This paper presents a method and application results of two-dimensional ship velocity retrieval from KOMPSAT-5 X-band SAR via Doppler parameter estimation. It is necessary to estimate both range and azimuth velocity in order to restore the information of heading and velocity of ships in coastal area. Field campaigns carried out in 2017 and 2018 with heading and speed-controlled ships for evaluating accuracy. The results showed an accuracy of 1.64 m/s with a squared correlation coefficient R2of 0.83. The measurement accuracy is greatly improved if the size of ship is larger than 30 m, a SCR larger than 9 dB and a speed higher than 1.39 m/s.

The thermal noise-induced distortions in a Sentinel-1 terrain observation with progressive scans synthetic aperture radar image cannot be corrected by the noise equivalent sigma nought (NESZ) subtraction only. Since the thermal noise is scaled during synthetic aperture radar processing, it resides not only as an additive noise in each pixel but also as a multiplicative noise in the interpixel contrast. In this paper, we investigate the noise characteristics and propose an efficient method for the multiplicative textural noise correction. The core ideas are to find the optimal coefficient of the noise-induced standard deviation (SD) and model the noise contribution to the local SD as a function of the NESZ and the signal-to-noise ratio. Denoising is accomplished by a subwindow-wise adaptive rescaling of the pixel values. The improvements in the first- and second-order statistical textural features demonstrate the effectiveness of the proposed method.

The intensity of a Sentinel-1 Terrain Observation with Progressive Scans synthetic aperture radar image is disturbed by additive thermal noise, particularly in the cross-polarization channel. Although the European Space Agency provides calibrated noise vectors for noise power subtraction, residual noise contributions are significant when considering the relatively narrow backscattering distribution of the cross-polarization channel. In this paper, we investigate the characteristics of noise and propose an efficient method for noise reduction based on a three-step correction process comprised of azimuth descalloping, noise scaling and interswath power balancing, and local residual noise power compensation. The core idea is to find the optimal correction coefficients resulting in the most noise-uncorrelated gentle backscatter profile over a homogeneous region and to combine them with the scalloping gain for a reconstruction of the complete 2-D noise field. Denoising is accomplished by subtracting the reconstructed noise field from the original image. The performance improvement in some applications by adopting the denoising procedure shows the effectiveness of the proposed method.

Rice is one of the most important crop, especially in Asian countries. In this paper, estimation of rice paddy height is conducted by Pol-InSAR technique, using a single-polarization TanDEM-X (TDX) data. It is necessary to modify a conventional Pol-InSAR inversion method for the single polarization because of the underdetermined problem in Random Volume over Ground (RVoG) model. In order to resolve this problem, a Digital Elevation Model (DEM) was generated using a TDX data acquired after the rice transplanting season. The ground surface was assumed flat due to the flooded water inside the rice paddy so that ground phase of the water surface could be estimated. The estimated heights of rice were compared to the in-situ data.

Despite several studies using the multiple-aperture interferometry (MAI) technique, X-band SAR has rarely been applied to MAI-based studies due to their shorter decorrelation timescale. However, the relatively short antenna length and high temporal resolution of the COSMO-SkyMed X-band SAR system provides an opportunity to measure the precise displacement in the along-track direction. In this study, we have assessed the MAI performance in comparison with GPS and established an empirical uncertainty model of MAI measurements with respect to interferometric coherence. It enables us to confirm the difference between theoretical and practical uncertainties of the MAI method. Moreover, this study will be helpful for evaluating the reliability of MAI measurements where GPS data are unavailable.

It is difficult to detect and measure slow moving natural objects from a space-borne SAR observation. This paper presents a simple and efficient method to retrieve moving velocity from quad-pol SAR data acquired by dual receive antenna (DRA). The core idea is to exploit the slight observation time difference between different polarizations (H- and V-pol transmitted signals). The difference of scattering centers between different polarizations can be removed by azimuth phase differentiation. It was applied to TerraSAR-X quad-pol SAR over slow drifting sea ice in the Arctic Ocean. The SAR measured velocity was about 1.4 km/hr (or 0.37 m/s) to 2.4 km/hr (or 0.67 m/s). While co-pol data (HH- and VV-pol) are useful to detect slow drifting sea ice because of the strength of returned signals, cross-pol (HV- and VH-pol) data seems more effective to measure the velocity.

