David Lyzenga

• Researcher at University of Michigan

The U.S. Navy demands accurate forecasts of winds and waves for efficient operations in coastal areas. The forecasts are usually lacking the necessary observations to constrain results. Innovative and non-traditional observations provide improved data coverage in these regions. For decades, high-frequency (HF) radar has been used to remotely measur...

Advanced controls optimization offers a promising pathway to improve performance, reduce structural loads and thereby reduce the Levelized Cost of Electricity (LCOE) for wave energy conversion (WEC) systems. Model predictive control (MPC), which remains the preferred algorithm framework for WEC devices requires a wave excitation force forecast on t...

Marine radars have proven to be useful for measuring ocean waves, but the accuracy of the measurements is limited by several factors including the look-angle dependence of the radar signals as well as noise in the radar data. The look-angle dependence introduces a systematic error or bias in the measurements, and noise causes a random error. This p...

Remote mapping of bathymetry can play a key role in gaining spatial and temporal insight into fluvial processes, ranging from hydraulics and morphodynamics to habitat conditions. This research introduces Multiple Optimal Depth Predictors Analysis (MODPA), which combines previously developed depth predictors along with additional predictors derived...

This paper describes a method of processing marine radar signals for the purpose of generating phase-resolved surface elevation maps as well as statistical measures of ocean surface wave fields. The method is well suited to the processing of data collected by marine radars because it allows for the incorporation of effects dependent on the radar lo...

This letter describes a simple model for the backscattered signal received from the ocean surface by a horizontal-polarization marine radar operating at low grazing angles, including the effects of the logarithmic amplifiers conventionally used in these radars. Shadowing is accounted for via geometric optics. The range dependence of the mean radar...

Inverse algorithms are presented to calculate the variable pressure acting on a stiffened steel plate. The analytical models are formulated to calculate the quasi-static pressure distribution caused by ice and wave loads. The loading pressure is calculated using strain measurements from a stiffened plate installed on a Keweenaw Peninsula lighthouse...

The University of Michigan is leading a team that includes subcontractors Ohio State University, Aquaveo, LLC, and Woods Hole Oceanographic Institute to design, implement, and test an Environmental and Ship Motion Forecasting (ESMF) system. The system has application to many challenges associated with offshore operations, including skin-to-skin tra...

734) 913-6840 – Phone  (734) 913-6880 – Fax  www.mtri.org Components: 1. An Acoustic Doppler Current Profiler (ADCP) 2. Ice Force Measuring System (IFMS) 3. 'Scene Capture System' (SCS) 4. Wideband Autocorrelation Radiometer ice thickness sensor (WiBAR). 5. Instrument Support System (ISS) 6. Solar power system: panel, batteries Project Objectives...

In this paper we describe the development of a low cost, high power coherent-on-receiver radar. The unit has a 25kW peak transmit power and is capable of accurately measuring velocity as well as range. The design of the radar is optimized for marine surveillance, although the techniques developed have general application. The radar system is valida...

One major impediment to using marine radars for real-time shipboard measurements of evolving ocean wavefields is the uncertainty in the transfer function that relates the radar cross section to sea-surface height. In this letter, a more direct approach is proposed to infer nonlinear sea-surface heights by using radial-velocity measurements from coh...

The effects of nonlinear energy transfer on the development of the short wave spectrum are evaluated using a diffusion approximation and a modification of this approximation to include nonlocal effects. Both formulations were used to compute the evolution of a JONSWAP-type spectrum, and the results are compared with direct numerical simulations. Te...

Ocean wave field observations using two types of Doppler radar systems are compared with time series measurements of the surface elevation at the USACE Field Research Facility (FRF) in Duck, NC.

A numerical study of the retrieval of sea surface height profiles from low grazing angle radar observations is described. The study is based on a numerical method for electromagnetic scattering from 1-D rough sea profiles, combined with the ldquoimproved linear representationrdquo of Creamer for simulating weakly nonlinear sea surface hydrodynamics...

