Investigation of subsidence of different parts of Marvdasht plain using ENVISATASAR radar images with C-wavelength of South Zagros region
Subject Areas : Journal of Radar and Optical Remote Sensing and GIS
1 - Master of Remote Sensing and GIS, Organization of Natural Resources and Agriculture Engineering System, Iran
Keywords: Groundwater, Geology, Subsidence, plain, ASAR images,
Abstract :
According to UNESCO, subsidence is the collapse or subsidence of the earth's surface that occurs on a large scale for a variety of reasons.Land subsidence is the gradual subsidence or sudden subsidence of the earth's surface. Land subsidence due to the movement of materials underground is often caused by the removal of water, oil, natural gas or mineral resources from the ground by pumping, breaking parts or mining activities. As a result, deep cracks are created in the ground, well pipes are tilted, buildings are destroyed or cracked, and part of the well pipes are pushed out of the ground.In this article, using ENVISAT ASAR radar images, C band is related to the years 2006-2009 using ENVI5.3.1 software, SARSCAPE plugin. After performing PHASE TO DISPLACEMENT CONVERSION AND GEOCODING, we obtained the subsidence map. The subsidence obtained from the maps was between -18 to +12 related to agricultural plains, river banks, mountain falls and deposits due to rainfall and soil dissolution due to geological type. In the plains, subsidence has probably occurred due to the drop in groundwater. Consecutive droughts and uncontrolled groundwater abstraction and lack of management in abstraction in the future will be witnessed by severe crises in various regions
Investigation of subsidence of different parts of Marvdasht plain using ENVISATASAR radar images with C-wavelength of South Zagros region
According to UNESCO, subsidence is the collapse or subsidence of the earth's surface that occurs on a large scale for a variety of reasons. It is commonly referred to as the vertical downward movement of the earth's surface that can be accompanied by a slight horizontal vector. This definition does not include phenomena such as landslides because their motion has a significant horizontal vector, as well as subsidence in hand soils, which have a different mechanism.
Land subsidence is the gradual subsidence or sudden subsidence of the earth's surface. Land subsidence due to the movement of materials underground is often caused by the removal of water, oil, natural gas or mineral resources from the ground by pumping, breaking parts or mining activities. It is good to know that subsidence is more likely to occur due to uncontrolled abstraction of groundwater. Due to this action and the outflow of water from the pores of the rocks, it is possible that the underground material becomes denser and with the increase of water withdrawal, the amount of this density also increases. As a result, deep cracks are created in the ground, well pipes are tilted, buildings are destroyed or cracked, and part of the well pipes are pushed out of the ground.
In this article, using ENVISAT ASAR radar images, C band is related to the years 2006-2009 using ENVI5.3.1 software, SARSCAPE plugin. After interferometry and ADAPT filters, GOLDESTON was used according to the type of area in terms of plains and mountains. After performing PHASE TO DISPLACEMENT CONVERSION AND GEOCODING, we obtained the subsidence map. The subsidence obtained from the maps was between -18 to +12 related to agricultural plains, river banks, mountain falls and deposits due to rainfall and soil dissolution due to geological type. In the plains, subsidence has probably occurred due to the drop in groundwater. Consecutive droughts and uncontrolled groundwater abstraction and lack of management in abstraction in the future will be witnessed by severe crises in various regions.
Keywords: subsidence, plain, ASAR images, groundwater, geology, wavelength
Introduction:
Land subsidence is one of the natural hazards that often occurs vertically and it is not noticeable in a short time. This phenomenon is generally localized and its mechanism depends on physical and natural processes. Land subsidence occurs under a number of conditions, including subsidence due to landslides, subsidence due to overuse of groundwater, subsidence due to the construction of large dams, and subsidence due to tectonics of salt domes. Subsidence can also be caused by natural disasters such as earthquakes, soil compaction, erosion, pit formation, and the addition of water to fine sediments. Subsidence can occur in very large areas, such as entire states or provinces, or in very small areas, such as corners of your yard.
If this phenomenon occurs in areas with infrastructure such as refineries, power plants, power lines, railways, airports, bridges, etc., we will see unfortunate accidents in these areas. If the volume of underground reservoirs decreases sharply, the soil layers will break and water will no longer be able to settle to the lower layers of the earth, as a result of which the water reservoirs will gradually drain and the aquifers may be destroyed forever, or the groundwater infiltration routes are closed and as a result, the aqueducts gradually dry up, and therefore the agricultural sector and etc., face serious problems.