We construct a 3-D surface displacement map for the March 5-9, 2011 Kamoamoa fissure eruption at Kilauea Volcano, Hawai'i, by integration of multitemporal InSAR and multiple aperture interferometry (MAI) measurements from the COSMO-SkyMed SAR system. It was the first attempt to measure along-track displacements by X-band data. In spite of the potential risk of decorrelation by their short-wavelength signal, the high temporal resolution of COSMO-SkyMed provides the opportunity to map the precise 3-D displacement maps effectively. To assess the measurement accuracies of the untested data, a comparison with GPS data has been carried out for multi-stacked MAI interferogram and the 3-D components of surface deformation. Root-mean-square errors of 0.99, 0.80, and 0.65 cm for the east, north, and up components, respectively, support the suitability and effectiveness of COSMO-SkyMed for the 3-D observation.

The main objective of this study is long-term monitoring of surface sediment on tidal flats using optical remote sensing. Tidal flat reflectance is sensitive to conditions that constantly change and cause variation of interstitial water contents along with exposure time, remnant water, etc. It is difficult to retrieve sediment grain size from optical reflectance alone without correcting the tidal condition effects. In this study, the tidal flat surface reflectance model according to grain size is proposed by two-step PCA transformation to remove tidal effects. The proposed method showed a potential to classify sediment by grain size regardless of exposure time and tidal conditions. We applied the method to nine scenes of LANDSAT TM images acquired between 1988 and 2009. The preliminary results well demonstrated that the proposed approach is effective to monitor changes of grain size distribution at a large scale independent of tidal conditions. However, this method has a limitation particularly over the vegetated areas and sand shoals mainly because of strong reflection in the NIR channels compared with other areas. For the validation, this study requires further field survey to obtain more in-situ data.

Interferometric synthetic aperture radar (InSAR) is a powerful technique that precisely measures surface deformations at a fine spatial resolution over a large area. However, the accuracy of this technique is sometimes compromised by ionospheric path delays on radar signals, particularly with L- and P-band SAR systems. To avoid ionospheric effects from being misinterpreted as ground displacement, it is necessary to detect and correct their contributions to interferograms. In this paper, we propose an efficient method for ionospheric measurement and correction and validate its theoretical and experimental performance. The proposed method exploits the linear relationship between the multiple-aperture interferometry phase and the azimuth derivative of the ionospheric phase. Theoretical analysis shows that a total electron content (TEC) accuracy of less than$1.0 \times 10^{-4}$TEC units can be achieved when more than 100 neighboring samples can be averaged (multilooked), and the coherence is 0.5. The regression analysis between the interferometric phase and the topographic height shows that the root-mean-square error can be improved by a factor of two after ionospheric correction. A 2-D Fourier spectral analysis indicates that the ionospheric wave pattern in the uncorrected power spectrum has disappeared in the power spectrum of the corrected interferogram. These results demonstrate that the proposed method can effectively remove ionospheric artifacts from an ionosphere-distorted InSAR image. Note that the method assumes that there is no appreciable surface displacement in the along-track dimension of the interferogram.

