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Coastal sea level changes measured by tide gauges are affected by the severity of coastal land motion. Subsidence due to natural and anthropogenic activities in the coastal regions were directly exacerbates the tide gauge records. In this study, we aim to monitor the coastal land motion at the tide gauges in Korean peninsula using multi-temporal InSAR techniques. We present the methodology that simply employs the selection of sequential and small temporal interferograms in the StaMPS-SBAS technique for increased coherent PS pixels over coastal regions. C-band Sentinel-1 SAR data from ascending and descending mode were acquired over Pohang and Yeosu regions to map the coastal land motion. The preliminary results showed significant increased number of initial PS pixel density than conventional StaMPS-SBAS technique, chosen by Amplitude-Dispersion Index (ADI) and revealed the subsidence about 2 cm/year in Pohang tide gauge and small uplift of 1.46 mm/year near Yeosu tide gauge.

Relative sea-level changes observed by tide gauges are commonly corrected for several components including crustal displacement, ocean dynamics, and vertical land motion. Vertical Land Motion (VLM) due to local land hydrology is a crucial component that observed as localized ground motion and varies with each tide gauges. Permanent GNSS stations are used to measure the VLM trend at tide gauges, however, only few tide gauges are equipped with collocated GNSS stations. Multi-temporal InSAR analysis provides ground displacements in both the spatial and temporal domains. Therefore, in our study, we applied the spaceborne Interferometric SAR technique to measure the local ground motion using Sentinel-1 SAR data. The Korean peninsula is surrounded by the East Sea/Sea of Japan, the Yellow Sea and the East China Sea have continuously monitoring tide gauges with a record length of more than 30 years. We acquire C-band Sentinel-1 SAR data (both ascending and descending mode) over the Korean Peninsula during 2014/11 and 2019/04. We estimate the high-resolution (~ 10 m) land motion at tide gauges (mm-level accuracy) over these 21 tide gauges and, compared with available collocated GNSS observations. 2D displacements (vertical and horizontal) are derived from ascending and descending mode InSAR displacements. The linear trend of VLM observed from our InSAR estimates is used to compensate for the relative velocity of sea-level changes observed from tide gauges.

Detection of changes caused by major events-such as earthquakes, volcanic eruptions, and floods-from interferometric synthetic aperture radar (SAR) data is challenging because of the coupled effects with temporal decorrelation caused by natural phenomena, including rain, snow, wind, and seasonal changes. The coupled effect of major events and natural phenomena sometimes leads to misinterpretation of interferometric coherence maps and often degrades the performance of change detection algorithms. To differentiate decorrelation sources caused by natural changes from those caused by an event of interest, we formulated a temporal decorrelation model that accounts for the random motion of canopy elements, temporally correlated dielectric changes, and temporally uncorrelated dielectric changes of canopy and ground. The model parameters are extracted from the interferometric pairs associated with natural changes in canopy and ground using the proposed temporal decorrelation model. In addition, the cumulative distribution functions of the temporally uncorrelated model parameters, which are associated with natural changes in canopy and ground, are estimated from interferometric pairs acquired before the event. Model parameters are also extracted from interferometric SAR data acquired across the event and compared with the cumulative probabilities of natural changes in order to calculate the probability of a major event. Subsequently, pixels with cumulative probabilities greater than 75% are marked as changed due to the event. A case study for detecting volcanic ash during the eruption of the Shinmoedake volcano in January 2011 was carried out using L-band Advanced Land Observation Satellite PALSAR data.

Coastal Subsidence is a global phenomenon that caused by both natural and anthropogenic activities. The impact of coastal subsidence can affect the monitoring of sea level rise by in-situ tide gauges. The Korean peninsula is one of such areas that reported considerably rapid sea level rise than the global average in the recent years. The objective of this study is to estimate the earth’s surface movements along the coastal areas of Pohang, South Korea. To achieve that, we acquired C-band Sentinel-1 data during 2016 – 2017. Time-series InSAR technique is applied to measure displacements at high-resolution with reduced decorrelation noise from interferograms. The results showed about 1.83 cm/year subsidence in the Pohang coastal area, where significant sea level rise is observed in this region. The results will provide further insight into the localized subsidence rates in the study sites and its impact on the sea level monitoring.

