Radar Backscattering of Intertidal Mudflats Observed by Radarsat-1 SAR Images and Ground-Based Scatterometer Experiments

Hoonyol Lee,Heesam Chae,Seong-Jun Cho IEEE 2011 IEEE transactions on geoscience and remote sensing Vol.49 No.5

<P>This paper presents the variation of the radar backscattering of intertidal mudflats in the west coast of Korea observed by Radarsat-1 synthetic aperture radar (SAR) images and investigates the related factors by an indoor experiment and a field experiment using a ground-based C-band scatterometer. The 15 Radarsat-1 SAR images of the intertidal mudflat near Jebu Island used in this study were all taken at around 6:30 p.m., which is an ideal local time for evaluating the daytime evaporation effects during the 12.4-h tidal cycle. An exposure time map and an evaporation time map of mudflats at the time of each SAR acquisition are calculated based on the tidal records, a digital elevation map generated by the waterline extraction method, and the normalized daily evaporation index. The radar backscattering of the upper intertidal mudflat did not show a monotonic change with evaporation time but a complex pattern. An indoor experiment using a C-band scatterometer on drying mud revealed an M-shaped change (increase-decrease-increase-decrease) of radar backscattering due to various factors that affect dielectric constant and roughness such as the drainage of surface water (increase), evaporation (decrease), mud cracking (increase), and further evaporation (decrease). The variation of backscattering observed from SAR images agreed well with the initial three stages of the indoor experiment (increase-decrease-increase) but did not show the final stage of decrease from continuous evaporation. A field experiment on natural intertidal mudflats showed not only the pattern related to the initial drainage and evaporation but also speckles from biological activity.</P>

Seasonal variation and dynamics of landfast sea ice near Jangbogo Antarctic Station observed by InSAR

Hoonyol Lee,Hyangsun Han 대한지질학회 2015 대한지질학회 학술대회 Vol.2015 No.10

Sentinel-1A/B 위성의 SAR 간섭영상을 활용한 지진 변위 분석

박지호(Jiho Park),이대라(Daera Lee),이권철(Gwoncheol Lee),이훈열(Hoonyol Lee) 대한지질학회 2017 대한지질학회 학술대회 Vol.2017 No.10

마이크로파 산란계를 이용한 벼, 콩 생육단계 추정

김이현(Yihyun Kim),홍석영(Sukyoung Hong),이훈열(Hoonyol Lee),이재은(Jae-Eun Lee),이경도(Kyungdo Lee) 한국토양비료학회 2012 한국토양비료학회지 Vol.45 No.4

본 연구에서는 마이크로파 산란계 시스템을 이용하여 벼, 콩 작물을 대상으로 후방산란계수와 작물생육변화를 관측하고 pauli decomposition을 통해 얻어진 인자값과 작물생육과의 비교를 통해 작물 생육단계를 추정하였다. Pauli decomposition 방법을 이용 생육시기에 따른 벼 산란특성을 분석한 결과 L-밴드는 벼 출수기 (DOY 222, 8월 10일) 이후 이중 산란 (σhh - σvv) 효과가 크게 나타났고, C-밴드는 생육기간동안 이중 산란과 체적 산란의 decomposition value가 거의 같았으며, X-밴드는 체적 산란이 이중 산란보다 높게 나타났다. Pauli decomposition 방법을 이용하여 콩 생육시기별 산란특성을 분석한 결과 L-밴드에서는 R2(DOY 224, 8월 13일) 시기에 이중 산란이 체적 산란보다 높게 나타났고, R4 (DOY 242, 8월 31일) 이후로는 두 요소간의 값 차이가 크게 나타났다. Pauli decomposition ratio을 이용한 벼, 콩 생육단계를 추정하는데 있어 이중 산란이 key factor로 작용하는 것을 알 수 있었다. 벼의 경우 L-밴드에서는 이중 산란이 차지하는 비율이 체적 산란 비율보다 높아지기 시작하는 시점이 분얼기 (DOY 183, 7월 1일)이며, 이중 산란 효과가 벼 출수기 이후 지속적으로 나타나기 때문에 분얼기와 벼 출수기의 생육단계 추정이 가능하다. C-밴드는 이중 산란 비율이 최대값을 나타내는 시점이 벼 출수기와 일치하여 이 시기 추정이 가능할 것으로 판단된다. X-밴드의 경우에는 이중 산란 비율이 최대값을 가지는 시점이 유수형성기 (DOY 206, 7월 24일)로 이 시기 추정이 가능하고, 표면 산란이 다시 증가하는 시점이 유숙기 (DOY 243, 8월 31일)로 이 시기도 pauli decomposition ratio를 이용하여 추정이 가능할 것으로 판단된다. 또한 콩의 경우에는 L-밴드의 이중 산란이 체적 산란보다 높아지는 시기가 R2 (DOY 224, 8월 13일) 임으로 이 시기 예측이 가능할 것으로 판단된다. 따라서 마이크로파 산란계에서 얻어진 decomposition 방법을 이용하여 벼, 콩 생육단계를 예측할 수 있음을 확인하였다. Microwave radar can penetrate cloud cover regardless of weather conditions and can be used day and night. Especially a A ground-based polarimetric scatterometer operating at multiple frequencies can continuously monitor the crop conditions. We analyzed scattering characteristics of rice and soybean using pauli decomposition method. Surface scattering (α) is the dominant component over the entire stages for all bands and pauli decomposition value was the highest for L-band. Double bounce scattering (β) and volume scattering (γ) were approximately equal for C-band and volume scattering was higher than double bounce scattering for X-band in rice field. In soybean, double bounce scattering becomes higher than volume scattering during the R2 stage (DOY 224) and there was a significant difference between the two components after the R4 stage (DOY 242) for L-band. The maximum growth stage of soybean can also be detected using L-band double bounce scattering. The peak of double bounce effect coincides with the peak of growth biophysical variables on DOY 271. We found that pauli decomposition can provide insight on the relative magnitude of different scattering mechanisms during the rice and soybean growth cycle.