Causes of subsidence: There are several factors that cause this phenomenon: Such as dissolution, melting of ice and compaction of deposits, slow movement of land and lava outflow or human operations such as mining or extraction of groundwater and mineral extraction, collapse of underground structures such as tunnels or the creation of cavities due to the dissolution of uncontrolled extraction of groundwater, oil and gas resources. The results of the study of geotechnical wells showed that in areas where the soil texture is fine-grained, it is related to the amount of subsidence, and in areas where silty fine grains are the alluvium of the region, it easily reacts to the stress of land subsidence. [1]
The main reason for subsidence can be the decrease of groundwater level and density of soil layers. Because no mining and volcanic activities have been carried out in this area. Also, between 2014 and 2016, no earthquake was recorded in this area. But what is obvious is the dependence of this region on groundwater and uncontrolled abstraction in recent years, which has led to the expansion of subsidence in the southern region of Tehran. High speed subsidence that will cause possible damages such as: increased earthquake risk, destruction of bridges and railway lines, etc. Therefore, it is necessary to apply strict laws regarding the control of well drilling and subsidence monitoring of the southern part of the Tehran-Karaj plain. [5]
Damage caused by subsidence
1. Uneven change in the height and slope of rivers and waterways and water transmission structures
2. Fracture or protrusion of well wall pipes as a result of compression stresses due to aquifer compaction
3. Progress of waves in coastal lowland areas
4. Irreversible reduction of all or part of the groundwater reservoir as a result of loss or reduction of useful porosity.
5. Reduction of surface permeability and subsequent expansion of desert areas and changes in topography and development of floodplains.
Among the effective factors in causing subsidence, it seems that excessive and unauthorized extraction of groundwater resources, sediment layer thickness and sediment engineering characteristics are the main factors causing subsidence in most plains of Iran. Subsidence in Iran is more critical than in other countries of the world. The intensity of subsidence in some plains of Iran, including Tehran, is at least 90 times higher than the most critical conditions in the developed countries of the world.
In Iran, the first land subsidence in Rafsanjan plain in 1346 along with the phenomenon of piping in agricultural wells has been reported [2]. History of subsidence in the world:
This phenomenon has been reported in different parts of the world, such as land subsidence due to water pumping in the last 35 years in Bangkok, Thailand, the maximum annual subsidence of 120 mm was reported in the early 1980s. The city of Venice, Italy, also had a subsidence of about 15 cm between 1930 and 1973.
Istanbul, especially in the 1960s, has been under industrialization and population growth, which has led to rapid urbanization and severe land use change. We have identified several sites along the earthen and coastal area of Istanbul that are sinking vertically at rates ranging from 5 mm per year to 15 mm per year.
in this study ,
PS-InSARtime series analysis was performed using 291 C-band SAR images to describe citizenship phenomena by combining InSAR sensor / multi-path datasets and providing insights into potential hazards arising from local soil conditions and human activities. . Using the PS-InSAR technique, sufficiently coherent time pixels were obtained at six different sites in Istanbul.
Accurate assessment of the impact of groundwater exploitation on land subsidence can provide scientific support for decision makers. Using the characteristics of land subsidence in Tongzhou, China, this paper develops a model of groundwater subsidence and subsequently classifies an early subsidence warning zone based on land subsidence rates. [6] The results show that land subsidence occurred in the whole Tongzhou area. Landslides were most severe in western Liuzhuang, Tanzhou and Taihu.
The maximum annual subsidence rate in the current groundwater extraction conditions reached 120 mm / mm 1 and the initial warning level for land subsidence reached its highest level. If groundwater pumping is reduced by 50% in the second and fourth aquifers and by 60% in the third aquifers, the level of early subsidence warning will be greatly reduced and will meet the requirements of land subsidence control [7]. In recent years, the incidence of geological fractures in the Beijing Plain has increased. Geological disaster accelerates soil erosion and negatively affects infrastructure construction in the region. [9]
Ground fault is one of the main geological hazards in China. By 2015, 5002 landslides had been discovered in more than 1,500 locations in 22 provinces. These cracks caused a lot of economic damage. Based on a series of geological researches, including in mapping, trenching, excavation and monitoring, the laws of spatial distribution and development of landfills are summarized and the kinetic characteristics of landfills are shown. These rifts show the following five regular patterns: clustering along fault zones, distribution along geomorphic boundaries, appearing at the edge of subsidence zones, scattering in the folding zone, and concentrating in large and medium-sized cities. The kinematic characteristics of ground slits can be divided into four types: tensile type, shear tensile type, tensile shear type and shear type. [8].
