A Monograph on Management of Salt-Affected Soils and Water for Sustainable Agriculture, 17-24 (2010) 2010 Sultan Qaboos University
Salinity Mapping in Oman using Remote Sensing Tools: Status and Trends Yaseen A. Al-Mulla College of Agricultural and Marine Sciences, Sultan Qaboos University, PO Box 34, Al-Khod 123, Sultanate of Oman
ABSTRACT: Soil salinity problems in Oman started to be noticed after the extensive agricultural activities followed by increase use of lands suitable for farming and overdraw of fresh groundwater to an extent of causing seawater intrusion. Several studies related to soil and water salinity assessment, and mapping were conducted in Oman using traditional and advanced techniques such as GIS. But salinity is a dynamic process and covers a widespread area over the country. Besides, these techniques produced salinity mapping for only the time of measurements and lead to lack of information for the current soil salinity situation. Therefore, a high tech method that is cost, time and labor effectives is recommended by several scientific researchers including the Ministry of Agriculture strategic plan. Remote sensing techniques have proven to provide useful tools in monitoring, delineating and mapping soil salinity either directly from bare soils or indirectly from vegetation conditions. This paper reviews the past efforts done in mapping soil salinity in Oman and and the current efforts of using remote sensing analysis for the same purpose.
Introduction Soil salinity problems in Oman started to be noticed in the mid 1990s after the extensive agricultural activities, coupled with increasing population, through the use of lands suitable for farming and overdraw of fresh groundwater to an extent of causing seawater intrusion. In addition to the nature of harsh climate featuring low amount of rainfall ranges from 20 to 300 mm/year, depending on the regions location in Oman, and high temperatures (Hussain, 2005; FAO, 2008; Asif and Ahmed, 2002; and Al-Belushi, 1997). These factors contributed in increasing the area of soil salinity to reach 13.9 million ha i.e., 44.2% of the total area of Oman (Hussain, 2005) causing land degradation and abandoning of productive farms mostly in Al-Batinah Area, north of Oman, (Hussain, 2005; FAO, 2008; Al-Belushi, 1997; Al-Belushi, 2003; and Al-Barwani and Helmi, 2006) where 52% of this region is affected by soil salinity (Hussain, 2005; and AlBelushi, 2003). Soil salinity is an environmental problem which has affected about 952 million hectares of lands around the world. It plays an important role in desertification in arid and semi-aid regions like Oman. The geographic information systems and remote sensing techniques have become tools for the purpose of identifying and classifying saline soils. Using such technique has given a good indication of its accuracy, cost effectiveness, speed, and labor saving for delineating salt affected soils in the most efficient manner. The integration of remote sensing data, in the form of satellite imagery, with the GIS has boosted up the ability of delineating and mapping soil salinity. It made many researchers of this field in resent years to follow such approach with different methods and applications. But salinity is a dynamic process. Therefore,
two important aspects are needed to be accomplished in order to monitor it: delineating the salt affected soils, and detecting the temporal and spatial changes in this occurrence. This paper reviews the past efforts done in mapping soil salinity in Oman and the current efforts of using remote sensing analysis for the same purpose. The Concept of Remote Sensing Remote sensing can be defined as the collection of data about an object from a distance. There are four basic components of a remote sensing system (Fig. 1) including: (1) a target; (2) an energy source; (3) a transmission path; and (4) a satellite sensor (Landsat, SPOT, or the SIR-C radar) which records the intensity of electromagnetic radiation (sunlight) reflected from the earth at different wavelengths. The Electromagnetic (EM) spectrum (Fig. 2) describes the continuous spectrum of energy (light) from high energy gamma rays and x-rays to very low energy microwaves and radio waves. Satellites ollect data by passing the reflected energy from the Earth through filters that separate the energy into small windows (Fig. 3) of the EM spectrum into discrete spectral bands. Different objects have fingerprint reflectance and absorption signatures that enable interpretation of the sensor outputs. The variations in spectral response of various Earth surface materials like soil, rock, vegetation, and water (Fig. 4) enable discrimination and identification of landscape properties. Satellite images (Fig. 5) show very large areas of land, 185 km swath width. The images detect features at
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Figure 1. Components of Remote Sensing system.
Figure 2. The electromagnetic spectrum.
Figure 3. Windows of the EM spectrum.
