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The variability and energetics of M-2 internal tides during their generation and propagation through the Kuroshio flows northeast of Taiwan are investigated using a high-resolution numerical model. The corrugated continental slopes, particularly the I-Lan Ridge and Mien-Hua Canyon, are first identified as the energetic sources of M-2 internal tides. The domain-integrated M-2 barotropic-to-baroclinic conversion rate under the Kuroshio influence is similar to 2.35GW, similar to 0.9GW of which is generated at the I-Lan Ridge, similar to 0.93GW at the Mien-Hua Canyon, and similar to 0.52GW at the north shelf. The M-2 internal tide generation is influenced by the horizontally varying, zonally tilting stratification associated with the Kuroshio. In this situation, the conversion rate decreases by similar to 30% at the I-Lan Ridge but increases to within similar to 10% at the Mien-Hua Canyon and north shelf, in comparison to the simulation initiated with horizontal homogeneous stratification. Internal tides from multiple sources interfere to form a three-dimensional baroclinic field. The interference by the internal tides from the Mien-Hua Canyon and north shelf is refracted by the Kuroshio and exhibits a mesoscale gyre pattern, which can explain the frequent occurrence of internal solitary waves. An energetic along-slope tidal beam (TBKC) from the I-Lan Ridge radiates southward against the northward Kuroshio flows, causing strong vertical displacement, which favorably compares with recently reported field measurements. The M-2 internal tide energy dissipates primarily near the source sites, and the remaining energy radiates outward over limited distances. Complex topographic features and background currents enhance the internal tide dissipation, which induces strong, inhomogeneous diapycnal mixing.

In this article, five typhoon cases observed by quasi-concurrent satellite-based synthetic aperture radar SAR and Moderate Resolution Imaging Spectroradiometer MODIS were studied with a feature-tracking technique. The rainband features around typhoon eyes were first delineated using wavelet analysis, and then the wind speeds were estimated by feature tracking using quasi-concurrent multi-sensor images. It was found that the feature tracking-estimated wind speeds are reasonable compared with the maximum wind speed reported by the Joint Typhoon Warning Center JTWC, which accounts for the radial dependence of wind speed using the Rankine combined vortex approximation. In a specific case, with the aid of Doppler radar observations near the northern coast of Taiwan, wind speed estimation based on the multi-sensor also shows consistent results. This study demonstrates that the local wind distribution of cyclonic winds around typhoon eyes at different radial distances from the typhoon centres may be derived from rainband feature tracking using quasi-concurrent multi-sensor images. This technique may offer useful wind information for typhoon simulations and forecasting.

This paper compares the typhoon centers from the tropical cyclone best track (BT) data sets of three meteorological agencies and those from synthetic aperture radar (SAR) and infrared (IR) images. First, we carried out algorithm comparison using two newly developed algorithms and one existing wavelet-based algorithm, which were used to extract typhoon eyes in six SAR images and two IR images. These case studies showed that the extracted eyes by the three algorithms are consistent with each other. The differences among them are relatively small. However, there is a systematic difference between the extracted centers and the typhoon centers from the three BT data sets, which were interpolated to the imaging times first. We then compared the typhoon centers determined from 25 SAR and 43 IR images with those from the three BT data sets to investigate the performance of the latter at the sea surface and at the cloud top, respectively. We found that the typhoon centers from the three BT data sets are generally closer to the locations extracted from the SAR images showing sea-surface imprints of the typhoons than those from the IR images showing cloud-top structures of the typhoons.

In this study, typhoon eyes have been delineated using wavelet analysis from the synthetic aperture radar (SAR) images of ocean surface roughness and from the warmer area at the cloud top in the infrared (IR) images, respectively. RADARSAT and ENVISAT SAR imagery, and multi-functional transport satellite (MTSAT) and Feng Yun (FY)-2 Chinese meteorological satellite IR imagery were used to examine the typhoons in the western North Pacific from 2005 to 2011. Nine cases of various typhoons in different years, locations, and conditions have been used to compare the typhoon eyes by SAR (on the ocean surface) with IR (at the cloud-top level) images. Furthermore, the best track data getting from the Joint Typhoon Warning Center (JTWC), Chinese Meteorological Administration (CMA), and the Japan Meteorological Agency (JMA) are checked for the calibration and validation along with the Moderate Resolution Imaging Spectroradiometer (MODIS) image. Because of the vertical wind shear, which acts as an upright tilt, the location of the typhoon eye on the ocean surface differs from that at the top of the clouds. Consequently, the large horizontal distance between typhoon eyes on the ocean surface and on the cloud top implies that the associated vertical wind shear profile is considerably more complex than generally expected. The upright tilt structure may be caused by the ocean’s feedback or the effect of island obstruction. This result demonstrates that SAR can be a useful tool for typhoon monitoring study over the ocean surface.

