Duk-jin Kim

Application of TerraSAR-X Data for Emergent Oil-Spill Monitoring

Synthetic aperture radar (SAR) signals can propagate through hazardous weather and atmospheric conditions with heavy cloud cover, volcanic dust, snow, or rain. The all-weather capabilities of SARs have attracted significant interest in remote sensing communities, since serious environmental disasters such as oil spills have been highly ¿elusive¿ to optical sensors, making visible spectrum data vulnerable to rapidly changing atmospheric conditions. In this paper, we discuss the technical functionalities of TerraSAR-X from the emergency response perspective, describing its technical abilities in terms of a damping ratio, radiometric accuracy, and noise level with reference to the actual Hebei Spirit oil-spill incident that occurred on the west coast of the Korean peninsula in December 2007. The damping ratios estimated from the TerraSAR-X data as a function of Bragg wavenumber for various wind speeds indicate that TerraSAR-X data can be effectively used to identify oil-spill areas with acceptable accuracy. We also received ERS-2, ENVISAT, RADARSAT-1, and ALOS PALSAR data for this oil-spill event, not simultaneously but with varying time delays. The processing results for the multitemporal data sets obtained from the X- and C-band SAR systems are useful since they can be used to determine the near-real-time migration of spilt oil. The results of the current study indicate that there are distinct advantages of using X-band TerraSAR-X data for oil-spill detection compared to the data obtained at other available frequencies.

Estimation of Surface Roughness Parameter in Intertidal Mudflat Using Airborne Polarimetric SAR Data

The coastal zones of the Korean peninsula are well known for their large tide ranges and vast expanse of intertidal flats. In this paper, methods of extracting the roughness of the scattering surface of intertidal mudflats from polarimetric synthetic aperture radar (SAR) data have been investigated. The L-band NASA/Jet Propulsion Laboratories airborne SAR data, which were acquired in the intertidal zone during PACRIM-II Korea campaign, were used to estimate the roughness of intertidal mudflats. Surface roughness can be utilized as a useful parameter to monitor the fishery activities in intertidal flats as well as the changes in textural characteristics of surface sediments. In order to retrieve roughness parameters, such as the rms height and the correlation length, of intertidal mudflats, three types of roughness inversion algorithms, based on the Integral Equation Method (IEM), semiempirical, and extended-Bragg models, have been investigated and developed. The inversion algorithms based on the IEM and semiempirical models can be applied to the dual-polarized SAR, while the extended-Bragg model-based inversion approach is also applicable to the fully polarimetric SAR observations. Results indicate the fully polarimetric approach is more pertinent to monitor geophysical parameters from space than the dual polarimetric approach, even if it is possible to reduce the number of unknown surface variables in the specific case of inversion problems.

Dependence of Waterline Mapping on Radar Frequency Used for SAR Images in Intertidal Areas

Waterline detection in the intertidal areas was investigated through synthetic aperture radar (SAR) images and field measurements. Two valuable facts were found in this letter: 1) A discrepancy of waterlines between L- and P-band airborne SAR images was discovered and investigated through precise global positioning system measurements and the theory of the SAR imaging mechanism. In the intertidal areas having low slopes, the Bragg waves resonant with the radar signal can reside in different depths depending on the radar frequency, with the result that the boundary between water and land can be mapped differently in the respective SAR images. 2) Intertidal areas covered with a water film present low radar backscatter in SAR images, which can cause mislocation of waterlines

Characterization of Arctic Sea Ice Thickness Using High-Resolution Spaceborne Polarimetric SAR Data

In this paper, we have investigated the relationship between the depolarization effects and the wintertime sea ice thickness in the landfast ice region where smooth thick first-year ice (FYI) and deformed old ice coexisted by using C- and X-band spaceborne polarimetric synthetic aperture radar (SAR) data (RADARSAT-2 and TerraSAR-X). We have found a strong correlation between the in situ sea ice thickness and the SAR-derived depolarization factors (copolarized correlation and cross-polarized ratio). The observed relationships have demonstrated not only a categorical difference between FYI and multiyear ice (MYI) but also a one-to-one continuity in the scatter plots, rather than being clustered. It clearly shows that the observed correlations are not merely from the categorical difference in scattering mechanism between FYI and MYI and that there might exist a one-to-one relationship between thickness and depolarization factors at least in our deformed ice case. This suggests that depolarization factors could be effective SAR parameters in the estimation of wintertime sea ice thickness. Numerical model simulations explained some portions of the correlation by employing multiple scattering on the sea ice surface and volume scattering within the low-density subsurface layer.

