The Remote Sensing Laboratory: The Challenge of Monitoring ... brochure.pdf · 1 The Remote Sensing Laboratory: The challenge of Monitoring Desertification from Space G enerally speaking,

The Jacob Blaustein Institutes for Desert Research

The Remote Sensing Laboratory:

The Challenge of Monitoring Desertification from Space

Ben-Gurion University of the Negev

RSL brochure blead.pub page 1

Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black

Monday, August 13, 2007 19:51

1 The Remote Sensing Laboratory: The challenge of Monitoring Desertification from Space

G enerally speaking, desertification is defined as spatial extension of desert-like conditions of soil and vegetation

into marginal areas outside the climatic desert and intensifica-tion of such conditions over a period of time. Desertification processes result from various factors, including climate varia-tions and human activities such as overgrazing, deforestation, drought, and the burning of extensive areas. Once com-menced, the desertification process is characterized by pro-gressive destruction of native vegetation, significant lowering of the water table, a reduced supply of surface water, in-creased salinity in natural waters and soils, encroachment of sand dunes, and an accelerated rate of erosion. Climatic ef-fects associated with this phenomenon include increased al-bedo, reduced atmospheric humidity, and greater atmospheric dust (aerosol) loading.

According to the United Nations, desertification is one of the most devastating and widespread threats to environmental security faced by many countries in the world. It affects one third of the world population, and impacts upon people on all continents. It is associated with social strife including poverty, hunger, social unrest, high infant mortality and disease. Re-

search into the abatement of desertification therefore contrib-utes to efforts to solve these problems.

Desertification can be difficult to assess from the ground, since ground observations are limited in space and time. For exam-ple, a farmer may realize that the topsoil is blowing away from his field or that salinization is occurring, but these observations do not indicate the state of degradation a few kilometers away. Each site requires manpower for intensive survey and sam-pling. Furthermore, since desertification processes fluctuate over time, repeated and ongoing observations are required to determine whether progressive degradation is actually occur-ring and to track its progress.

Monitoring desertification processes over vast and distant ar-eas therefore necessitates innovative techniques. Remote sensing from satellites offers a considerable potential means to do this all over the globe. Spaceborne systems derive infor-mation about the ground from measurements made at a dis-tance and without coming into physical contact with it. Such measurements are based on analyzing the electromagnetic radiation that is reflected or emitted from the Earth’s surface or the atmosphere.

Monitoring Desertification—The Challenge

"Man must rise above the Earth to the top of the universe and beyond, for only then will he fully understand the world in which he lives" [Socrates, 400 BC]


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


2

Jacob Blaustein Institutes for D

esert Research, B

en-Gurion U

niversity of the Negev

The Remote Sensing Laboratory

T he Remote Sensing Laboratory at the Jacob Blaustein Institutes for

Desert Research, Ben-Gurion Univer-sity of the Negev, was established in 1988 in order to advance scientific theories, methodology, and applica-tions of remote sensing, image proc-essing, and geographic information system (GIS) management of the Earth's resources with a special inter-est in dryland applications. Such re-mote sensing implementations are necessary to meet the need for low cost management of information over vast expanses of unsettled lands. The laboratory has a long record of na-tional and international research on assessing the extent, intensity, and rate of change of many desertification phenomena around the world.


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black



Vegetation Degradation in Sinai (Egypt)

T he brightness contrast across the Israeli-Egyptian political borderline is a typical example

of a desertification phenomenon triggered by human impacts on a fragile ecosystem [1]. The sand dunes of the Negev (Israel) are almost completely cov-ered by biological soil crusts undis-turbed by anthropogenic activity. These crusts consist of microorgan-isms called cyanobacteria along with fine soil particles [2].

On the other side of the border, in the sand dunes of Sinai (Egypt), such crusts are absent from the topsoil due to inten-sive trampling by humans and animals. Conse-quently, the Israeli Negev dunes are stable with more vegetation, while the Sinai dunes are bare and mobile. The two sides of the political borderline, although similar from geological, geomorphological, pedological, and climatic points of view, demon-strate opposing processes of desertification in Egypt and rehabilitation in Israel.

[2] Filaments of biological soil crust consist-ing of cyanobacteria and fine soil particles.

[1] The sharp contrast across the Israel-Egypt border as seen in satellite images.


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


4


esert Research, B

en-Gurion U


Another important property of biogenic soil crusts is their thermal property, which is considerably higher than the substrate base soil. Since the biological soil crusts are darker than the bare sands, the Negev dunes are 3-4 ºC hot-ter than the adjacent Sinai dunes, espe-cially during summertime. The border-line is clearly visible in thermal images [3].