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Salinity mapping in Oman using remote sensing tools: status and trends
Figure 4. Fingerprint reflectance of earth surface materials.
wavelengths not visible to the human eye. They are regularly and routinely acquired and archived. They are the most cost-effective dataset for monitoring change over large areas. It is worth mention, however, that satellites do not “see” in color. Hence, every image is obtained in black and white at a precise wavelength (usually between 0.4 to 12.0 microns) and satellites can obtain many images at the same time in different parts of the spectrum.
Ministry of Agriculture and Fisheries) produced general soil map of Oman (1990-1991), by which soil salinity levels in different farms where determined and documented (Fig. 6) presents an example of these maps showing Barka region). In 1993 and 1997 the Ministry of Agriculture also conducted two integrated studies of Al-Batinah region, among the results, it covered levels of saline soils in the south and north part of the region (MAF, 1993). Al-Belushi (2003) explored the main reasons for desertification in Al-Batinah coast where he classified the soil types in the area and showed how the characteristics of some of these soils contributed in speeding the desertification process. He presented different groundwater salinity mapping for different catchments locations in Al-Batinah area (obtained from 1992 Ministry of water resources survey) and concluded that water in coastal areas of Al-Batinah region has been affected severely by seawater intrusion. Based on field and statistical analysis Al-Belushi (2003) found that there is a relationship between the water salinity and soil salinity in the Al-Batinah region resulting from the irrigation practices followed in this region. The average soil EC level reached 10,400 µS/cm. He also produced a soil salinity map (Fig. 7) for al-Batinah region, north and south, based on his field analysis. Bajjali (2003) conducted a thorough study on the quality of groundwater of different regions in Oman from north to south including Al-Batinah region (Fig. 8) by analyzing 20,000 wells and mapping the regions using geographic information systems. It can be noticed from the maps of the regions he covered that Al-Batinah is the most affected area among all other areas where most of its coastal lines have groundwater with Total Dissolved Solids (TDS) ranging between 4,000 and 35,000 mg/l. Because of the importance of the salinity problems, the Ministry of Agriculture recently prepared a ten years
Salinity Mapping in Oman Several studies and research projects related to soil and water salinity monitoring, assessment, and mapping were conducted in Oman. Ministry of Agriculture (formerly
Figure 5. A 185 km swath width satellite image of northern Oman.
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Figure 6. Soil salinity level in Barka farms in south Al-Batinah (MA-Sheet # 9519).
Figure 7. Soil salinity map for North and South Al-Batinah (adapted from Al-Belushi, 2003).
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Salinity mapping in Oman using remote sensing tools: status and trends
Figure 8. Groundwater salinity in Al-Batinah using GIS (Adapted from Al-Bajjali, 2003).
strategic plan for combating water and soil salinity in Oman (Hussain, 2005). Al-Barwani and Helmi (2006) used Geographical Information System and Autocad techniques to map groundwater salinity levels in the coastal area of Al-Batinah plain based on water electrical conductivity surveys conducted by the Ministry of Regional Municipalities and Water Resources (formerly Ministry of Water Resources) for 20 years since 1984. They found that lands suitable for agriculture have been reduced by 7% in the period of 2000 - 2005. They also reported that the salinity water moved
12 km towards inland in areas like Barka. Figure 9 shows groundwater salinity map produced by Al-Barwani and Helmi (2006) for Barka in south Al-Batinah. The role of remote sensing in soil salinity mapping in Oman The previous efforts in mapping soil salinity in Oman, for the past 15-20 years, were nicely addressed and produced. However, they covered only the time of measurements and lead to lack of information for the current soil salinity situation (Hussain, 2005). Besides, salinity is a dynamic
Figure 9. Ground water salinity map for Barka, Al-Batinah South. (Adapted from Al-Barwani and Helmi, 2006).
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Figure 10. Supervised classification of 1994 satellite image of Wadi Al-Maawel. (adapted from Al-Belushi, 1997).