A new method for estimating the atmospheric transmittance and wind speed over the ocean from WindSat data is derived using a simplified model for the ocean surface reflectivity. The simplified reflectivity model is used to calculate both the surface emissivity and the reflection of downwelling atmospheric radiation. The wind-speed dependence of the...

Real-time sea state measurements could be used to greatly enhance the safety and efficiency of offshore operations. In this paper, a variational data assimilation scheme is developed to improve ocean wave field estimates from marine navigation radars. The assimilation scheme minimizes a cost function which is defined as the difference between radar...

Subsurface Internal Waves(IWs) can be detected in satellite images as periodic alternating brighter/darker stripes. It is known that there are two types of IWs-depression type and elevation type-depending on the water depth in stratified oceans. In this study, we have quantitatively verified the process of converting polarity from depression waves...

The surface currents induced by large-scale internal waves can cause a steepening of short and intermediate scale surface waves. These surface effects are responsible for the appearance of internal wave-related patterns on remote sensing imagery, including synthetic aperture radar and visible/infrared images. Radar backscatter variations are due pr...

A simple method for estimating water depths from multispectral imagery is described and is applied to several IKONOS data sets for which independent measurements of the water depth are available. The methodology is based on a physical model for the shallow-water reflectance, and is capable of correcting for at least some range of water-quality and...

An efficient method for estimating atmospheric transmittance is presented for WindSat polarimetric microwave radiometer data. The method is dependent on an approximation that is valid for earth incidence angles near 53deg. By combining the estimated atmospheric transmittances at different frequencies, the water vapor and cloud liquid water can be r...

The Naval Research Laboratory WindSat polarimetric radiometer was launched on January 6, 2003 and is the first fully polarimetric radiometer to be flown in space. WindSat has three fully polarimetric channels at 10.7, 18.7, and 37.0 GHz and vertically and horizontally polarized channels at 6.8 and 23.8 GHz. A first-generation wind vector retrieval...

Predictions of the polarized microwave brightness temperatures over the ocean are made using a two-scale surface bidirectional reflectance model combined with an atmospheric radiative transfer model. The reflected atmospheric radiation is found to contribute significantly to the magnitude and directional dependence of the brightness temperatures. T...

http://deepblue.lib.umich.edu/bitstream/2027.42/6412/5/bac8526.0001.001.pdf http://deepblue.lib.umich.edu/bitstream/2027.42/6412/4/bac8526.0001.001.txt

We present a method for evaluating characteristics of wind vector retrieval errors from polarimetric radiometer measurements. We focus on wind direction errors due to ambiguous solutions.

We study interaction of surface gravity-capillary waves with surface currents using a system of coupled nonlinear evolution equations for two surface variables: the free surface elevation and the velocity potential at the free surface. Results of our numerical simulations found via a pseudo-spectral method are compared with solutions of the wave ac...

To gain insight into the effects of currents in tidal channels on SAR imaging, a series of hydrodynamic and SAR simulations were conducted using an idealized tidal channel. Preliminary results from the hydrodynamic and SAR modeling reveal the following: (1) peak modulations lie over mid-channel during flood and over the channel banks during ebb, (2...

A simplified version of the energy balance equation is solved to obtain an expression for the ocean wave equilibrium spectrum, which is then used with a two-scale electromagnetic scattering model to calculate the radar cross section of the ocean surface. Two parameters in the energy balance equation are adjusted to minimize the difference between t...

This paper explores the possibility of estimating small-scale vector wind fields from SAR data by applying certain dynamical constraints to the wind field. The method is illustrated for the case of a diverging surface flow field that is intended to represent a precipitation-induced downdraft. A simulated radar cross section map generated from this...

The microwave reflectivity of the ocean surface is determined mainly by the surface roughness or wave spectrum. Since direct measurement of the wave spectrum at centimeter wavelengths is very difficult, microwave measurements are currently the largest source of information for this region of the spectrum. This paper discusses a procedure to determi...

