W.A. Oost

Evaluation Of A Two-scale Model Using Extensive Radar Backscatter And Wave Measurements In A Large Wind-wave Flume

One of the aims of the VIERS-1 project is to develop improved models for radar backscatter from water surfaces, based on a description of the underlying physical phenomena instead of an emperical parameterization. To this end, extensive wind, wave and radar backscatter measurements have been compared with model results.

First results of the VIERS-1 experiment

In February 1988, combined measurements of microwave backscatter, wind, waves and gas exchange have been carried out in the large Delft Hydraulics wind/wave tank. This experiment was the first in a series of experiments in the frame of the VIERS-1 project. In this project a number of Dutch and German laboratories cooperate. Main objective is to come to a physical description of the processes involved in wind scatterometry and, from that point, to an improvement of the algorithms used for determination of wind speed and direction from satelliteborne microwave scatterometers. A second objective is to study the relation between the gas exchange at the water surface and the microwave backscatter. To achieve these objectives two wind/wave tank experiments and one ocean based platform experiment are scheduled. In this paper, the VIERS-1 programme will be outlined. The Delft wind/wave tank experiment will be described and some first results of a preliminary comparison of backscatter and wave slope measurements will be shown.

Comparisons of Backs Cantering Calculations with Measurements Made in a Large Wind/wave Flume

In preparation of tlie launch of tlie ERS-1 satellite, a group of Dutch and German laboratories started a study to improve the wind extraction algorithms for the scatterometer. T h e aim of this s tudy is t o create a model for wind retrieval based on physics. In this paper results of microwave backscattering calculations with three different models will be compared with measurenients in a large wind/wave flume. T h e three models are a two-scale model and two models based on approximations of the integral equation. T h e input for the bnckscattering models are measured wave parameters so the comparison permits a direct evaluatiQn of the accuracy of the model within the experimental accuracies.

Comparison Of X-band Radar Backscatter Measurements With Area Extended Wave Slope Measurements Made In A Large Wind/wave Tank.

Combined measurements of microwave backscatter, wind, waves, and gas exchange have been carried out in the large Delft Hydraulics wind/wave tank. This experiment was the first of a series of experiments in the VIERS-1 project. In this project, a number of Dutch and one German laboratory cooperate to come to a physical description of the process involved in wind scatterometry and, from that point, to an improvement of the algorithms used for determination of wind speed and direction from satellite-borne microwave scatterometers. A second objective is to study the relation between the gas exchange at the water surface and the microwave backscatter. Two wind/wave tank experiments and the ocean-based platform experiment are scheduled. The VIERS-1 program is outlined. The Delft wind/wave tank experiment is described, and some first results of a comparison of backscatter and wave slope measurements are shown.

A summary of the VIERS-1 scatterometer model

The VIERS-1 (Verification and Interpretation ERS-1) project has resulted in a new algorithm for the interpretation of the wind scatterometer, based on a physical model of air/sea/radar interaction in which the radar backscatter is calculated from wind and wave conditions. The model is inverted to obtain the wind from the radar backscatter. For operational purposes the model was coupled to the WAM wave model, which provides first-guess wave information. The performance of VIERS-1 has been compared with that of CMOD4, the algorithm presently in operational use, which is mainly based on statistical fitting. Using operational data it has been found that the results of VIERS-1 were comparable with those of CMOD4, with VIERS-1 outperforming CMOD4 slightly at both high and low wind speeds, but with CMOD4 providing a somewhat closer fit in backscatter space.

Modulation of the Microwave Backscatter by Long Gravity Waves As Measured in a Very Large Wind/wave Flume

In preparation of the launch of the ERS-1 satellite, a number of Dutch and German laboratories have started a study to improve the wind extraction algorithms for the scatterometer. The aim of this study is to create a model for wind retrieval based on physics. The study consists of a theoretical effort together with two experiments in large wind/wave flume as well as a verification experiment from an ocean based platform. This paper deals with the second experiment, conducted in the huge Delta flume (I x w x d = 250 x 5 x 5m3) of Delft Hydraulics in the Netherlands. The influence of long, mechanically generated waves on the microwave backscatter in X-band is studied experimentally. A comparison is made with a simple tilt modulation model. The VIERS-1 project is a multi-disciplinary cooperation of Dutch, German and US institutes and laboratories. It is financed by the Netherlands Remote Sensing Board, the European Community and by contributions of each of the participating institutes.