Geomorphologic Domination on Urban Sprawl of Southern Riyadh, Saudi Arabia Using Differential Interferometric Synthetic Aperture Radar (DInSAR)

This study tests the southern part of the Riyadh City growth domination by the Early Quaternary-Holocene trans-tensional Central Arabian graben system reactivation and the subsequent dissolution-induced collapses and karstification. This study utilizes Synthetic Aperture Radar (SAR) and Differential Interferometric Synthetic Aperture Radar (DinSAR) to examine the morphology of arid landscape, south of Riyadh. Eight Single Look Complex (SLC) amplitude images are calibrated, filtered, georeferenced and orthorectified at a resolution of 20 meters, and compared with one another by producing 17 diachronic images of the pairs at different intervals (1996, 2003-2005, 2008). The diachronic SAR intensity imageries suggest a downthrown displacement reaching 600 m and eastward tilting at the bottoms of the grabens. Also, the structurally-controlled valleys are developing an eastward-running drainage system towards the oasis of Al-Kharj and capturing an older hydrologic system. Moreover, a 12-year period (1996-2008) of the SAR data was obtained to examine the average annual rate of southern Riyadh’s urban sprawl, which is estimated at approximately 390 metres/year over the 12 years and constrained by geomorphological features towards the deformed area. DInSAR imageries show the primary results obtained from the 26 May 2004 and 31 Jan. 2005 pair of images, merged with 30 m resolution DEM-SRTM data for the arid region south of Riyadh to eliminate the influence of topography. DInSAR is applied in this study for its ability to detect small displacements at the centimetre scale (1/2 wavelength). Although the DInSAR’s coherence and phase imageries suggest a fairly stable region since the last tectonic and subsequent How to cite this paper: Daoudi, M., Hachemi, K. and Bamousa, A.O. (2021) Geomorphologic Domination on Urban Sprawl of Southern Riyadh, Saudi Arabia Using Differential Interferometric Synthetic Aperture Radar (DInSAR). International Journal of Geosciences, 12, 541-559. https://doi.org/10.4236/ijg.2021.126030 Received: May 3, 2021 Accepted: June 14, 2021 Published: June 17, 2021 Copyright © 2021 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
This study tests the ability of recent techniques and methodology to create shortperiod monitoring and analyses via available SAR and DInSAR images. It utilises these data to summarise the natural and artificial evolution and changes that had occurred in different areas such as those during a period of almost 12 years. The radar data are provided with colour composition (diachronic) images that represent a 12-year period for monitoring potential hazardous features witnessing several constructions that have multiplied on the periphery of and outside the city of Riyadh. This study tests the ability of the SAR and DInSAR imageries and applies them on arid region for the reported karstification (e.g. [1] and recent activities of the Sahba fault and valley, to the east of Al-Kharj [2]. Very little detailed work was carried out on the study area using the radar, for example, shuttle radar images have been used to detect several geological features in the Arabian Peninsula [3], aeolian sand covers [4] and faults and landslides under the Quaternary sands of the Ad-Dahna Desert [2]. In the field of cartography, [5] showed the usefulness of the interpretation of SAR imagery from the Radarsat-l satellite in mapping applications in Riyadh. Another regional study was conducted by [6] on the integration of multispectral and radar images for geological, geomorphic, and structural study in the Al Qunfudhah region. An additional study by [7] employed optical and radar images for the identification and monitoring of active/inactive landforms in the driest desert of Saudi Arabia. Radar images have the advantage of being taken in all weather conditions, day, and night, and regardless of cloud cover, unlike platforms that operate within the visible range. The use of satellite radar imagery allows for regular and precise spatial and temporal monitoring of surfaces. The response of the radar signal is particularly sensitive to surface topography, roughness, and moisture, making it possible to determine any natural or artificial changes that occur between two image acquisitions. Synthetic-aperture radar (SAR) is a form of radar that is used to create two-or three-dimensional landscape images. It provides large image coverage (100 km × 100 km) for both generalised and global studies of regions. SAR sensors measure the two components of the backscattered signal, amplitude and phase, where phase (waves) depends on geometrical characteristics, such as distance information between the radar and the target. Phase cor-  [18]. Differential interferometric synthetic-aperture radar (DInSAR) uses two or more SAR satellite images to generate maps of surface deformation or digital elevation, using differences in the phase of the waves returning to the satellite (e.g. [19]). This makes it possible to measure vertical ground displacements up to 28 mm in the case of the C-band, when each fringe is multiplied by 28 mm.
DInSAR can yield significant results between two different dates in the same area; one can measure the extensive, precise, and dense ground changes that occur between these two periods.
The main aim of this study is to test the hypothesis of urban sprawl domination by active trans-tensional tectonism and subsequent karstification during the Quaternary Era, in southern Riyadh. The ultimate objective of this work is to alert the community and preserve the area over the south of Riyadh and east of Al-Kharj, in Central Saudi Arabia, for future water and food security, for economic aspects, and as a national geopark for scientific research and tourism.