Interferometric synthetic aperture radar (InSAR) observations of wetlands reveal spatially detailed measurements of water-level changes and quantitative images of flow dynamics. However, lateral variability of wetland vegetation results in a heterogeneous scattering medium, which can affect interferometric coherence levels and can even limit the applicability of the technique. Here, we analyze coherence variations in Southern Florida, which consist of various wetland vegetation types, including sawgrass, graminoid, cypress, mixed shrubs, and mangrove marsh. We use JERS-1, ERS-1/2, ENVISAT, and RADARSAT-1 data, to investigate the effect of acquisition parameters and temporal baseline (time span between acquisitions) on the coherence level in the various wetland vegetation environments. The main findings of our coherence analysis are as follows: (1) Woody wetlands, such as cypress and mixed shrubs swamps, have higher coherence levels than herbaceous wetlands of sawgrass and graminoid (cattail) in all SAR data types; (2) the coherence level of C-band data is strongly dependent on temporal baseline, whereas the coherence level of L-band data depends mainly on perpendicular baseline, but to some degree also on temporal baseline; (3) backscatter from JERS-1 and RADARSAT-1 is correlated with coherence in four wetland vegetation types (sawgrass, cypress, mixed shrubs, and mangrove), but ERS backscatter has no relation to coherence, except over sawgrass marsh. Finally, our study clearly indicates that high resolution, HH polarization, and small incidence angle observations are most suitable for wetland InSAR applications.

The objective of this study is to develop a tidal flat reflectance model according to tidal conditions. Tidal flat reflectance greatly varies with tidal conditions twice a day that causes changes in water contents along with exposure time, remnant water, etc. It is difficult to retrieve sediment grain size from optical reflectance alone without correcting the tidal condition effects. The Geostationary Ocean Color Imager (GOCI) is the first ocean color sensor mounted on the geostationary satellite, and provides images 8 times a day. A preliminary tidal flat reflectance model was obtained from 72 cloud free GOCI images in March, 2011. Two reflectance models were found to be minimally required for mud and mixed flats, while the differences between mixed and sand flats were insignificant. The models accommodate tidal conditions of flood or ebb tide. The results lead to a conclusion that the remnant surface water on the recently exposed tidal flats plays a significant role in influencing the optical reflectance. The surface reflectance increases gradually during the ebb tide, while the slope of decrease is steep during the flood tide.

This paper applied an adaptive neuro-fuzzy inference system (ANFIS) based on a geographic information system (GIS) environment using landslide-related factors and location for landslide susceptibility mapping. Landslide-related factors such as slope, soil texture, wood type, lithology and density of lineament were extracted from topographic, soil, forest and lineament maps. Landslide locations were identified from interpretation of aerial photographs and field surveys. Landslide-susceptible areas were analyzed by the ANFIS method and mapped using occurrence factors. In particular, we applied various membership functions (MFs), and analysis results were verified by using the landslide location data. The predictive maps using triangular, trapezoidal, and polynomial MFs were the best individual MFs for modeling landslide susceptibility maps (84.96% accuracy), proving that ANFIS could be very effective in modeling landslide susceptibility mapping.

Coastal shoreline movement due to erosion and deposition is a major concern for coastal zone management. Shoreline changes by natural cause or development constructions. Shoreline change is threatening and destroying living things in the marine environment. Topography of coastal area changes frequently due to a drastic sediment movement. In this study, we monitor the shoreline change and movement of sandbar using aerial photographs, satellite imagery and LiDAR data in coastal area, Korea. The result revealed that shoreline near the nuclear power plant showed linear pattern in 1971 and 1980, however the pattern was changed after 2000. As a result of the sandbar monitoring, sandbar moved toward the land. Location and shape of the sandbar have been significantly changed during the monitoring period, from 2003 to 2010. In the future work, we need a precise investigation of the shoreline change and the sandbar movement through the sedimentary and physical studies.

This study presents results of assessment of X-band SAR image for mapping salt marsh. Multi-temporal TerraSAR-X data were acquired with different incidence angle (23°, 31°, and 39°) in mono- and dual polarization modes (HH, VH/VV) for backscattering analysis. Backscattering coefficients from industrial areas were used to confirm the calibration. The types of land cover were differentiated based on seasonally averaged backscattering coefficients of classes. The behavior of backscattering coefficients was also analyzed as a function of SAVI (soil adjusted vegetation index). Decision trees were used to build classification rule sets. Accuracy of classification was estimated by reference image generated from field works and ancillary data.