Monitoring land subsidence is important to prevent and manage disasters. The extent of land subsidence can be measured by various ways and one of them is PSI technique. Guatemala City has geologically weak structure and suffered from disasters such as sinkhole and landslide. The purpose of this study was to measure wide range of relative movement in Guatemala City and to analyze obtained values. C-band Sentinel-1 A/B data during November 2014 to March 2018 were used in this study. By gathering information from both ascending and descending paths, relative movements were decomposed from line of sight of each path to vertical and horizontal component. As a result 4 regions in Guatemala City showed significant subsidence patterns with average vertical movement going down with a scale of 14 mm/year.

Subsidence is a widespread phenomenon caused by both natural and anthropogenic activities, particularly in the coastal areas. Eventually, the impact of coastal subsidence can affect the monitoring of sea level rise by in-situ tidal gauge stations. The Korean peninsula is one of such areas that reported considerably rapid sea level rise than the global average in the recent years. Therefore, there is a need for assessing the land subsidence component of relative sea level rise for better future prediction models. Space borne Interferometric SAR technique provides millimeter level of accuracy in displacement measurements. The objective of this study is to estimate the earth’s surface movements along the coastal areas of Pohang, South Korea. To achieve that, we acquired C-band Sentinel-1 data during 2016 – 2017. Time-series Stanford Method of Persistent Scatter (StaMPS) InSAR analysis proved technique to measure displacements at highresolution with reduced decorrelation noise from interferograms. The results showed about 1.83 cm/year subsidence in the Pohang coastal area, whereas significant sea level rise is observed in this region. The results will provide further insight into the localized subsidence rates in the study sites and its impact on the sea level monitoring.

Extensive intertidal flats along the west coast of the Korean Peninsula form very unique coastal ecosystems providing habitat for a variety of benthic species. Spatial variation of physical surface properties and structures in intertidal flats can be associated to different polarimetric Synthetic Aperture Radar (SAR) signatures, which have a great potential for intertidal flat mapping. We find that complex and rough surface structures of densely populated wild oyster reefs can cause very strong diffused-multiple scattering and depolarization at C- and X-bands, while not at a relatively longer wavelength, L-band. Along the outer margin of intertidal flats adjacent to the land, very dark radar backscattering signatures are observed, which result from specular reflection on shallow water puddles formed by Submarine Groundwater Discharge (SGD). This chapter demonstrates distinct radar scattering signatures of wild oyster habitat and SGD in intertidal flats based on polarimetric SAR observations and theoretical scattering models, and suggests how they can be quantitatively mapped using multi-frequency polarimetric SAR. Finally, the correlation between the distribution of wild oyster habitat and the occurrence of SGD is discussed.

Submarine groundwater discharge (SGD) is a global phenomenon that carries large volumes of groundwater and dissolved chemical species such as nutrient, metals, and organic compounds to coastal zones. We report the influence of SGD on the coastal waters of Jeju Island, Korea, using high-resolution aerial thermal infrared (TIR) mapping techniques and field investigations. An aircraft-based system was implemented using a cost-effective TIR camera for aerial TIR mapping. Ground-based calibrations and system integration with GPS/IMU (global positioning system/inertial measurement unit) were performed for the aerial systems. The aerial surveys showed distinct low-temperature signatures of SGD along the coasts of Jeju Island, revealing large groundwater inputs from the coastal aquifers to the ocean. Multiple aerial surveys over a range of seasons and tidal stages revealed that SGD rates dynamically affect the sea surface temperature (SST) of the coastal zone. The in-situ measurements supported that SGD has a substantial influence on the coastal water chemistry as well as SST. Our observations highlight the extent to which aerial-based TIR mapping can serve as a powerful tool for studying SGD and other coastal processes. Copyright © 2016 John Wiley & Sons, Ltd.