Study Area
Desert, semi-arid, and degraded land areas are considered arid regions, despite the presence of irrigated vegetation and oasis areas [20]. The Central Arabia, south of Riyadh, between latitudes 24˚ -25˚N and longitudes 46˚ -47˚E has similar conditions, in that it is occupied by an oasis, known as the Al-Kharj oasis, and wadi of Nisah-Sahaba grabens, surrounded and influenced by the Ad-Dahna desert [2]. The abundant groundwater and seasonal hydrological water enhanced the feasibility of circular irrigated farms, accommodated by the depressions and grabens, to the west of the Al-Kharj oasis ( Figure 1)  the Wadi Nisah-Sahaba grabens into the Al-Kharj oasis. The degree of material removal from the base of the slopes by fluvial and aeolian processes is strongly influences the landscape weathering at different temporal and spatial scales [21].
The landscape morphology of this arid region has evolved through a long period of geological process, geomorphological evolution, and human processes,

Data and Methods
To fulfil the abovementioned objectives, the available radar data are acquired; two radar wave components of ERS-1/2 and ENVISAT images are found between 1996 and 2008 (Table 1). Eight amplitude images are produced, multi-dated, calibrated, filtered, georeferenced and orthorectified at a resolution of 20 meters.  The region south of Riyadh using SAR images underwent the application of the derivative of the differential interferometry (DInSAR) technique, the coherence image, which distinguishes stable areas that have retained the phase from non-stable areas that disturb the phase. DEM-SRTM images are used for the arid region south of Riyadh with a resolution of 30 m to eliminate the influence of topography. The choice of the two dates used in the coherence image is based on feasibility conditions; data are considered by temporal baseline interval (Btemp) from one day to 12 years, adopting a spatial baseline of <1000 m. This study used the GAMMA software, under the Linux and Windows (Cygwin) operating systems, for the realisation of the differential interferograms. The GAMMA software developed by [25] supports the entire processing chain from SAR raw data to end products such as DEM (Digital Elevation Model), displacement maps and land use maps. All the pairs are formed from these data, and the calculated geometric characteristics of the images for each pair are processed ( Table  2). The DInSAR was performed using the Centre national d'études spatiales (CNES) method, using two passes and an external DEM. The carried-out treatments of differential interferograms show fringes corresponding to the phase difference. Coherence images demonstrate the reliability of the interferograms producing (0 = minimum coherence; 1 = maximum coherence). Coregistered amplitude images correspond to the realised differential interferograms and unwinding of the realised phase difference. These images are compared with one another by making colour composites at different intervals ranging from one day (24 hours) to 11 years and seven months (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008); the processing steps perform and extract eight calibrated, georeferenced, orthorectified, and filtered amplitude  Figure 3). 17 colour composition pairs are produced for different satellite intervals (ERS and ENVISAT). These intensity (colour composition) image pairs of the study area are shown in Figure 4. The colour of each pixel of the resulting image is processed by the equation: in which a(p) and b(p) represent values depending on the signal strength of the pixel for the oldest and most recent component respectively; thus, pixel appears in Red [R]. Table 3 summarises the results of colour composite enhancements, while Table 4 shows the legend of the low and high signal and the reflected colour. For a pixel appearing in black and in white, signal strength is equal to: a(p) = 0, and b(p) = 1; hence c(p) = [R] (2)  Table 4. The following legend shows the key to interpreting colour composition images in Figure 4 and Figure 6.

