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Geoelectrical mapping and tomography for archaeological prospection at Al Ghouri mausoleum, Islamic Cairo, Egypt
International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156 www.elsevier.com/locate/jag
Geoelectrical mapping and tomography for archaeological prospection at Al Ghouri mausoleum, Islamic Cairo, Egypt Sultan Awad Sultan* National Research Institute of Astronomy and Geophysics, 11722, Helwan, Cairo, Egypt Received 30 October 2003; accepted 5 October 2004
Abstract Geoelectrical resistivity techniques are widely used in the investigation of archaeological sites. A dipole–dipole configuration has been carried out at the graveyard area of Al Ghouri mausoleum to identify below-ground archaeological objects. The 3D imaging survey was carried out at a grid of 15 m 23 m to detect targets at different levels up to 6 m depth. Fifteen dipole–dipole parallel profiles were measured with a spacing of 1 m and with an electrode spacing of 1 and 2 m at each profile, respectively. All measured profiles consist of seven dipole–dipole spreads. The measured data are collected into one file to contain 2298 readings for processing and interpretation using RES3DINV program. Results of interpretation revealed that the subsurface section consists of four groups of archaeological objects. The first group represents a path to Al Ghouri mausoleum, which was constructed below the funeral chamber at a depth ranging from 0.35 to 2.71 m, located in the northwestern part of the area. The second group corresponds to a graveyard area located at the central part of the study area. The third group includes pools and plates of high resistivity values of limestone blocks located at the western part at a depth of 0.55 m. The fourth group shows low resistivity values corresponding to site of dug well bored at the southern part of the area. # 2004 Elsevier B.V. All rights reserved. Keywords: Geoelectrical mapping; Tomography; Al Ghouri mausoleum
1. Introduction Islamic Cairo is a very old area, surrounded by walls dating from the Middle Ages. It was the cultural, religious and intellectual center of the entire Arab * Tel.: +20 2 5246833/5560645; fax: +20 2 5548020. E-mail address: [email protected].
world. Monumental buildings, palaces, many famous mosques and religious schools, numerous markets and the oldest university in the world (Al-Azhar University) still stand witness to a glorious past. Mosque and mausoleum of Al Ghouri, which are both worth a visit. This complex is a beautiful reminder of the Mamluk era of Egypt, when slaves were kings, but it was Al Ghouri who turned the rule over to the
0303-2434/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jag.2004.10.001
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Ottomans with his defeat in Syria. Of interest is that Sufi performances are held in the mausoleum. The Al Ghouri mausoleum, built around 1504 by Sultan Qansuh al-Ghuri, functions today as a cultural center that occasionally produces plays. It is distinguishable from his mosque, which is on the adjacent corner by its unfinished cupola and a sabil-kuttab. From the vestibule, the funeral chamber is on the right, and to the left is a prayer hall with three liwans evenly distributed around the raised and covered part of a lantern (Fig. 1). In the present time, the Egyptian government is in the process restoring the buildings of the Al Ghouri
mausoleum. It intends to have confirmed whether the subsurface contains any archaeological objects. The graveyard area lies at the western part of Al Ghouri mausoleum, covering 337.5 m2. The aim of the present study is to detect any buried archaeological objects before injection by reinforced concrete around walls of the mausoleum buildings. The ground surface of the study area has an elevation, which decreases about 1.5 m from the level of Al Azhar street. Its surface contains several activations such as dug wells at the southern part, and small pools constructed from limestone at the southwestern part. The area is flat and surrounded from the eastern part by a high wall. The
Fig. 1. Location map of the study area.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
Fig. 2. Location map of the dipole–dipole profiles.
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S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
Fig. 3. Boreholes drilled in the study area.