This chapter compares the typhoon centers from the tropical cyclone best track (BT) datasets of three meteorological agencies and those from synthetic aperture radar (SAR) and infrared (IR) images. First, we carried out algorithm comparison, using two newly developed and one existing wavelet-based algorithms, which were used to extract typhoon eyes in six SAR images and two IR images. These case studies showed that the extracted eyes by the three algorithms are consistent with each other. The differences among them are relatively small. However, there is a systematic difference between these extracted centers and the typhoon centers from the three BT datasets, which are interpolated to the imaging times first. We then compared the typhoon centers determined from 25 SAR and 43 IR images with those from the three BT datasets to investigate the performance of the latter at the sea surface and at the cloud top, respectively. We found the typhoon centers from the three BT datasets are generally closer to the locations extracted from the SAR images showing sea surface imprints of the typhoons than those from the IR images showing cloud top structures of the typhoons. We also evaluate the effect caused by rain to the SAR wind field retrieval. By using RADARSAT-2 data, National Centers for Environmental Prediction (NCEP) reanalysis data and Tropical Rainfall Measuring Mission satellite (TRMM) precipitation radar rainfall data, rain-induced attenuation, raindrop volumetric scattering are calculated and the perturbation of the water surface is simulated by rainfall and incident angle. The performance of this model is further proved by one typhoon case.

Temporal and spatial variability of internal tides (ifs) in the deep basin west of the Luzon Strait were examined, based on two 9-month mooring current observations from autumn 2008 to summer 2009. The baroclinic current measurements exhibited north-south asymmetry and temporal variation. At the southern site (19.5 degrees N), the kinetic energy of diurnal IT was dominant over that of semidiurnal IT by a factor of 3 to 4, whereas at the northern site (similar to 21 degrees N), the diurnal energy was comparable to or a little larger than semidiurnal energy. At both sites, the motions of semidiurnal IT were recognized as seasonally invariant, while diurnal IT showed notable seasonal variation, namely, stronger in summer and winter but weaker in spring and autumn. The seasonal variation was mainly modulated by the astronomical tides in the Luzon Strait rather than by the seasonal thermocline. Both diurnal and semidiurnal ifs contained stronger coherent signals than incoherent counterparts at two sites, but the IT at the southern site was more coherent than that at the northern site. Diurnal IT is more coherent than the semidiurnal IT at each site. The spatial-temporal variations were probably due to IT interferences from various sources within the Luzon Strait and modulation by varying background conditions. (C) 2014 Elsevier B.V. All rights reserved.

In this review, recent studies on the observations of typhoon eyes by images acquired by multiple sensors, including synthetic aperture radar (SAR), and infrared (IR) radiometer, are first summarized. Large horizontal distances between typhoon eyes on the ocean surface by SAR and those on the cloud top by IR sensors have been demonstrated; these have previously been ignored but should not be ignored in typhoon forecasts and numerical simulations. Then, based on nine published typhoon cases, the horizontal shifts and vertical tilt angles from the cloud-top typhoon eye locations by IR sensors on board the Feng-Yun 2 (FY-2) and Multi Functional Transport Satellite (MTSAT) to those at sea surface by SAR are further estimated. This shift difference between different sensors raises an issue on project distortion and navigation system errors for FY-2 and MTSAT satellites, which are of concern to both space agencies and data users. Finally, issues for current ongoing study and future research related to typhoon e...

In this paper, More than 1000 satellite images including Terra/Aqua MODIS, Sentinel-1A SAR images from 2013 to 2015 were analyzed to obtain spatio-temporal distribution of internal waves in the Andaman Sea. The statistical results demonstrate that the internal wave have been observed mostly in four areas by the remote sensing: northern Sumatra Island, western Malay Peninsula, northeast of the Nicole Islands and eastern Andaman Islands in Andaman Sea. Internal waves in the middle and the gradually changing bathymetric gradients areas of the Andaman Sea have been unobserved by the remote sensing. Internal waves can be observed in Andaman Sea all through the year, most in hot season (February to April), next rainy season( May to October). And a minimum number of internal waves are observed in rainy(June to August), however, this may be caused by the small amount of clear MODIS images in rainy in the Andaman Sea, it need to further proof by using more remote sensing images.

