• Proceedings of the KSRS Conference
• /
• v.2
• /
• pp.981-984
• /
• 2006

Oil pollution of the ocean is a major environmental problem, especially in its coastal zones. Synthetic aperture radar (SAR) flown on satellites, such as ERS-2 and Envisat, has been proved to be a useful tool in oil spill monitoring due to its wide coverage, day and night, and all-weather capability. The total 120 SAR images containing oil spill over the East China Sea were collected and analyzed, ranging in date from July 23, 2002 to November 11, 2005. After preprocessed, SAR images were segmented by adaptive threshold method. The oil spill images were incorporated into GIS after distinguished from look-like phenomena, finally we presented the oil spills distribution map for the East China Sea. The wide-swath and quick-looks SAR imagery for mapping of oil spill distribution over large marine areas were proved to be useful when full resolution data are not available. After the temporal and spatial distribution of the oil spills were analyzed, we found that most of oil spills were distributed along the main ship routes, which means the illegal discharge by ships, and the occurrence of oil spill detected on SAR images acquired during morning and summer is much higher than during evening and winter.

• Korean Journal of Remote Sensing
• /
• v.33 no.1
• /
• pp.37-46
• /
• 2017

Sinabung volcano in Indonesia was formed due to the subduction between the Eurasian and Indo-Australian plates along the Pacific Ring of Fire. After being dormant for about 400 years, Sinabung volcano erupted on the 29th of August, 2010 and most recently on the 1st of November, 2016. We measured the deformation of Sinabung volcano using Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar(ALOS/PALSAR) interferometric synthetic aperture radar(InSAR) images acquired from February 2007 to January 2011. Based on multi-temporal InSAR processing, we mapped the ground surface deformation before, during, and after the 2010 eruption with time-series InSAR technique. During the 3 years before the 2010 eruption, the volcano inflated at an average rate of ~1.7 cm/yr with a markedly higher rate of 6.6 cm/yr during the 6 months prior to the 2010 eruption. The inflation was constrained to the top of the volcano. From the 2010 eruption to January 2011,the volcano subsided by approximately 3 cm (~6 cm/yr). We interpreted that the inflation was due to magma accumulation in a shallow reservoir beneath Sinabung. The deflation was attributed to magma withdrawal from the shallow reservoir during the eruption as well as thermo-elastic compaction of erupted material. This result demonstrates once again the utility of InSAR for volcano monitoring.

• Proceedings of the KSRS Conference
• /
• 2007.10a
• /
• pp.629-632
• /
• 2007

While conventional interferometric SAR (InSAR) technique is an excellent tool for displacement observation, it is only sensitive to one-dimensional deformation along the satellite's line-of-sight (LOS). Recently, a multiple aperture interferogram (MAI) technique has been developed to overcome this drawback. This method successfully extracted along-track displacements from InSAR data, based on split-beam InSAR processing, to create forward- and backward- looking interferograms, and was superior to along-track displacements derived by pixel-offset algorithm. This method is useful to measure along-track displacements. However, it does not only decrease the coherence of MAI because three co-registration and resampling procedures are required for producing MAI, but also is confined to a suitable interferometric pair of SAR images having zero Doppler centroid. In this paper, we propose an efficient and robust method to generate MAI from interferometric pair having non-zero Doppler centroid. The proposed method efficiently improves the coherence of MAI, because the co-registration of forward- and backward- single look complex (SLC) images is carried out by time shift property of Fourier transform without resampling procedure. It also successfully removes azimuth flat earth and topographic phases caused by the effect of non-zero Doppler centroid. We tested the proposed method using ERS images of the Mw 7.1 1999 California, Hector Mine Earthquake. The result shows that the proposed method improved the coherence of MAI and generalized MAI processing algorithm.