[3] Thermal contrast across the Israel-Egypt border as observed in satellite images.

References

Karnieli, A. and Tsoar, H. 1995. Satellite spectral reflectance of biogenic crust developed on desert dune sand along the Israel-Egypt border. Inter-national Journal of Remote Sensing, 16, 369-374.

Qin, Z., Karnieli, A. and Berliner, P. 2001. Thermal variation in the Israel-Sinai (Egypt) peninsula region. Interna-tional Journal of Remote Sensing, 22, 915-919.


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black



Mineral Dust Storms

D ry bare soils in arid environments are the major source of fine particles (or aerosols), termed min-

eral dust, that are blown up in dust storms. Huge dust storms originating in the north African and Mediterra-nean deserts cross the Atlantic and settle in areas as far as Europe and the Americas, while dust storms from China and Mongolia may cross the Pacific. Apart from the health and environmental consequences of these storms, mineral dust particles can affect climate through the absorption and scattering of solar radiation and, in the case of large particles, by interaction with thermal radiation. Therefore, it is important to monitor satellite data of such storms to obtain information on dust coverage at climatic scales.

While remote sensing of dust over the ocean or dark targets is possible, since the reflectance received by the satellite is mainly related to aerosol content, this task is made much more difficult over bright desert surfaces [4].

[4] Saharan dust over the eastern Mediterranean. Note that the dust can be clearly seen over the sea but is hardly detectable over the bright desert surface (image courtesy of NASA Visible Earth).


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


6


esert Research, B

en-Gurion U


Since the desert surface reflectance is high, the satellite signal is only slightly affected by the dust-scattering contribu-tion. Therefore, adequate techniques for remote sensing over land still have to be developed. The Aerosol Index is a meas-ure of how much ultraviolet light is ab-sorbed by aerosol particles within the at-mosphere, and its ability to sense dust clouds even over desert surfaces is illus-trated in [5].

Reference

Kaufman, Y.J., Karnieli, A. and Tanre, D. 2000. Detection of dust over deserts using satellite data in the solar wavelengths. IEEE Transactions on Geoscience and Remote Sensing, 20, 525-531.

[5] Aerosol Index indicates a large cloud of dust blowing from northeastern Africa across Egypt, the Sinai Peninsula, over Israel and into the Mid-dle East region on March 19, 2002. Red areas indicate high aerosol index values and corre-spond to the densest portions of the dust cloud, while yellows and greens are moderately high values (image courtesy of NASA Visible Earth).


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black



Dune Encroachment

M any deserts around the world are aeolian, dominated by winds that are an important

erosive force where there is little soil surface protection by organic matter or vegetation cover. Destruction of the vegetative cover or biological soil crusts over sandy areas may accelerate wind erosion and depletion of soil fertility. Areas of blowing sands can be easily identified in sat-ellite images. The role of remote sensing is to identify zones of active and inactive sand dunes and assess the rate of migration of the dunes towards settled or cultivated areas. A special spectral Crust Index developed in the Remote Sensing Laboratory enables separation of differ-ent lithological/morphological units such as ac-tive dune sands, stabilized crusted interdune areas, and playas in the north-western Negev Desert. The absence, presence, and distribution of soil crusts are important items of information for desertification and climate change studies [6].

Based on change detection techniques applied to satellite images from 1973, 1992, and 2002, we estimated that sand dunes in the Gobi desert of Mongolia moved about 47 m during the 29-year study period [7].

[6] Spectral Crust Index showing the distinction between stabilized surfaces, covered by soil biological crusts, and mobile sands in the north-western Negev Desert .

Original aerial photograph

Crust Index

Active dune sands

Stabilized crusty inter dune area

Playa


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


8


esert Research, B

en-Gurion U


[7] Change detection technique reveals that a barhan (arc-shaped) dune moved 47 m during 29 years in the Gobi De-sert . Photograph credit: Jean Jacques CORDIER.

References

Karnieli, A. 1997. Development and implementation of spectral crust index over dune sands. International Journal of Remote Sensing, 18, 1207-1220.

Bayarjargal, Y. and Karnieli, A. 2004. Assessing land-use and land-cover change in Bulgan Soum by remote sensing change detection technique. Arid Ecosys-tems, 10, 127-133.