Simultaneous microwave and video measurements of shallow water breaking waves are presented. A comparison of the data from the two sensors shows that short-duration spikes in the measured X-band radar cross section are highly correlated with the presence of breaking waves in the video imagery. In addition, the radar backscatter from shallow water b...

Measurements of the directional spectrum of waves generated by turbulent flow beneath an air-water interface are presented. The flow was a round turbulent jet issuing beneath and parallel to the free surface. The jet was centered two diameters below the free surface, had a Reynolds number of 12,700 and a Froude number of 8.0, based on the diameter...

First Page of the Article

This paper compares simultaneous microwave radar and video camera signals from shallow water breaking waves. The results show that the radar cross section (RCS) is well correlated with the size of the turbulent breaking region estimated from the video camera. This indicates that microwave radar is a good breaking wave detector and can be used for t...

A procedure for inverting the nonlinear relationship between the waveheight spectrum and the SAR image spectrum is presented, and this procedure is evaluated using simulated data as well as actual ERS SAR data collected near Duck, NC. Results of this nonlinear inversion are compared with those obtained from a quasi-linear estimation procedure using...

In this study we examine and comparatively analyze synthetic aperture radar and near infrared Thematic Mapper signatures observed in the restricted tidal channel of a shallow lagoonal estuary. Both imaging systems show coherent structures, identified as longitudinal convergence zones, that appear as bright and dark bands aligned parallel with the a...

Abstract—The two-scale model provides a framework for explaining the polarization and angular dependence of the microwave radiation emitted from the ocean surface. In this model the surface is viewed as a collection of randomly oriented facets. The emissivity of each facet is calculated using the small perturbation method (SPM), and that of the ent...

For Pt. I see ibid. vol. 26, pp. 181-200 (2001). This paper describes the results of experimental investigations into the microwave backscatter from mechanically generated transient breaking waves. The investigations were carried out in a 110 m×7.6 m×4 m deep model basin, utilizing chirped wave packets spanning 0.75-1.75 Hz. Backscatter measurement...

This paper describes the results of an experimental investigation of the microwave backscatter from several laboratory generated transient breaking waves. The breaking waves were generated mechanically in a 35 m×0.7 m×1.14 m deep wave tank, utilizing chirped wave packets spanning the frequency range 0.8-2.0 Hz. Backscatter measurements, were taken...

A critical issue in the design of large floating structures, such as those being considered in the mobile off-shore base effort currently being pursued by the US Navy, is the nature of the ocean-wave field, viewed on scales of 2km or more. Of prime concern is the ability to assess the spatial ‘coherence’ of the wave field, or the probability of occ...

A critical issue in the design of large floating structures such as those being considered in the Mobile Offshore Base (MOB) effort currently being pursued by the U.S. Navy is the nature of the ocean-wave field viewed on scales of 2 km or more. Of prime concern is the ability to assess the spatial coherence of the wave field or the probability of o...

INTRODUCTION Oceanic fronts and eddies with current shear, convergence and divergence zones influence wind-wave-current interactions leading to small scale surface roughness anomalies that in turn can provide distinct expressions in SAR images. Several well documented examples of this type of image expression including near coincident SAR/AVHRR/ATS...

The USCG R&D Center performed a feasibility study of the use of satellite and airborne synthetic aperture radar data to support ocean search and rescue planning. Three field experiments were performed to assess the capability of synthetic aperture radar images of surface features associated with ocean currents to provide surface current estimates f...

Radar backscatter measurements from stationary breaking waves were used to examine how the surface roughness generated by wave breaking affects radar backscatter at moderate incidence angles. Stationary breaking waves were generated by submerging a stationary hydrofoil in a uniform flow. X band radar backscatter measurements were made at numerous s...

Assessment of water quality parameters from SeaWiFS data proved to be nowadays operational for case I waters, i.e., oceanic and marine open waters. Relatively simple algorithms based on ratios of water-leaving radiance at two or more SeaWiFS wavelengths are successfully used for retrieval of algae pigments in such waters. However, water quality ret...

