D. van Halsema

Coastal DEMs with cross-track interferometry

Digital elevation models (DEMs) are produced from airborne radar cross-track interferometric measurements. Radar DEMs recorded from perpendicular orientations are intercompared, and compared to DEMs derived from airborne laser altimetry.

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.

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.

Satellite radar measurements of land subsidence

The potential of satellite borne interferometric measurements for the mapping of slow land subsidence has been investigated. Two test sites, covered by the ERS-1 satellite, were selected in the Netherlands: the provinces of Groningen and Zeeland. In situ measurements on the weather and the actual subsidence were gathered. It is shown that under favourable conditions measurement accuracies for land subsidence in the range of millimetres are feasible. Atmospheric effects together with temporal decorrelation are the major limitations to the accuracy of the technique for this type of long term measurement.The potential of satellite borne interferometric measurements for the mapping of slow land subsidence has been investigated. Two test sites, covered by the ERS-1 satellite, were selected in the Netherlands: the provinces of Groningen and Zeeland. In situ measurements on the weather and the actual subsidence were gathered. It is shown that under favourable conditions measurement accuracies for land subsidence in the range of millimetres are feasible. Atmospheric effects together with temporal decorrelation are the major limitations to the accuracy of the technique for this type of long term measurement.

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.

Realization of a scalable airborne radar

Modern airborne ground surveillance radar systems are increasingly based on active electronically scanned array (AESA) antennas. Efficient use of array technology and the need for radar solutions for various airborne platforms, manned and unmanned, leads to the design of scalable radar systems. The design and realisation of such a system is described. At the core of the design is a new generation of transmit-receive modules, developed and used also for naval radar systems. The radar architecture is largely based on the miniSAR system, which is close to completion. Design aspects are discussed for various envisaged versions of the scalable radar.

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.

A High Resolution Scalterometer for Radar Backscatter Measurements of Wind Generated Waves in Wind/Wave Tanks

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, with wind generated waves. In March 1989 a second exaperiment took place in the huge outdoor wave tank, the Delta tank, with wind generated waves and mechanically generated waves. These experiments were perfonned in the framework of the VIERS-1 project. In this project a number of Dutch and German institutes cooperate. Main objective is to increase the knowledge about the physics involved in the interaction of microwaves and the ocean surface 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-l program will be outlined. The features of a specially designed high resolution scatterometer will be described and some results of both tank expermnents will be shown.