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Remote Sensing: Fundamentals, Types and Monitoring Applications of Environmental Consequences of War

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Book cover Environmental Consequences of War and Aftermath

Part of the book series: The Handbook of Environmental Chemistry ((HEC3,volume 3U))

Abstract

The chapter deals with the fundamentals of remote sensing, basic principle of electromagnetic radiation and its interaction with the earth, atmosphere and surface materials. The types of sensors, digital data formats, basic image processing techniques, including image enhancement techniques and classification methods are explained in details. Besides the image processing techniques, applications of remote sensing in Kuwait are presented in a section on applications, that include techniques for mapping subsidence in oil fields, estimation of recharge to shallow aquifers and freshwater lenses, calibration of satellite precipitation data and mapping of hydrocarbon contamination using land surface temperature estimates.

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References

  1. Curran PJ (1985) Principles of remote sensing. Longman Publishing Co., London, pp 208–224

    Google Scholar 

  2. Jensen JR (1986) Introductory digital image processing: a remote sensing perspective. Printice-Hall, Englewood Cliffs, NJ, pp 1–9, 177–229

    Google Scholar 

  3. Lillesand TM, Kiefer RW (1987) Remote sensing and image interpretation, 2nd ed. Wiley, New York, p 721

    Google Scholar 

  4. Pratt WK (1992) Digital image processing, 2nd ed. Wiley, New York, p 698

    Google Scholar 

  5. Sabins, Floyd F (1987) Remote sensing – principles and interpretation. Freeman and Company, New York, p 449

    Google Scholar 

  6. Lee CC (1983) Elimination of redundant operations for fast sobel operator. IEEE Trans Syst Man Cybern, vol SMC-13, No 3, pp 242–245

    Google Scholar 

  7. Pizer SM (1987) Adaptive histogram equalization and its variations. Comput Vision Graph Image Process 39:355–368

    Article  Google Scholar 

  8. Chavez PS Jr, Berlin GL, Sower LB (1982) Statistical method for selecting LANDSAT MSS ratios. J Appl Photograph Eng 8:23–30

    Google Scholar 

  9. Roberts LG (1965) Machine perception of three-dimensional solids in optical and electro-optical information processing. JT Tippett et al. (ed) MIT Press, Cambridge, MA, pp 159–197

    Google Scholar 

  10. Kirsch R (1971) Computer determination of the constituent structure of biomedical images. Comput Biomed Res 4(3):315–328

    Article  CAS  Google Scholar 

  11. Lewis TO, Odell PL (1971) Estimation in linear models. Prentice-Hall, Englewood Cliff, NJ

    Google Scholar 

  12. Prewitt JMS (1970) In: Lopkoin BS, Rosenfeld A (eds) Object enhancement and extraction in picture processing and psychopictorics. Academic Press, New York

    Google Scholar 

  13. Press WH, Flamery BP, Tenkolsky SA, Vetterling WT (1988) Numerical recipes in C: The art of scientific computing. Cambridge University Press, New York

    Google Scholar 

  14. Jahne B (1995) Digital image processing, concept, algorithms and scientific applications, 3rd ed. Springer-Verlag, Berlin, p 383

    Google Scholar 

  15. Rosenfeld A, Kak AC (1982) Digital image processing, 2nd ed., vol. I and II. Academic Press, Orlando

    Google Scholar 

  16. Short NM (1982) The LANDSAT tutorial workbook. Basics of satellite remote sensing. National Aeronautics and Space Administration, Reference Publication 1078, Washington, DC

    Google Scholar 

  17. Loeve M (1955) Probability theory. D. Van Nostrand Company, Princeton, NJ

    Google Scholar 

  18. Castleman KR (1977) Digital image processing. Prentice Hall, Englewood Cliff, NJ

    Google Scholar 

  19. Kwarteng AY, Al-Ajmi D (1997) Satellite remote sensing applications in the State of Kuwait. Kuwait Institute for Scientific Research, Kuwait, p 101

