high precision kinematics survey on theground, cadastral surveying, geodetic control network densification, high precision aircraftpositioning, photogrammetry without ground control, monitoring deformations,hydrographic surveys, active control survey and many other similar jobs related tonavigation and positioning,. The outcome of a typical GPS survey includes geocentricposition accurate to 10 m and relative positions between receiver locations to centimeterlevel or better. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  42. 42. 41Various Segments: For better understanding of GPS, we normally consider three major segments viz.space segment, Control segment and User segment. Space segment deals with GPSsatellites systems, Control segment describes ground based time and orbit controlprediction and in User segment various types of existing GPS receiver and its applicationis dealt (Fig.3).Table 2 gives a brief account of the function and of various segments along with input andoutput information.Segment Input Function Output Space Navigation message Generate and P-Code Transmit code and C/A Code carrier phases and L1,L2 carrier navigation message Navigation message Control P-Code Observations Produce GPS time Navigation message Time predict ephemeris manage space vehicles User Code observation Carrier Navigation solution Position velocity phase observation Navigation Surveying solution time MessageGLONASS (Global Navigation & Surveying System) a similar system to GPS is beingdeveloped by former Soviet Union and it is considered to be a valuable complementarysystem to GPS for future application.Space Segment: Space segment will consist 21 GPS satellite with an addition of 3 active spares.These satellites are placed in almost six circular orbits with an inclination of 55 degree.Orbital height of these satellites is about 20,200 km corresponding to about 26,600 km Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  43. 43. 42from the semi major axis. Orbital period is exactly 12 hours of sidereal time and thisprovides repeated satellite configuration every day advanced by four minutes with respectto universal time. Final arrangement of 21 satellites constellation known as "Primary satelliteconstellation" is given in Fig.4. There are six orbital planes A to F with a separation of 60degrees at right ascension (crossing at equator). The position of a satellite within aparticular orbit plane can be identified by argument of latitude or mean anomaly M for agive epoch. GPS satellite are broadly divided into three block (Table 3) Block-I satellitepertains to development stage, Block II represent production satellite and block IIR arereplenishment/spare satellite.Table 3 Status of GPS satellite (July 1992) Launch Satellite PRN Code Launch date Orbit Plan Status Sequence Vertical BLOCK I I-1 01 04 02/78 --- Unusable 7/85 I-2 02 07 05/78 --- Unusable 7/81 I-3 03 06 10/78 Marginal Use I-4 04 08 12/78 Unusable 10/89 I-5 05 05 02/80 Unusable 11/83 I-6 06 09 04/80 Unusable 3/91 I-7 07 -- -- Launch Failure I-8 08 11 07/83 C3 Operational I-9 09 13 06/84 C1 Operational Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  44. 44. 43 I-10 10 12 09/84 A1 Operational I-11 11 03 10/85 C4 Operational BLOCK II II-1 14 14 02/89 E1 Operational II-2 13 02 06/89 B3 " II-3 16 16 08/89 E3 " II-4 19 19 10/89 A4 " II-5 17 17 12/89 D3 " II-6 18 18 01/90 F3 " II-7 20 20 03/90 B2 " II-8 21 21 08/90 E2 " II-9 15 15 10/90 D2 " BLOCK-II R II-10 23 23 11/90 E4 Operational II-11 24 24 07/91 D1 " II-12 25 25 02/92 A2 " II-13 28 28 04/92 C2 " II-14 26 26 -7/92 " II-15 " Under Block-I, NAVSTAR 1 to 11 satellites were launched before 1978 to 1985 intwo orbital planes of 63 degree inclination. Design life of these prototype test satelliteswas only five years but as indicated in Table 2 the operational period has been exceededin most of the cases. The first Block-II production satellite was launched in February 1989using channel Douglas Delta 2 booster rocket. A total of 28 Block-II satellites are plannedto support 21+3 satellite configuration. Block-II satellites have a designed lifetime of 5-7years. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  45. 45. 