Results
This section introduces the coming amplitude, intensity, coherence, and interferometric phase imageries results which distinguished the following landscapes: mountainous areas, depressions and grabens, sand dune areas visible on Landsat image ( Figure 5), and areas of human activity (urbanisation, roads, and agricultural fields). The radar data have also given rise to several different geomorphological phenomena, such as river captivity and the fragmentation of the surface topography of the plateaus by the grabens and depressions.

Amplitude and Intensity Images
The amplitude illustrates the specificities of the different landscapes of this region, such as the grabens and the Tuwaiq mountain range. It also shows the overlying urban extension of the city of Riyadh towards the deformed areas ( Figure 6).  This extension is characterised by four directions from the southeast to the southwest, estimated at different rates, related to the encountered complexity of the terrain (Table 5). City limits difference shown in image intensity between 13

Differential Interferometry
The produced coherence image shows the reliability of the performed differential interferogram (Figure 8). In the 280-day period noted above, the southern If (k) is equal to (1), the lowest altitude value is equal to (2π). Therefore, the interval of the provided range is equal to 50 m/colour, ranging from 400 m to 1000 m according to the topographic map ( Figure 9). Figure 10 shows the primary results for the amplitude differential interferometry SAR obtained from the pair of images on 26 May 2004 and 31 Jan. 2005.

Diachronic Image Interpretation
The

Discussion
Utility, digital processing, visualisation, and interpretation of radar data (ENVISAT, ERS 1-2) at different dates and the application of differential interference methods, such as interferometric SAR (InSAR), DInSAR, small baseline subset synthetic-aperture radar interferometry (SBAS-InSAR), and pulse-doppler radar (PS), were applied worldwide. Synthetic-aperture radar (SAR) wavelengths and polarisations provide the best results for detecting, identifying, and mapping exposed and buried channels under the sand by detecting reflectance contrast differences between the bed of buried valleys or rivers and the surrounding environment. In arid and semi-arid areas, the amplitude image with a DEM has shown effectiveness in determining soil surface moisture (e.g. [9]). They have their own applications in geological and structural mapping (e.g. [10] [11] The Sahba fault cuts through the biggest inland oil field (known as the Gawar oil field) and the Quaternary sand dunes, reaching the Arabian Gulf and connecting with the Zagros Mountain thrust belt. Also, with other regional Wadi Al Batin and Az-Zulfi faults forming a regional feature within Arabia, the East Arabian Block holds most of the oil and gas fields in the world (e.g. [2] [22]. Therefore, this study is conducted based on three factors. Firstly, there is the importance for the people of the oasis, built thousands of years ago for its mild weather, good resources of water, and agriculture, which are essential elements for living humans and animals. Secondly, the reported karstification, fault activities and the extensional geomorphology might have the potential for hazards, especially if triggered by artificial activities and expansion of the nearby cities. Finally, the study area for the surrounding oil and gas fields has its place in the economy. Moreover, this study also investigates whether a reactivation of the faults and grabens by oil and groundwater extraction in the monitored 12 years period is present.

Conclusion
This study is a regional and remote sensing investigation of the morphology of an arid region. It is possible to clearly distinguish the different aspects that characterise the area. Multi-temporal analysis, conducted using amplitude images, has shown the possibility of mapping surface changes at different dates. It also shows the ability to determine and locate faults, fractures, and other geological features. It makes it possible to understand the evolution of drainage networks over different periods. These radar images address the major issue of urban sprawl, which must be reviewed and planned in a preventive manner. This research can serve as a tool for city planners and decision-makers to prepare future projects for the benefit of the environment and society. Finally, this study contributes to the development of methodologies in similar conditions, including spatial and temporal identification of areas potentially exposed to natural ha-International Journal of Geosciences zards. This study recommends preserving the region of Wadi Nisah as a national geopark by the Ministry of Environment, Water and Agriculture for several reasons. In this way, all municipalities would take this area out of plans for making new residential areas to expand the two cities of Riyadh and Al-Kharj. The study area has the potential for groundwater, oil, and gas resources. The second potential is the faults' and grabens' reactivations. The third potential is that, as an oasis that has been built thousands of years ago, it can be preserved for long-standing food supply and therefore food safety. This study also recommends sustaining the groundwater for water safety by changing the type and style of irrigated farms to another style that consumes less groundwater.