عنوان مقاله [English]
نویسندگان [English]چکیده [English]
One of common dangers is subsidence phenomenon at world.Subsidence phenomenon occurrence is very common at rural and city regions because of underground waters irregular extraction. Severe subsidence rate can destroy irrigation systems and agricultural soils (by lowering their porosity) and change region hydrology, causes floods and damages buildings, streets, bridges ,highways ,railroads lines, soil dams, refineries, waste water ,gas ,water lines (Abbas Salmanpooor, industry development journal). According to united state geology institute, Subsidence phenomenon is including falling down or collapsing down toward of earth surface that is vertical movement from few millimeters to few meters and horizontal movement is very low and little(USGS,2011)
If we do not manage this phenomenon correctly, it causes irreparable damages for regions affected by this phenomenon. Detection subsidence regions and measuring its rate have very important role at control management of this phenomenon. Different techniques such as radar interferometer, GPS, precision balancing are used for recognizing and detecting subsidence. Nowadays, radar interferometer technique is used as a common and popular technique for measuring crust surface deformation. Properties such as expanded covering and good resolution of radar images and acceptable accuracy and precision have turned this technique into useful tool for studying different geology phenomenon's such as earthquake, subsidence, slips. Radar interferometer measures earth surface movement differential with height precision (centimeters) and place resolution few thousand kilometers (amikhpi, 1388)
Our purpose at this research is to model subsidence at neyshabour plain by using results from radar interferometer and to examine the relationship between underground water lowering and earth subsidence and finally gaps at parts of neyshabour plain.
2. Materials and methods:
This research method is measuring by using libratory method. At the first, libratory method is used for image and data processing then by resulted findings from libratory stage, field and recorded data are collected, at next stage we measure accuracy of the results of libratory processing by using field and recorded data, at the end , we model the results of libratory processing.
We use time series of Europe satellite data ENVISATVat C band at libratory stage.subsidence regions are detected by computer processing through special software SARSCAPE at ENVI platform and using interferometer. Then by using field and measuring operations and using GPS tool, we recognize resulting damages from subsidence phenomenon and defined regions at libratory stage at earth surface are recognized .the finding of this stage are very useful for determining results accuracy at first stage.Also at this research, findings of radar interferometer method for subsidence rate and range are compared with resulting figures from level changes of underground water by using piezometery well and at last stage, we model resulted findings from radar interferometer method for subsidence rate and range.
In the following table has mentioned the used ASAR images in this survey with time and place basis line intervals.
Table 1: The used ASAR images in neyshabour withcomplete details
Base line Temporal line data Image mod
188/958 419 2003 ASA_IMS
50/933 144 2004 ASA_IMS
59/229 875 2005 ASA_IMS
27/093 244 2007 ASA_IMS
261/797 385 2008 ASA_IMS
292/647 420 2009 ASA_IMS
3. The studied areas
Neyshabour is one the most important plains of Razavi Khorasan because of agricultural
Productivity and population concentration. Neyshabour is located in 17' 58Â° longitude to east 20' 59Â° and 40' 35Â° latitude to north 29' 34Â° and in area 405800 â 72800 and 3949500 â 405800 meters (according to UTM ) .This plain is IRAN , s central salt desert sub basin .
Also it was mentioned that underwater resource situation in neyshabour are 2589 deep and shallow wells (5/07 piezometery wells), 914 the opening of spring and 930 subterranean canal that there are in studied area .In total, nearly underground water 1174/82 million (m3) was exploited. The most achieved water from wells and springs is used in irrigation of agricultural fields.
4. Data analysis:
In this survey,we determined radar data, subsidence rate and range by interferometer methodinneyshabour plain. In order to plan space pattern maps and determine subsidence rate and range for interferometer operation, weused two ASAR images in different time periods with DEMSRTM model (by 90 meter accuracy). In thefollowing, we used change data of pizometery well level to model achieved data of field level and piezometery well level changes. Then, we should correct achieved data from interferometer method, by GPS station data of IRAN permanent geodynamic network (IPGN) situated in neyshabour plain. Because of data normality confirmation by SHAPIRO-WICK tests, by TI GEFTI CHON test, significant level (p>%5) was achieved. Then, there are no significant difference between read numbers and achieved numbers of differential method and interferometery method .Then achieved data accuracy of interferometer method was confirmed.
In this survey,we used step by step regression method for achieving the model between field subsidence and piezometery well level changes.We used field subsidence results by radar interferometer and piezometery well level changes in 2003-2009 years.
By attention to achieved results, we can write standard regression equation.
Field subsidence (meter) = - 0/ 272 * underground water exploitation (meter)
We compare the achieved model by2009-2010 model and it was obtained %8 error .This error ignore .we can conclude that anticipated model is relatively suitable.
According to mentioned discussions, it was showed that radar interferometer method in this survey was introduced suitable capacity of it,s capability in determination of subsidence rateand range in studied area level. Environment drought was moderated phase change effect resulting from atmosphere compounds, especially humidity and was provided appropriate accuracy from phase difference resulting from level displacement. Also, vegetation lack minimized radar images non uniformity and provided possibility for measuring phase changes at annual time ranges for BAND data. This finding, by emphasizing resulting efficiency because of using this method, showed that there is significant relationship between underground water removing and subsidence. Also, it has worthy to mention that movement rate has estimated 7 centimeters 2003-sep-27 until 2004-nov-20 ,4 centimeters 2004-oct-16 until 2005-jul-23 ,18 centimeters2005-jun-18 until 2007-nov-10,4/5 centimeters 2007-nov-10 until 2008-jul-12,7 centimeters 2008-jul-12 until 2009-aug-01 ,7 centimeters 2009-aug-01 until 2010-sep-25 at neyshabour station by using ASAR data ,also the relation between subsidence and underground water removing shows that if piezometery well lowering is 3 centimeters ,subsidence is./81 centimeters.