Backscattering coefficients of Sentinel-1 synthetic aperture radar (SAR) data of drifting multi-year sea ice in the western Beaufort Sea during the transition period between the end of melting and onset of freeze-up are analyzed, in terms of the incidence angle dependence and temporal variation. The mobile sea ice surface is tracked down in a 1 km by 1 km region centered at a GPS tracker, which was installed during a field campaign in August 2019. A total of 24 Sentinel-1 images spanning 17 days are used and the incidence angle dependence in HH- and HV-polarization are −0.24 dB/deg and −0.10 dB/deg, respectively. Hummocks and recently frozen melt ponds seem to cause the mixture behavior of surface and volume scattering. The normalized backscattering coefficients in HH polarization gradually increased in time at a rate of 0.15 dB/day, whereas the HV-polarization was relatively flat. The air temperature from the ERA5 hourly reanalysis data has a strong negative relation with the increasing trend of the normalized backscattering coefficients in HH-polarization. The result of this study is expected to complement other previous studies which focused on winter or summer seasons in other regions of the Arctic Ocean.

Ice rumples are locally-grounded features of flowing ice shelves, elevated tens of meters above the surrounding surface. These features may significantly impact the dynamics of ice-shelf grounding lines, which are strongly related to shelf stability. In this study, we used TanDEM-X data to construct high-resolution DEMs of the Thwaites ice shelf in West Antarctica from 2011 to 2013. We also generated surface deformation maps which allowed us to detect and monitor the elevation changes of an ice rumple that appeared sometime between the observations of a grounding line of the Thwaites glacier using Double-Differential Interferometric SAR (DDInSAR) in 1996 and 2011. The observed degradation of the ice rumple during 2011–2013 may be related to a loss of contact with the underlying bathymetry caused by the thinning of the ice shelf. We subsequently used a viscoelastic deformation model with a finite spherical pressure source to reproduce the surface expression of the ice rumple. Global optimization allowed us to fit the model to the observed deformation map, producing reasonable estimates of the ice thickness at the center of the pressure source. Our conclusion is that combining the use of multiple high-resolution DEMs and the simple viscoelastic deformation model is feasible for observing and understanding the transient nature of small ice rumples, with implications for monitoring ice shelf stability.

Oceanic internal waves are known to be important to the understanding of underwater acoustics, marine biogeochemistry, submarine navigation and engineering, and the Earth’s climate. In spite of the importance and increased knowledge of their ubiquity, the wave generation is still poorly understood in most parts of the world’s oceans. Here, we use satellite synthetic aperture radar images, in-situ observations, and numerical models to (1) show that wave energy (having relatively high amplitude) radiates from a shallow sill in the East China Sea in all directions, but with a significant time lag dependent on background conditions, (2) reveal that wave fronts are locally formed with often favorable conditions for re-initiation, and (3) demonstrate the resulting variety of wave patterns. These findings would be the case for any broad shelf having shallow sills with time-varying conditions, and therefore have significant implications on the redistribution of energy and materials in the global as well as regional ocean.

Thwaites Ice Shelf in the Amundsen Sea is one of the biggest ice shelves in West Antarctica and is well known for significant mass changes. In the shear zone between Thwaites Glacier Tongue and its eastern ice shelf, shear stress forced by different flow rates of the ice shelves is causing the ice to break apart. A time series analysis of remote sensing data obtained by Landsat 7 Enhanced Thematic Mapper Plus (ETM+), TerraSAR-X, and airborne synthetic aperture radar (SAR) revealed that the shear zone has extended since 2006 and eventually disintegrated in 2008. We quantified the acceleration of Thwaites Ice Shelf with time by using the feature tracking method. The buttressing loss induced by the extension of the shear zone and progressive disintegration accelerated the flow of Thwaites Glacier Tongue, which in turn increased the shear stress on its eastern ice shelf. We determine causes of disintegration in the newly formed shear zone to be oceanic basal melting and structural weakening induced by Circump...