Fig. 4. Dipole–dipole cross section along profile 3.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
western part is surrounded by the funeral room and the prayer hall, where as the northern part is surrounded by the front of the mausoleum to Al Azhar street and the southern part lies at the rest of the building of mausoleum (Fig. 2). The shallow subsurface stratigraphy consists of clastic sediments as shown by bore holes nos. 1 and 2 (Fig. 3). Bore hole no. 1 is located at the southern part of the area and consists of fill unit composed of sand and rock fragments reaching to a depth of 3.3 m, followed by gravels and sand to a depth of 4 m and sand to a depth of 21 m. Bore hole no. 2 is located at
147
the northern part and contains fill unit composed of rock fragments and sand to a depth of 1.1 m, followed by mud and clay to a depth of 2 m, gravels and sand of a depth of 3.3 m and sand up to 21 m.
2. Geoelectrical measurements and interpretation 2.1. Data acquisition The geoelectrical data have been measured using an ‘‘ABEM, SAS 1000’’ instrument of accuracy of
Fig. 5. Three-dimensional resistivity image slices using RES3DINV program.
148
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
0.1 V m configured as a dipole–dipole array. Fifteen profiles have been measured with a spacing of 1 m between the profiles (Fig. 2). The apparent resistivity value for the dipole–dipole array is given by: ra ¼ pnðn þ 1Þðn þ 2ÞaR where R is the measured resistance, a the spacing between the P1 and P2 electrodes and n is the ratio of the distances between C1 and P1 electrodes to the P1– P2 spacing. This array has the advantage of a very good horizontal resolution, but its main disadvantage
is its relatively low signal strength. The use of a larger spacing between (C1 and C2) (and P1 and P2) electrodes is to increase the signal strength. The voltage measured by P1–P2 pair is inversely proportional to n3. Normally, the maximum value for n equals 8. To get a deeper penetration, spacing between C1 and C2 (and between P1 and P2) is increased. One method to reduce the effect of noise is to make additional measurements using different combinations of the n factor and the (a) spacing. In this study, the unit of electrode spacing is 1 m. First measurements are made
Fig. 6. True resistivity map at depth 0.177 m.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
with a = 1 m, and with n equals to 1, 2, 3, 4, 5, 6 and 7. Next, measurements are made with a = 2 m. and similar values of n. The dipole–dipole spacing (a) was 1 m to detect small objects and 2 m to detect objects up to 6 m depth. This depth is adequate and needed to detect the required information about the near-surface archaeological targets in the study area. All measurements were done manually as a multi cables system was not available. Each profile consists of numbers of dipole–dipole spreads, while each spread contains seven values of resistivities at different
149
depths. The RMS errors for measurements range from 0.1 to 3 V m. 2.2. Data processing and interpretation Processing and interpretation of the obtained data have been done using the commercial (RES3DINV, 2000), software for geoelectrical 3D inversion. This program automatically determines a threedimensional (3D) resistivity model for the subsurface using the data obtained from a 3D electrical
Fig. 7. True resistivity map at depth 0.55 m.
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S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
imaging E-SCAN type of survey (Li and Oldenburg, 1992). Electrodes for such a survey are arranged in a rectangular grid. It should be first emphasized that full 3D surveys are not merely a series of 2D surveys, but a different approach has to be used. The inversion routine used by the RES3DINV program is based on the smoothness-constrained leastsquares method (deGroot et al., 1990, Sasaki, 1992). A new implementation of the least-squares method based on a quasi-Newton optimization technique (Loke and Barker, 1996) can also be used. The inversion
program divides the subsurface into a number of small rectangular prisms, and attempts to determine the resistivity values of the prisms so as to minimize the difference between the calculated and observed apparent resistivity values. Resistivity methods are used to prospect the archaeological features of some small parts of the huge city of Piramesses (Abdallatif et al., 2003). 2.2.1. The measured dipole–dipole cross sections The measured data are carried out along 15 profiles with (a) spacing 1 and 2 m. These profiles were
Fig. 8. True resistivity map at depth 0.98 m.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
located at 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14 and 15 m along the x-coordinate and the measurements were carried out along the y-coordinate. These section show variations of resistivity values especially at shallow depths as shown in Fig. 4. The important part of the study area are seen in the sections no. 1, 2, 3, 4 and 5 at a distance ranging from 5 to 7.5 m at the y-coordinate of high resistivity values up to 60 V m which corresponding to path connecting to the Al Ghouri mausoleum below the funeral chamber. The other sections
151
exhibit low resisitivity values at the most parts of these sections. 2.2.2. Three-dimensional resistivity slices The interpretation of dipole–dipole electrical data using RES3DINV program produced nine slices at different depths (Fig. 5). Their depths are 0–0.35, 0.35–0.75, 0.75–1.22, 1.22–1.75, 1.75–2.36, 2.36– 3.06, 3.06–3.87, 3.87–4.80 and 4.80–5.88 m, respectively. Slices no. 1, 2 and 3 show large variation in resistivity values, where as the western part has high
Fig. 9. True resistivity map at depth 1.48 m.