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black



Drought

D rought can be defined as a period of abnormally dry weather that persists long enough to produce a serious

ecological, agricultural, or hydrological imbalance (e.g., crop damage, water shortage, etc.). The severity of the drought depends upon the degree of moisture deficiency, the dura-tion, and the size of the affected area. In this context, mete-orological drought refers to a prolonged period of below-average precipitation. Drought is one of the causes of de-sertification and exacerbates already poor situations.

Drought years are a very frequent phenomenon in Israel. Between the years 1994/5 and 2001/2,

Israel experienced five drought years. Consequently the Yatir forest, a pine forest lo-cated on the desert fringe [8], suffered from a notable water shortage. Remote sens-ing methods enable us to detect and assess inter-annual changes in the forest trees with respect to the drought effect. The state of the forest was studied by applying a spectral vegetation index, namely the Normalized Difference Vegetation Index (NDVI), based on spaceborne images. High NDVI values are referred to healthy conditions while low values to stress conditions [9 A and B]. The degree of change between the two years is estimated by applying a change detection technique on the two NDVI products [9 C]. It can be seen that in 2000, after five consecutive drought years, the Yatir forest was suffering from severe water shortage.

[8] A satellite image of central Israel. Note the location of the Yatir forest on the desert fringe, visible as the sharp contrast between bright tones (semi-arid zone) and dark tones (sub-humid zone).

[9] NDVI as indicator of bio-physiological condi-tion of the Yatir forest. (A) High index values (winter 1995); (B) low values (winter 2000); and (C) detected change between the two years products (C).

Reference Volcani, A., Karnieli, A. and Svoray, T. The use of remote sensing and GIS for spatio-temporal analysis of the physiological state of a semi-arid forest with respect to drought years. Forest Ecology and Management, 215, 239–250.

A B

C


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


10


esert Research, B

en-Gurion U


Plant Invasion Due to Overgrazing in Mongolia

The Mongolian railway, more than 1000 km in length from the northern border with Russia to the southern border with China, was established in the 1960s. Since then, it has been protected along its length by fences to prevent animals from crossing the railway. As a result, no grazing occurs inside the fences, in con-

trast to the intensive grazing that characterizes the surrounding area. Advantage was taken of this unique fencing phenomenon to investigate anthropogenic rangeland degradation in the steppe biome, through which the railway passes. When the track curves the area between the fences can be as wide as 4

km, enabling the use of remote sensing meth-ods using high resolution imagery [10 A]. Im-age processing has revealed unpalatable toxic species that invaded the grazed areas at the expense of the native palatable grasses. The large extent of this phenomenon over the steppe biome of Mongolia indicates severe vegetation degradation due to overgrazing [10 B and C].

Reference

Karnieli, A., Bayarjargal, Y. and Bayasgalan, M. 2005. Do Vegetation Indices Reliably Assess Vege-tation Degradation? Proceedings of the In-ternational Conference on Remote Sensing and Geoinformation Processing , September 7th to 9th, 2005, Trier (Germany).

[10] Grazing pressure along the rail-way in Mongolia has led to invasion of unpalatable toxic species.


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


[12] Landsat-TM image of the Kyzylkum Desert, Kazhastan. Each small bright dot indicates a watering point. The agri-cultural fields, in red, are located along the Syr Darya River.


Grazing Gradient Around Watering Points in Kazakhstan

D esertification around watering points has been well observed by satellite im-

ages in many drylands around the world. It can be identified as radial belts of brightness fading as a function of distance from wells [11]. The primary goal of our study was to characterize spatial and temporal land deg-radation/rehabilitation in Central Asian dry-lands in terms of vegetation and soil pat-terns, in different time periods, with respect to socio-economic conditions before and af-ter the collapse of the Soviet Union. In order to implement this goal we developed a geo-statistical model based on high-resolution satellite imagery [12] in three key time peri-ods (mid-late 1970s, late 1980s, and 2000) [13 A and B]. We conducted a change de-tection analysis in order to assess the direc-tion and intensity of changes between the study periods and specifically we linked the findings to the socio-economic conditions before and after the collapse of the Soviet Union that influenced the grazing gradients and hence the land-use/ land-cover state of the study sites.

[11] Watering point in the Sahel. Radial brightness belts fading as a function of dis-tance from the wells can be seen. Photograph credit: Dr. Compton J. Tucker.


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


12


esert Research, B

en-Gurion U


References

Karnieli, A., Gilead, U., Ponzet, M., and Svoray, T. 2005. Satellite Image Processing and Geo-statistical Methods for Assessing Land Degrada-tion around Watering Points in the Central Asian Deserts. Proceedings of the International Conference on Remote Sensing and Geoin-formation Processing , September 7th to 9th, 2005, Trier (Germany).