Intertidal flats which are located between land and ocean are productive and rapidly changing places. But these places are now facing many environmental challenges related to climate change and human-induced impacts. Topographic change related to sedimentation or erosion in intertidal flats is the most evident sign of the environmental changes. The intertidal flats usually have small topographic variations (less than 5m) and experience ebb and flood tides every day. Thus, the conventional SAR interferometric techniques (repeat-pass InSAR) cannot be applied for generating DEMs in these intertidal flats. In this study, we developed a long-baseline single-pass airborne interferometric SAR (InSAR) system that has small ambiguity height and collected airborne InSAR data in several intertidal flats, the west coast of Korean peninsula. The constructed topographies using the long-baseline airborne InSAR system were compared with TanDEM-X DEM obtained during long-baseline mission phase.

Definite surface topography of ice provides fundamental information for most glaciologists to study climate change. However, the topography at the marginal region of ice sheets exhibits noticeable dynamical changes from fast flow velocity and large thinning rates; thus, it is difficult to determine instantaneous topography. In this study, the surface topography of the marginal region of Thwaites Glacier in the Amundsen Sector of West Antarctica, where ice melting and thinning are prevailing, is extracted using TanDEM-X interferometry in combination with data from the near-coincident CryoSat-2 radar altimeter. The absolute height offset, which has been a persistent problem in applying the interferometry technique for generating DEMs, is determined by linear least-squares fitting between the uncorrected TanDEM-X heights and reliable reference heights from CryoSat-2. The reliable heights are rigorously selected at locations of high normalized cross-correlation and low RMS heights between segments of data points. The generated digital elevation model with the resolved absolute height offset is assessed with airborne laser altimeter data from the Operation IceBridge that were acquired five months after TanDEM-X and show high correlation with biases of 3.19 m and −4.31 m at the grounding zone and over the ice sheet surface, respectively. For practical application of the generated DEM, grounding line estimation assuming hydrostatic equilibrium was carried out, and the feasibility was seen through comparison with the previous grounding line. Finally, it is expected that the combination of interferometry and altimetery with similar datasets can be applied at regions even with a lack of ground control points.

One of the main limitations in measuring ground deformation using synthetic aperture radar interferometry (InSAR) is atmospheric phase delay effects. In volcanic regions, the atmospheric phase delay effects can cause serious problems in detecting volcanic unrest because atmospheric thickness is inversely related with the elevation of a volcanic mountain. It is commonly known that the atmospheric phase screen (APS) can be decomposed spatially into stratified and turbulent components. In this paper, the stratified and turbulent atmospheric conditions of a volcanic area were simulated using weather research and forecasting (WRF) model, and the simulated atmospheric conditions were compared with in situ radiosonde data. The comparison results proved that the stratified APS from the WRF model could reflect the reasonable patterns of seasonal changes and vertical profiles with dependable quality. We also found that the stratified APS was significantly correlated with time and sometimes severely contaminated the quality of volcanic deformation estimation. These results indicate that the temporal high-pass (HP) filtering, which has been usually applied in time series InSAR analysis for extracting and removing APS, cannot work properly in volcanic area. Thus, we propose a new method that employs the stratified APS obtained from the WRF model by correlating with topography and the (residual) turbulent APS that can be effectively eliminated by temporal HP filtering in persistent scatterer interferometry (PSI). We applied the proposed method (atmosphere-corrected PSI) to Advanced Land Observing Satellite Phased Array type L-band SAR data that cover Shinmoedake volcano, Japan, and found that the estimated surface deformation and APS agreed well with those measured from GPS and Moderate-Resolution Imaging Spectroradiometer data, respectively.