Surface deformation caused by an intrusion and small eruption during June 17-19, 2007, along the East Rift Zone of Kilauea Volcano, Hawaii, was three-dimensionally reconstructed from radar interferograms acquired by the Advanced Land Observing Satellite (ALOS) phased-array type L-band synthetic aperture radar (SAR) (PALSAR) instrument. To retrieve the 3-D surface deformation, a method that combines multiple-aperture interferometry (MAI) and conventional interferometric SAR (InSAR) techniques was applied to one ascending and one descending ALOS PALSAR interferometric pair. The maximum displacements as a result of the intrusion and eruption are about 0.8, 2, and 0.7 m in the east, north, and up components, respectively. The radar-measured 3-D surface deformation agrees with GPS data from 24 sites on the volcano, and the root-mean-square errors in the east, north, and up components of the displacement are 1.6, 3.6, and 2.1 cm, respectively. Since a horizontal deformation of more than 1 m was dominantly in the north-northwest-south-southeast direction, a significant improvement of the north-south component measurement was achieved by the inclusion of MAI measurements that can reach a standard deviation of 3.6 cm. A 3-D deformation reconstruction through the combination of conventional InSAR and MAI will allow for better modeling, and hence, a more comprehensive understanding, of the source geometry associated with volcanic, seismic, and other processes that are manifested by surface deformation.

A method measuring Doppler parameters by joint time-frequency analysis is presented. Two-dimensional velocity retrieval can be achieved by estimation of the Doppler center frequency and Doppler frequency rate for the range and azimuth velocity components, respectively. The Doppler spectrum along a Doppler phase history line in the time-frequency domain was reconstructed and projected onto the frequency and time dimensions. The peak of the frequency axis projected spectrum corresponds to the Doppler center frequency, while that of the time axis indicates an azimuth time of closest approach. The Doppler frequency rate is obtained by measuring the slope of the Doppler spectrum in the time-frequency domain. Simulation using TerraSAR-X and Envisat ASAR parameters indicated that the velocity errors were less than 1 m/s or 5% for moving objects with a velocity higher than 3 m/s. While the measurement of Doppler center frequency was reliable over the entire velocity range, errors in Doppler frequency rate became large if the velocity was slower than 3 m/s (or 10.8 km/h). Range migration correction plays a key role for the precision of Doppler parameter estimation. An experiment using TerraSAR-X and truck-mounted corner reflectors validated the measurement accuracy of the approach. The absolute and percent errors of the range velocity (49.6 km/h) were 1.4 km/h and 2.8%, respectively, and the azimuth velocity (23.8 km/h) measurement was comparatively accurate, with a percent error of 1.8% under an assumption of zero acceleration. To apply the method to single-look complex data, the full Doppler bandwidth must be preserved.

Ground subsidence susceptibility at a coal mine by integration of L-band SAR measurements and a subsidence hazard model incorporated in GIS was estimated. A subsidence hazard map was constructed using JERS-1 SAR data from the early 1990s and the subsidence hazard model. A certainty factor analysis was employed for estimating the relative weights of four control factors influencing coal mine subsidence. The relative weight of each factor was then integrated to generate a subsidence hazard index (SHI) by a fuzzy combination operator. The hazard map was validated by comparison with subsidence observed by ALOS PALSAR interferometry in 2007-2008. The results showed a good agreement between the predicted locations vulnerable to subsidence and the actual subsidence occurrences with an accuracy of about 72.5%. These results showed that the map produced by integration of InSAR and GIS can be used to predict and monitor coal mine subsidence hazards, especially in remote regions.

Spatial relationships between surface sediment distribution and channel networks were estimated for the Ganghwa-Do southern tidal flat, Korea. Tidal channels were extracted from high spatial resolution satellite data and used to derive maps of channel density and distance from channels. The map of surface sediment distribution was produced from grain-size data on sediment samples. Then, for each surface sedimentary facies, the relations with tidal channels were estimated in terms of the fractal analysis, channel density and distance from the channel. The results demonstrate a significant spatial relationship between the distribution of surface sediment in a tidal flat and tidal channel distribution. We conclude that tidal channel should be considered an important factor in mapping surface sedimentary facies in tidal flat environments, and that patterns of tidal channel are a useful adjunct to spectral reflectance in classifying the surface sediment from remotely sensed data with high spatial resolution.

