Sang-Wan Kim

Polarimetric Features of Oyster Farm Observed by AIRSAR and JERS-1

The polarimetric features of an oyster farm in a coastal area are analyzed to verify the applicability of radar polarimetry and interferometry. L-band Airborne Synthetic Aperture Radar (AIRSAR) data and Japan Earth Resources Satellite (JERS-1) data are used to examine the unique structure of an oyster farm located in South Korea. A specific feature of the oyster farm is the presence of numerous arrays of structures of various orientations that consist of exercise-bar-shaped poles protruding above sea level. This paper demonstrates that tide level is strongly correlated with the double-bounce scattering power from the vertical pole structures. This phenomenon is also verified by laboratory measurements using a network analyzer. In the laboratory experiment, double-bounce scattering and total power showed increasing trends with increased height of the vertical poles. Single-bounce scattering is sensitive to the orientation of horizontal poles relative to antenna orientation. HH-polarization is the most effective technique for imaging oyster farms from L-band polarimetric AIRSAR data. The authors were able to use a three-component decomposition of the AIRSAR data to distinguish an exposed tidal flat from a submerged tidal flat. The characteristics of the exposed tidal flat are similar to those of the carbon sponge in the laboratory test, except that the double-bounce scattering power is slightly greater in the real-world example. The single-bounce scattering component in AIRSAR data is generally greater than that in laboratory measurements because of sea-surface conditions and oyster growth. When the horizontal pole was aligned normal to the radar look direction, single-bounce scattering was greater than the double-bounce scattering, even under water-covered conditions. While a difference in tide height of 10 cm contributed approximately 3.0 dB in the laboratory experiment, a difference in tide height of 20 cm contributed to only approximately 1.7 dB in the JERS-1 SAR image intensity. JERS-1 SAR image intensity for areas dominated by double- and single-bounce scattering was 0.78 and 0.56, respectively. Results confirm that polarimetric SAR data are useful in selecting areas dominated by double-bounce scattering in oyster farms

An application of L-band synthetic aperture radar to tide height measurement

A method for measuring the tide height near the coast from L-band synthetic aperture radar (SAR) data is presented. Twenty-one coherent interferograms have been successfully constructed from Japanese Earth Resources Satellite 1 (JERS-1) SAR data obtained over oyster sea-farming structures. A coherence analysis of the 21 interferometric pairs showed that a perpendicular baseline of less than 3 km, with a temporal baseline within 500 days, are required to obtain a coherent pair, with a coherence higher than 0.25, in the study area. The coherent phases preserved in the interferograms showed a close relation with the sea level. The problem of phase unwrapping to restore an absolute tide height was overcome by introducing normalized image intensities. The radar measurements estimated by the proposed method were verified using tide gauge data, and comparison of the two datasets yielded a correlation coefficient R/sup 2/ of 0.91, with a root mean square error of 5.76 cm. The results demonstrate that radar interferometry can be applied for a tide height measurement near the coast given sufficient structures that return off-nadir radar pulses to the antenna. The multipolarized L-band SAR system will provide better results, using only double-bounced signals, in the future.

Measurements of soil compaction rate by using JERS-1 SAR and a prediction model

The soil compaction rate in a reclaimed land has been estimated by using the Japanese Earth Resources Satellite 1 (JERS-1) synthetic aperture radar (SAR) two-pass differential interferometry (DInSAR) and magnetic probe extensometer (an accuracy of /spl plusmn/1 mm) from 42 ground stations. Twelve JERS-1 SAR interferometric pairs were acquired in the study area. We applied a soil compaction prediction model based on a hyperbolic method using the ground truth data and the DInSAR measurements. The hyperbolic model fitted well to the ground measurements with an rms error of 1.65 cm. The rms error of the model driven by DInSAR measurements was 2.24 cm. The two model results agreed well, showing a difference of 8.1% (12.9 cm) in permanent settlement that is defined as the amount of vertical subsidence as time goes to infinity. A two-dimensional (2-D) subsidence map was constructed from five qualified pairs. The correlation coefficient R between the radar measurements and the ground truth data was 0.87 with an rms error of 1.44 cm. The results demonstrate that the L-band DInSAR combined with a prediction model is useful for geotechnical applications.