Materials and Methods
Marvdasht city is one of the cities of Fars province in Iran. The center of this city is Marvdasht. This city is located 40 km north of Shiraz and its climate is mountainous and temperate. Marvdasht city is the center of Marvdasht city. The population of this city according to the census of 2016 is equal to 148,858 people. The geological configuration and structure of each region has a special effect on the development of that region, and this effect, in addition to the establishment of settlements, includes related economic issues. The morphological and tectonic features of each geographical location, taking into account its climatic potential, have drawn the main lines of the site's capabilities. And by studying tectonics, we can point to the strong link between the structure of the earth and its geomorphological features to the type of livelihood and economic activities of humans.
Figure 1: Map of the study site for the production of Marvdasht plain DEM
The table of project steps is as follows.
Figure 2: Steps to prepare a DEM map of C-band radar images for 2006-2007
In this study, we obtained radar images from the European Space Agency website. Using ASAR sensor images, the required information was collected from the study area. The ASAR sensor is one of the ENVISAT satellite sensors. The wavelength of this sensor is in the C band range and is equal to 5.5 cm with a frequency of 5.331 GHz, which can record changes in the earth's surface up to an accuracy of less than a millimeter. In the radar interferometry method, by processing two radar images at the desired time, the interference is generated. In these maps, the regions that have been displaced are separated from the stable regions by creating a band of red color spectrum.
Before preparing the Interfrogram of the images, the most important thing to do is to determine the Base Line between them to determine whether it is possible to perform the mentioned processing on these images or not? In the first stage, obtaining SLC radar images is conditional on making radar corrections before doing the work. Then determine the Base Line in the amount of 7.5 meters and less than this is the best and normal. In this study, in order to analyze the ASAR sensor data and determine the amount of displacement, we used interferometry and time series analysis of interferograms. It is necessary to mention brief explanations about it.
Global Monitoring | Wave Mode | Altemating/Cross Polarization | Wide Swath Mode | Image Mode | Imaging mode | ||
VV or HH | VV or HH | HH/HV or VV/HH VV/VH or | VV or HH | VV or HH | Polarization | ||
950 m x 980 m | 28 m x 30 m | 29 m x 30 m | 150 m x 150 m | 28 m x 28 m | Spatial resolution | ||
>=400 km | 5km | Up to 100 km | 400 km | Up to 100 km | Extraction width | ||
5.331 GHz (C-band) | Frequency | ||||||
Table 1: Information of C-band radar images for 2006-2007 for use and production of subsidence
The Radar menu in SARscape software works with the power section and has nothing to do with phase. The Radar menu is not capable of working with the phase section and generating the Interferogram, because we need PHAS for all our calculations. So we use the SARscape menu. The steps of working with radar images and preparing a land subsidence map are briefly described.
1. IMPORT IMAG: After taking the images, the space agency data format was first prepared and converted to SLC format, which can be read by SARSCAPE software.
2. Base line estimation: To see how far apart the two images are and whether the distances between them allow us to build an interfrogram or not, we estimate the base line. And then we make the interfrogram. In this part of the ASAR image, the smaller the base line, the better the result.
3. Generate Interferogram and identify all outputs and their properties
The phase difference between two SAR images is obtained by multiplying the first image by the conjugate of the second image:
The image resulting from this mixsed multiplication is called an interferogram. The amplitude of the interferogram is equal to the product of the amplitude of the two original images, and the phase of the interrogram is equal to the phase difference between the two images; Therefore, interferogram pixels also have mixed values.
Figure 3: Phase difference between two images in interferogram production
1- Power image: The image from which the phase is separated and only gives us the Power output.
2- Int: It is the same interfrogram, leading to the interfrogram from which the topographic effect has not been removed
3- dint: A file created in dint format from which the topographic effect has been removed, and if we want to calculate the amount of ground and fringes, we will use this file. In interfrogram outputs, three states may occur: seen in the interfrogram, these phenomena are:
1-RAMP phenomenon: This is a tape phenomenon, and occurs for two reasons: the topographic effect and the sensor vibration during imaging.
2-JAMP phenomenon: means phase jump. If there is a phase difference of more than 10π between two pixels, the JAMP phenomenon occurs
3-BAMP phenomenon: is the dome of the interfrogram. If the interfrogram becomes dome, it indicates a defect in the original data.
These three phenomena are not good phenomena. But the first two phenomena can be largely corrected with the help of filters.
Sint Image: This file is a Synthetic Interferogram, meaning a virtual interfrogram made from a digital model. Srdem image: This is a digital model file created on the inclined arm.
4. Types of filters and their function in radar images:
There are three types of filters so that we can produce the degree of coherence and also use filters to calculate the displacement of the fringes, each of these filters has advantages and disadvantages that we will explain:
1. Adaptive filter: When we use this filter when we do not have a lot of inconsistency, the Adaptive filter does not touch the phases at all and keeps the accuracy, and also has a great effect on the altitude accuracy in the production stage of the digital terrain model.