    Google Scholar 

  20. Saifuddin, Al Dousari A, Literathy P (2008) Evidence of hydrocarbon contamination from the Burgan Oil Field, Kuwait – interpretations from thermal remote sensing data. J Environ Manage 86:605–615

    Article  Google Scholar 

  21. Saif ud din, Al Dousari A, Ramdan A, Al Ghadban AN (2008b) Site specific precipitation estimate from TRMM data using bi-linear weighted interpolation technique – an example from Kuwait. J Arid Environ. doi:10.1016/j.jaridenv.2007.12.013

    Google Scholar 

  22. McClain EP, Pichel WG, Walton CC (1985) Comparative performance of AVHRR-based multichannel sea surface temperatures. J Geophys Res 90:11587–11601

    Article  Google Scholar 

  23. Richter R (1990) A fast atmospheric correction algorithm applied to Landsat TM. Int J Remote Sens 11:159–166

    Article  Google Scholar 

  24. Pearce AF, Prata AJ, Manning CR (1992) Comparison of NOAA/AVHRR-2 sea surface temperatures with surface measurements in coastal waters. Int J Remote Sens 10:37–52

    Article  Google Scholar 

  25. Qin Z, Karnieli A, Berliner P (2001) A mono-window algorithm for retrieving land surface temperature from Landsat TM data and its application to the Israel–Egypt border region. Int J Remote Sens 22(18):3719–3746

    Article  Google Scholar 

  26. Liang S (2001) An optimization algorithm for separating land surface temperature and emis-sivity from multispectral thermal infrared imagery. IEEE Trans Geosci Remote Sens 39(2):264–274

    Article  Google Scholar 

  27. Sobrino JA, Li ZL, Stoll MP, Becker F (1996) Multi-channel and multi angle algorithm for estimating sea and land surface temperature with ASTER data. Int J Remote Sens 17(11):2089–2114

    Article  Google Scholar 

  28. Gillespie AR, Rokugawa S, Matsunaga T, Cothern J, Hook S, Khale A (1998) A temperature and emissivity separation algorithm for advanced spaceborne thermal emission and reflection radiometer (ASTER) images. IEEE Trans Geosci Remote Sens 36:1113–1126

    Article  Google Scholar 

  29. Jimenez-Munoz JC, Sobrino JA (2003) A generalized single channel method for retrieving land surface temperature from remote sensing data. J Geophys Res 108. doi:10.1029/2003JD003480

    Google Scholar 

  30. Sobrino JA, Jimenez-Munoz JC, Paolini L (2004) Land surface temperature retrieval from Landsat TM 5. Remote Sens Environ 90:434–440

    Article  Google Scholar 

  31. Markham BL, Barker JL (1986) Landsat MSS and TM post calibration dynamic ranges, atmospheric reflectance and at satellite temperature. EOSAT Landsat Technical Notes 1 (Lanham, Maryland: Earth Observation Satellite Company), pp 3–8

    Google Scholar 

  32. Schneider K, Mauser W (1996) Processing and accuracy of landsat TM data for lake surface temperature measurement. Int J Remote Sens 16:2111–2124

    Google Scholar 

  33. Hurtado E, Vidal A, Caselles V (1996) Comparison of two atmospheric correction methods for Landsat TM thermal band. Int J Remote Sens 17:237–247

    Article  Google Scholar 

  34. Literathy P (1992) Environmental consequences of the Gulf War in Kuwait: impact on water resources. Water Sci Technol 26:21–30

    CAS  Google Scholar 

  35. Litherathy P (1993) Considerations for assessment of environmental consequences of the 1991 Gulf War. Marine Pollut Bullet 27:349–356

    Article  Google Scholar 

  36. Kwarteng AY (1998) Multitemporal remote sensing data analysis of Kuwait's oil lakes. Environ Int 24(1/2):121–137

    Article  Google Scholar 

  37. Kwarteng AY (1999) Remote sensing assessment of oil lakes and oil-polluted surfaces at the Greater Burgan oil field, Kuwait. Int J Appl Earth Obs Geoinf 1(1):36–47