The objective of this study is to investigate the generation and evolution of mode-two internal waves on the shelf break. In this study, some historical mooring and satellite data have been investigated for the detection of mode-two solitons in the ocean. A recent field experiment in May 2009 near Dong-Sha Island in the South China Sea (SCS) is first described and analyzed. During the experiment, a small mode-two wave was observed following a huge mode-one soliton on the shelf. Then, the environmental conditions for the evolution of mode-two internal waves were assessed for parametric and sensitivity study based on the CTD data from previous experiment in SCS. The generation of mode-two waves on the shelf by disintegration of mode-one solitons in the deep ocean is proposed and analyzed based on the theory of modal-decomposition. For comparison, the soliton characteristics of mode-one and -two waves from environmental parameters have been estimated. It’s been shown that the soliton width of large mode-two waves is much wider than mode-one waves.

Dynamics of Arctic sea ice, including motion and deformation, are studied utilizing data from the Advanced Microwave Scanning Radiometer for the Earth Observing System (EOS) (AMSR-E) during 2005 and 2007. We first derive sea ice motion maps from the satellite data in a grid of 100 km × 100 km using a two-dimensional wavelet method. These sea ice motion results are compared with those derived from buoy data from the International Arctic Buoy Programme. Secondly, it is well known that sea ice deformation can be characterized by a strain-rate tensor calculated from the ice velocity field. Two components of the strain-rate tensor quantify the divergence and the shearing of the ice field, respectively. Daily maps for both sea ice motion and strain-rate tensor, as well as monthly averages and spatial sums, are computed and analysed. Comparison of the monthly ice motion maps for May 2005 and May 2007 indicates that the anti-cyclonic Beaufort Gyre and Transpolar Drift Stream in the western Arctic are relatively s...

The propagation and fission process of internal solitary waves (ISWs) with amplitudes of about 170 m are simulated in the northeast of the South China Sea (NSCS) by using the generalized Korteweg-de Vries (KdV) equation under continuous stratification. More attention is paid to the effects of the ebb and flood background currents on the fission process of ISWs. This kind of background current is provided by the composed results simulated in terms of monthly mean baroclinic circulation and barotropic tidal current. It is found that the obtained relation of the number of fission solitons to the water depth and stratification is roughly in accordance with the fission law derived by Djordjevic and Redekopp in 1978; however, there exists obvious difference between the effects of the ebb and flood background currents on the wave-lengths of fission solitons (defined as the distance between two neighboring peaks of ISWs). The difference in nonlinearity coefficient α between the ebb and flood background currents is a main cause for the different wave-lengths of fission solitons.

In this study, typhoon eyes are delineated using wavelet analysis from synthetic aperture radar (SAR) and infrared (IR) images to detect the “eyes” on the sea surface and at the cloud top, respectively. Because of the vertical wind shear, which acts as an upright tilt, the location of the typhoon eye on the sea surface differs from that at the top of the clouds. Consequently, the large horizontal distance between typhoon eyes on the sea surface and on the cloud top implies that the vertical wind shear profile is considerably more complex than generally expected. The upright tilt may be caused by the ocean's feedback or the effect of island obstruction.

Based on in-situ time series data from the acoustic Doppler current profiler (ADCP) and thermistor chain in Wenchang area, a sequence of internal solitary wave (ISW) packets was observed in September 2005, propagating northwest on the continental shelf of the northwestern South China Sea (SCS). Corresponding to different stratification of the water column and tidal condition, both elevation and depression ISWs were observed at the same mooring location with amplitude of 35 m and 25 m respectively in different days. Regular arrival of the remarkable ISW packets at approximately the diurnal tidal period and the dominance of diurnal internal waves in the study area, strongly suggest that the main energy source of the waves is the diurnal tide. Notice that the wave packets were all riding on the troughs and shoulders of the internal tides, they were probably generated locally from the shelf break by the evolution of the internal tides due to nonlinear and dispersive effects.

This paper presents a study of sea ice motion and deformation in the marginal ice zone (MIZ) of the Bering Sea in the winter season. Segmentation techniques and statistical methods are applied to high‐resolution synthetic aperture radar (SAR) images to derive ice motion and deformation maps. These techniques involve dynamic local thresholding (DLT), which allows separation of sea ice into different classes of thickness and type. Two ice motion characteristics are observed, one consisting of a translation and a rotation at a scale larger than about 10 km day−1 and the other consisting of field deformations at a spatial scale of less than about 5 km over a 3‐day period. Sea ice deformation rates are calculated, and the divergence and shear feature of the sea ice in different regions identified. Possible causes, associated with wind, wave, current and internal ice forces, for the sea ice motion and deformation are discussed.

