High Resolution Current & Bathymetry Determined by Nautical X-Band Radar in Shallow Waters

The wave and current monitoring system WaMoS II is a remote sensing system based on a nautical X-Band radar generally used for navigation and ship traffic control. It has been used in recent years to monitor sea state information from moored platforms, coastal sites and moving vessels. A nautical radar can scan the sea surface over a large area (~ 10km2 ) with a high spatial (~7.5m) and temporal resolution (~2s). Directionalwave spectra and standard sea state parameters such as significant wave height, peak wave period and direction can be derived by analyzing the sea surface image sequences. Using the temporal and spatial evolution of the sea surface wave images it is also possible to determine high resolution current and bathymetry information. In the paper a brief introduction into the measuring principle of WaMoS II is given and results of a high resolution current and bathymetric mapping technique for shallow water areas (<20m) are presented. For validation these results are compared with model data and in-situ measurements

Wind, waves, and surface currents in the Southern Ocean:Observations from the Antarctic Circumnavigation Expedition

The Southern Ocean has a profound impact on the Earth's climate system. Its strong winds, intense currents, and fierce waves are critical components of the air-sea interface and contribute to absorbing, storing, and releasing heat, moisture, gases, and momentum. Owing to its remoteness and harsh environment, this region is significantly undersampled, hampering the validation of prediction models and large-scale observations from satellite sensors. Here, an unprecedented data set of simultaneous observations of winds, surface currents, and ocean waves is presented, to address the scarcity of in situ observations in the region-https://doi.org/10.26179/5ed0a30aaf764 (Alberello et al., 2020c) and https://doi.org/10.26179/5e9d038c396f2 (Derkani et al., 2020). Records were acquired underway during the Antarctic Circumnavigation Expedition (ACE), which went around the Southern Ocean from December 2016 to March 2017 (Austral summer). Observations were obtained with the wave and surface current monitoring system WaMoS-II, which scanned the ocean surface around the vessel using marine radars. Measurements were assessed for quality control and compared against available satellite observations. The data set is the most extensive and comprehensive collection of observations of surface processes for the Southern Ocean and is intended to underpin improvements of wave prediction models around Antarctica and research of air-sea interaction processes, including gas exchange and dynamics of sea spray aerosol particles. The data set has further potentials to support theoretical and numerical research on lower atmosphere, air-sea interface, and upper-ocean processes.

On the Reliability of Surface Current Measurements by X-Band Marine Radar

Real-time quality-controlled surface current data derived from X-Band marine radar (MR) measurements were evaluated to estimate their operational reliability. The presented data were acquired by the standard commercial off-the-shelf MR-based sigma s6 WaMoS&reg; II (WaMoS&reg; II) deployed onboard the German Research vessel Polarstern. The measurement reliability is specified by an IQ value obtained by the WaMoS&reg; II real-time quality control (rtQC). Data which pass the rtQC without objection are assumed to be reliable. For these data sets accuracy and correlation with corresponding vessel-mounted acoustic Doppler current profiler (ADCP) measurements are determined. To reduce potential misinterpretation due to short-term oceanic variability/turbulences, the evaluation of the WaMoS&reg; II accuracy was carried out based on sliding means over 20 min of the reliable data only. The associated standard deviation &sigma; W a M o S = 0.02 m/s of the mean WaMoS&reg; II measurements reflect a high precision of the measurement and the successful rtQC during different wave, current and weather conditions. The direct comparison of 7272 WaMoS&reg; II/ADCP northward and eastward velocity data pairs yield a correlation of r &nbsp; &ge; 0.94 , with | b i a s &Delta; | &nbsp; &le; 0.06 m/s and &sigma; S = 0.05 m/s. This confirms that the MR-based surface current measurements are accurate and reliable

The effect of stratification on tidal current profiles in a region of freshwater influence

Observations of the semi-diurnal tidal current ellipses within the Rhine ROFI are reported. The vertical structure of these tidal ellipses are observed to be significantly different for stratified and well mixed conditions. in particular, during well mixed conditions, tidal currents are essentially rectilinear and directed parallel to the coast. With the onset of stratification, significant cross-shore components, reaching 40% of the magnitude of the along-shore components appear. These components are 180 degrees out of phase from near surface to near-bottom with surface currents rotating anticyclonically, and bottom currents cyclonically. It is proposed that this phenomenon may be explained by a decoupling of the upper and lower portions of the water column during stratified periods due to reduced viscosity within the pycnocline. A two layer model is used to examine this hypothesis and appears to be successful in reproducing many of the features of the observed semi-diurnal tidal ellipse variability

Analysis of an Event of "Parametric Rolling" Onboard RV "Polarstern" Based on Shipborne Wave Radar and Satellite Data