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resistivity values up to 60 V m and low resistivity values at different parts of the area down to 1 V m. Slices no. 7, 8 and 9 did not show variation in resistivity values for more depths through the study area. This means that at depths beyond 4 m archaeological objects do not occur. 2.2.3. True resistivity maps The results can be exported into xyz format for depths ranging from 0.17 to 5.34 m. This file is then reprocessed by using Oasis montaj (1999) software to
clear the anomalies at different depths. It is divided into nine files according to the calculated depths (0.17, 0.55, 0.98, 1.48, 2.05, 2.71, 3.47, 4.34, 5.34 m), each file containing x-coordinate, y-coordinate, and depth and resistivity columns. A base map is constructed using mapping and processing system of Oasis montaj, then the resistivity values for all files at different depths were grided using the same software of Oasis montaj. Finally each map contains a base and a gridded file to represent a true resistivity map at certain depth to illustrate the important anomalies
Fig. 10. True resistivity map at depth 2.05 m.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
153
Fig. 11. True resistivity map at depth 2.71 m.
corresponding to the archaeological objects may be buried in the subsurface according to its resistivity values (Figs. 6–14).
3. Results and conclusion The surface layer of the study area is represented by a rubble layer composed of sand and fragments of limestone saturated with groundwater. This layer covers most of the area except the western part,
which consists of blocks of limestone manufactured as pools or plates. The interpretation of the dipole– dipole cross sections, 3D slices and true resistivity maps indicate that this surface layer extends to a depth ranging from 0.17 to 0.5 m (Fig. 6). Also, interpretation of the resistivity data shows that the subsurface section consists of different units, which have different values of resistivity at different depths. Based on the obtained results the study area is divided into four subsurface groups according to its resisitivity ranges.
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S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
Fig. 12. True resistivity map at depth 3.47 m.
The first group (A) is the important group which represented by high resistivity zone up to 60 V m, located at northwestern part. It represents 3 m width at the y-axis with 5 m at the x-axis that reach 2.71 m depth. The resisitivity values decrease with depth to reach of 30 V m, where the blocks of limestone saturated with groundwater and alter to marly limestone. This zone may be used as a road to the Al Ghouri mausoleum, which constructed below the funeral chamber where, this road may be made of limestone blocks of high resistivity values. The funeral
chamber does not contain any visible paths to the mausoleum; these proved that the first group of the results represents the path to Ghouri mausoleum. These are clear in Figs. 7–12. The second group (B) represents the central part of the area of moderate resistivity values, which consists of sand and blocks of limestone. This unit covers low resistivity zone. This zone was used for buried dead people and consists of space with some debris filled with groundwater. This group could be seen through slices no. 1, 2 and 3 of Figs. 5–8, which correspond to
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
155
Fig. 13. True resistivity map at depth 4.34 m.
graveyard area prepared to bury general people at shallow depth up to 1 m. The length of this group is about 16 m and its width is about 4 m. The third group (C) has high restivity values corresponding to some pools and plates constructed from pieces of limestone exposed at the surface. Also, these objects were constructed beside dug well and part of groundwater used from dug well through these objects as waterspout. This group represents the western and southwestern parts of the study area, and has shallow depths ranging from surface to 0.55 m as shown in Figs. 6 and 7.