    Article  Google Scholar 

  38. Al-Dousari A (2001) Analysis of change in the tarcrete layer on the desert surface of Kuwait using satellite imagery and cell-based modeling. PhD thesis remote sensing & GIS. Boston University (unpublished)

    Google Scholar 

  39. Saif uddin, Al-Dousari A, Al-Ghadban AN, Aritoshi M (2006) Use of interferometric techniques for detecting subsidence in the oil fields of Kuwait using Synthetic Aperture Radar Data. J Petrol Sci Eng 50:1:1–10

    Article  Google Scholar 

  40. Al-Senafy MN, Viswanathan MN, Senay Y, Sumait A (1997) Soil contamination from oil lakes in northern Kuwait. J Soil Contaminat 6(5):481–494

    CAS  Google Scholar 

  41. Robertson FR, Fitzjarrald DE, Kummerow CD (2003) Effect of uncertainty in TRMM precipitation radar path integrated attenuation on interannual variations of tropical oceanic rainfall. Geophy Res Lett 30(4). doi:10.1029/2002GL016416

    Google Scholar 

  42. Anon (2005) Tropical rainfall mission office – introduction. lba.cptec.inpe.br/lba/eng/trmm/doctrmmi.html

  43. Bowman KP (2005) Comparison of TRMM precipitation retrievals with rain gauge data from ocean buoys. J Climate 18:178–190

    Article  Google Scholar 

  44. Saif ud din, Al Dousari A, Al Ghadban AN (2007) Sustainable freshwater resources management in northern Kuwait – A remote sensing view from Raudatain basin. Int J. Appl. Earth Obs. Geoinfo 9:21–31

    Article  Google Scholar 

  45. Brito AE, Chan SH, Cabrera SD (2003) SAR image superresolution via 2-D adaptive extrapolation. Multidimen Syst Signal Process 14:83–104

    Article  Google Scholar 

  46. Kuhel H, Sacchi MD (2003) Least squares wave equation migration for AVP/AVA inversion. Geophysics 68:262–273

    Article  Google Scholar 

  47. Gribbon KT, Bailey DG (2004) A novel approach to real-time bi-linear interpolation. Second IEEE international workshop on electronic design, test and applications, p 126

    Google Scholar 

  48. Foley TA (1987) Weighted bicubic spline interpolation to rapidly varying data. ACM Trans Graph 6(1):1–18

    Article  Google Scholar 

  49. Arnold DN, Boffi D, Falk RS (2002) Approximation by quadrilateral finite element. Math Comput 71:909–922

    Article  Google Scholar 

  50. Nespor V, Sevruk B (1999) Estimation of wind induced error of rainfall gauge measurements using a numerical simulation. J Atmos Oceanic Technol 16:450–464

    Article  Google Scholar 

  51. Habib E, Krajewski WF, Nespor V (1999). Numerical simulation studies of rain gauge data correction due to wind effect. J Geophy Res 104:19,723–19,734

    Article  Google Scholar 

  52. Krajewski WF, Ciach GJ, McCollum JR, Bacotiu C (2000) Initial validation of Global precipitation climatology project monthly rainfall over United States. J Appl Meteorol 39:1071–1086

    Article  Google Scholar 

  53. Serra YL, A'Hearn P, Freitag HP, McPhaden MJ (2001) ATLAS self-siphoning rain gauge error estimates. J Atmos Oceanic Technol 18:1989–2002

    Article  Google Scholar 

  54. Bell TL, Kundu PK (2003) Comparing satellite rainfall estimates with rain gauge data: Optimal strategies suggested by spectral model. J Geophy Res 108 (D3) 4121, pp ACL 7-1- 15

    Article  Google Scholar 

  55. Sawaya WN (1986) Dates of Saudi Arabia. Regional agriculture and water research center. Ministry of Agriculture and Water, Riyadh, Saudi Arabia, p 200

    Google Scholar 

  56. Zang Y (2001) Texture – integrated classification of urban treed areas in high resolution color infrared imagery. Photogram Eng Remote Sens 67(12):1359–1365

    Google Scholar 

  57. Barnsley MJ, Barr SL (1996) Inferring urban land use from satellite sensor images using kernel-based spatial reclassification. Photogram Eng Remote Sens 62:949–958

    Google Scholar 

  58. Gao J, Skillcorn D (1998) Capability of SPOT XS data in producing detailed land cover maps at the urban-rural periphery. Int J Remote Sens 19:2877–2891

    Article  Google Scholar 

  59. EEC (1997) Decision No. C (97)2690. Decision of commission of the financing of an action concerning counting of the number of Olive trees in member states.