During the Antarctic summer season 2008/2009 the wave radar system WaMoS II was installed onboard of the German research vessel �Polarstern.� The purpose was to collect quasi-in situ data for the comparison with satellite-borne SAR and altimeter instruments (Envisat, TerraSAR-X, Jason). The experiment was part of the German research project DeMarine- Security. On 7 March 2009 in the central South Atlantic Ocean, �Polarstern� was heading towards Punta Arenas against a rough cross sea. In the night, a sudden event of heavy rolling, i.e., an oscillation about its length axis, hit the vessel and lasted for a few minutes. Using WaMoS II data, as well as ENVISAT and wave model data, we investigate the conditions under which the event occurred. It is shown that the rolling was caused by a �parametric� resonance when the period of encounter came close to one half of the vessels�s natural rolling period. We conclude that an onboard wave radar can be helpful in diagnosing and forecasting critical conditions

On the Effect of Interferences on X-Band Radar Wave Measurements

X-band radars are in growing use for various oceanographic purposes, providing spatial real-time information about sea state parameters, surface elevations, currents, and bathymetry. Therefore, it is very appealing to use such systems as operational aids to harbour management. In an installation of such a remote sensing system in Haifa Port, consistent radially aligned spikes of brightness randomly distributed with respect to azimuth were identified. These streak noise patterns were found to be interfering with the common approach of oceanographic analysis. Harbour areas are regularly frequented with additional electromagnetic transmissions from other ship and land-based radars, which may serve as a source of such interference. A new approach is proposed for the filtering of such undesirable interference patterns from the X-band radar images. It was verified with comparison to in-situ measurements of a nearby wave buoy. Regardless of the actual source of the corresponding pseudo-wave energy, it was found to be crucial to apply such filtration in order to improve the performance of the standard oceanographic parameter retrieval algorithm. This results in better estimation of the mean sea state parameters towards lower values of the significant wave height. For the commercial WaMoSII system this enhancement was clearly apparent in the improvement of the built-in quality control criteria marks. The developed prepossessing procedure improves the robustness of the directional spectra estimation practically eliminating pseudo-wave energy components. It also extends the system&rsquo;s capability to measure storm events earlier on, a fact that is of high importance for harbour operational decision making

Wave modulation by tidal currents near Cook Strait

Wave-current interactions are studied through the WAve and current MOnitoring System (WAMOS II) based on an HR Radar, installed at Makara, near Cook Strait (NZ). At Makara, the tidal regime generates currents up to 2.5 m/s parallel to the coastal line. Waves propagate through the strait mainly from the S quadrant. We observed that the waves are strongly modulated by the tidal currents and undertake a clear refraction pattern. The refraction is further explained and discussed exclusively through the geometrical optics. The modulation is also seen for significant wave height, absolute peak period and peak wavelength. When waves approach shallow regions they become steeper and eventually break. In these circumstances the currents are in turn modulated by the waves and WAMOS reveals a localised strong current jet. A wave model which fully represents the wave action balance equation (SWAN model) was also implemented. The mean WAMOS wave spectrum was applied as a constant boundary condition and propagated over the varying current field. The wave parameter modulations are well represented by the model. It is concluded that the current field is effectively inhomogeneous, and because of this generates wave height and wavelength modulations, and unsteady, which fact is responsible for absolute peak period oscillations. Therefore currents are an important factor to be considered when modelling waves near Cook Strait

Evaluation of X-band MR surface and ADCP subsurface currents obtained onboard the German research vessel Polarstern during ANT-XXXI expedition 2015/16

Limits of a comparative evaluation of the performance of a conventional X-band marine radar (MR) sigma S6 WaMoS® II used for surface current measurements are dicussed. Main focus of the paper is to address challenges when comparing current measurements from different measuring devices for evaluation purpose. Although the current measurement principles of MRs and acoustic Doppler current profilers (ADCPs) are disparate, they are often used to validate the quality of MR current measurements. In fact, differences in MR and ADCP derived currents can have a variety of physical reasons and do not necessarily indicate measurement errors. One possible cause of deviation is the comparison of dissimilar quantities

On the Reliability of Surface Current Measurements by X-Band Marine Radar

Real-time quality-controlled surface current data derived from X-Band marine radar (MR) measurements were evaluated to estimate their operational reliability. The presented data were acquired by the standard commercial off-the-shelf MR-based sigma s6 WaMoS&#174; II (WaMoS&#174; II) deployed onboard the German Research vessel Polarstern. The measurement reliability is specified by an IQ value obtained by the WaMoS&#174; II real-time quality control (rtQC). Data which pass the rtQC without objection are assumed to be reliable. For these data sets accuracy and correlation with corresponding vessel-mounted acoustic Doppler current profiler (ADCP) measurements are determined. To reduce potential misinterpretation due to short-term oceanic variability/turbulences, the evaluation of the WaMoS&#174; II accuracy was carried out based on sliding means over 20 min of the reliable data only. The associated standard deviation &#963; W a M o S = 0.02 m/s of the mean WaMoS&#174; II measurements reflect a high precision of the measurement and the successful rtQC during different wave, current and weather conditions. The direct comparison of 7272 WaMoS&#174; II/ADCP northward and eastward velocity data pairs yield a correlation of r &nbsp; &#8805; 0.94 , with | b i a s &#916; | &nbsp; &#8804; 0.06 m/s and &#963; S = 0.05 m/s. This confirms that the MR-based surface current measurements are accurate and reliable