This paper presents the categorization and restoration of defective lines developed in pushbroom images. About 100 of the 3000 SPOT 4 SWIR detectors malfunction, which degrades image quality. Conventional methods have difficulties in effectively detecting and restoring defective lines, because they ignore the heterogeneity of the ground surface and the presence of sporadically unstable detectors with gain and offset that vary during a scan. While all defective lines have previously been considered as a single type, here they are categorized into three types according to the variation pattern in the scanning direction: constant defective lines, irregular defective lines, and irrecoverable defective lines. The detection procedure utilizes summed data and standard deviation data that consist of abnormal peaks originating from defective lines and a slowly varying baseline reflecting the surface characteristics within the image. The defective lines are detected by finding abnormal peaks, and classified and restored by using either a moment-matching method or interpolation, depending upon their types. Three SPOT 4 images were used to test and evaluate the performance of the proposed method. From the test results, the constant defective line was the most common type, comprising about 60%, while the irregular defective lines caused serious image degradation because of the difficulty of detecting and classifying them. Commission and omission errors were less than 10% and detection accuracy was higher than 90%. The analysis of signal-to-noise ratio (SNR) showed that the low SNR created by the defective lines was effectively removed. Our method gave a significant improvement of the detection and restoration capability.

Multiple-aperture synthetic aperture radar (SAR) interferometry (MAI) enables the measurement of along-track surface deformations by means of split-beam SAR processing. This paper examines the effects of flat-Earth and topographic phases on the MAI phase and derives formulas to correct them. Detailed MAI processing steps are introduced and discussed with particular consideration given to coherence improvement, as well as to computational efficiency. Forward- and backward-looking MAI pairs have different perpendicular baselines, which play a key role in phase distortion; consequently, an orbital deviation of only a few centimeters could result in a significant flat-Earth phase. A second-order polynomial model was used to estimate the perpendicular baseline difference. European Remote Sensing 2 satellite SAR data sets of the Hector Mine earthquake event in 1999 were used for performance evaluation. The proposed processing with the flat-Earth and topographic phase corrections achieved precision of along-track deformation ranging from 10.2 to 13.1 cm. Two coseismic pairs were compared and the standard deviation of the difference between the two independent measurements was 7.0 cm, with a mean difference of -0.24 cm. Thus, the measurement accuracy of MAI was improved using flat-Earth correction and coherence enhancement.

ERS-ENVISAT cross-interferometry with a small height ambiguity is useful to measure the topography in the regions of low slope. Azimuth common-band filtering is a key pre-processing for the cross-interferometry. An adaptive block azimuth filtering was designed and applied to the ERS-ENVISAT tandem pair. As range bin increases, the Doppler centroid of the ERS increases while that of the ENVISAT decreases. It results in systematic increment of the Doppler centroid differences as range bin increases. The coherence of 0.7 in the near range reduced to 0.2 in the far ranges. The block azimuth filter estimates Doppler centroids of at each block, and adjusts band width of the filter. The coherence degradation caused by range-dependent Doppler centroid can be compensated by this method. The coherence is better than conventional azimuth filtering about 0.1 in far range. The resulting interferogram shows improved coherences between 0.8 to 0.4 in near and far range, respectively. However there is still gap of coherence in near and far ranges, it is resulted from inherent problem of less overlapped bandwidth at far range. Although the total improvement was not significant, it is valuable for selection of permanent scatterers in the far range. Test results are discussed in this paper.