Spratly Islands, located in the southern part of the South China Sea (SCS), consist of more than 100 small islands, coral reefs and banks. Remote sensing is the only way to obtain a synoptic view of all of the islands in such a large area. It has been demonstrated that satellite synthetic aperture radar (SAR) imagery is a very powerful tool for monitoring meso-scale and small-scale ocean processes in a large area. In this study, satellite SAR images were used to study the ocean environment in the area of Spratly Islands. The aim was to understand the capability of satellite remote sensing to monitor ocean processes and provide information for future field studies. Two sets of high-resolution European Remote Sensing satellite (ERS)-2 SAR images over the entire Spratly Islands area were collected in April and December 2005. The ocean features were identified/extracted from the SAR images to overlay the bathymetric map for comparison. Some case studies of SAR mapping on Spratly Islands are described and issues regarding existing navigation charts are discussed.

Synthetic aperture radar (SAR) sensors aboard polar-orbiting satellites have the abilities to acquire high spatial resolution images of the Earth's surface under all weather conditions, but their temporal sampling intervals are long. However, currently two SAR sensors aboard the European remote sensing satellite-2 (ERS-2) and the environment satellite (ENVISAT) have almost the same flight paths with ERS-2 following ENVISAT by approximately 28 minutes. Thus, high spatial resolution images from these two SAR can be jointly used to achieve a high temporal sampling interval for ocean feature monitoring and tracking. This approach has been used to track internal wave refraction along Dong-Sha Atoll in the South China Sea (SCS) on 16 April 2003. On that same day, the moderate resolution imaging spectro-radiometer (MODIS) aboard Terra passed though the same location 28 minutes after ERS-2 and collected data under almost no cloud condition. Therefore, Terra MODIS images provide another source for monitoring the wave refraction and validating the internal wave speed around Dong-Sha Atoll.

Daily Arctic sea-ice motion maps during the winter seasons (December–March) from December 1988 to March 2003 derived from NSCAT, QuikSCAT, SSM/I, and AMSRE data by a wavelet analysis method have been merged with those derived from buoy data. These merged sea-ice motion data have been used to study the circulation regimes and winter-to-winter variability of Arctic sea-ice motion. The relation between sea-ice motion and the pressure field in the Arctic Ocean was also studied by applying Principal Component Analysis (PCA) to the monthly merged sea-ice motion data and the monthly pressure field data from IABP. The mean Arctic sea-ice motion map of the 15 winter seasons has two distinct features: the Beaufort Gyre and a cyclonic circulation system in the Eurasian Basin, which moves ice from the Laptev Sea to Fram Strait. The strengths and sizes of the two features change from one winter season to another. Seasons with a strong or normal Beaufort Gyre alternate with seasons with a weak or no Beaufort Gyre every one to three seasons. The principal components of the first two modes of PCA of the monthly sea-ice motion are closely correlated with their counterparts of the monthly pressure field in the Arctic Ocean. The mode-one components of these two anomalies alternate between anticyclonic and cyclonic circulation systems. The correlation between Arctic Oscillation indexes and the principal components of the first mode of PCA of the monthly Arctic sea-ice motion is low but statistically significant.

During the recent Asian Seas International Acoustics Experiment (ASIAEX), extensive current meter moorings were deployed around the continental shelf-break area in the northeastern South China Sea. Thirteen RADARSAT SAR images were collected during the field test to integrate with the in situ measurements from the moorings, ship-board sensors, and conductivity/temperatire/depth (CTD) casts. Besides providing a synoptic view of the entire region, satellite imagery is very useful for tracking the internal waves, locating surface fronts, and identifying mesoscale features. During ASIAEX in May 2001, many large internal waves were observed at the test area and were the major oceanic features studied for acoustic volume interaction. Based on the internal wave distribution maps compiled from satellite data, the wave crests can be as long as 200 km with an amplitude of 100 m. Environmental parameters have been calculated based on extensive CTD casts data near the ASIAEX area. Nonlinear internal wave models have been applied to integrate and assimilate both synthetic aperture radar (SAR) and mooring data. Using SAR data in deep water as an initial condition, numerical simulations produced the wave evolution on the continental shelf and compared reasonably well with the mooring measurements at the downstream station. The shoaling, turning, and dissipation of large internal waves at the shelf break have been studied and are very important issues for acoustic propagation.

