Expert of the Week   for  06 - 12 Apr 2015

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Fatma Canaslan Comut

Director Planning and Mitigation

Disaster and Emergency Directorate of Denizli (AFAD) Expertise:  My area of expertise is the preparing of disaster and emergency plans for quick and effective interventions during and after disaster. Furthermore, the application of methodologies to detect high-risk areas for landslides or floods using advanced remote sensing techniques.

Graduate of Geomatics Engineering Department of Selcuk University, Mrs. Canaslan Çomut worked as a lecturer at Selcuk University Department of Geomatics and received her M.Sc Degree in 2010. She has specialized in geodesy, remote sensing and GIS applications applied to disaster risk reduction. She started her Ph.D. work in 2010 in the Geodesy Department of The Institute of Natural and Applied Sciences at Selcuk University. Now she is working at the Disaster and Emergency Directorate of Denizli (AFAD) in Turkey, where since 2012 she has been the director of the Planning and Mitigation Department. In addition, Mrs. Canaslan Çomut has worked as a project manager for several GIS projects on disaster and emergency planning. Her previous and current experience has also included working with applications of differential interferometry and permanent scatterer inteferometry on various field characteristics such as urban and vegetated areas since 2007. Then she is also working on the monitoring of land subsidence and landslides areas for urban risk management using effective remote sensing techniques. She is currently setting up a new project related to flood response in Metropol. This project aims at improving her organization's current planning and response capacity. Lastly, she is also preparing her final Phd thesis as a Phd candidate, hoping to finish by the end of this year.

Monitoring of land subsidence and landslide areas on different characteristic fields for urban risk management by satellite-based geodetic techniques

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QQuestion by Mr Milan Lazecky

Dear Fatma,
first, let me congratulate you for your "expert of the week" opportunity!
While reading the "Sendai Framework for DRR 2015-2030" document, I realized the current UN interest in application of satellite remote sensing for disaster risk mitigation. Can you please write me some real-life example of how this InSAR helped your area, why it can be so unique for risk prevention?
Thank you!

Mr Milan Lazecky postdoc | VSB-TUO
Czech Republic

APosted on 10 Apr 2015

Dear Dr Lazecky,

I am very fortunate to have the opportunity to be part of United Nations as an expert of the week. If I come to your question, let me say many thanks for a very fundamental question in need of answering and for the very important and wide-reaching question.

You are absolutely right that The World Conference in Sendai and the other international agendas in 2015 (especially climate change and sustainable development goals) included satellite remote sensing for disaster mitigation. For understanding disaster risk, policies and practices for disaster risk management should be based on an understanding of disaster risk in all its dimensions of vulnerability, capacity, exposure of persons and assets, hazard characteristics and the environment. To achieve this over Global and regional levels, it is important to promote and enhance, through international cooperation, including technology transfer, geospatial and space – based technologies and related services. 

In terms of implementation, there are some good examples where the people who are exposed to disaster risks are often in the best place to manage and reduce their impact. 

There are also examples where we expect disaster such landslide, land subsidence before occurrence by means of Interferometric Synthetic Aperture Radar (InSAR) Technique. To explain the simplest form, thus the field under probable risk is monitored using SAR satellites with different SAR images which acquire different time interval. The disaster area like landslide which is known to be active can be examined in detail by remote sensing and the results can be compared with the results of the previous studies. In addition, after the remote sensing work, detailed field observations can be done to get the relationship between structural elements (faults, cracks, etc.) and landslide.

The results are interpreted and compared by experienced staff, then the risk area declared “Exposed to Disaster Zone" by General Directorate of the Council of Ministers. So we can directly say that using satellite based technologies are very helpful for detecting ground deformations and thanks to this technologies also help to improve the capacity of quick and early decision for disaster risk reduction and management.  

For giving more examples in real-life especially in my area, there should be more applications which can be evaluated by Government. But for now, the studies are more academic and we try to lead our results conventionality. We have two examples which are waiting for acceptance by government. One of this study is about land subsidence detection over a huge closed basin in Turkey which is called Konya closed basin is located in a 55 000 km2 area of Anatolian peninsula, is the biggest closed basin of Turkey involving four big city (Konya, Karaman, Nigde and Aksaray provinces). In this study we compare the InSAR results with interpolated GPS (Global Positioning System) velocities results. As a result we detect subsidence rates approximately 7 cm/yr especially in Konya city center. With this significant results we can help city planning by indicate subsidence risk field. Our other study is about landslide detection. In this research, we investigated Babadağ landslide (Denizli in western Turkey) by using the InSAR techniques. An active landslide in Babadağ County has been issued in the study by using DInSAR (Differential InSAR) to monitor the vertical deformation amount.  We focused on the analyses of Babadağ landslide by using the InSAR technique and compared to our earlier research in which PSInSAR technique had been used. Even Babadağ landslide analyses have representative good results for the amount of vertical deformation. The area indicated by InSAR map that is previously declared dangerous for landslide. So, all the houses and shops were evacuated and were carried out demolitions of old houses and work places.

As I clearly understand from your question, you expect may be more real-life examples, but this techniques are very new and it will take some time to seen it is helpful sight by Government. We should increase such studies and I hope it will work.

Many thanks again for your interesting question.

Best regards.

QQuestion by Mr Murat ONUNCUYIL

How does InSAR differ from conventional measuring methods and how is it possible that from ~800 km altitude, such precision is achieved (millimeters per year)?

Mr Murat ONUNCUYIL Freelancer (Geophysicist) | NONE

APosted on 09 Apr 2015

Dear Mr Onuncuyıl,

Thanks for the great question, you've certainly brought up a very topical issue!

At first, I should mention that altitudes of Synthetic Aperture Radar (SAR) Satellites are commonly different from each other, such all satellites. Because of this we cannot restrain SAR satellite altitude for only 800 km.  In other words, all satellites equipped with SAR sensors orbit the EARTH on a near – polar orbit at an altitude ranging from 500 to 800 km above Earth’s surface, depending on the satellite platform hosting SAR sensor. Let me explain for all InSAR applications some of most common satellites and their altitude specifications can be summarized as follows.

Radarsat-1: 793-821 km, Radarsat-2: 798 km, Sentinel-1: 693 km, Sentinel-2: 786 km, ALOS: 692 km, COSMO-Skymed: 619 km, Envisat, ERS1-2: 782 km, TerraSAR-X: 514 km

Additionally, SAR interferometry makes use of the phase shift information by subtracting the phase value from one SAR data acquisition from that of another, for the same point on the ground. The resulting phase difference, represented by interferometric fringes, is directly related to topographic height. The result is an interferogram. Interferometric fringes can be thought of as a collection of height contours, with each fringe corresponding to a phase difference of 0 to 360°.

Assuming the interferogram has been flattened (corrected for the curvature of the Earth), each complete interferometric fringe cycle (e.g. from black through to white) represents a specific elevation interval for all fringes across the interferogram. This interval is known as the altitude of ambiguity and is a function of radar wavelength (ranges from 5.6cm to 23.6cm), satellite altitude (in the region of 800km), incidence angle (typically between 23-50°) and the perpendicular baseline (anything from m to km). 

If your question is specifically about the altitude and precision relationship, the answer is simple. Precision is not totally depend altitude. This is because the distance is not relevant to the measurement technique. The basis of the measurements is the use of the interferometric phase. Because the phase of the electromagnetic wave can be measured with sufficient precision, it does not matter how long the distance is.

Hope this helps, thanks for your question!

With my best wishes.