Inter-satellite atmospheric and radiometric correction for the retrieval of Landsat sea surface temperature by using Terra MODIS data

한향선,Hoonyol Lee 한국지질과학협의회 2012 Geosciences Journal Vol.16 No.2

Thermal infrared images of Landsat-5 TM and Landsat-7 ETM+ sensors have been unrivalled sources of high resolution thermal remote sensing (120 m for TM and 60 m for ETM+) for more than two decades. As the sensors have only one thermal channel, however, the correction of atmospheric effect has been virtually limited, degrading the accuracy of sea surface temperature (SST) measurement. Launched in 1999, MODIS sensor onboard Terra satellite is equipped with two thermal channels that can provide accurate atmospheric correction at 1 km resolution. In this paper we propose an inter-satellite calibration method to correct the radiometric and atmospheric effect of Landsat brightness temperature by using the atmospherically corrected Terra MODIS SST which lags Landsat pass by 30 minutes only. Comparison of the corrected Landsat SST with in situ SST near the coast of South Korea showed a significant improvement in root mean square error from 2.31 ûC before the correction to 0.96 ûC after the correction. Errors from spatial and temporal inhomogeneities over 1 km × 1 km window could be masked out by identifying negative correction term and applying a root mean square deviation criterion between Landsat and MODIS SSTs. We expect that Landsat SST product obtained after the launch of Terra can be atmospherically corrected by using the method proposed in this paper while maintaining the merit of high-resolution Landsat thermal infrared imagery

Surface strain rates and crevassing of Campbell Glacier Tongue in East Antarctica analysed by tide-corrected DInSAR

Han, Hyangsun,Lee, Hoonyol Taylor and Francis Group 2017 Remote Sensing Letters Vol. No.

Assessment of SSM/I sea ice concentration using Kompsat-1 EOC imagery

Hyangsun Han,Hoonyol Lee 대한지질학회 2007 대한지질학회 학술대회 Vol.2007 No.0

Radar Backscattering of Lake Ice During Freezing and Thawing Stages Estimated by Ground-Based Scatterometer Experiment and Inversion From Genetic Algorithm

Han, Hyangsun,Lee, Hoonyol IEEE 2013 IEEE transactions on geoscience and remote sensing Vol.51 No.5

<P>Lake ice under phase transition shows large variation on radar backscattering due to the changes of dielectric constant and roughness of ice surface and thus the transmissivity of microwave into ice body. To study the effects of freezing/thawing of ice on radar backscattering in a short time, we spread water over lake ice and continuously measured radar backscattering by using a ground-based microwave scatterometer system operated in C-band HH polarization. By establishing scattering models and applying inversion from genetic algorithm, radar returns were separated into ice-surface, volume, and ice-bottom scatterings, and the changes in dielectric constant and roughness parameters of ice surface were estimated as well. Immediately after spreading water on ice surface, ice-surface scattering was strongest due to high dielectric constant of surface water while volume and ice-bottom scatterings were very weak due to low microwave transmissivity into ice body. As surface water was being frozen, ice-surface scattering became weak with decreasing dielectric constant while volume and ice-bottom scattering increased due to higher transmissivity into ice body. In a transition stage, when surface water was almost frozen, all three scatterings increased simultaneously. Crystallization of ice produced rougher surface overcoming the decrease in dielectric constant, resulting in the increase of ice-surface scattering, while volume and ice-bottom scattering was continuously increased due to increasing transmissivity. At the end of the experiment, air temperature rose above freezing point, and ice surface thawed again so that ice-surface scattering increased while volume and ice-bottom scattering were decreased.</P>