Recently, higher sea surface temperature and less sea ice extents have been reported because the polar environments are dramatically transforming because of climate change. Measurements of sea ice thickness are important for assessing climate change. Thus, it is required to constantly monitor sea ice thickness to accurately measure and estimate the future trends of the polar environment. In this study, the average sea ice thickness in the Arctic Ocean was calculated by using elevation data from a laser rangefinder installed on the icebreaker, RV Araon, operated by Korea Polar Research Institute (KOPRI). The freeboard was calculated by using the elevation data from the top of the bow, and the ice draft was calculated using hydrostatic equilibrium. The results showed that the sea ice thickness increased with higher latitudes and from east to west and the obtained data are expected to be a fundamental basis for the future research of climate change by monitoring the polar region.

Intertidal flats are productive and rapidly changing places. However, these places are facing many environmental challenges related to climate change and human-induced impacts. Topographic change due to sedimentation or erosion in intertidal flats can be the key indicator for recognizing these environmental changes. The intertidal flats usually have small topographic variations (less than 5m) and high-moistured soil surfaces (greater than 50%). The conventional SAR interferometric techniques cannot be used for generating DEMs in these intertidal flats. In this study, we developed a long-baseline airborne interferometric SAR (InSAR) system that has small ambiguity height and collected airborne InSAR data in Jebu intertidal flat, west coast of Korean peninsula. The constructed topographies using the long-baseline airborne InSAR were compared with TanDEM-X DEM (acquired during long-baseline mission phase) and GPS-RTK measurements.

Detection of changes induced by major events such as earthquakes, flooding and volcanic eruptions from interferometric SAR data is difficult due to the coupled effects with temporal decorrelation caused by natural phenomena such as rain, snow, wind and seasonal changes. In this study, we aim to separate the decorrelation caused by natural changes from the one caused by the major event by analyzing the coherence behavior using a temporal decorrelation model. We formulated the temporal decorrelation model that accounts for the random motion and dielectric changes. By applying the model into the multi-temporal coherence before the event, we extracted the temporal decorrelation components induced by natural phenomena. Based on the extracted parameters, their decorrelation probabilities related to natural changes were estimated in canopy and ground. The model parameters are also extracted from the interferometric SAR data acquired across the event. We compared probabilities between the natural phenomena and the certain event in order to assign the changed regions. Pixels with cumulative probabilities greater than 80% are selected as changed due to the event. A case study for detecting volcanic ash during the eruption of the Shinmoedake volcano in January 2011 was carried out using L-band Advanced Land Observation Satellite (ALOS) PALSAR data.

Grounding line estimation has substantial importance of determining vulnerability of ice mass in the Polar Regions. In this study, high resolution digital elevation model is utilized to estimate and update grounding line of Thwaites Glacier in West Antarctica in 2011. Estimation is done by comparing the calculated bottom topography of ice with the bathymetry model from Operation IceBridge. The bottom topography is computed by subtracting ice thickness which is also estimated from surface elevation assuming hydrostatic equilibrium. The updated grounding line infers its retreat of up to 5km inland when compared with the grounding line in 2009. The retreat is conspicuous over the bathymetric trough. Conceivable error sources are still present such as ice column density, bathymetry accuracy and firn height. Nonetheless, high resolution digital elevation model shows high practicability of estimating grounding line.