A moored array of current, temperature, conductivity, and pressure sensors was deployed across the Chinese continental shelf and slope in support of the Asian Seas International Acoustics Experiment. The goal of the observations was to quantify the water column variability in order to understand the along and across-shore low-frequency acoustic propagation in shallow water. The moorings were deployed from April 21-May 19, 2001 and sampled at 1-5 min intervals to capture the full range of temporal variability without aliasing the internal wave field. The dominant oceanographic signal by far was in fact the highly nonlinear internal waves (or solitons) which were generated near the Batan Islands in the Luzon Strait and propagated 485 km across deep water to the observation region. Dubbed trans-basin waves, to distinguish them from other, smaller nonlinear waves generated locally near the shelf break, these waves had amplitudes ranging from 29 to greater than 140 m and were among the largest such waves ever observed in the world's oceans. The waves arrived at the most offshore mooring in two clusters lasting 7-8 days each separated by five days when no waves were observed. Within each cluster, two types of waves arrived which have been named type-a and type-b. The type-a waves had greater amplitude than the type-b waves and arrived with remarkable regularity at the same time each day, 24 h apart. The type-b waves were weaker than the type-a waves, arrived an hour later each day, and generally consisted of a single soliton growing out of the center of the wave packet. Comparison with modeled barotropic tides from the generation region revealed that: 1) The two clusters were generated around the time of the spring tides in the Luzon strait; and 2) The type-a waves were generated on the strong side of the diurnal inequality while the type-b waves were generated on the weaker beat. The position of the Kuroshio intrusion into the Luzon Strait may modulate the strength of the waves being produced. As the waves shoaled, the huge lead solitons first split into two solitons then merged together into a broad region of thermocline depression at depths less than 120 m. Elevation waves sprang up behind them as they continued to propagate onshore. The elevation waves also grew out of regions where the locally-generated internal tide forced the main thermocline down near the bottom. The "critical point" /spl alpha/ where the upper and lower layers were equal was a good indicator of when the depression or elevation waves would form, however this was not a static point, but rather varied in both space and time according to the presence or absence of the internal tides and the incoming trans-basin waves themselves.

In a recent study, satellite images have shown that internal solitons are active in the northern South China Sea (SCS). During the Asian Seas International Acoustic Experiment (ASIAEX) pilot studies, current profiler and thermistor chain moorings were deployed in the spring of 1999 and 2000 to investigate internal solitons northeast of Tung-Sha Island on the continental slope of the northern SCS. Most of the observed internal solitons were first baroclinic mode depression waves. The largest horizontal current velocity, vertical displacement, and temperature variation induced by the internal solitons were around 240 cm/s, 106 m, and 11/spl deg/C, respectively, while the estimated nonlinear phase speed was primarily westward at 152 /spl plusmn/ 4 cm/s. The observed internal solitons could be categorized as four types. The first type is the incoming wave from deep water and can be described reasonably well with the KdV equation. The second and third types are in the transition zone before and close to the turning point (where the upper and lower layer depths are equal), respectively. These two types of solitons were generally near the wave-breaking stage. The fourth type of soliton is a second baroclinic mode and probably was locally generated. The time evolutions are asymmetric, especially at the middle depths. A temperature kink following the main pulse of the soliton is often seen. Higher order nonlinear and shallow topographic effects could be the primary cause for these features. The appearance/disappearance of internal solitons coincides mostly with spring/neap tide. The internal soliton is irregularly seen during the neap tide period and its amplitude is generally small. The time interval between two leading solitons is generally around 12 h. The first baroclinic mode of the semidiurnal tide has a larger amplitude than the diurnal tide and could redistribute its energy into the soliton.

Internal wave distribution maps have been compiled from more than one hundred ERS-1/2, RADARSAT and Space Shuttle SAR images in the South China Sea (SCS) from 1993 to 2000. Based on these distribution maps, most of the internal waves in the north-east part of the SCS were propagating westward. The wave crest can be as long as 200 km with an amplitude of 100 m, due to strong current from the Kuroshio branching out into the SCS. In a recent SCS internal wave study, moorings were deployed in April 1999 and 2000. Simultaneous SAR coverage from ERS-2 and RADARSAT were also collected. The ERS-2 high-resolution SAR images collected from the Taiwan ground station were processed in near real-time to coordinate the field test. SAR data are then used to compare with mooring data. SAR data and Acoustic Doppler Current Profiler (ADCP) data show internal solitons induced by the semi-diurnal tides with a wave speed of 2.4 m s−1.

Spaceborne synthetic aperture radar (SAR) observation is an important tool for monitoring and studying changes in various geophysical elements in and above world oceans. Because of SAR's ideal imaging capability and high resolution, the collection of SAR data will likely extend well into the 21st century. As the data become increasingly abundant and computers faster and more affordable, it naturally leads to an increasing need for an automated procedure to replace the labour-intensive manual screening process. In this paper, an integrated scheme for detection, extraction and classification of linear ocean features in SAR imagery is attempted for the purpose of automated screening. The methodology consists of feature detection based on greyscale histogram screening, feature extraction based on two-dimensional wavelet analysis and feature classification based on texture analysis. Using these algorithms on SAR data, several case studies of linear ocean features, including fronts, ice edges and a polar low, a...