Glacial and tidal strain of landfast sea ice in Terra Nova Bay, East Antarctica, observed by interferometric SAR techniques

Han, Hyangsun,Lee, Hoonyol Elsevier 2018 Remote sensing of environment Vol.209 No.-

<P><B>Abstract</B></P> <P>The dynamics of landfast sea ice, also called fast ice for short, has a large influence on the variability of polynyas and marine ecosystems, and the logistics for research stations near the Antarctic coast. Therefore, it is important to accurately measure the strain of fast ice and its seasonal variations, and to identify the cause of stresses on the ice. In this paper, we separate the strains from glacial stress and tidal stress of fast ice near the Campbell Glacier Tongue (CGT) in Terra Nova Bay, East Antarctica. This was done using observations from a series of one-day tandem COSMO-SkyMed Interferometric Synthetic Aperture Radar (InSAR) images obtained from December 2010 to January 2012. Firstly, we discriminated fast ice from pack ice and open water by analyzing the interferometric coherence values. We then identified the characteristics of the strains by investigating the equi-displacement lines of fringes in weekly InSAR and double-differential InSAR (DDInSAR) images. The weekly InSAR images predominantly showed glacial shear strain of the fast ice with fringes parallel to the sides of the CGT. This was due to the cumulative flow of the CGT for a week, while oscillating tidal signals were relatively small. The DDInSAR images, which cancelled glacial strain rates in two one-day InSAR images, showed a deformation of the fast ice by tidal sea surface tilt, with the fringes parallel to the coastline. Based on the unique characteristics of these strains, we separated them from the one-day InSAR images by decomposing the fringe patterns into glacial and tidal strain. Glacial shear strain rates of fast ice attached to the east of the CGT decreased from May to August owing to ice thickening and then stabilized until December. Those to the west of the CGT increased from May to July. This was possibly due to bottom melting of the ice by the increased ocean circulation during the expansion period of the nearby polynya. The glacial strain then decreased until December because of reduced polynya activity. The fast ice near the Jang Bogo Station (JBS) only showed tidal strain as it was isolated from the CGT by cracks and leads. Tidal strain rates of the fast ice were strongly correlated with the magnitude of tidal variations in all these regions, which represents shows that the tidal strain represents tidal sea surface tilt. The tidal response of fast ice to the west of the CGT and near the JBS was stronger than that to the east of the CGT, probably owing to thinner ice thickness there.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Glacial and tidal strain of fast ice near Campbell Glacier Tongue was investigated. </LI> <LI> Characteristics of the strains were identified from weekly InSAR and DDInSAR images. </LI> <LI> The strains were decomposed from one-day InSAR signals based on the characteristics. </LI> <LI> Glacial strain of fast ice varied seasonally due to the changes in ice thickness. </LI> <LI> Tidal strain representing tidal sea surface tilt was correlated with tide variations. </LI> </UL> </P>

Continuous Monitoring of Rice Growth With a Stable Ground-Based Scatterometer System

Yihyun Kim,Hoonyol Lee,Sukyoung Hong IEEE 2013 IEEE geoscience and remote sensing letters Vol.10 No.4

<P>Ground-based polarimetric scatterometers have been effective tools to monitor the growth of rice crop, with much higher temporal resolution than satellite synthetic aperture radar systems. However, scatterometer data obtained in every few days, as were the case for the previously reported studies, were not enough to address the effects of ever-changing weather conditions. In this letter, we constructed a highly stable X-, C-, and L-bands polarimetric scatterometer system in an air-conditioned shelter. The incidence and azimuth angles of the antenna were fixed to 40<SUP>°</SUP> and 0 <SUP>°</SUP>, respectively, to avoid uncertainty in repositioning error. Season-long daily backscattering coefficients from transplanting to harvesting were compared with rice growth data. Total fresh weight, leaf area index, and plant height were highly correlated with L-HH (0.97, 0.96, and 0.88, respectively) due to the deeper penetration and the dominance of double bounce in lower frequency. High-quality backscattering data clearly revealed the dual-peaked pattern in X-band, among which X-VV correlated best with grain dry weight and gravimetric grain water content (0.94 and 0.92, respectively) due to the better interaction of grain and rice canopy with microwave of higher frequency. These results will be useful in retrieving crop biophysical properties and determining the optimum microwave frequency and polarization necessary to monitor crop conditions.</P>