Radar Scattering from Modulated Wind Waves: Proceedings of the Workshop on Modulation of Short Wind Waves in the Gravity-Capillary Range by Non-Uniform Currents, held in Bergen aan Zee, The Netherlands, 24–26 May 1988 PDF
Preview Radar Scattering from Modulated Wind Waves: Proceedings of the Workshop on Modulation of Short Wind Waves in the Gravity-Capillary Range by Non-Uniform Currents, held in Bergen aan Zee, The Netherlands, 24–26 May 1988
Radar Scattering from Modulated Wind Waves Radar Scattering from Modulated Wind Waves Proceedings of the Workshop on Modulation of Short Wind Waves in the Gravity-Capillary Range by Non-Uniform Currents, held in Bergen aan Zee, The Netherlands, 24-26 May 1988 Edited by G.J. Komen and W.A. Oost Royal Netherlands Meteorological Institute (KNMI). De Bitt. The Netherlands KLUWER ACADEMIC PUBLISHERS DORDRECHT / BOSTON / LONDON Library of Congress Cataloging in Publication Data Workshop on Modulation of Short Wind Waves in the Gravity-Capillary Range by Non-Uniform Currents (1988 Bergen aan Zee. Netherlands) Radar scattering from mOdulated wind waves: proceedings of the Workshop on ModulaTion of Short Wind Waves in the Gravity-Capillary Range by Non-Uniform Currents I edited by G.J. Ko~en and W.A. Oost. p. cm. "Bergen aan Zee. the Netherlands. 24-26 May 1988." Includes indexes. 1. Ocean waves--Remote sensing--Congresses. 2. Raaar--Congresses. I. Komen. G. J. II. Oost, W. A. (Wiebe Aaldert), 1938- III. Title. GC206.W67 1988 551.47·022--dc19 89-2820 ISBN-13: 978-94-010-7537-4 e-ISBN-13: 978-94-009-2309-6 001: 10.1007/978-94-009-2309-6 Published by Kluwer Academic Publishers, P.O. Box 17, 3300 AA Dordrecht, The Netherlands. Kluwer Academic Publishers incorporates the publishing programmes cif D. Reidel, Martinus Nijhoff, Dr W. Junk and MTP Press. Sold and distributed in the U.S.A. and Canada by Kluwer Academic Publishers, 101 Philip Drive, Norwell, MA 02061, U.S.A. In all other countries, sold and distributed by Kluwer Academic Publishers Group, P.O. Box 322, 3300 AH Dordrecht, The Netherlands. printed on acid free paper All Rights Reserved © 1989 by Kluwer Academic Publishers Softcover reprint of the hardcover 1s t edition 1989 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner. CONTENTS Editor' 5 Preface ix SESSION 1 TIDAL CURRENTS AND BATHYMETRY Chairman: G.P. de Loor Determining the currents over Phelps Bank 3 D.A. Greenberg, G.R. Valenzuela and D.T. Chen Studies of the sea surface with radar in the Netherlands 19 G.P. de Loor SESSION 2 ELECTROMAGNETIC SCATTERING Chairman: G.J. Komen Calculation of microwave Doppler spectra from the ocean surface with a time-dependent composite model 27 D.R. Thompson Limitations of the two-scale theory for microwave backscatter from the ocean 41 P.L.C. Jeynes First results of the VIERS-1 experiment 49 D. van Halsema, B. Jahne, V.A. Oost, C. Calkoen and P. Snoey SESSION 3 THE ENERGY BALANCE IN SHORT WAVES Chairman: V.A. Oost Effects of reduced surface tension on short waves at low wind speeds in a fresh water lake 61 K.B. Katsaros, H. Gucinski, S.S. Atakturk and R. Pincus The energy balance in short gravity waves 75 G.J. Komen \'\ Derivation of Phillips a parameter from turbulent diffusion as a damping mechanism 81 W. Rosenthal Temporal and spatial variability of the wind stress vector 89 G.L. Geernaert Energy balance in small scale waves - An experimental approach using optical slope measuring technique and image processing 105 B. Jahne On the changes in phase speed of one train of water waves in the presence of another 121 S.J. Hogan, I. Gruman and M. Stiassnie SESSION 4 PERTURBATION OF THE GRAVITY-CAPILLARY WAVE SPECTRUM BY CURRENT VARIATION Chairman: W. Alpers SAR imaging of ocean waves in the presence of variable currents 141 G.R. Valenzuela The Modulation Transfer Function: concept and applications 155 W.J. Plant Measurement of short wave modulation by long waves using stereophotography and a laser-slope sensor in TOWARD 173 O.H. Shemdin The surface signatures of internal waves in the ocean: Introduction and systematics 183 J.O. Thomas and A.C. Edwards The surface signatures of internal waves in the ocean: Some particular cases 195 A.C. Edwards and J.O. Thomas Short wave modulation and breaking, experimental results 201 S. Stolte Nonlinearity as the missing link between wavelets and currents 211 K. van Gastel The trickle down of wave modulations from swell to gravity- capillary waves 219 D. Sheres \ i i The mapping of underwater bottom topography with SLAR 231 J. Vogelzang, D. Spitzer, W.A. van Gein, G.P. de Loor, H.C. Peters, H. Pouwels and G.J. Wensink SESSION 5 GENERAL DISCUSSION General discussion on electromagnetic scattering 245 G.R. Valenzuela General discussion on the energy balance in short wind waves 249 W.J. Plant General discussion on perturbation of the gravity- capillary wave spectrum by current variations 253 K. van Gastel SUBJECT INDEX 255 AUTHOR INDEX 267 LIST OF FARTICIFANTS 271 EDITOR'S PREFACE. Ten years ago, de Loor and co-workers at TNO, The Netherlands, were the first to report bottom topography patterns in real aperture radar (RAR) images of the southern North Sea. At that time, this was a real puzzle. The skin depth of microwaves for sea water is only of the order of centimeters while the sea bottom is about 20 meters below the surface. Electromagnetic radiation therefore cannot probe the bottom directly. Similar phenomena were found in radar imagery from SEASAT and SIR-AlB synthetic aperture radars (SAR's) of Nantucket Shoals, the English Channel and many other coastal areas. Since then theory and ocean field experiments (Le., Phelps Bank, Georgia Straits, SARSEX, TOWARD, FASINEX, etc.) have advanced our understanding considerably. We now know that these surface signatures are the results of surface currents, perturbed by the bottom topography, which refract the propagation and modulate the energy of (short) surface waves so as to cause microwave backscatter power variations. Hence, any large scale ocean features containing nonuniform surface currents (i.e. internal waves, eddies, fronts, etc.) will cause similar manifestations in the radar imagery by means of current-wave-microwave interactions. Observations confirm this. The whole issue of modulation of radar backscatter by oceanographic features has received increased attention because of the development of the scatterometer ~s a wind sensor. In fact, SEASAT not only provided SAR pictures, but also the first surface winds over the sea measured from space with a microwave scatterometer. The basic assumption behind this technique is that radiation from the scatterometer on board the spacecraft is received back from the sea surface through scattering from small sea waves with approximately the same wavelength as the microwaves (a few cm in the case of the SEASAT scatterometer). These small sea waves are generated locally by the wind, and so the backscattered radiation is a measure for the wind at the sea surface. This technique, which is going to be implemented again on the oncoming ERS-l satellite, gives global coverage of the wind field over the oceans. It is evident that a correct interpretation of the scatterometer data requires a good understanding of the oceanographic processes responsible for short wave modulation. There is a vast variety of such processes. In addition to nonuniform currents we have modulation and tilting by the larger ones, as well as the effect of surfactants and temperature variations on wave spectra and wind-wave relations. Breaking waves and other nonlinear effects furthermore complicate the situation. In a discussion between Dr. G.R. Valenzuela of the Naval Research Laboratory and one of us (GJK) , it was felt that time was ripe for a review of recent experimental and theoretical research on the modulation of short gravity-capillary waves by non-uniform currents, and related topics, such as microwave probing and imaging mechanisms. i\ x Such a review could best be obtained in the interactive atmosphere of a workshop with a group of invited scientists, active in all related disciplines. An organ1z1ng committee was therefore established, consisting of Dr. G.R. Valenzuela, Prof. W. Alpers of the University of Bremen (FRG) , Dr. K. van Gastel (University of Utrecht, the Netherlands) and the present editors. The workshop was supported by the US Office of Naval Research and the Dutch National Remote Sensing Board. It took place on May 24-26, 1988 in the Dutch coastal resort of Bergen aan Zee under the title: "The Modulation of Short Wind Waves in the Gravity-Capillary Range by Non~Uniform Currents". The meeting was characterized by enthusiastic and lively contributions which made it an inspiring and fruitful event. It is not without pride that we present the proceedings. G.J. Komen and W.A. Oost. Session 1 Tidal currents and Bathymetry Chairperson: G. P. de Loor DETERMINING THE CURRENTS OVER PHELPS BANK DAVID A. GREENBERG Physical and Chemical Sciences Branch Department of Fisheries and Oceans Bedford Institute of Oceanography Dartmouth Nova Scotia Canada B2Y 4A2 GASPAR R VALENZUELA and DAVIDSON T CHEN Space Sensing Branch Space Systems Technology Department Naval Research Laboratory Washington, D. C., 20375-5000 USA ABSTRACT. The Mz tidal currents over Phelps Bank are examined using a fully nonlinear model. Simulations with resolutions of 2'x 2' and 0.5'x 0.5' were made of the full area covering Nantucket Shoals south of Cape Cod. A fine resolution model (0.125'x 0.125') was also run over a limited area surrounding Phelps Bank. Agreement was good in amplitude and phase when compared to surface elevation data. The agreement with current meter data was fair in amplitude and poor in phase with the exception that agreement was good at the one Phelps Bank mooring when compared with models of the full area. The limited area model showed signs of instability that were damped out with a horizontal eddy viscosity. Agreement of this model with data from the one available current meter mooring was worse. Different options are available to go from model predictions to the currents necessary for calibration of microwave data obtained over Phelps Bank. 1. Introduction There has been a large effort to collect and examine microwave data over Phelps Bank (e.g. see Valenzuela et al., 1985). Images (Valenzuela et al., 1983) of microwave backscatter over shallow areas have exhibited features that closely mirror the bottom topography. It is felt that these images reflect the modification of short gravity waves by currents with magnitude roughly inversely proportional to the depth. For a proper calibration of the microwave signal, the currents should be accurately known. The approach taken here is to use a barotropic numerical model to determine the Mz tidal currents, and use these as a basis for future 3 G. J. Kamen and W. A. Oost (eds.), Radar Scattering/rom Modulated Wind Waves, 3-17. © 1989 Government a/Canada.
The list of books you might like