In this study, detection of icebergs that have various scattering characteristics aroundWilkinson glacier in West Antarctica is investigated using C-band fully-polarimetric RADARSAT-2SAR data. Various polarimetric analyses including Freeman-Durden decomposition, H/A/ @a decomposition, entropy (H) and anisotropy (A) method, and Wishart unsupervised classification, wereapplied for the RADARSAT-2 data used in this study. The polarimetric decomposition methods weresuccessfully classified most of the iceberg, yet some iceberg with similar intensity of volume andsurface scattering as sea ice were indistinguishable. Unsupervised classification with a combination ofthe polarimetric parameter, [1-H][1-A], gave a possibility to distinguish those unclassified iceberg.Key Words : Iceberg, West Antarctica, Polarimetry, RADARSAT-2, Classification i ¤ ™ A ² × ² i O c A$ – a8JMLJOTPO B Þ± o A“d Þ × i ¨ a ‘ AE `U8 I × B ‘8 Š c š ($ O X3"%"34"5 D io ž u a ? ³ ƒ eI 4"3 W 3I Þ E N a uS × Ý e8 E ³ Þ O i io ž u4"3 W Ax a uS × i ¨ a Ý e \oyW Ý u ‘ AE ` ?8 u ˆ a uS ×'SFFNBO %VSEFO EFDPNQPTJUJPO ) " @a EFDPNQPTJUJPO O ; ŠFOUSPQZ ) iBOJTPUSPQZ " Ý e \ — io ž u4"3W D ( 3$ c8JTIBSU – E ) ( e8 E ³N E4"3 W Ax Þ O i O ~ — 'SFFNBO %VSEFO ) " @a EFDPNQPTJUJPO8I a Ý e \7 D B ‘ \8\ ( Þ ON E c B — : $ a ´ v ‘ AE — Sx ‘ AE8 >N ŠS × B ‘7 ³ :N ‹ “ i E v ) i"D‘ a o uo Þ aK o u 3I a – E ) ( e7I Þ a B ‘ \8\ ³ Þ O i

Exposed oyster reefs in tidal flats have complex and rough surfaces because of their unique surface texture, which are quite distinct from the surrounding mud or sand flats. Here we investigate the microwave signatures, backscattered from naturally distributed oyster reefs in tidal flats, utilizing the polarimetric analysis techniques to fully polarimetric RADARSAT-2 (C-band) and ALOS PALSAR (L-band) data. The study areas include the tidal flats around Jebu Island and Hampyung Bay on the west coast of the Korean peninsula. We analyzed the microwave scattering mechanisms associated with oyster reefs and surrounding areas using the polarimetric target decomposition theorem and quantitatively measu ρ HHVV red target depolarization effects (the cross-polarized ratio (HV/VV), the co-polarized correlation coefficient ( ρ HHVV ), and the co-polarized phase difference between HH and VV). On the basis of a large increase in the cross-polarized backscattering (HV) in the C-band SAR data, one can observe strong volume (or multiple) scattering and depolarization effects over oyster reefs areas, whereas only surface scattering was dominant in most parts of the background tidal areas. In oyster reefs, the proportion of volume scattering and the cross-polarized ratio were greater than 0.7 and −8 dB, respectively. These scattering characteristics were also verified from in-situ measurements in the field using a ground-based polarimetric scatterometer system. However, almost no difference was observed between the scattering signatures of oyster reefs and background mudflat areas from L-band data, which have a considerably longer wavelength than C-band. The study clearly suggests that multi-frequency (C- and L-band) polarimetric SAR systems can be used to detect the naturally distributed oyster reefs in tidal flats.

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.

Most space-borne sensors cannot detect subsurface features. Groundwater is a typical subsurface feature, and its discharge to coastal ocean waters plays an important role in transporting terrestrial chemical constituents and providing habitats for various species of fauna and flora. This is the first paper to report observational evidence for submarine groundwater discharge (SGD) in tidal flats using space-borne synthetic aperture radar (SAR). Tidal flats are composed of high-moisture-saturated sediments and water puddles. These shallow water puddles were imaged effectively by using SAR systems. The presence of water puddles is usually indicated by low radar backscatter in SAR images due to specular reflections on the water surface. This effect was proved by comparing radar backscattering coefficients obtained from two space-borne SAR systems, TerraSAR-X and RADARSAT-2, with those obtained from two theoretical scattering models, IEM and Oh model. We observed relatively large, widely distributed water puddles in belt shape along the upper parts of the tidal flat, which were confirmed to be related to the discharge of groundwater. The results of this research suggest that SAR can be a powerful tool for observing and determining the areal distributions of possible groundwater discharge in large tidal flats, which is normally difficult to detect with traditional measurement tools or survey techniques for groundwater discharge. We firmly believe that this technique can reduce significantly the efforts of field work to confirm SGD in tidal flats.