The fourth group (D) has very low resistivity values. It corresponds to the dug well used to dump groundwater through waterspout at the surface and some building at high levels especially prayer hall and funeral chamber. This group is located at the southwestern part and has depths up to the end of the geolectrical slices as shown in Figs. 7–14. 3.1. Conclusions The conclusion of this study indicates that the subsurface section of the study area contains very
156
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
Fig. 14. True resistivity map at depth 5.34 m.
important archeological objects buried at shallow depths. The author recommends that no injection for the subsurface with any reinforce concrete material for saving of the archeological objects during repair the buildings of Al Ghouri mausoleum.
References Abdallatif, T.F., Mousa, S.E., El Bassiony, A., 2003. Geophysical investigation for mapping the archaeological features at Qantir Shrqyia, Egypt. Archaeol. Prospect. 10, 27–42.
DeGroot-Hedlin, C., Constable, S., 1990. Occam’s inversion to generate smooth, two-dimensional models form magneto telluric data. Geophysics 55, 1613–1624. Li, Y., Oldenburg, D.W., 1992. Approximate inverse mappings in DC resistivity problems. Geophys. J. Int. 109, 343–362. Loke, M.H., Barker, R.D., 1996. Rapid least-squares inversion of apparent resistivity pseudosections by a quasi-Newton method. Geophys. Prospect. 44, 131–152. Oasis Montaj, 1999. Geosoft provides data processing and analysis (DPA) software and services for geological, geophysical, geochemical. UXO detection and environmental applications. Geosoft Inc., 1999. Sasaki, Y., 1992. Resolution of resistivity tomography inferred from numerical simulation. Geophys. Prospect. 40, 453–464.
Geoelectrical mapping and tomography for archaeological prospection at Al Ghouri mausoleum, Islamic Cairo, Egypt Sultan Awad Sultan* National Research Institute of Astronomy and Geophysics, 11722, Helwan, Cairo, Egypt Received 30 October 2003; accepted 5 October 2004
Abstract Geoelectrical resistivity techniques are widely used in the investigation of archaeological sites. A dipole–dipole configuration has been carried out at the graveyard area of Al Ghouri mausoleum to identify below-ground archaeological objects. The 3D imaging survey was carried out at a grid of 15 m 23 m to detect targets at different levels up to 6 m depth. Fifteen dipole–dipole parallel profiles were measured with a spacing of 1 m and with an electrode spacing of 1 and 2 m at each profile, respectively. All measured profiles consist of seven dipole–dipole spreads. The measured data are collected into one file to contain 2298 readings for processing and interpretation using RES3DINV program. Results of interpretation revealed that the subsurface section consists of four groups of archaeological objects. The first group represents a path to Al Ghouri mausoleum, which was constructed below the funeral chamber at a depth ranging from 0.35 to 2.71 m, located in the northwestern part of the area. The second group corresponds to a graveyard area located at the central part of the study area. The third group includes pools and plates of high resistivity values of limestone blocks located at the western part at a depth of 0.55 m. The fourth group shows low resistivity values corresponding to site of dug well bored at the southern part of the area. # 2004 Elsevier B.V. All rights reserved. Keywords: Geoelectrical mapping; Tomography; Al Ghouri mausoleum
1. Introduction Islamic Cairo is a very old area, surrounded by walls dating from the Middle Ages. It was the cultural, religious and intellectual center of the entire Arab * Tel.: +20 2 5246833/5560645; fax: +20 2 5548020. E-mail address: [email protected].