44 To sustain the GPS facility, the development of follow-up satellites under BLock-IIR has already started. Twenty replenishment satellite will replace the current block-IIsatellite as and when necessary. These GPS satellites under Block-IIR will have additionalability to measure distances between satellites and will also compute ephemeris onboard for real time information. Fig.5 gives a schematic view of Block-II satellite Electrical power in generatedthrough two solar penal covering surface area of 7.2 square meter each. However,additional battery backup is provided to provide energy when the satellite moves intoearth`s shadow region. Each satellite weighs 845kg and has a propulsion system forpositional stabilization and orbit maneuvers. GPS satellites have very high performanceof frequency standard with an accuracy of between 1X10-12 to 1X10-13 and are thuscapable of creating precise time base. Block-I satellites were partly equipped with onlyquartz oscillators but Block-II satellites have two cesium frequency standards and tworubidium frequency standards. Using fundamental frequency of 10.23 MHz, two carrierfrequencies are generated to transmit signal codes.Observation principle and signal structure: NAVSTAR GPS is a one-way ranging system i.e. signals are only transmitted bythe satellite . Signal travel time between the satellite and the receiver is observed and therange distance is calculated through the knowledge of signal propagation velocity. Oneway ranging means that a clock reading at the transmitted antenna is compared with aclock reading at the receiver antenna. But since the two clocks are not strictlysynchronized hence the observed signal travel time is biased with systematicsynchronization error. Biased ranges are known as pseudoranges. Simultaneousobservations of four pseudoranges are necessary to determine X, Y, Z coordinates of userantenna and clock bias. Real time positioning through GPS signals is possible by modulating carrierfrequency with Pseudorandom Noise (PRN) codes. These are sequence of binary values Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  46. 46. 45(zeros and ones or +1 and -1) having random character but identifiable distinctly. Thuspseudoranges are derived from travel time of an identified PRN signal code. Two differentcodes viz. P-code and C/A code are in use. P means precision or protected and C/Amean clear/acquisition or coarse acquisition. P- code has a frequency of 10.23 MHz. This refer to a sequence of 10.23 millionbinary digits or chips per second. This frequency is also referred to as the chipping rate ofP-code. Wavelength corresponding to one chip is 29.30m. The P-code sequence isextremely long and repeats only after 266 days. Portions of seven days each areassigned to the various satellites. As a consequence, all satellite can transmit on thesame frequency and can be identified by their unique one week segment. This techniqueis also called as Code Division Multiple Access (CDMA). P-code is the primary code fornavigation and is available on carrier frequencies L1 and L2. The C/A code has a length of only one millisecond, its chipping rate is .023 MHzwith corresponding wave length of 300 meters. C/A code is only transmitted on L1 carrier.GPS receiver normally have a copy of the code sequence. For determining the signalpropagation time. This code sequence is phase-shifted in time step by step andcorrelated with the received code signal until maximum correlation is achieved. Thenecessary phase-shift in the two sequence of codes is a measure of the signal travel timebetween the satellite and the receiver antennas. This technique can be explained as codephase observation. For precise geodetic applications, the pseudoranges should bederived from phase measurements on the carrier signals because of much higherresolution. Problems of ambiguity determination is vital for such observations. The thirdtype of signal transmitted from a GPS satellite is the broadcast message sent at a ratherslow rate of 50 bits per second (50 bps) and repeats every 30 seconds. Chip sequence ofP-code and C/A code are separately combined with the stream of message bit by binaryaddition ie the same value for code and message chip gives 0 and different values resultin 1. The main features of all three signal types used in GPS observation viz carrier, codeand data signals are given in Table 4. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010
  47. 47. 46Table 4 GPS Satellite Signals Atomic Clock (G, Rb) fundamental 10.23. MHz frequency L1 Carrier Signal 154 X 10.23 MHz L1 Frequency 1575.42 MHz L1 Wave length 19.05 Cm L2 Carrier Signal 120 X 10.23 MHz L2 Frequency 1227.60 MHz L2 Wave Length 24.45 Cm P-Code Frequency (Chipping Rate) 10.23 MHz (Mbps) P-Code Wavelength 29.31 M P-Code Period 267 days : 7 Days/Satellite C/A-Code Frequency (Chipping Rate) 1.023 MHz (Mbps) C/A-Code Wavelength 293.1 M C/A-Code Cycle Length 1 Milisecond Data Signal Frequency 50 bps Data Signal Cycle Length 30 Seconds The signal structure permits both the phase and the phase shift (Doppler effect) tobe measured along with the direct signal propagation. The necessary band width isachieved by phase modulation of the PRN code as illustrated in Fig 6.Structure of the GPS Navigation Data: Structure of GPS navigation data (message) as shown in fig. 7. The user has todecode the data signal to get access to the navigation data. For on line navigationpurposes, the internal processor within the receiver does the decoding. Most of themanufacturers of GPS receiver provide decoding software for post processing purposes. Remote Sensing: An Overview for Decision Makers IIRS/LN/DMC/2010