SAR change detection is useful when emergency situations occurred and weather conditions are unfavourable. In this study, a change detection using multi-temporal polarimetric UAVSAR data was investigated in urban environment. The most robust polarimetric parameter was evaluated, and change detction techniques using maximum likelihood ratio and hyperbolic tanget function were applied to the selected parameters. The comparison results with Google Earth's historical images showed a quite good agreement. A fitting of hyperbolic tangent function to the multi-temporal polarimetric parameters much reduced the false alarm rate, and it also provide whether the building was constructed or destructed and when the the changes occurred.

TanDEM mission enables the generation of high resolution digital elevation model over fast changing surfaces such as the Antarctic ice sheets. This study assesses the surface elevation over the marginal region of Thwaites Glacier in West Antarctica. The absolute height of SAR interferometry was derived by utilizing CryoSat-2 radar altimeter over the same region with minimizing temporal differences between the datasets. Then, the derived heights are compared with the airborne laser and radar altimetry data from the Operation IceBridge. The results show that surface and coherence are two main factors causing height offsets between the datasets, however, each effect must be separated for more accurate analysis.

The surface heights of the marginal region of ice sheets are of interest among most glaciologist and remote sensing studies of glaciers. There have been a number of difficulties in estimating accuracy surface information in the marginal regions due to rough surfaces and high slope angles. In this study, the surface heights of the marginal region of Thwaites Glacier are calculated in high resolution using SAR interferometry of TanDEM-X. The calculated surface heights are compared after the absolute offset correction using CryoSat-2 radar altimeter. The results show that the general surface patterns are highly correlated, however, the RMS heights are larger than expected. The possible explanations can be related to the footprint size of CryoSat-2 and snow penetration depth due to different radar frequencies. Besides, absolute phase offset needs to be calculated accurately. In general, the possibility of utilizing TanDEM-X and CryoSat-2 data in the marginal regions is expected to be promising.

Tidal flat plays an import role in purifying pollutants discharged from land and in providing marine products such as oyster and many kinds of shellfishes. Oyster in tidal flat usually has rough structures, causing a strong depolarization in microwave backscattering. The signatures can be detected using multi-frequency polarimetric synthetic aperture radar (SAR) data. Strong volume and depolarization effects were observed in the oyster reefs of C-band SAR data, while only surface scattering was dominant in the L-band SAR data. We also investigated why the oyster reefs distributed in those areas and how they generated naturally. We focused on groundwater discharge to relate the distribution of oyster in tidal flat, and found obvious signatures of groundwater discharge along the marginal part of the tidal flat from SAR data.