world. Monumental buildings, palaces, many famous mosques and religious schools, numerous markets and the oldest university in the world (Al-Azhar University) still stand witness to a glorious past. Mosque and mausoleum of Al Ghouri, which are both worth a visit. This complex is a beautiful reminder of the Mamluk era of Egypt, when slaves were kings, but it was Al Ghouri who turned the rule over to the
0303-2434/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jag.2004.10.001
144
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
Ottomans with his defeat in Syria. Of interest is that Sufi performances are held in the mausoleum. The Al Ghouri mausoleum, built around 1504 by Sultan Qansuh al-Ghuri, functions today as a cultural center that occasionally produces plays. It is distinguishable from his mosque, which is on the adjacent corner by its unfinished cupola and a sabil-kuttab. From the vestibule, the funeral chamber is on the right, and to the left is a prayer hall with three liwans evenly distributed around the raised and covered part of a lantern (Fig. 1). In the present time, the Egyptian government is in the process restoring the buildings of the Al Ghouri
mausoleum. It intends to have confirmed whether the subsurface contains any archaeological objects. The graveyard area lies at the western part of Al Ghouri mausoleum, covering 337.5 m2. The aim of the present study is to detect any buried archaeological objects before injection by reinforced concrete around walls of the mausoleum buildings. The ground surface of the study area has an elevation, which decreases about 1.5 m from the level of Al Azhar street. Its surface contains several activations such as dug wells at the southern part, and small pools constructed from limestone at the southwestern part. The area is flat and surrounded from the eastern part by a high wall. The
Fig. 1. Location map of the study area.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
Fig. 2. Location map of the dipole–dipole profiles.
145
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S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
Fig. 3. Boreholes drilled in the study area.
Fig. 4. Dipole–dipole cross section along profile 3.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
western part is surrounded by the funeral room and the prayer hall, where as the northern part is surrounded by the front of the mausoleum to Al Azhar street and the southern part lies at the rest of the building of mausoleum (Fig. 2). The shallow subsurface stratigraphy consists of clastic sediments as shown by bore holes nos. 1 and 2 (Fig. 3). Bore hole no. 1 is located at the southern part of the area and consists of fill unit composed of sand and rock fragments reaching to a depth of 3.3 m, followed by gravels and sand to a depth of 4 m and sand to a depth of 21 m. Bore hole no. 2 is located at
147
the northern part and contains fill unit composed of rock fragments and sand to a depth of 1.1 m, followed by mud and clay to a depth of 2 m, gravels and sand of a depth of 3.3 m and sand up to 21 m.
2. Geoelectrical measurements and interpretation 2.1. Data acquisition The geoelectrical data have been measured using an ‘‘ABEM, SAS 1000’’ instrument of accuracy of
Fig. 5. Three-dimensional resistivity image slices using RES3DINV program.
148
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
0.1 V m configured as a dipole–dipole array. Fifteen profiles have been measured with a spacing of 1 m between the profiles (Fig. 2). The apparent resistivity value for the dipole–dipole array is given by: ra ¼ pnðn þ 1Þðn þ 2ÞaR where R is the measured resistance, a the spacing between the P1 and P2 electrodes and n is the ratio of the distances between C1 and P1 electrodes to the P1– P2 spacing. This array has the advantage of a very good horizontal resolution, but its main disadvantage
is its relatively low signal strength. The use of a larger spacing between (C1 and C2) (and P1 and P2) electrodes is to increase the signal strength. The voltage measured by P1–P2 pair is inversely proportional to n3. Normally, the maximum value for n equals 8. To get a deeper penetration, spacing between C1 and C2 (and between P1 and P2) is increased. One method to reduce the effect of noise is to make additional measurements using different combinations of the n factor and the (a) spacing. In this study, the unit of electrode spacing is 1 m. First measurements are made
Fig. 6. True resistivity map at depth 0.177 m.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
with a = 1 m, and with n equals to 1, 2, 3, 4, 5, 6 and 7. Next, measurements are made with a = 2 m. and similar values of n. The dipole–dipole spacing (a) was 1 m to detect small objects and 2 m to detect objects up to 6 m depth. This depth is adequate and needed to detect the required information about the near-surface archaeological targets in the study area. All measurements were done manually as a multi cables system was not available. Each profile consists of numbers of dipole–dipole spreads, while each spread contains seven values of resistivities at different
149
depths. The RMS errors for measurements range from 0.1 to 3 V m. 2.2. Data processing and interpretation Processing and interpretation of the obtained data have been done using the commercial (RES3DINV, 2000), software for geoelectrical 3D inversion. This program automatically determines a threedimensional (3D) resistivity model for the subsurface using the data obtained from a 3D electrical
Fig. 7. True resistivity map at depth 0.55 m.