Integration of a subsidence model and SAR interferometry for a coal mine subsidence hazard map in Taebaek, Korea

Coal mine subsidence hazard can be effectively evaluated by geographic information system (GIS) analysis if sufficient data is provided. It is, however, difficult to obtain ground-based data, especially in remote and less populated mining areas. In this study, we construct and validate a coal mine subsidence hazard map in Taebaek, Korea, by integration of space-borne L-band synthetic aperture radar (SAR) measurements and a fuzzy-based subsidence model. There is an approximately 15-year time interval between the radar measurements used for the subsidence hazard model and those used to validate the subsidence. A subsidence hazard map was constructed using Japanese Earth Resources Satellite (JERS-1) SAR data from the early 1990s and the subsidence model. For the coal mine subsidence hazard mapping, a certainty factor analysis was used to estimate the relative weights of four control factors influencing coal mine subsidence, and the relative weight of each factor was then integrated to produce a subsidence hazard index by a fuzzy combination operator. The predicted hazard areas were then investigated and validated by comparison with subsidence occurrences observed by Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR) interferometry in 2007–2008. The results showed a good agreement between the predicted locations vulnerable to subsidence and the actual subsidence occurrences with a prediction accuracy of about 73% and a root mean square error of about 0.35. These results demonstrate that a map produced by integration of a subsidence model and SAR interferometry can be used to predict and monitor coal mine subsidence hazards, especially in remote regions.

Multi temporal JERS-1 SAR investigation of Mt. Baekdu stratovolcano using differential interferometry

Mt. Baekdu, a Cenozoic stratovolcano, was studied using twenty-three JERS-1 SAR and two ERS-2 SAR images. A 70-day ERS-2 interferogram produces a very poor interferogram because of the temporal decorrelation probably due to vegetation and the layover effects. However, JERS-1 SAR data pairs produce coherent interferograms even when some of the time intervals between the data take was as long as 6 years. The measurement of surface changes was numerically implemented from 1992 to 1998 using three different SAR interferometry approaches: i) interferometry with large altitude of ambiguity, ii) 2-pass, and iii) 3-pass differential SAR interferometry (DInSAR). Analysis of 11 differential interferograms indicates that the large surface area surrounding Mt. Baekdu (several tens of kilometers) subsides, particularly the southwestern part of it. When the computed displacement vectors are projected onto the vertical components, the maximum subsidence rate is estimated at 9 cm/year. Although the estimated ubsidence rate is not confirmed in the field due to the lack of ground-truth data and accurate DEMs as well as logistic problems, the results provide important volcano-tectonic implications on the background information for future long-term monitoring of Mt. Baekdu.

Application of ICHD-II criteria for headaches in a TMJ and orofacial pain clinic

The aim of this study was to identify and diagnose headache in a temporomandibular joint and orofacial pain clinic population using the second edition of The International Classification of Headache Disorder criteria. In 502 temporomandibular disorder and orofacial pain patients, 246 patients (49%) were diagnosed with tension-type headache (TTH), followed by migraine without aura (14.5%), probable migraine (12.9%), migraine with aura (7%), probable TTH (4.8%) and cluster headache (0.2%). The prevalence of headaches was compared between male and female patients, and the prevalence of migraine was found to be higher in women than in men. In evaluating by age, the prevalence of migraine was highest in patients in their 20s and 30s and declined as age increased above 40. TTH showed the highest rate throughout all age groups, but it also decreased as age increased. In this study, the prevalence of migraine was lower than that reported in Dr Kim etu2009al.s study, and the prevalence of TTH much higher than that reported in the previous study. Of the headache patients, 81.1% presented with masseter muscle pain and 47.8% with temporal muscle pain. This finding suggests that pericranial muscle pain may be an inducing factor of primary headache.

Line-of-sight vector adjustment model for geopositioning of SPOT-5 stereo images

We formulate and present a new geopositioning method for SPOT-5 High-Resolution Geometric (HRG) stereo images, named the line-of-sight (LOS) vector adjustment model. It is applicable to satellites that move along a well-defined close-to-circular elliptical orbit with a predicted orbit close to true. SPOT-5 satisfies these requirements because it has the improved capability of providing accurate satellite attitude and a look angle for each detector. The method’s core idea is that only the LOS vector was adjusted when correcting the geometric distortion of SPOT-5 imagery. One advantage of this method is that it achieves high geopositioning accuracy with a limited number of ground control points (GCPs). Although a minimum of three GCPs is needed for processing, a test result satisfied the accuracy requirement within one pixel of a SPOT-5 panchromatic image even with only three GCPs. The performance in terms of root mean square error (RMSE) improved as the number of GCPs increased. Five GCPs were found to be the optimal number in the practical application of the LOS vector adjustment model. Using five GCPs, the RMSEs were 0.48 m and 0.64 m in planimetry and height, respectively. The test results indicate that the proposed method is superior to the bundle adjustment method for the geopositioning of SPOT-5 HRG stereo images.