[13] Geostatistical modeling of the grazing gradient around watering points in the Kyzalkum Desert of Kazakhstan. Most of the area recovered after 1991 due to socio-economic changes resulting in reduced grazing after the collapse of the Soviet Union.

Our results were mixed. On one hand we found that the Kyzalkum Desert of Kazakhstan is characterized by land reha-bilitation process in rangelands that can be explained by the his-torical events of the last decades [13 C]. Following independ-ence of the former Soviet states in 1991 and the imposition of difficult economic conditions with transition reforms, several ma-jor socio-economic changes occurred that caused drastic de-clines in livestock populations, with a major drop in the number

of sheep and goats, and hence vegetation recovery. However, in the Ust-Urt Plateau of Kazakhstan, degradation of the area continues to occur due to recent exploration and exploitation of the gas and oil reserves in the region. Consequently, large ar-eas underwent intensive 'technological desertification', i.e. the use of heavy duty equipment, large-scale plants, and vehicles that damage the soil surface.

A Grazing gradient model 1991 C Change detection analysis (2000-1991) B Grazing gradient model 2000


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black



I n semi-arid and arid areas of the world, where surface water is very scarce, water supply is produced from inland water bodies or shallow groundwater

aquifers at depths of around 100 m. The spatial extent and depth of these aqui-fers, along with their characteristics, are important factors in determining their use. Drying up of lakes [14] or depletion of the aquifers due to climatic fluctua-tions or intensive use, or even lowering of the groundwater level below depths allowing efficient pumping with simple instruments and/or the root zone, is one of the main reasons for desert encroachment and the migration of people and herds to other areas.

Since spaceborne imagery detects only the surface of the Earth (and not the subsurface), identification of shallow aquifers and monitoring their status is a major challenge for the potential applications of remote sensing techniques to hydrological studies. It can be achieved by using indirect indicators that are cor-related to hydrogeological factors, themselves indirectly related to the presence of groundwater. One example is the visible vegetation along the Amatzia Fault in the northern Negev [15 A]. The vegetation indicates water seepages from underground aquifers. A similar example is observed at the edges of the allu-vial fans of the Turfan Depression in China [15 B].

[14] Comparison of two satellite images (2001 vs. 1990) dem-onstrating the disappearance of a water lake in the Gobi De-sert (Mongolia) and drying up of the adjacent vegetation (seen in red in the 1990 image) due to climate change. Salty soils (in white) appear instead of the lake in the 2001 image.

Hydrology and Water Resources


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


14


esert Research, B

en-Gurion U


[15] Indirect evidences for existence of groundwater aquifers. Presence of vegetation (seen in red) indicates seepages along the Amatzia Fault, Negev desert, Israel (A) and at the edges of the alluvial fans of the Tur-fan Depression, China (B) .

References

Bayarjargal, Y. and Karnieli, A. 2004. Assessing land-use and land-cover change in Bulgan Soum by remote sensing change detection technique. Arid Ecosystems, 10, 127-133.

B A


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black



Salty Dust Storms Around the Aral Sea (Kazakhstan and Uzbekistan)

T he recession of the Aral Sea water level is probably the most staggering

environmental crisis of the twentieth cen-tury. Until the 1960s the Aral Sea was the world's fourth-largest fresh water lake. However, since then, Soviet planners di-verted water from the two main rivers feeding the lake for irrigating cotton and rice fields, the most water-demanding crops. Satellite images document the continual shrinking of the lake to less than half its original size [16 A-C]. This mis-managed engineering project led to accel-erated desertification process in the whole region. Agricultural areas were irreversi-bly destroyed by secondary salinization. The local climate has reportedly shifted, with hotter, drier summers and colder, longer winters. Thirty six thousand square kilometers of salty soil lake-bed was ex-posed and blown by the strong winds common in the region.

A 1973 B 1989


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


16


esert Research, B

en-Gurion U


[16] Drying up of the Aral Sea as observed by satellite images in different years (A – C) with respect to the 1964 shoreline (in yel-low). Salty dust storm blowing from the for-mer lake-bed towards the agricultural areas south of the lake (D).

Reference

Orlovsky L., Orlovsky N. and Durdyev A. 2005. Dust storms in Turkmeni-stan. Journal of Arid Environ-ments, 60, 83-97.

Dust storms blow up to 75,000 tons of this exposed soil annually [16 D], dis-persing salt particles and pesticide residues. This air pollution has caused widespread nutritional and respiratory problems in humans, and crop yields have been diminished by the added toxic salt deposits, even in some of the same fields irrigated with the diverted water.