150
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
imaging E-SCAN type of survey (Li and Oldenburg, 1992). Electrodes for such a survey are arranged in a rectangular grid. It should be first emphasized that full 3D surveys are not merely a series of 2D surveys, but a different approach has to be used. The inversion routine used by the RES3DINV program is based on the smoothness-constrained leastsquares method (deGroot et al., 1990, Sasaki, 1992). A new implementation of the least-squares method based on a quasi-Newton optimization technique (Loke and Barker, 1996) can also be used. The inversion
program divides the subsurface into a number of small rectangular prisms, and attempts to determine the resistivity values of the prisms so as to minimize the difference between the calculated and observed apparent resistivity values. Resistivity methods are used to prospect the archaeological features of some small parts of the huge city of Piramesses (Abdallatif et al., 2003). 2.2.1. The measured dipole–dipole cross sections The measured data are carried out along 15 profiles with (a) spacing 1 and 2 m. These profiles were
Fig. 8. True resistivity map at depth 0.98 m.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
located at 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14 and 15 m along the x-coordinate and the measurements were carried out along the y-coordinate. These section show variations of resistivity values especially at shallow depths as shown in Fig. 4. The important part of the study area are seen in the sections no. 1, 2, 3, 4 and 5 at a distance ranging from 5 to 7.5 m at the y-coordinate of high resistivity values up to 60 V m which corresponding to path connecting to the Al Ghouri mausoleum below the funeral chamber. The other sections
151
exhibit low resisitivity values at the most parts of these sections. 2.2.2. Three-dimensional resistivity slices The interpretation of dipole–dipole electrical data using RES3DINV program produced nine slices at different depths (Fig. 5). Their depths are 0–0.35, 0.35–0.75, 0.75–1.22, 1.22–1.75, 1.75–2.36, 2.36– 3.06, 3.06–3.87, 3.87–4.80 and 4.80–5.88 m, respectively. Slices no. 1, 2 and 3 show large variation in resistivity values, where as the western part has high
Fig. 9. True resistivity map at depth 1.48 m.
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resistivity values up to 60 V m and low resistivity values at different parts of the area down to 1 V m. Slices no. 7, 8 and 9 did not show variation in resistivity values for more depths through the study area. This means that at depths beyond 4 m archaeological objects do not occur. 2.2.3. True resistivity maps The results can be exported into xyz format for depths ranging from 0.17 to 5.34 m. This file is then reprocessed by using Oasis montaj (1999) software to
clear the anomalies at different depths. It is divided into nine files according to the calculated depths (0.17, 0.55, 0.98, 1.48, 2.05, 2.71, 3.47, 4.34, 5.34 m), each file containing x-coordinate, y-coordinate, and depth and resistivity columns. A base map is constructed using mapping and processing system of Oasis montaj, then the resistivity values for all files at different depths were grided using the same software of Oasis montaj. Finally each map contains a base and a gridded file to represent a true resistivity map at certain depth to illustrate the important anomalies
Fig. 10. True resistivity map at depth 2.05 m.
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
153
Fig. 11. True resistivity map at depth 2.71 m.
corresponding to the archaeological objects may be buried in the subsurface according to its resistivity values (Figs. 6–14).