Estimation of sea surface wind vector using RADARSAT data

Abstract Synthetic aperture radars (SAR) have higher spatial resolution than scatterometers and we can obtain more detailed wind vector information from space-borne SAR data. This type of high spatial resolution wind information can be very useful particularly in coastal regions, where the scatterometer wind information can be altered by the coastal effects because the larger footprint spatial averaging of backscattered energy is unavoidable. This paper tested RADARSAT data with CMOD_4 and CMOD_IFR2 algorithms for extracting wind information over selected coastal test areas around the Korean peninsula. Because the CMOD algorithms were originally developed for the C-band, VV-Polarized scatterometer data, we applied currently available polarization ratio models (e.g., Kirchhoff, Elfouhaily, and Thompson models) for RADARSAT data processing. Three test areas, the West Sea and East Sea on both sides of the Korea peninsula and the open sea off Jeju Island, were tested with the RADARSAT Fine, Standard, and ScanSAR beam mode data. The correlation of the wind vector results with the buoy and meteorological station data agrees well with each other but with some variations. The RMS error for the SAR-derived wind direction is somewhat great, and the wind speed RMS error using CMOD_4 algorithm is about 1.7 m/s (Kirchhoff), 1.84 m/s (Elfouhaily), and 2.4 m/s (Thompson polarization ratio model), respectively.

RADARSAT-2 and Coastal Applications: Surface Wind, Waterline, and Intertidal Flat Roughness

RADARSAT-2 is a follow-up to RADARSAT-1 and is an all weather Earth observation satellite with fully polarimetric imaging capability. The synthetic aperture radars (SARs) onboard both RADARSATs are C-band imaging radars and they are well suited for Earths ecosystem monitoring and maritime surveillance, because of the near polar orbit and their unique all weather imaging capability, independent of solar illumination. In this paper, RADARSAT-2 is first introduced and several applications of various modes of SAR data to coastal zone problems are discussed, including the coastal surface wind, waterline mapping, and polarimetric SAR data inversion for topographic and geological parameters of tidal flats. Coastal zones, the important interface between the land and the ocean, where a large proportion of the worlds population inhabits, continuously change and evolve. The dynamic interaction of coastal winds, coupled with the coastal waves and currents, continuously erode rocks and land mass, and move and deposit various sediments on a continuous basis, along with the tides. Estimation of wind speeds and directions in coastal areas are empirically formulated and can further be improved with the available fully polarimetric data from RADARSAT-2. The water line mapping critically depends on the SAR frequency, or the wavelength of the SAR data used, and RADARSAT-2 SAR data using C-band should map waterlines more accurately than the longer wavelength L- or P-band SAR systems. The roughness parameters and partial information on the tidal flat compositions can be obtained from fully polarimetric SAR data. Some results obtained from NASA AIRSAR(2000) L-band data and RADARSAT-2(2008) C-band data do not fully agree with field measurements and further investigation is in progress. The inversion of polarimetric SAR data is a very complex problem and critically depends on the SAR signal frequency and model functions. RADARSAT-2 is an imaging radar, which is very flexible and powerful tool for potential coastal zone applications. Key RADARSAT-2 features and potential coastal zone application capabilities are also briefly reviewed.

Measurements of ocean surface waves and currents using L- and C-band along-track interferometric SAR