The polarimetric features of an oyster farm in a coastal area are analyzed to verify the applicability of radar polarimetry and interferometry. L-band Airborne Synthetic Aperture Radar (AIRSAR) data and Japan Earth Resources Satellite (JERS-1) data are used to examine the unique structure of an oyster farm located in South Korea. A specific feature of the oyster farm is the presence of numerous arrays of structures of various orientations that consist of exercise-bar-shaped poles protruding above sea level. This paper demonstrates that tide level is strongly correlated with the double-bounce scattering power from the vertical pole structures. This phenomenon is also verified by laboratory measurements using a network analyzer. In the laboratory experiment, double-bounce scattering and total power showed increasing trends with increased height of the vertical poles. Single-bounce scattering is sensitive to the orientation of horizontal poles relative to antenna orientation. HH-polarization is the most effective technique for imaging oyster farms from L-band polarimetric AIRSAR data. The authors were able to use a three-component decomposition of the AIRSAR data to distinguish an exposed tidal flat from a submerged tidal flat. The characteristics of the exposed tidal flat are similar to those of the carbon sponge in the laboratory test, except that the double-bounce scattering power is slightly greater in the real-world example. The single-bounce scattering component in AIRSAR data is generally greater than that in laboratory measurements because of sea-surface conditions and oyster growth. When the horizontal pole was aligned normal to the radar look direction, single-bounce scattering was greater than the double-bounce scattering, even under water-covered conditions. While a difference in tide height of 10 cm contributed approximately 3.0 dB in the laboratory experiment, a difference in tide height of 20 cm contributed to only approximately 1.7 dB in the JERS-1 SAR image intensity. JERS-1 SAR image intensity for areas dominated by double- and single-bounce scattering was 0.78 and 0.56, respectively. Results confirm that polarimetric SAR data are useful in selecting areas dominated by double-bounce scattering in oyster farms

Mokpo city is a coastal city located at the south western coast of the Korean Peninsula. Large regions within Mokpo are subjected to significant subsidence because about 70% of the city area is a reclaimed land from the sea. In this study, we aimed to estimate the subsidence rate over Mokpo city by using twenty-six JERS-1 SAR dataset from September 1992 to October 1998. Several tens of differential interferograms were processed from JERS-1 dataset and STRM 3-arc DEM. The results indicate continuous subsidence in Dongmyung-dong, Hadang-dong and Wonsan-dong in city, and the subsidence velocity reach over 4 cm/yr in the most highly sinking area. For facilitating the analysis of time-varying surface change, we also carried out an interferometric SAR time series analysis using permanent scatterer and consequently determined space-time maps of surface deformation at each acquisition time of JERS-1 SAR.

It is necessary to detect and monitor the distribution of mircophytobenthos (or algal mat) in tidal flats. KOMPSAT-2 will provide multi-spectral images with a spatial resolution of 4 m comparable with IKONOS. Using IKONOS and Landsat data, algal mat detection was tested in the Saemangeum area. Micro-benthic diatoms are abundant and a major primary product in the tidal flats. Fine grained upper tidal flats is considered to be the best conditions for microphythobenthos. A different type of microphytobenthos was found in coarse grained lower tidal flats. The newly reported microphytobenthos are algae and they began to exist after dike construction. A linear spectral unmixing (LSU) method was applied to the test data. The end-members were obtained by both spectral libraries built from field surveys and a remotely sensed image itself. End-members from spectral library were slightly more effective than those from image itself. A high resolution multi-spectral sensor in KOMPSAT-2 will provide useful data for long-term monitoring of microphytobenthos in tidal flats.

A method for measuring the tide height near the coast from L-band synthetic aperture radar (SAR) data is presented. Twenty-one coherent interferograms have been successfully constructed from Japanese Earth Resources Satellite 1 (JERS-1) SAR data obtained over oyster sea-farming structures. A coherence analysis of the 21 interferometric pairs showed that a perpendicular baseline of less than 3 km, with a temporal baseline within 500 days, are required to obtain a coherent pair, with a coherence higher than 0.25, in the study area. The coherent phases preserved in the interferograms showed a close relation with the sea level. The problem of phase unwrapping to restore an absolute tide height was overcome by introducing normalized image intensities. The radar measurements estimated by the proposed method were verified using tide gauge data, and comparison of the two datasets yielded a correlation coefficient R/sup 2/ of 0.91, with a root mean square error of 5.76 cm. The results demonstrate that radar interferometry can be applied for a tide height measurement near the coast given sufficient structures that return off-nadir radar pulses to the antenna. The multipolarized L-band SAR system will provide better results, using only double-bounced signals, in the future.

