Hee-Young Yoo

The Applicability for Earth Surface Monitoring Based on 3D Wavelet Transform Using the Multi-temporal Satellite Imagery

Satellite images that have been obtained periodically and continuously are very effective data to monitor the changes of Earth`s surface. Traditionally, the studies on change detection using satellite images have mainly focused on comparison between two results after analyzing two images respectively. However, the interests in researches to catch smooth trends and short duration events from continual multi-temporal images have been increased recently. In this study, we introduce and test an approach based on 3D wavelet transform to analyze the multi-temporal satellite images. 3D wavelet transform can reduce the dimensions of data conserving main trends. Also, it is possible to extract important patterns and to analyze spatial and temporal relations with neighboring pixels using 3D wavelet transform. As a result, 3D wavelet transform is useful to capture the long term trends and short-term events rapidly. In addition, we can expect to get new information through sub-bands of 3D wavelet transform which provide different information by decomposed direction.

Analysis of the Geological Structure of the Hwasan Caldera Using Potential Data

A geophysical mapping was performed for Hwasan caldera which is located in Euisung Sub-basin of the southeastern part of the Korean Peninsula. In order to overcome the limitation of the previous studies, remote sensing technic was used and dense potential data were obtained and analyzed. First, we analyzed geological lineament for target area using geological map, digital elevation model (DEM) data and satellite imagery. The results were greatly consistent with the previous studies, and showed that N-S and NW-SE direction are the most dominant one in target area. Second, based on the lineament analysis, highly dense gravity data were acquired in Euisung Sub-basin and an integrated interpretation considering air-born magnetic data was made to investigate the regional structure of the target area. The results of power spectrum analysis for the acquired potential data revealed that the subsurface of Euisung Sub-basin have two density discontinuities at about 1 km and 3-5 km depth. A 1 km depth discontinuity is thought as the depth of pyroclastic sedimentary rocks or igneous rocks which were intruded at the ring vent of Hwasan caldera, while a 3-5 km depth discontinuity seems to be associated with the depth of the basin basement. In addition, three-dimensional gravity inversion for the total area of Euisung Sub-basin was carried out, and the inversion results indicated two followings; 1) Cretaceous Palgongsan granite and Bulguksa intrusion rocks, which are located in southeastern part and northeastern part of Euisung Sub-basin, show two major low density anomalies, 2) pyroclastic rocks around Hwasan caldera also have lower density when compared with those of neighborhood regions and are extended to 1.5 km depth. However, a poor vertical resolution of potential survey makes it difficult to accurately delineate the detailed structure caldera which has a vertically developed characteristic in general. To overcome this limitation, integrated analysis was carried out using the magnetotelluric data on the corresponding area with potential data and we could obtain more reasonable geologic structure.

Implementation of 3D discrete wavelet scheme for space-borne imagery classification and its application

A three dimensional discrete wavelet transform (3D DWT) expands planes of the 2D DWT into volume data. The 3D DWT scheme has advantages of analyzing spectral characteristics in the order of frequency and analyzing changes of spatial information and spectral information simultaneously. Nonetheless, few researchers have attempted to classify multi-spectral images using the 3D DWT. This study aims to apply the 3D DWT to the classification of multi-spectral images and synthetic aperture radar image. To classify these images, we employ two numerical values: The 3D wavelet coefficients and the energy of each band. And then we evaluate their results quantitatively with those of traditional classification techniques including the 2D wavelet scheme. Therefore, the results show that the classification technique of the 3D DWT is more effective than that of traditional techniques, especially in complicated imagery. The accuracy of the 3D energy in SAR imagery is higher. This study provides new numerical values to classify images effectively. Furthermore, these values can be extended to the image retrieval and pattern recognition in high-resolution imagery and this scheme can be employed in image dataset obtained at other times.

A Feasibility Study of AMT Application to Tidal Flat Sedimentary Layer

The marine seismic prospecting using a research vessel in the shallow sea near the coastal area has certain limits according to the water depth and survey environment. Also, for the electrical resistivity survey at seashore area, one may need a specially designed high-voltage source to penetrate the very conductive surface layer. Therefore, we have conducted a feasibility study on the application of magnetotelluric method (MT), a passive geophysical method, on investigating of shallow marine environment geology. Our study involves both theoretical modeling and field survey at the tidal flat area which represent the very shallow marine environment. We have applied the audio-frequency magnetotelluric (AMT) method to the intertidal deposits of Gunhung Bay, west coast of Korea, and analysed the field data both qualitatively and quantitatively to investigate the morphology and sedimentary stratigraphy of the tidal flat. The inversion of AMT data well reveals the upper sedimentary layer of Holocene intertidal sediments having a range of 13-20 m thickness and the erosional patterns at the unconformable contact boundary. However, the AMT inversion results tend to overestimate the depth of basement (30-50 m) when compared with the seismic section (27-33 m). Since MT responses are not significantly sensitive to the resistivity of middle layer or the depth of basement, the AMT inversion result for basement may have to be adjusted using the comparison with other geophysical information like seismic section or logging data if possible. But, the AMT method can be an effective alternative choice for investigating the seashore area to get important basic informations such as the depositional environment of the tidal flat, sea-water intrusion and the basement structure near the sea shore.

Transportation analysis with high-resolution satellite imagery by wavelet analysis scheme

The wavelet transform has been regarded as the advanced and effective scheme for signal or image processing. DWT, which stands for discrete wavelets transform, can provide information associated with the quantitative analysis with respect to various feature characteristics contained in a given image. By the way, the application scheme by the wavelet signal/image processing, being composed of these wavelet transformations and its inverse processing as inverse discrete wavelets transform (IDWT), allows multi-source data fusion in the actual application domains. In this study, we attempt to apply the wavelet analysis scheme for transportation problems. The transportation application with remotely sensed imagery has expanded as the increasing uses of high-resolution imageries according that being available commercial uses of them. However, wavelet-based analysis schemes toward some transportation applications are rarely reported yet. In this study, we used wavelet transform and texture analysis to get road or building boundary and pavement information. We used space-borne imagery of 1 M high resolution with KOMPSAT-EOC because KOMPSAT-2 will provide high spatial resolution similar to IKONOS. As the tentative results, this research will be expected to help road construction or repair planning.