2. Goldstein filter: This filter strongly manipulates the phases in order to produce better fringes. Performs interpolation in a way that brings all INCOHERENCES closer together. That is, it coaxes the waves as much as it can, so it has to touch the phases and change them, so this filter reduces the accuracy of the work somewhat. We have to use this filter when our incoherency status is unfavorable.
3. Boxcar filter: This filter also does not touch the phases, so it is classified between Adaptive and Goldstein.
In this step, the amount of Incoherency is also calculated, which means that the amount of Incoherency varies between 0-1 per pixel. The closer it is to zero, the more inconsistent the contents of the two pixels are in terms of phase. (Meaning that the waves are not coherent with each other on that pixel) and the closer they are to one, the more coherent the waves are. When coherent waves are returned to the satellite from all pixels, then it can give us very good fringes, and then it can calculate the amount of displacement and the digital elevation model very accurately. At this stage we must use a filter that does not touch the phases.
5. Correction and opening of phases through Phase unwrapping
In this step, it calculates the amount of displacement for all pixels, that is, it says where a few cm went up and where a few cm went down. Must convert all height changes to a coefficient of π. What this section does is break down the entire topography and bring it between -π to π. This is called Phase unwrapping.
6. Process review of topographic effect and final modification of phases and satellite orbit through Refinement And Re-flattening
Refinement: means to improve again (improvement). At this stage, we want to once again check all the work that has happened from the beginning until now and make sure that there are no flaws in the work.
Checks all phases once more, does two more things. One is to check the orbit once again. That is, it checks the distances of all the pixels on the earth from the original orbit (the orbit in which the satellite rotates) again, There is no place where something went wrong and the actual amount was allocated.
7. PHASE TO DISPLACEMENT CONVERSION AND GEOCODING stage: By doing this stage, finalizing the work of the plain subsidence map is obtained. The obtained map shows the subsidence of different points.
Figure 4: Marvdasht subsidence map ASAR band C images of 2006-2009 areas shown in red
Table 2: Color range of Marvdasht subsidence map Figure 5: Histogram of Marvdasht plain subsidence map
subsidence map subsidence map
Figure 6: Transverse profile images of subsidence areas of Marvdasht plain in different areas
Figure 7: Images of subsidence and the creation of a gap in the east of the Marvdasht plain and next to the historical monuments of Naghsh-e Rostam with Google Earth images
Discussion and results:
Based on the results of radar interferometry, ENVISAT ASAR band C images from 2006-2009 show plain subsidence in different areas. These subsidence are in agricultural and residential plains, next to seasonal streams, as well as mountainous areas upstream of the catchment area of Dorodzan Dam. Most subsidence in mountainous areas indicates the fall of mountains, probably due to heavy seasonal rainfall at that time.
But subsidence in the plains has occurred due to recent droughts and groundwater abstraction without water management. According to the studies of Fars Geological and Mineral Exploration Organization, since the drought, subsidence process in the plains of Fars province and Marvdasht is occurring slowly in agricultural plains, which in some plains has appeared as cracks and depressions.
According to the studies, field visits and general analysis of the obtained data, one of the most important factors of subsidence of Marvdasht plain is due to the increase of permitted and unauthorized wells, uncontrolled abstraction of groundwater and decrease in rainfall. Subsidence damage due to inhomogeneous subsidence of the surface of earth as a result of falling groundwater levels in the foothills, which have changes in thickness and facies from larger sediments to finer grains are more visible. [3]
The results obtained from the basic subsidence risk raster model (LSRM) of Seydan-Farooq plain show 2 areas with very high subsidence risk 5.57% of the area of Seydan-Farooq plain and Region 2 with a high risk of subsidence is 19.76% of the area of Seydan-Farooq plain. Due to the heterogeneity of the aquifer, conditions are created for subsidence cracks along the weakness levels and cracks are created. Considering the outcrop of karst and calcareous formations near the villages of Kuh-e Rahmat and Kuh-e Siah and the calcareous bedrock of this region, it can be expected that the formation of dissolved "sinkholes" in the alluvial aquifer bedrock is another effective factor in land subsidence. [4]
The results of radar images show that the highest subsidence in the northern regions of Marvdasht plain is related to the fall of mountains and deposits in the amount of 18 and the lowest in the plains is 3.5 cm. General management in groundwater abstraction and optimal use for agricultural, industrial and drinking purposes.
Acknowledgments:
Greetings and best regards to Dr. Al-Modarressi, the honorable professor who patiently guided and helped me.
Persian reference:
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