Measurement of the water level in reservoirs from TerraSAR-X SAR interferometry and amplitude images

Measurement of water levels is important in many hydrological fields. Synthetic Aperture Radar (SAR) satellites, such as TerraSAR-X, TanDEM-X and COSMO-SkyMed, can provide useful high-resolution images for inaccessible regions and over wide areas. This letter has two research goals. First, an accurate boundary line between a dam slope and a water body was extracted using the SAR Edge Detection Hough Transform (SEDHT) approach, as proposed here. Second, after Digital Elevation Model (DEM) generation using SAR interferometry, the reservoir water level is measured. This approach will be helpful to estimate water level accurately at limited areas without emergent vegetation for double bounce that is required for conventional interferometric SAR (InSAR) approach. As a result of applying to two images of TerraSAR-X data in the study areas, the mean water level was determined to be 151.13 m on 5 November 2010 and 150.69 m on 16 November 2010 through the proposed method. The water level according to gauge data was 151.22 m on 5 November 2010 and 150.68 m on 16 November 2010, thus showing a water level difference ofu2009−9 cm and 1 cm, respectively.

Using Tandem-X Science Phase Observations to Extract Glacial Topography

Space-based Interferometric Synthetic Aperture Radar (InSAR) applications have been widely used to monitor the cryosphere over past decades. Because of temporal decorrelation, interferometric coherence often severely degrades on fast moving glaciers. In addition, higher sensitivity ambiguity occurs in large baseline configurations, which are needed for extracting topographic information over low relief areas such as the surface of a glacier. TerraSAR-X add-on for Digital Elevation Measurement (TanDEM-X) observations, which overcome the temporal decorrelation because of their simultaneous measurements by two satellite constellations, have used a short baseline sufficient for generation of excellent digital elevation models in most locations around the world. However, it remains difficult to estimate detailed topographic characteristics over low slope glacier surfaces because of the relatively less sensitive height ambiguity from the small baselines. In this study, we used the TanDEM-X pursuit monostatic mode with large baseline formation following a scientific phase timeline to develop highly sensitive topographic elevation models of the Petermann Glacier of Northwest Greenland. As expected, coherent interferometric phases (> 0.8) were well maintained over the glaciers despite their fast movement thanks to the nearly simultaneous TanDEM‐X measurements. The height ambiguity, which defined as the altitude difference correspondent to 2uf070 phase change of flattened interferogram, of the dataset was 10.63 m, which is favorable for extracting topography in a low relief region. We validated the TanDEM‐X derived glacial topography by comparing it to the SAR/Interferometric radar altimeter observations acquired by CryoSat‐2 and the IceBridge Airborne Topographic Mapper laser altimeter measurements. Both observations showed very good correlation within a few meters of the offsets (‐12.5 – ‐3.1 m) with respect to the derived glacial topography. Because of highly sensitive ambiguity, we could successfully extract detailed geomorphological features on the glaciers. Routine TanDEM-X observations will be very useful to better understand the dynamics of glacial movements and topographic change.

Surface deformation in Mokpo area observed with synthetic aperture radar interferometry

Mokpo city is a coastal city located at the south western coast of the Korean Peninsula. Large regions within Mokpo are subjected to significant subsidence because about 70% of the city area is a reclaimed land from the sea. In this study, we aimed to estimate the subsidence rate over Mokpo city by using twenty-six JERS-1 SAR dataset from September 1992 to October 1998. Several tens of differential interferograms were processed from JERS-1 dataset and STRM 3-arc DEM. The results indicate continuous subsidence in Dongmyung-dong, Hadang-dong and Wonsan-dong in city, and the subsidence velocity reach over 4 cm/yr in the most highly sinking area. For facilitating the analysis of time-varying surface change, we also carried out an interferometric SAR time series analysis using permanent scatterer and consequently determined space-time maps of surface deformation at each acquisition time of JERS-1 SAR.