• Journal of Korean Society for Geospatial Information Science
• /
• v.20 no.3
• /
• pp.41-48
• /
• 2012

Using multi-sensor or multi-temporal high resolution satellite images together is essential for efficient applications in remote sensing area. The purpose of this paper is to estimate geometric difference of translations between high-resolution optical and SAR images automatically. The geometric and radiometric pre-processing steps were fulfilled to calculate the similarity between optical and SAR images by using Mutual Information method. The coarsest-level pyramid images of each sensor constructed by gaussian pyramid method were generated to estimate the initial translation difference of the x, y directions for calculation efficiency. The precise geometric difference of translations was able to be estimated by applying this method from coarsest-level pyramid image to original image in order. Yet even when considered only translation between optical and SAR images, the proposed method showed RMSE lower than 5m in all study sites.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.47 no.2
• /
• pp.130-142
• /
• 2019

For a preemptive strike against a Time Critical Target(TCT), such as Transporter-Erector-Launcher(TEL), the detection capability of capturing launch signals in the Area of Interest(AoI) is important. In this study, the characteristics of the revisit time and the response time of 6~48 small SAR constellation satellites were analyzed. In particular, the revisit time was analyzed for all regions of North Korea and specific regions, and the response time was classified into [Scenario 1] to identify fixed targets and [Scenario 2] to detect and identify moving targets. In particular, the response time analysis for the TCT detection mission operation in [scenario 2] was performed through optimization analysis of observation cumulative coverage for a specific area. Finally, the configuration of constellation satellites for optimal performance of the detection mission was estimated.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.443-443
• /
• 2022

적설은 자주는 아니지만 가끔 비교적 넓은 범위에 피해를 발생시킨다. 적설에 의한 피해를 예방하기 위해서는 피해를 유발하는 적설심을 미리 파악해 둘 필요가 있다. 하지만 관측하고 있는 적설심은 특정 관측지점으로 한정되어 피해를 유발하는 한계적설심을 파악하는데 어려움이 있다. 이를 극복하기 위한 일반적인 방법은 관측지점의 적설을 보간하여 공간적으로 확대하는 것이다. 하지만 이것은 매우 적은 자료를 가지고 넓은 영역을 통계적으로 추정해야하는 한계로 인해 피해 유발 한계적설심의 구명에 더 혼란을 주기도 한다. 이를 보완하기 위해서는 넓은 영역을 관측하는 위성영상을 활용할 수 있으며, 그 중에서도 합성개구레이더(Synthetic Aperture Radar; SAR)를 이용한 InSAR(Interferometric Synthetic Aperture Radar) 기법은 이를 위해 적절한 방법일 수 있다. 영상의 간섭계는 두 개의 다른 시기에 측정된 합성개구레이더 영상의 위상차를 이용한 것으로 일반적으로 다른 조건들이 일치할 때 지형의 변화를 추적할 때 사용되곤 한다. 그런데 만약 두 시기 사이에 특별한 지형적인 변화를 일으키는 요인이 없고 단지 적설만이 존재한다면 두 영상의 위상차는 적설의 효과로 볼 수 있을 것이다. 적설이 전파의 전달경로를 다르게 만들어 위상차를 발생시키는 것으로 가정할 수 있다. 이때 발생하는 위상차는 적설심과 적설의 굴절률에 의해 다를 수 있다. 이에 본 연구에서는 적설 전후에 수집된 인공위성 합성개구레이더 자료의 위상차를 분석한 간섭영상을 이용해 적설심의 공간분포를 추정하여 비교해 보고자 한다. 이를 위해 적설에 대한 투과가 가능한 C밴드 레이더를 사용하는 Sentinel-1의 영상을 사용하였다. 적설심의 공간분포는 실제 피해발생지역의 적설심을 보다 정확하게 추정하는데 기여할 수 있으며, 이것은 실제 피해유발적설심을 파악하는데 도움이 될 것이다.