    Google Scholar 

  60. Howard JA (1991) Remote sensing of forest resources. Chapman & Hall, London

    Google Scholar 

  61. Marceau DJ, Gratton DJ, Fournier RA, Fortin JP (1994) Remote sensing and the measurement of geographical entities in a forested environment. 2. The optimal spatial resolution. Remote Sens Environ 49(2):105–117

    Article  Google Scholar 

  62. Woodcock CE, Strahler AH (1987) The Factor of scale in remote sensing. Remote Sens Environ 21:311–332

    Article  Google Scholar 

  63. Dreyer P (1993) Classification of land cover using optimized neural nets on spot data. Photogramm Eng Remote Sens 59:617–621

    Google Scholar 

  64. Anys H, Bannari A, He DC, Morin D (1994) Texture analysis for the mapping of urban areas using airborne MEIS-II images. Proceedings of the first international airborne remote sensing conference and exhibition, Strasbourg, France, vol 3, pp 231–245

    Google Scholar 

  65. St-Onge BA, Cavayasm F (1997) Automated forest structure mapping from high resolution imagery based on directional semivariogram estimates. Remote Sens Environ 61:82–95

    Article  Google Scholar 

  66. Culvenor DS, Coops N, Preston R, Tolhurst K (1999) A spatial clustering approach to automated tree crown delineation. Proceedings of the international forum on automated interpretation of high spatial resolution digital imagery for forestry, 10–12 February, Victoria, BC, Canada, Natural Resources Canada, pp 67–80

    Google Scholar 

  67. Coops N, Culvenor DS (2000) Utilizing local variance of simulated high spatial resolution imagery to predict spatial pattern of forest strands. Remote Sens Environ 71:248–260

    Article  Google Scholar 

  68. Wulder M, Niemann KO, Goodenough DG (2000) Local maxima filtering for the extraction of tree locations and Basdal area from high spatial resolution imagery. Remote Sens Environ 73:103–114

    Article  Google Scholar 

  69. Granlund GH (1999) The complexity of vision. Signal Process 74:101–126

    Article  Google Scholar 

  70. Kay S, Leo O, Peedel S, Giardino G (2000) Computer assisted recognition of olive tree in digital imagery. Space Applications Institute JRC of the European Commission, Ispra, Italy

    Google Scholar 

  71. Karantzalos K (2003) Combining anisotropic diffusion and alternating sequential filtering for satellite image enhancement and smoothing. Proceedings international conference of image and signal processing for remote sensing IX, SPIE, Barcelona, Spain

    Google Scholar 

  72. Alvarez L, Lions PL, Morel JM (1992) Image selective smoothing and edge detection by nonlinear diffusion. SIAM – JNA 29:845–866

    Google Scholar 

  73. Biegert EK, Berry JL, Oakley SD (1997) Oil field subsidence monitoring using spaceborne interferometric SAR – A Belridge 4-D Case History. Proceeding annual meeting of the American association of petroleum geologists, Dallas, April′97

    Google Scholar 

  74. Carne C, Massonnet D, King C (1996) Two examples of the use of SAR interferometry on displacement fields of small spatial extent. Geophys Res Lett 23(24):3579

    Article  Google Scholar 

  75. Briole P, Massonnet D, Delacourt C (1997) Posteruptive deformation associated with the 1986– 1987 and 1989 lava flows of Etna detected by radar interferometry. Geophys Res Lett 24(1):37

    Article  Google Scholar 

  76. Fielding EJ, Blom RG, Goldstein RM (1998) Rapid subsidence over oil fields measured by SAR interferometry. Geophys Res Lett 25:3215