Arctic sea ice motion for the period from October 1999 to March 2000 derived from QuikSCAT and ocean buoy observations.Special Sensor Microwave/Imager (SSM/I) data using the wavelet analysis method agrees well with ocean buoy observations. Results from QuikSCAT and SSM/I are compatible when compared with buoy observations and complement each other. Sea ice drift merged from daily results from QuikSCAT, SSM/I, and buoy data gives more complete coverage of sea ice motion. Based on observations of six months of sea ice motion maps, the sea ice motion maps in the Arctic derived from QuikSCAT data appear to have smoother (less noisy) patterns than those from NSCAT, especially in boundary areas, possibly due to constant radar scanning incidence angle. For late summer, QuikSCAT data can provide good sea ice motion information in the Arctic as early as the beginning of September. For early summer, QuikSCAT can provide at least partial sea ice motion information until mid-June. In the Antarctic, a case study shows that sea ice motion derived from QuikSCAT data is consistent with pressure field contours.

Typhoon eyes have been delineated from the smoother area in the Radarsat Synthetic Aperture Radar (SAR) images of ocean surface roughness and from the warmer area in the Multi-functional Transport Satellite (MTSAT) infrared images by using wavelet analysis. Case studies for different typhoons and environment have been investigated to demonstrate that SAR can be a powerful tool to help in typhoon tracking and prediction, especially at the ocean surface. It is found that the distance between the center locations of these typhoon’s eyes, as determined by SAR and MTSAT, respectively, is quite significant (14–26 km) for all five cases. The result of large center distance between typhoon eyes at the cloud level from MTSAT data and on the ocean surface from SAR data implies that the eyewall shaft may be highly tilted and the vertical wind shear profile is more complex than generally expected. Some of the issues concerning the definition of typhoon eye and typhoon tracking/prediction have been identified and compared with other data sets. Also, the tilted structure and associated vertical wind shear, especially during typhoon turning and staggering, may be caused by the ocean feedback or island blocking effects.

The two-dimensional wavelet transform is a highly efficient band-pass filter, which can be used to track features in satellite images from sequential paths. Wavelet analysis of NASA scatterometer and Special Sensor Microwave/Imager data has been used to obtain daily sea-ice drift information for the Arctic region. Comparison with ice motion derived from ocean buoys shows good quantitive agreement. Furthermore, the scatterometer results definitely complement passive-microwave radiometer results when there are cloud or surface effects. This outcome allows three sets of sea-ice-drift daily results from scatterometer, radiometer and buoy data to be merged as a composite map by data-fusion techniques. Based on the composite maps, the ice-flow streamlines are highly correlated with surface air-pressure contours. In order to quantify the wind effects on ice motion, empirical orthogonal functions are used in the principal-component analysis to isolate generalized patterns inherent in 6 months (fall/winter) of daily sea-ice motion data. It is found that 30% of sea-ice motion is highly correlated with 50% of the pressure field in modes 1 and 2. For the higher modes, sea-ice motion is also affected by ocean current, bathymetry and coastal boundary and therefore is not highly correlated with the wind field.

Two powerful tools, wavelet transformation (WT) and conventional empirical orthogonal function (EOF) analysis, were combined tentatively. The combination of these two techniques might be called wavelet EOF (WEOF), and has potential for analyzing complicated signals associated with modal structures. The WT is versatile in handling transient or nonstationary time series, and EOF is capable of detecting statistically coherent modal structures from arrayed observations. WEOF inherits the advantages of both WT and EOF. This paper presents some basic formulations of WEOF and postulates a method to correlate empirical and dynamical modes. Monte Carlo simulations have been used to assess the practicality of the theory. Moreover, the method is applied to a real-time series of water temperature profile measured in a submarine canyon. The results of WEOF analysis reveal some unique properties of local internal tides, including the inequality of frequency composition between the surface and internal tides an...

RESUMEEn se basant sur la recente compilation des cartes representant la repartition des vagues internes, on constate que presque toutes les vagues internes de la Mer de la Chine du Sud se propagent vers l'ouest. La plupart de ces vagues internes sont generees dans les hauts fonds ou ses rebords du Detroit de Luzon. La crete de ses vagues peut faire jusqu'a 200 km de long avec une amplitude de 100 m. Grâce aux images collectees par RADARSAT ScanSAR les 26 avril et 4 mai 1998, de gigantesques solitons internes ont pu etre observes pres des iles Dongsha, ils avaient une crete de plus de 200 km de long et une vitesse pouvant aller jusqu'a 1,9 m/s. Les decouvertes les plus interessantes sont l'elevation des vagues internes dans les eaux peu profondes (220 m) et les depressions des vagues sur les brisants (500 m de profondeur). Les deux phenomenes peuvent etre observes sur les meme images SAR (Radar ouverture synthetique) prises le 4 mai 1998. Des simulations numeriques ont montre que le temps necessaire a la ...