• Journal of the Korean earth science society
• /
• v.32 no.6
• /
• pp.575-585
• /
• 2011

The effect of wavelet pair choice in the compression of the satellite images is studied. There is a trade-off between compression rate and perception quality. The encoding ratio is used to express the compression rate, and Peak Signal-to-Noise Ratio (PSNR) is also used for the perceptional performance. The PSNR and the encoding ratio are not matched well for the images with various wavelet pairs, but the tendency is remarkable. It is hard to find the pattern of PSNR for sampled images. On the other hand, there is a pattern of the variation range of the encoding ratio for each image. The satellite images have larger values of the encoding ratio than those of nature images (close range images). Depending on the wavelet pairs, the PSNR and the encoding ratio vary as much as 13.2 to 21.6% and 16.8 to 45.5%, respectively for each image. For Synthetic Aperture Radar (SAR) images the encoding ratio varies from 16 to 20% while for the nature images it varies more than 40% depending on the choice of wavelet pairs. The choice of wavelet for the compression affects the nature images more than the satellite images. With the indices such as the PSNR and the encoding ratio, the satellite images are less sensitive to the choice of wavelet pairs. A new index, energy concentration ratio (ECR) is proposed to investigate the effect of wavelet choice on the satellite image compression. It also shows that the satellite images are less sensitive than the nature images. Nevertheless, the effect of wavelet choice on the satellite image compression varies at least 10% for all three kinds of indices. However, the important of choice of wavelet pairs cannot be ignored.

• Korean Journal of Remote Sensing
• /
• v.39 no.6_3
• /
• pp.1671-1678
• /
• 2023

The Korea multi-purpose satellite (KOMPSAT) series consisting of multi-sensors has been used in various fields such as land, environmental monitoring, and disaster analysis since its first launch in 1999. Recently, as various information processing technologies (high-speed computing technology, computer vision, artificial intelligence, etc.) that are rapidly developing are utilized in the field of remote sensing, it has become possible to develop more various satellite image processing and analysis algorithms. In this special issue, we would like to introduce recently researched technologies related to the KOMPSAT image application and research topics participated in the 2023 Satellite Information Application Contest.

• Journal of Korea Water Resources Association
• /
• v.56 no.8
• /
• pp.497-508
• /
• 2023

Agricultural reservoirs are crucial structures for water resources monitoring especially in Korea where the resources are seasonally unevenly distributed. Optical and Synthetic Aperture Radar (SAR) satellites, being utilized as tools for monitoring the reservoirs, have unique limitations in that optical sensors are sensitive to weather conditions and SAR sensors are sensitive to noises and multiple scattering over dense vegetations. In this study, we tried to improve water body detection accuracy through optical-SAR data fusion, and quantitatively analyze the complementary effects. We first detected water bodies at Edong, Cheontae reservoir using the Compact Advanced Satellite 500(CAS500), Kompsat-3/3A, and Sentinel-2 derived Normalized Difference Water Index (NDWI), and SAR backscattering coefficient from Sentinel-1 by K-means clustering technique. After that, the improvements in accuracies were analyzed by applying K-means clustering to the 2-D grid space consists of NDWI and SAR. Kompsat-3/3A was found to have the best accuracy (0.98 at both reservoirs), followed by Sentinel-2(0.83 at Edong, 0.97 at Cheontae), Sentinel-1(both 0.93), and CAS500(0.69, 0.78). By applying K-means clustering to the 2-D space at Cheontae reservoir, accuracy of CAS500 was improved around 22%(resulting accuracy: 0.95) with improve in precision (85%) and degradation in recall (14%). Precision of Kompsat-3A (Sentinel-2) was improved 3%(5%), and recall was degraded 4%(7%). More precise water resources monitoring is expected to be possible with developments of high-resolution SAR satellites including CAS500-5, developments of image fusion and water body detection techniques.

• Journal of Satellite, Information and Communications
• /
• v.9 no.4
• /
• pp.117-126
• /
• 2014

The COSPAS-SARSAT Search-and-Rescue System detects and locates emergency beacons activated by aircraft, ships and individuals. In particular, when this system is used in wartime and the signal is leaked to the enemy, it can cause the loss of the rescuers and the survivors. This paper proposes an improved method which protects the COSPAS-SARSAT search-and-rescue signal itself from being disclosed during its operation. In addition, there is presented a new protocol which maintains the stabilized security status between survivors and rescuers, using the Galileo/SAR return link.