    Article  Google Scholar 

  77. Galloway DL, Hudnut KW, Ingebristen SE, Philips SP, Peltzer G, Rogez F, Rosen PA (1998) InSAR detection of aquifer system compaction and land subsidence, Antelope Valley, Mojave Desert, California: Water Resources Research, vol 34, pp 2573–2585

    Google Scholar 

  78. Galloway DL, Jones DR, Ingebristen SE (1999) Land subsidence in the United States: US Geological Survey Circular 1182, pp 1–117

    Google Scholar 

  79. Galloway DL, Jones DR, Ingebristen SE (2000) Measuring land subsidence from space; US Geological Survey fact sheet 051–00, pp 1–4

    Google Scholar 

  80. Hoffmann J, Zebker HA, Galloway DL, Amelung F (2001) Seasonal subsidence and rebound in Las Vegas valley, Nevada, observed by synthetic aperture radar interferometry. Water Resour Res 37(6):1551–1566

    Article  Google Scholar 

  81. Tuttle M, Ehrismann J, Hulshof B. (1998) Detection and monitoring of surface subsidence using synthetic aperture radar interferometry in Yibal Oil Field, Sultanate of Oman. http:// petroleum.berkeley.edu/papers/patzek/spe59295.pdf

  82. Gray AL, Farris-Manning PJ (1993) Repeat pass interferometry with airborne synthetic aperture radar. IEEE Trans Geosci Remote Sens 31(1):189–191

    Google Scholar 

  83. Hoffmann J (2003) The application of satellite radar interferometry to the study of land subsidence over developed aquifer systems. PhD dissertation, Department of Geophysics, Stanford University, USA, pp 1–211

    Google Scholar 

  84. Zebker HA, Werner CL, Rosen PA, Scott H (1994) Accuracy of topographic maps derived from ERS – 1 interferometric radar. IEEE Trans Geosci Remote Sens 32(4):823–836

    Article  Google Scholar 

  85. Ferretti A, Prati C, Rocca F (2000) Non-linear subsidence rate estimation using permanent scatter in differential SAR Interferometry. IEEE Trans Geosci Remote Sens 35(5):2202–2212

    Article  Google Scholar 

  86. Khalaf FI, Gharib IM, Al-Hashash MZ (1984) Types and characteristics of the recent deposits of Kuwait, Arabian Gulf. J Arid Environ 7:9–33

    Google Scholar 

  87. El-Baz F, Al-Sarawi M, Al-Shamlan AA (2000) Atlas for the State of Kuwait from Satellite Images. Kuwait Foundation for the Advancement of Sciences, pp 1–145

    Google Scholar 

  88. Abusada SM (1981) Interpretation of environmental isotope data of Kuwait groundwater. Proceeding first symposium on the future development of water resources in the Gulf and Arabian Peninsula. J Arab Gulf Arab Peninsula Stud 2:8–92

    Google Scholar 

  89. Burdon DJ, Al Sharhan A (1968) The problem of the paleokarstic Dammam Limestone Aquifer in Kuwait. J Hydrol 6:358–404

    Article  Google Scholar 

  90. Himida IH, El-Yaqubi SA (1979) Hydrogeological and hydrogeochemical aspects of the mail groundwater fields in Kuwait, Arabian Gulf first geological congress of the middle east, Ankara, Turkey, pp 1–4

    Google Scholar 

  91. Anderson JR, Hardy EE, Roach JT, Witmer RE (1976) A landuse and landcover classification system for use with remote sensor data. USGA Professional Paper 964, p. 28

    Google Scholar 

  92. Beven KJ, Wood EF, Sivapalan M (1988) On hydrological heterogeneity: Catchment morphology and catchment response. J Hydrol 100:353–375

    Article  Google Scholar 

  93. Menenti M, Bastiaanssen WGM, van Eick D, El Karim MAA (1989) Linear relationships between surface reflectance and temperature and their application to map actual evaporation of groundwater. Adv Space Res 9(1):165–176

    Article  Google Scholar 

  94. Menenti M (1993) Understanding land surface evapotranspiration with satellite multispectral measurements. Adv Space Res 13(5):89–100