Synthetic aperture radar (SAR) images from ERS-1 and ERS-2 have been used to study the characteristics of internal waves in the East China Sea. Rank-ordered packets of nonlinear internal waves in the East China Sea are often observed in the SAR images, especially in the northeast of Taiwan. In this region, the internal wave field is very complicated, and its generation mechanisms include the influence of the tide and the upwelling, which is induced by the intrusion of the Kuroshio across the continental shelf. The internal wave distributions in the East and South China Seas have been compiled based on the SAR observations from satellites. The Kortweg–deVries (KdV) type equation has been used to study the evolution of internal wave packets generated in the upwelling area. Depending on the mixed layer depth, both elevation and depression waves can be generated based on numerical simulations as observed in the SAR images. The merging of two wave packets from nonlinear wave–wave interaction in the Yellow Sea has been observed in the SAR image and is demonstrated by numerical results.

A method for comparing sea ice velocity, divergence, and shear at the large-scale between buoys and Special Sensor Microwave Imager (SSM/I) is presented. For initial testing, the method is applied in the Eurasian Basin because of its relatively simple circulation dominated by the wind. Using eight Argos buoys, 11 strain rate arrays 100–600 km in size are constructed. Daily 100 km resolution sea ice motion derived from SSM/I 85 GHz brightness temperatures is sampled 100–1000 km from the center of the buoy arrays. Over this range of possible scales, a minimum RMS difference (RMSD) for deformation is used to identify an optimal inclusion radius of 600 km corresponding to a length scale of 1000 km. This length scale is typical of local storms confirming a strong connection between wind and observed sea ice motion. On the basis of all 11 arrays, an average RMSD of 2.48±0.05 cm s−1 for velocity vector and 8.8±0.9×10−8 s−1 using all four deformation components (∂ui/∂χj∥ is found at the optimal inclusion radius corresponding to average correlation coefficients of 0.896±0.002 and 0.729±0.030, respectively. RMSD are found to scale with the temporal and spatial uncertainties of the SSM/I suggesting that even better results can be achieved with higher resolution instruments.

Wavelet analysis of NASA scatterometer (NSCAT) backscatter and DMSP special sensor microwave imager (SSM/I) radiance data can be used to obtain daily sea ice drift information for the Arctic region. This technique provides improved spatial coverage over the existing array of Arctic Ocean buoys and better temporal resolution over techniques utilizing data from satellite synthetic aperture radars. Comparisons with ice motion derived from ocean buoys give good quantitative agreement. Both comparison results from NSCAT and SSM/I are compatible, and the results from NSCAT can definitely complement that from SSM/I when there are cloud or surface effects. Then, three sea ice drift daily results from NSCAT, SSM/I, and buoy data can be merged as a composite map by some data fusion techniques. The ice flow streamlines are highly correlated with surface air pressure contours. Examples of derived ice drift maps in December 1996 illustrate large-scale circulation reversals over a period of 4 days. These calibrated/validated results indicate that NSCAT, SSM/I merged daily ice motions are suitably accurate to identify and closely locate sea ice processes and to improve our current knowledge of sea ice drift and related processes through the data assimilation of ocean-ice numerical model.

Synthetic Aperture Radar (SAR) images from ERS-I have been used to study the characteristics of internal waves northeast and south of Taiwan in the East China Sea, and east of Hainan Island in the South China Sea. Rank-ordered packets of internal solitons propagating shoreward from the edge of the continental shelf were observed in the SAR images. On the basis of the assumption of a semidiurnal tidal origin, the wave speed can be estimated and is consistent with the internal wave theory. By using the SAR images and hydrographic data, internal waves of elevation have been identified in shallow water by a thicker mixed layer as compared with the bottom layer on the continental shelf. The generation mechanism includes the influences of the tide and the Kuroshio intrusion across the continental shelf for the formations of elevation internal waves. The effects of water depth on the evolution of solitons and wave packets are modeled by the nonlinear Kortweg-deVries (KdV) type equation and linked to satellite image observations. The numerical calculations of internal wave evolution on the continental shelf have been performed and compared with the SAR observations. For a case of depression waves in deep water, the solitons first disintegrate into dispersive wave trains and then evolve to a packet of elevation waves in the shallow water area after they pass through a “turning point” of approximately equal layer depths that has been observed in the SAR image and simulated by the numerical model. The importance of the dissipation effect in the coastal area is also discussed and demonstrated.