Synthetic aperture radar (SAR) imagery showing two types of features near the inshore edge of the Gulf Stream are compared with nearly simultaneous estimates of the sea surface slope field derived from optical shipboard measurements. One class of feature consists of a set of narrow, dark lines having radar signal modulations of about -10 dB at L ba...

Ocean mesoscale phenomena such as eddies and current convergence zones can often be seen in synthetic aperture radar (SAR) images due to characteristic patterns caused by natural film induced damping of the waves. Such films have also been found to exert a significant effect on air-sea gas exchange, which may be important for the global scale clima...

A new mechanism is proposed to explain the large changes in radar backscatter observed at high microwave frequencies (X band and C band) near ocean fronts and internal waves. The proposed mechanism involves the interaction of short ``Bragg'' waves with intermediate-scale waves having wavelengths of the order of 1 m, as well as the interaction of bo...

Two-dimensional surface currents are estimated over an area of ~100 km2 near the inshore edge of the Gulf Stream by correlating the surface slick patterns observed on two synthetic aperture radar (SAR) images collected about 20 min apart. The currents obtained from this analysis are found to agree well with shipboard acoustic Doppler current profil...

Presents two algorithms for estimating near-shore bathymetry from synthetic aperture radar (SAR) data. The first algorithm utilizes the kinematics of the shoaling waves to extract depths under the assumption of no significant current in the direction of wave propagation. The second algorithm utilizes the average radar cross section to estimate the...

A review and intercomparison has been performed for numerical simulation models which aim to predict the SAR signatures of upper ocean current frontal features. The specific models whose performance is compared in detail are (i) The ERIM Ocean Model (EOM), developed by the Environmental Research Institute of Michigan and the Naval Research Laborato...

This report presents the results of a twelve month study initiated and supported by ESA on SAR imaging of the ocean surface. It was jointly conducted by the Nansen Environmental and Remote Sensing Center, ARGOSS and the Institute of Oceanography of the University of Hamburg. The objective of the study has been to intercompare and improve SAR retrie...

Although two-scale models for radar imaging of the ocean surface often perform well, they have been observed to underestimate radar modulations for certain environmental and observation conditions. In recent years, three-scale theories that incorporate interactions between intermediate (meter-scale) and short (centimeter-scale) waves have been deve...

Multifrequency SAR images of fronts and internal waves collected under moderately low wind speeds indicate that the wavelength dependence of such features is contrary to the predictions of models that take into account only Bragg wave interactions with surface currents. Observations under very low wind speeds also show features that are inconsisten...

A numerical solution of the surface-current integral equation is used to calculate the radar backscatter for several wavelike surfaces. The surfaces used in this study represent solutions of the water wave equations for finite amplitude, irrotational gravity waves, with steepnesses selected so as to produce minimum radii of curvature ranging from z...

An iterative method for numerically solving the surface current integral equation is applied to wedge-like surfaces in order evaluate its applicability to surfaces that give rise to substantial edge diffraction. The convergence properties and accuracy of this approach are examined by comparing its results with the analytic Sommerfeld solution for i...

Imaging radars, under certain environmental conditions, can provide an extensive description of shallow submarine topography. In this investigation, sand waves were observed in shallow water and under light winds, weak flow, and highly stratified conditions with an L band synthetic aperture radar and X band real aperture radar. An analysis of the r...

Ocean mesoscale phenomena such as eddies and current convergence zones can often be seen in SAR images due to characteristic patterns caused by natural film induced damping of the waves. Such films have also been found to exert a significant effect on air-sea gas exchange, which may be important for the global scale climate system. Satellite synthe...

The interaction of ocean waves with surface currents having a significant horizontal shear causes either an amplification or a reduction of the surface wave spectral density, depending on the wave propagation direction. The radar backscatter modulations that result from this interaction are therefore also a function of the radar look direction rela...

Optical properties of Delaware Bay were measured using ship and airborne instruments.