Along-track interferometric synthetic aperture radar (ATI-SAR) is an active coherent imaging system, utilizing two antennas separated along the platform flight direction. The phase information of ATI-SAR from the Doppler shift of the backscattered signal represents the line-of-sight velocity of the water scatterers. While the advent of ATI-SAR provided us with a potentially powerful technique for ocean surface current and wave mapping, the surface current has not been measured exactly from the ATI-SAR velocity because the Doppler shift is not simply proportional to the component of the mean surface current. It also includes other types of contributions associated with the phase velocity of the Bragg waves and orbital motions of all ocean waves that are longer than Bragg waves. In this paper, we review how the phase difference measured by ATI-SAR is related to the mean Doppler frequency, and we develop a new and practically useful method to extract the surface current component utilizing simultaneously measured L- and C-band ATI-SAR data. Since the measured ATI-SAR velocity shows a different value at a different radar-frequency, we investigate the influence of Bragg-resonant waves and long ocean wave motions on the ATI-SAR velocity according to the radar frequency. The Bragg-wave phase velocity component, which is a significant source of error for extracting the surface current, can be effectively eliminated by using L- and C-band ATI-SAR. The method is applied to L- and C-band ATI-SAR measurements acquired at the Ulsan coast in the southeastern part of the Korean peninsula. The resulting ocean surface current vectors are compared with in situ measurements collected by recording current meter. We furthermore extract ocean surface wave information from the ATI-SAR phase image using a quasi-linear transform.

Monitoring of urban land surface subsidence using PSInSAR

Space-borne and ariborne SAR (Synthetic Aperture Radar) systems and SAR application technology have recently advanced greatly and interferometric SAR (InSAR) techniques can now be more effectively applied and used in many geological and engineering problems. There are several SAR data acquisition geometries for interferometric applications and PS (Permanent Scatter) InSAR (SAR interferometry) technique can accurately measure very small deformations on the Earths surface with greatly increased precision. In this paper, the PSInSAR technique is tested and utilized to monitor and measure the land surface subsidence of areas near Incheon Port, and selected locations in Busan, Korea. All available JERS-1 (Japanese Earth Resource Satellite-1) L-band SAR data were acquired, processed and used to estimate the ground subsidence and subsidence rates, which range up to 30 mm/year.

Melt Pond Mapping With High-Resolution SAR: The First View

Melt pond statistics (size and shape) have previously been retrieved from aerial photography and high-resolution visible satellite data. These submeter- or meter-resolution visible data can provide reasonably accurate information on melt ponds, but are greatly constrained by the limited solar illumination and frequent cloud cover in the Arctic region. In this study, we venture into exploring high-resolution synthetic aperture radar (SAR) or imaging radar method for melt pond mapping, which is not severely disrupted by cloud or low solar zenith angle. We analyzed high-resolution airborne SAR images (0.3-m resolution) of midsummer sea ice, acquired from a helicopter-borne SAR system in the northern Chukchi Sea. The pond area and shape (circularity) derived from the airborne SAR images showed that the statistics were comparable to those previously observed from aerial photographs. We argue that high-resolution SAR, together with one-to-one comparison with coincident aerial photographs, can be used to map melt ponds at a level of detail comparable to aerial photography or high-resolution optical satellite remote sensing. Our encouraging results suggest the possibility of using high-resolution SAR (current or future systems) to map melt ponds in the Arctic region.

Observed impact of mesoscale circulation on oceanic response to Typhoon Man-Yi (2007)

The oceanic response to a typhoon, where mesoscale ocean circulations co-exist, was investigated by analyzing the independent observations of profiling floats data at three different locations, satellite altimetry data near the eye of Typhoon Man-Yi (2007) before and after its passage, and synthetic aperture radar data taken during the typhoon’s passage. In spite of the nearly symmetric wind pattern around the eye, the distribution of mesoscale eddies had a major impact on the surface currents and mixed layer (ML) depths. As a result, the entrainment of the water below the ML into the ML was affected by the mesoscale circulation and became asymmetric, which accounted for most of the changes observed in the temperature profiles. Changes in the isotherms were driven primarily by the westward propagation of the mesoscale pattern rather than by the typhoon-induced shoaling. The typhoon-induced shoaling could have played a significant role in the generation of high-frequency (e.g., near-inertial) oscillations and/or sub-mesoscale structures. Although a similar or even greater energy flux was observed at the surface, the entrainment within the anticyclonic circulation was weaker than that within the cyclonic circulation and at the edge of the anticyclonic circulation because of the thick pre-existing ML. A strong ocean response to Typhoon Man-Yi (2007) within a cyclonic circulation or at the edge of an anticyclonic circulation, rather than within an anticyclonic eddy, has implications for the role of mesoscale ocean circulations in better understanding and forecasting the typhoon intensity.