Figure 11. NDSI analyses on 1991 and 2005 satellite image show clearly how soil salinity increased in 2005 (Adapted from Al-Mulla and Al-Adawi, 2009).
of the images showed a noticeable change in agriculture in this region over the 22 years period. Al-Hammadi (2008) investigated the effective use of remote sensing techniques in evaluating the distribution of soil salinity in eastern part of United Arab Emirates (UAE) and Al-Batinah region of Oman. He analyzed two satellite images dated 1980 and 2000 by using Soil Adjusted Vegetation Index (SAVI). He concluded that the use of remote sensing was efficient and provided very
good information with regards to the status of vegetation conditions in UAE and Oman. Al-Mulla and Al-Adawi (2009) worked on mapping changes in soil salinity with time in Al-Rumais (near Barka) using remote sensing analysis. They used two satellite images, a 1991 Landsat (TM) and a 2005 Landsat (ETM+). They performed different image enhancements on the two satellite images in order to separate between the features in these images to assist in delineating salt
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Salinity mapping in Oman using remote sensing tools: status and trends
Figure 12. Change in vegetation due to soil salinity between 1991 and 2005 (adapted from Al-Mulla and Al-Adawi, 2009).
affected soils. That included the use of different spectral indices like NDVI, II, SAVI, and Normalized Difference Salinity Index or NDSI (Fig. 11) in addition to detection of temporal changes in soil salinity using change analysis techniques (Fig. 12).
Seeb and Suwaiq, Sultanate of Oman. Agricultural and Marine Sciences - A Research Journal, 11( S.I):55-69. Al-Belushi A. A. 1997. Detection of saline stressed vegetation and change analysis in an arid coastal plain by remote sensing from Landsat TM data. Case study: northern coastal plain of Oman. MSc Thesis. University of Aberdeen. UK. Al-Belushi, A.S. 2003. Desertification in Al-Batinah Plain, Sultanate of Oman. PhD Dissertation. Jordanian University. Jordan (in Arabic). Alhammadi, M.S. 2008. Soil salinity assessment using remote sensing tools. Power Point presentation. International Symposium Geotunis 2008. Tunis, Tunisia. Al-Mulla, Y.A. and S. Al-Adawi. 2009. Mapping temporal changes of soil salinity in Al-Rumais region of Oman using geographic information system and remote sensing techniques. American Society of Agricultural and Biological Engineers (ASABE) Annual International Meeting. Paper No. 095777. Reno, NV, USA. Asif, S. and M. Ahmed. 2002. Using State-of-the-Art RS and GIS for Monitoring Waterlogging and Salinity. Development of a Research Programme in Irrigation and Drainage. International Programme for Technology
Conclusion Soil salinity is considered as an important factor in desertification in arid regions and semi-aid regions like Oman. Several studies and research projects, using traditional or more advanced methods like GIS, related to soil and water salinity monitoring, assessment, and mapping were conducted in Oman. However, they covered only the time of measurements and did not address the dynamic nature of salinity process and its coverage of large areas in Oman. Hence, remote sensing analysis has been introduced and proven to be a new, cheaper and faster technique than the traditional ones in delineating and mapping soil salinity. Although some efforts have been done in using remote sensing tools for this purpose, more researches are needed in this direction. References Al-Barwani, A. and T. Helmi. 2006. Sea water intrusion in a coastal aquifer: a case study for the area between
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and Research in Irrigation and Drainage. Programme Formulation Report. No. 9. Bajjali, W. 2003. Evaluation of the groundwater salinity throughout Sultanate of Oman using GIS. Available at: http://frontpage.uwsuper.edu/bajjali/proj/oman/o5.htm. Dohai, B.S. 2007. Modeling of invasive exotic plants dynamics in arid region using remote sensing and GIS: a case study of Prosopis juliflora in the UAE. MSc. Thesis. United Arab University, UAE. El-haddad, A. and L.A. Carcia. 2006. Detecting soil salinity levels in agricultural lands using satellite imagery. Presented and published in the Proceedings of the American Society for Photogrammetry and
Remote Sensing Annual Conference, Reno, NV, May 1-5, 2006. FAO. 2008. Oman. Available at: http://www.fao.org_/nr/ water/aquastat/countries/oman/index.stm. Harris, R. 2003 Remote sensing of agriculture change in Oman. Int. J. Remote Sensing, 24(23):4835-4852. Hussain, N. 2005. Strategic Plan for Combating Water and Soil Salinity in Sultanate of Oman for 2005-2015. Ministry of Agriculture and Fisheries. Oman pp. 117. MAF (Ministry of Agriculture and Fisheries). 1993. South Batinah Integrated Study: Soil Survey and Land Classification Project OMA/87/0111. Directorate General of Agricultural Research. Sultanate of Oman.
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