3. Results and conclusion The surface layer of the study area is represented by a rubble layer composed of sand and fragments of limestone saturated with groundwater. This layer covers most of the area except the western part,
which consists of blocks of limestone manufactured as pools or plates. The interpretation of the dipole– dipole cross sections, 3D slices and true resistivity maps indicate that this surface layer extends to a depth ranging from 0.17 to 0.5 m (Fig. 6). Also, interpretation of the resistivity data shows that the subsurface section consists of different units, which have different values of resistivity at different depths. Based on the obtained results the study area is divided into four subsurface groups according to its resisitivity ranges.
154
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
Fig. 12. True resistivity map at depth 3.47 m.
The first group (A) is the important group which represented by high resistivity zone up to 60 V m, located at northwestern part. It represents 3 m width at the y-axis with 5 m at the x-axis that reach 2.71 m depth. The resisitivity values decrease with depth to reach of 30 V m, where the blocks of limestone saturated with groundwater and alter to marly limestone. This zone may be used as a road to the Al Ghouri mausoleum, which constructed below the funeral chamber where, this road may be made of limestone blocks of high resistivity values. The funeral
chamber does not contain any visible paths to the mausoleum; these proved that the first group of the results represents the path to Ghouri mausoleum. These are clear in Figs. 7–12. The second group (B) represents the central part of the area of moderate resistivity values, which consists of sand and blocks of limestone. This unit covers low resistivity zone. This zone was used for buried dead people and consists of space with some debris filled with groundwater. This group could be seen through slices no. 1, 2 and 3 of Figs. 5–8, which correspond to
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
155
Fig. 13. True resistivity map at depth 4.34 m.
graveyard area prepared to bury general people at shallow depth up to 1 m. The length of this group is about 16 m and its width is about 4 m. The third group (C) has high restivity values corresponding to some pools and plates constructed from pieces of limestone exposed at the surface. Also, these objects were constructed beside dug well and part of groundwater used from dug well through these objects as waterspout. This group represents the western and southwestern parts of the study area, and has shallow depths ranging from surface to 0.55 m as shown in Figs. 6 and 7.
The fourth group (D) has very low resistivity values. It corresponds to the dug well used to dump groundwater through waterspout at the surface and some building at high levels especially prayer hall and funeral chamber. This group is located at the southwestern part and has depths up to the end of the geolectrical slices as shown in Figs. 7–14. 3.1. Conclusions The conclusion of this study indicates that the subsurface section of the study area contains very
156
S. Awad Sultan / International Journal of Applied Earth Observation and Geoinformation 6 (2004) 143–156
Fig. 14. True resistivity map at depth 5.34 m.
important archeological objects buried at shallow depths. The author recommends that no injection for the subsurface with any reinforce concrete material for saving of the archeological objects during repair the buildings of Al Ghouri mausoleum.
References Abdallatif, T.F., Mousa, S.E., El Bassiony, A., 2003. Geophysical investigation for mapping the archaeological features at Qantir Shrqyia, Egypt. Archaeol. Prospect. 10, 27–42.
DeGroot-Hedlin, C., Constable, S., 1990. Occam’s inversion to generate smooth, two-dimensional models form magneto telluric data. Geophysics 55, 1613–1624. Li, Y., Oldenburg, D.W., 1992. Approximate inverse mappings in DC resistivity problems. Geophys. J. Int. 109, 343–362. Loke, M.H., Barker, R.D., 1996. Rapid least-squares inversion of apparent resistivity pseudosections by a quasi-Newton method. Geophys. Prospect. 44, 131–152. Oasis Montaj, 1999. Geosoft provides data processing and analysis (DPA) software and services for geological, geophysical, geochemical. UXO detection and environmental applications. Geosoft Inc., 1999. Sasaki, Y., 1992. Resolution of resistivity tomography inferred from numerical simulation. Geophys. Prospect. 40, 453–464.