C 2000 D Salty dust storm


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black



Soil Compaction, Soil Crusting, Infiltration, and Erosion

S oil compaction, soil crusting, infiltration, and erosion are all terms associated with me-

dium- and fine-textured soils e.g. clay. Physical soil crusts [17] can be formed by natural proc-esses such as the impact of rainfall (or sprinkled water) on the topsoil along with physiochemical dispersion of clay minerals; sedimentation of fine material during floods; or by human activities such as intensive agriculture involving more and heavier machinery. Physical crust formation is a common and widespread phenomenon in arid and semi-arid soils. Once the topsoil is en-crusted, less rainwater infiltrates to the subsur-face and more runoff is created. Intensive runoff on bare desert soils creates sheet and gully (small channels) erosion. Significant correlation was found between encrusted soil and soil re-flectance properties, enabling us to map the infil-tration rate from a remote distance, using ad-vanced hyperspectral technology [18].

Reference

Ben-Dor, E., Goldshalager, N., Braun, O., Kindel, B., Goetz, A.F.H., Bonfil, D., Agassi, M., Margalit, N., Binayminy, Y. and Karnieli, A. 2004. Moni-toring of infiltration rate in semiarid soils using airborne hyperspectral technology. International Journal of Remote Sensing, 25, 2607-2624.

[17] Physical soil crust.

[18] Use of advanced hyperspectral remote sensing data for mapping infiltration rate.


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


18


esert Research, B

en-Gurion U


S alinization of groundwater (downward salinization) and of soils (upwards salinization) is one of the main desertification processes in arid and semi-

arid regions, especially in agricultural areas. Anthropogenic activities such as irrigation, water drainage, regulation of surface flow, modification of hydro-graphic networks, and construction of water reservoirs affect the stability and rhythm of natural processes and cause significant changes in ecology at local and regional scales. Negative consequences include upward secondary salinization, waterlogging, and increased mineralization of return drainage flow.

Although there is a pressing need to identify salt-affected soils, detection and monitoring of such areas have posed problems to remote sensing applications since most of the salts are featureless in the reflectivity portion of the electro-magnetic spectrum. Different indirect methods need to be developed and tested. These could be based on detecting changes in soils (over different seasons), vegetation status data, integration of thermal data, principal compo-nent analysis, and more.

Turkmenistan is one country that suffered severely from secondary saliniza-tion due to mismanaged irrigation schemes. Irrigation in Turkmenistan is mainly concentrated in oases, where water is diverted from several local rivers and from a long system of canals. Water is lost at a considerable rate from the unprotected banks of the canals. This has caused massive waterlogging and salinization of the surrounding land. In undrained irrigated fields, dis-solved salts are pushed deeper into the soil by the irrigation water, and at the field margins, these salts spread to vacant lands. Figure [19] demonstrates remote sensing methods we have developed to detect and map different de-grees of salinization in the Dashguz oasis in northern Turkmenistan.

Soil Salinity and Water Logging

[19] Image clarification of different lev-els of sanitization and water logging in the Dashoguz Oasis, Turkmanistan.

Reference

Ben-Dor, E., Patkin, K., Banin, A. and Karnieli, A. 2002. Mapping of several soil properties using DAIS-7915 hyperspectral scanner data: A case study over clayey soils in Israel. International Journal of Remote Sensing, 23, 1043-1062.


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


The Remote Sensing Laboratory: The Challenge of Monitoring Desertification from Space

The Jacob Blaustein Institutes for Desert Research Ben-Gurion University of the Negev

CONTACTS

The Remote Sensing Laboratory The Jacob Blaustein Institutes for Desert Research

Ben-Gurion University of the Negev Sede-Boker Campus 84990, ISRAEL

Prof. Arnon Karnieli — Head Telephone: +972-8-6596855

Fax: +972-8-6596805 E-mail: [email protected]

Mazal Adar — Secretary Telephone: +972-8-6596846

Fax: +972-8-6596805 E-mail: [email protected]

http://www.bgu.ac.il/BIDR/research/phys/remote

Gra

phic

desig

n: N

urit A

gam

www

.nurit

agam

.com


Cyan

Magenta

Yellow

Black

Cyan

Magenta

Yellow

Black


Documents

The Remote Sensing Laboratory: The Challenge of Monitoring ... brochure.pdf · 1 The Remote Sensing Laboratory: The challenge of Monitoring Desertification from Space G enerally speaking,