Melt ponds, a common feature on Arctic sea ice, absorb most of the incoming solar radiation and have a large effect on the melting rate of sea ice, which significantly influences climate change. Therefore, it is very important to monitor melt ponds in order to better understand the sea ice-climate interaction. In this study, melt pond retrieval models were developed using the TerraSAR-X dual-polarization synthetic aperture radar (SAR) data with mid-incidence angle obtained in a summer multiyear sea ice area in the Chukchi Sea, the Western Arctic, based on two rule-based machine learning approaches—decision trees (DT) and random forest (RF)—in order to derive melt pond statistics at high spatial resolution and to identify key polarimetric parameters for melt pond detection. Melt ponds, sea ice and open water were delineated from the airborne SAR images (0.3-m resolution), which were used as a reference dataset. A total of eight polarimetric parameters (HH and VV backscattering coefficients, co-polarization ratio, co-polarization phase difference, co-polarization correlation coefficient, alpha angle, entropy and anisotropy) were derived from the TerraSAR-X dual-polarization data and then used as input variables for the machine learning models. The DT and RF models could not effectively discriminate melt ponds from open water when using only the polarimetric parameters. This is because melt ponds showed similar polarimetric signatures to open water. The average and standard deviation of the polarimetric parameters based on a 15 × 15 pixel window were supplemented to the input variables in order to consider the difference between the spatial texture of melt ponds and open water. Both the DT and RF models using the polarimetric parameters and their texture features produced improved performance for the retrieval of melt ponds, and RF was superior to DT. The HH backscattering coefficient was identified as the variable contributing the most, and its spatial standard deviation was the next most contributing one to the classification of open water, sea ice and melt ponds in the RF model. The average of the co-polarization phase difference and the alpha angle in a mid-incidence angle were also identified as the important variables in the RF model. The melt pond fraction and sea ice concentration retrieved from the RF-derived melt pond map showed root mean square deviations of 2.4% and 4.9%, respectively, compared to those from the reference melt pond maps. This indicates that there is potential to accurately monitor melt ponds on multiyear sea ice in the summer season at a local scale using high-resolution dual-polarization SAR data.

Various polarimetric analyses were carried out in order to verify the break-up of the Thwaites Ice Tongue. The hypothesis was that the observed crack on the ice tongue must be filled with sea ice if completely broken. Although the recently published paper asserted that the ice tongue had been completely broken, we found that it is too early to come into the conclusion. The depolarization ratio is mainly used to compare and distinguish between certain features of the ice surface and entropy, as well as mean alpha angle, is also computed as complementary information.

Polarimetric signatures of oyster reefs in tidal flats were investigated using multi-frequency polarimetric SAR data. The scattering mechanism in tidal flats was analyzed by the Freeman-Durden target decomposition and the target depolarization effect was quantitatively measured using the cross-polarized ratio. Strong multiple scattering and depolarization effect were observed in oyster reefs areas from C- and X-band data. These scattering signatures were also verified from in-situ measurenments using a ground-based polarimetric scatterometer system. However, no difference was observed between the scattering signatures of oyster reefs and mud flat areas from L-band data, which have a relatively longer wavelength. These results suggest that multi-frequency polarimetric SAR observations can be used to quantitatively detect the spatial distribution of oyster reefs in tidal flats.

In this study we investigated the relationship between the depolarization effects and winter-time sea ice thickness m the landfast ice region where smooth first-year ice and deformed old ice co-existed, by using C- and X-band polanmetric satellite SAR data. Acquisitions of high-resolution SAR data with multiple satellite platforms (TerraSAR-X and Radarsat-2) were coordinated during a sea ice field campaign examining landfast sea ice on the coast of northern Greenland. We describe a sensitivity study of depolarization factors (co-polarized correlation and cross-polarized ratio), which can be used to estimate the degree of the depolarization effect using extended Bragg model. We found a strong correlation between ice thickness and the depolarization factors, suggesting that depolarization factors can be effective parameters in the estimation of sea ice thickness, particularly in an area where thick FYI and MYI co-exit.

In this study, we derived the relationship between target depolarization factor and physical parameters of sea ice in order to estimate the thickness using dual-polarization C-and X-band space-borne Synthetic Aperture Radar (SAR) data. The target depolarization factor, the cross-polarized ratio of C-band SAR data, which can explain the target depolarization effect, were strongly related to changes in surface roughness of thick First-Year Ice (FYI) and Multi-Year Ice (MYI), and were almost insensitive to variations in the surface dielectric constant of thick FYI and MYI and the incidence angle of C-band SAR data. This relationship showed a high correlation between target depolarization factor of C-band SAR data, the cross-polarized ratio, and thick FYI and MYI thickness. We validated the estimated method using RADARSAT-2 and TerraSAR-X data and ground-truth data acquired in the Arctic Sea off the northern coast of Greenland.