In this study the surface features and the radar backscatter associated with breaking waves generated by a uniform flow past a stationary submerged hydrofoil were examined. The level of energy dissipation due to breaking was varied by changing the foil angle of attack. Time series of surface elevation profiles were obtained for the breaking crest r...

Estimates of ocean wave spectra obtained from conventional synthetic aperture radar (SAR) images suffer from the azimuth falloff effect which limits the range of azimuth wavenumbers that can be observed by such systems. This effect was earlier predicted to be modified by the use of a second receive antenna which is displaced from the first in the a...

This paper discusses some considerations involved in modeling the transient effects associated with unsteady or non-uniform wind fields over the ocean. The spectral energy balance equation is solved for some simple cases in which the wind varies in time or space, using various formulations for the wind input and dissipation terms. An overshoot effe...

This paper examines the role of wave breaking in the formation of the bright linear features that appear in SAR images collected near the edge of the Gulf Stream. Results from a recent set of laboratory experiments are used to develop a relationship between the rate of energy dissipation and the generation of small-scale roughness by breaking waves...

This paper describes a PC-based multilayered data integration and classification system that is under development for monitoring coastal oceanographic processes. For data integration and sensor fusion, the authors have developed a multilayered “hypercube” that includes data from satellite ERS-1, multi-frequency airborne SAR imagery, AVHRR imagery,...

The ERS SAR sensors have demonstrated their capability for imaging ocean waves, internal waves, underwater topography, eddies, fronts, natural slicks, oil slicks, and atmospheric features in the marine boundary layer such as wind. In order to quantify the mesoscale upper ocean and atmospheric boundary layer processes, a tandem ERS-1/2 ESA AO experi...

Radar backscatter measurements were conducted on transient breaking waves in a 330 foot laboratory wave facility. The radar measurements were taken using a dual polarization K-band (24.125 GHz) CW Doppler radar positioned at various azimuth angles relative to the direction of wave propagation. Backscatter measurements were made for low energy (mini...

An experiment was conducted in a 110 m×7.6 m×4 m deep Marine Hydrodynamics facility to study the hydrodynamics of intermediate scale breaking waves and how they effect radar backscatter. An energetic spilling breaking wave, characterized by considerable whitecapping, was chosen for analysis. To characterize the wave, an array of seven capacitance w...

In observing oceans using synthetic aperture radar (SAR), researchers have shown that small-scale water surface waves can significantly affect the radar backscatter from an ocean surface. Furthermore, these small scale water surface waves are known to have a significant role in affecting the ocean's drag coefficients and gas-exchange rates. Unfortu...

ERS 1 C band synthetic aperture radar (SAR) data were collected during the Norwegian Continental Shelf Experiment (NORCSEX) both in November 1991 during the ERS 1 commissioning phase and at different seasons in 1992 and 1993. Characteristic SAR image expressions are observed in relation to perturbation of the surface current-short wave interaction...

Simultaneous P-band, L-band and C-band synthetic aperture radar (SAR) images collected by the JPL AIRSAR system off the coast of Norway reveal surface features associated with presence of slicks, ocean fronts, internal waves and ship wakes. The features observed in these three radar bands are markedly different, and in most cases these differences...

This paper focuses on recovering surface topography from shape-from-refraction data. The authors' solution features a hybrid genetic algorithm and a model estimation approach. The authors briefly describe The University of Michigan (U-M) wave-slope optical instrument that is currently under calibration. Topographic results are reported with data fr...

This report summarizes the digital processing activities which have been carried out on the SAR data sets collected during the two ONR/NRL High Resolution field experiments held in September 1991 and June 1993. Features associated with the Gulf Stream boundary are observed in these data sets, with signatures that are dependent on the wind speed, ra...

ERS-1 SAR image expressions of mesoscale coastal ocean circulation features are examined. The dominating geophysical quantities and processes that are participating in the formation of the image expression are discussed. An attempt to characterise dynamics of the current features is carried out employing a SAR simulation model. Preliminary results...