Synthetic aperture radar (SAR) data have serious geometric distortions caused by inherent side looking geometry and are usually corrupted by speckle noises so that it is difficult to identify ground control points (GCPs). The location of the pixel in a given SAR image can be derived from the knowledge of sensor position and velocity. We propose a GCP extraction algorithm that has an improved capability. The algorithm is based on the geocoding process of the radar image and requires precise orbit information. Whereas conventional geolocation algorithms depend on the knowledge of the target height relative to an assumed Earth ellipsoid model, more precise positioning can be achieved if utilizing an available digital elevation model (e.g. USGS GTOPO-30 DEM, SRTM DEM, etc.). The ERS SAR data with precise Delft orbit information and the national digital elevation model (DEM) were used. We analyze the accuracy of the results from our algorithm by using digital map. In case of using SRTM DEM, the mean values of the planimetric distance error are 9.1 m and 14.7 m with standard deviations of 6.4 m and 9.3 m in northing and easting direction, respectively. The errors in northing direction depend mainly on the imaging pulse time, and those in easting direction are related to the accuracy of used digital elevation model. The GCPs extracted were used for georectification of optical images as well as SAR data.

We have succeeded in estimating tide height in the coastal area with an r.m.s. error of 5.7 cm by exploiting interferometeric phase and image intensity of JERS-1 SAR data in our previous work. We used an array of oyster farming frames, composed of two vertical poles and one horizontal pole for each frame, as permanent scatterers. In this paper, we investigate the backscattering characteristics of the structure using AIRSAR data and results of experiment in laboratory. AIRSAR polarimetric images show L-band HH- and VV-polarization produce strong returns from the target structures. Classification of L-band polarimetric AIRSAR data confirms the double-bounce scatter is dominant scattering mechanism. Odd-number scatter is, however, not negligible. The ratio of single-bounce to double-bounce scattering depends of the relative radar look direction to the target array and sea surface conditions. Laboratory experiments were carried out using Ku-band according to the target scale. The results of the experiments can be summarized as: i) the structures produce a mixed signal of double-bounce and odd-bounce scatter; ii) the backscattering from horizontal pole is very sensitive to radar look direction; iii) the signals from vertical poles are stronger than that from horizontal pole. From the results, it is concluded that water level change can be most effectively estimated when vertical poles in the water are observed by L-band HH- or VV-polarization

We present a method to measure tide height from L- band synthetic aperture radar (SAR) data. We have successfully constructed 17 coherent interferograms from JERS-1 SAR data over oyster sea-farming structures. The coherent phases preserved in the interferograms showed a close relation with sea level. The problem of phase unwrapping to restore an absolute tide height was overcome by introducing a normalized image intensity, which resolved the wrapped phase ambiguity in 15 out of 17 pairs. The radar measurements estimated by the proposed method were verified by using tide gauge data, and comparison of the two data sets yielded a correlation coefficient of 0.95 with an r.m.s. error of 5.76 cm. The results demonstrate that radar interferometry may be applied to the measurement of tide height near the coast.

The subsidence rate in a reclaimed coastal land has been estimated using JERS-1 L-band SAR two-pass differential interferometry (DInSAR). Owing to the severe temporal decorrelation induced by frequent soil loading and to the intense deformation gradient, the L-band was effective for observation of subsidence in the reclaimed land. Permanent scatterers were also used to remove residual phase. We evaluated the accuracy of the estimated subsidence rate using field measurements obtained by magnetic probe extensometer with an accuracy of /spl plusmn/1 mm from 42 ground stations. Two-dimensional subsidence map was achieved from 5 qualified interferograms. The correlation coefficient between the two-dimensional radar measurements and the in situ data was 0.87 with an r.m.s. error of 1.44 cm. The results demonstrate that L-band DInSAR is useful for geological engineering applications.