The two-dimensional wavelet transform is a very efficient bandpass filter, which can be used to separate various scales of processes and show their relative phase/location. In this paper, algorithms and techniques for automated detection and tracking of mesoscale features from satellite imagery employing wavelet analysis are developed. The wavelet transform has been applied to satellite images, such as those from synthetic aperture radar (SAR), advanced very-high-resolution radiometer (AVHRR), and coastal zone color scanner (CZCS) for feature extraction. The evolution of mesoscale features such as oil slicks, fronts, eddies, and ship wakes can be tracked by the wavelet analysis using satellite data from repeating paths. Several examples of the wavelet analysis applied to various satellite images demonstrate the feasibility of this technique for coastal monitoring.

Synthetic aperture radar (SAR) images of the ocean surface can show evidence of the sheltering elTects of barriers, such as islands, on the incoming long ocean waves. In the presence of high background noise in SAR images, these elTects arc not always observed by visual inspection. As shown in this paper, they can be determined most effectively in the spectral domain. From the ERS–1 SAR data of 17 October 1991, we noticed that two separate swell components almost perpendicular to each other were incident on the Semidi Islands in the Gulf of Alaska. By spectral analysis, the shadow zone associated with each wave component can be identified. The distribution of an equivalent dilTraetion coefficient has been estimated at the Ice of the Chowiet Island which has a sharp tip. It has been compared to that obtained from the Sommerfeld solution of dilTraction for a semi-infinite barrier. The SAR data shows a similar dilTraction pattern to the model solution but has a slower fall-off into the geometric sha...

The ability of Synthetic Aperture Radar (SAR) for monitoring surface signatures of swells, wind fronts, bottom features, oil slicks, and eddies has been amply demonstrated. The combined use of IR (AVHRR), ocean color (SeaWiFS, MODIS), and SAR (ERS-1/2, ENVISAT, RADARSAT) data can provide frequent high resolution coverage of the coastal area for the evolution study of oceanic processes. This chapter presents examples of these applications. During the Bering Sea Fisheries-Oceanography Coordinated Investigation (FOCI) field test, simultaneous satellite SAR data and in-situ measurements from moorings and ships were collected. Ships and their wakes are commonly observable in high-resolution satellite SAR imagery. This can be useful in national defense intelligence, shipping traffic, and fishing enforcement, especially when combined with the Vessel Monitoring System (VMS). SAR images can track the movement of the ice edge and floes in the marginal ice zone (MIZ). Results are relevant to climate change and fishery management. Sea-ice motion derived by satellite data can be used to interpret the Arctic ice retreat in the summer of 2007. Underwater bathymetry has been mapped by satellite remote sensing (SAR, SPOT, and LANDSAT) in the Spratly Islands of South China Sea (SCS) for ship navigation. As presented by these case studies, the use of SAR-derived observations can supply valuable information for the protection of the environment.

During the Labrador Ice Margin Experiments, LIMEX ‘87 in March 1987 and LIMEX ‘89 in March and April 1989, the Canada Centre for Remote Sensing (CCRS) CV‐580 aircraft collected synthetic aperture radar (SAR) image data over the marginal ice zone off the east coast of Newfoundland, Canada. One aspect of these experimental programs was the observation of ocean waves penetrating into the marginal ice zone (MIZ). Based upon directional wavenumber spectra derived from SAR image data, the wave attenuation rate is estimated using SAR image spectra and compared with predictions from a model developed by Liu and Mollo‐Christensen (1988). The wave and ice conditions were considerably different in LIMEX ‘87 and LIMEX ‘89. However, the model‐data comparisons are very good for all ice conditions observed. Both the model and the SAR‐derived wave attenuation rates show a characteristic roll‐over at high wavenumbers. A model for the eddy viscosity is proposed, using dimensional analysis, as a simple function of ...

[1] Surface signatures associated with non-linear internal waves are often seen in satellite images of the western South China Sea (SCS) slope and shelf. Observation in the deep sea, to the east, are rare. Here we report on the evolution of an energetic packet as it propagated through the deep central basin of the SCS, toward the western slope and shelf. The waves have amplitudes estimated at 170 m, half widths of 3 km, and phase speeds of 2.9 ± 0.1 m/s, faster than the mode-1 linear phase speed of 2.6 m/s. The shape and observed phase speed were consistent with the Korteweg-deVries (KdV) model over the 65-km path that they were tracked. The intrinsic velocity shear of the waves is small compared to pre-existing shears, and the waves exhibit weak turbulence. The KdV fit and a satellite-derived estimate of horizontal wave extent imply a westward energy flux of 4.5 GW for each crest.