    Article  Google Scholar 

  95. Bastiaanssen WGM, Hoekman DH, Rorbrling RA (1994) A methodology for assessment of surface resistance and soil water storage variability at mesoscale based on remote sensing measurements. IAHS Special Publications 2, Institute of Hydrology, Wallingford, UK, p 66

    Google Scholar 

  96. Bastiaanssen WGM, Menenti M, Dolman AJ, Feddes RA, Pelgrum H (1996) Remote sensing parameterization of meso scale land surface evaporation. In Raschke E (ed) Radiation and water in the climate system: remote measurements. Springer-Verlag, Berlin, pp 401–429

    Google Scholar 

  97. Bastiaanssen WGM, Menenti M, Feddes RA, Holtslag AAM (1998). A remote sensing surface energy balance algorithm for land (SEBAL). Part 1: formulation. J Hydrol 212–213:198–212

    Article  Google Scholar 

  98. Bastiaanssen WGM, Pelgrum H, Wang J, Ma Y, Moreno JF, Roerink GJ, van der Wal T (1998). A remote sensing surface energy balance algorithm for land (SEBAL).: Part 2: Validation J Hydrol 212–213:213–229

    Article  Google Scholar 

  99. Bastiaanssen WGM, Noordman EJM, Pelgrun H, Davids G, Thoreson BP, Allen RG (2005) SEBAL Model with remotely sensed data to improve water resource management under actual field condition. J Irrigat Drain 131(1):85–93

    Article  Google Scholar 

  100. Edgell HS (1997) Aquifers of Saudi Arabia and their geological framework. Arab J Sci Engg 22(1C):4–31

    Google Scholar 

  101. Al Sulaimi J, Khalaf FJ, Mukhopadhyay A (1997) Geomorphological analysis of paleo drainage systems and their environmental implications in the desert of Kuwait. Environ Geol 29(1–2):94–111

    Article  Google Scholar 

  102. SCS (1985) National engineering handbook, Section 4: Hydrology, US Department of Agriculture, Soil Conservation Service, Engineering Division, Washington DC

    Google Scholar 

  103. Walters MO (1990) Transmission losses in arid regions. J Hydraul Eng ASCE 116:129–138

    Article  Google Scholar 

  104. Linsley RK, Kohler MA, Paulhus JLH (1975). Hydrology for engineers. McGraw Hill, New York, NY

    Google Scholar 

  105. Gheith H, Sultan M (2002) Construction of a hydrologic model for estimating Wadi runoff and groundwater recharge in the Eastern Desert, Egypt. J Hydrol 262:36–55

    Article  Google Scholar 

  106. Senay Y (1977) Groundwater resources and artificial recharge in Raudatain waterfield. Ministry of Electricity and Water, Kuwait, p 35 (unpublished)

    Google Scholar 

  107. Kwarteng AY, Viswanathan MN, Al Senafy AN, Rashid T (2000) Formation of fresh ground-water lenses in northern Kuwait. J Arid Environ 46:137–155

    Article  Google Scholar 

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Authors
  1. Dhari Al Ajmi
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  2. Saif ud din
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Editors and Affiliations

  1. Department of Civil, Construction and Environmental Engineering, Oregon State University, 202 Apperson Hall, Corvallis, 97331, OR, USA

    Tarek A. Kassim

  2. Department of Environmental Chemistry, IDAEA-CSIC, C/Jordi Girona 18–26, Barcelona, 08034, Spain

    Damià Barceló

  3. Catalan Institute for Water Research (ICRA), Parc Científic i Tecnològic de la Universitat de Girona, Edifici Jaume Casademont, 15, Girona, E-17003, Spain

    Damià Barceló

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Ajmi, D.A., din, S.u. (2009). Remote Sensing: Fundamentals, Types and Monitoring Applications of Environmental Consequences of War. In: Kassim, T.A., Barceló, D. (eds) Environmental Consequences of War and Aftermath. The Handbook of Environmental Chemistry, vol 3U. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-87963-3_3

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