Patterns are observed on radar images of the ocean surface on scales of 10-1000 meters which are related to phenomena such as internal waves, current or temperature fronts, and tidal flow over shallow bottom topography. These features are caused by a complex set of interactions between surface waves, air flow above the surface, current fields at an...

Capillary-gravity wave spectra are measured using a scanning laser slope gauge (SLSG), and simultaneously by X and K band Doppler radars off the Chemotaxis Dock at the Quissett campus of the Woods Hole Oceanographic Institution at Woods Hole, Massachusetts. Wave spectral densities estimated from the radar measurements using the Bragg theory agree w...

A frequently observed characteristic of Synthetic Aperture Radar (SAR) imagery of moving ships is an area of increased backscatter immediately behind the ship extending approximately one ship length. The region causing these signatures has been termed the near-field disturbed water (NFDW) region of the ship. In this report a simple prediction model...

The imaging capabilities of the ERS-l C-band, vertical polarization, SAR over the ocean will be discussed based on results from the Norwegian Continental Shelf Experiment (NORCSEX '91) and an ongoing surface slick study along the coast of Norway. We will document that the SAR can provide observations of the mesoscale surface current circulation pat...

The ERIM Ocean Model (EOM) model was used as part of an end-to-end- simulation of the centerline shipwake. EOM was modified to include Milgram's turbulent damping formulation with Snyder's growth rate and Lyzenga's source- and-sink description. The EOM simulations showed that turbulent dissipation can explain the large negative modulation observed...

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Synthetic aperture radar (SAR) images collected during a 1989 surface ship wake experiment are analyzed using a linear imaging model which includes contributions due to velocity bunching, tilt modulation and hydrodynamic modulation as well as azimuth falloff and coherent speckle effects. This model adequately predicts the overall shape of the image...

First Page of the Article

Airborne C band synthetic aperture radar (SAR) data were collected during the Norwegian Continental Shelf Experiment (NORCSEX) carried out in March 1988. Unique signature variations in the SAR backscatter due to upper ocean circulation features and wind fronts were found. It is documented that a current jet of 0.3 m s - • with a shear of about 0.3...

Data from synthetic aperture radar, (SAR) systems can be used to estimate ocean wave directional spectra, but the method is limited by nonlinearities associated with the velocity bunching mechanism and the azimuth falloff effect, which reduces the range of azimuth wavelengths that can be observed. A theoretical analysis which suggests that the use...

Quasi-simultaneous measurements of the ocean surface by the Canada Centre for Remote Sensing (CCRS) Convair-580 (CV-580) synthetic aperture radar (SAR) were acquired on March 20, 1988, along an ascending pass of the Geosat radar altimeter as part of the prelaunch ERS-1 Norwegian Continental Shelf Experiment (NORCSEX'88). Over a region where the SAR...

The interaction of short surface waves with shearing and converging currents is investigated by means of an approximate analytical solution of the wave action spectral transport equation. Spectral perturbations of less than 10% are predicted at centimeter wavelengths for moderately strong ocean fronts, although much larger perturbations are expecte...

A technique developed for measuring the surface tension of fluid based on the resonant scattering of microwave radiation from gravity-capillary waves on the surface of the fluid is discussed. The method was implemented by generating monochromatic water waves in a tank, illuminating them with microwave radiation, and then tuning the water-wave frequ...

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Applications of remote sensing for studies of coastal and estuarine features and processes are described.

Algorithms were developed for remotely sensing and modeling water quality in estuaries

The SAR ocean images obtained in the Tower Ocean Wave and Radar Dependence Experiment (TOWARD) are carefully analyzed at different focus settings and compared with simulated results based on various theories for imaging surface waves. The agreement between the experimental data and all the SAR simulations except one is found to be favorable. There...

A variety of instruments have been developed during the past thirty years for measuring ocean wave spectra. The simplest of these devices is designed to measure, either directly or indirectly, the surface elevation at a given location in space as a function of time. The observed temporal fluctuations of the surface elevation are described statistic...