High precision digital elevation model (DEM) in tidal flat is valuable for coastal erosion monitoring. To monitor active coastal changes, a DEM having an accuracy of better than 20 cm is required. We tested two methods: waterline method using optic images and space-borne radar interferometry. Two test sites were selected from Korean tidal flats, Gomso Bay and Saemangeum, and ground truth data have been obtained by leveling in both sites. In the waterline method, band selection was found to be critical especially on the ebb tide, and near infrared was superior to short wavelength infrared. The accuracies of the estimated DEMs were 10.9 cm and 9.8 cm at Gomso Bay and the Saemangeum tidal flat, respectively. We also successfully constructed DEMs using ERS-1/2 tandem pairs. The ERS-1/2 tandem pairs are very useful and as effective as the waterline method. The coherence of the interferogram was generally agreed with the reflectances of Landsat TM bands 4 and 5 with a correlation coefficient of about 0.7. Using sophisticated future spaceborne SAR systems such as Cartwheel, a high precision tidal flat DEM will possibly be constructed if data acquisition plans are properly made.

The soil compaction rate in a reclaimed land has been estimated by using the Japanese Earth Resources Satellite 1 (JERS-1) synthetic aperture radar (SAR) two-pass differential interferometry (DInSAR) and magnetic probe extensometer (an accuracy of /spl plusmn/1 mm) from 42 ground stations. Twelve JERS-1 SAR interferometric pairs were acquired in the study area. We applied a soil compaction prediction model based on a hyperbolic method using the ground truth data and the DInSAR measurements. The hyperbolic model fitted well to the ground measurements with an rms error of 1.65 cm. The rms error of the model driven by DInSAR measurements was 2.24 cm. The two model results agreed well, showing a difference of 8.1% (12.9 cm) in permanent settlement that is defined as the amount of vertical subsidence as time goes to infinity. A two-dimensional (2-D) subsidence map was constructed from five qualified pairs. The correlation coefficient R between the radar measurements and the ground truth data was 0.87 with an rms error of 1.44 cm. The results demonstrate that the L-band DInSAR combined with a prediction model is useful for geotechnical applications.

The waterline extraction is one of the most effective satellite remote sensing tools for studying tidal flat environments and its changes, but has not been investigated in detail. A series of field surveys have been carried out to obtain grain size, moisture contents, field spectrometer measurement, and waterline tracking simultaneously with satellite observation. A neural networks algorithm was developed for extracting waterline in tidal flat from satellite-based remote. sensing data and applied to the Gomso tidal flat, Korea. Characteristics of tidal flats and spectral reflectance associated with waterline were analyzed first. We have chosen three bands as input data of neural networks: NIR reflects the amount of suspended sediment content at lower tidal flats; SWIR is sensitive to moisture content and is seriously affected by remaining surface water in sedimentary structures; and TIR appears to be the best among the three bands but its low spatial resolution reduces its utility. The neural network method developed here is independent of tidal situations and robust. The neural networks not only distinguish between tidal flats and seawater out of the images, but it also provides continuous outputs that represent mixed compositions of both features. The values of 0.3 - 0.4 were turned out to be waterline in neural networks output The neural networks output provided the closest to the ground truth and that of the ETM TIR band.

The objective of this study is to investigate the control factors of spectral reflectance and microwave scattering in tidal flat. The control factors are generally considered as grain size, soil moisture content, local slope, and creeks. We have carried out field data sampling in the Gomso Bay, Korea, including grain size, soil moisture content and its variation with time, surface roughness, ground levelling, and field spectral reflectance measurement. We have analyzed Landsat TM, EOS-Terra ASTER, RADARSAT, ERS-1/2, and JERS-1 SAR data. L- and C-band radar scattering modelling was also conducted. The results show that tidal condition and remnant surface water are important additional parameters. SWIR is shown to be correlated most with sediment grain size. The grain size of 0.0625 mm has normally been considered as a critical size of mud and sand discrimination. But we propose here that 0.25 mm is more practical grain size criterion in optic remote sensing. The radar scattering modelling show variation of less than 15 dB within the tidal flat, and L-band HV-polarization is turned out to be the best for tidal flat observation. The SAR data is also sensitive to the effective exposed area (EEA) effect.