High Resolution Wind and Bathymetry Maps from Synthetic Aperture Radar to increase Ship Safety and ShipTraffic Monitoring from Space

Abstract

In this work satellite images taken by space borne sensors are used to explain atmospheric as well as oceanographic features, e.g. wind fields or ocean wave heights, all are compared to operational numerical model output. One focus in the first paper was to understand the synergy of high resolution passive microwave satellite sensors and optical sensors on different space scales. The jointly retrieved meteorological and oceanographical parameters, e.g. wind speed and significant wave height, show the high quality of space based data in understanding of complex systems, e. g. wave fields. A space based Radar and imaging spectrometers are used to analyse wind and waves during extreme weather conditions, in particular, to describe the spatial evolution of the atmospheric boundary layer processes involved in cold air outbreaks. The behaviour of wind fields in coastal and offshore regions is investigated and compared to numerical model results. For wind field retrieval a geophysical model function is used. High resolution radar satellites provide a fine scale structure of wind fields and information on small-scale atmospheric features as well as more extreme values of environmental parameters during high impact 2 weather, which are not captured well by the numerical models. One case study showed that cloud patterns seen in the optical data and radar cross-section modulation give a consistent dynamical picture of the atmospheric processes. The relevance of space based data for assimilation into numerical models and for offshore wind farming is discussed. Waves are the most obvious feature in Synthetic Aperture Radar (SAR) images over the ocean. The modulation of sea surface roughness by wind makes them visible in radar images and thus variations of wave fields can be detected. Due to the high horizontal resolution of SAR data (down to 1m) wave refraction and shoaling of swell can be monitored. Radar sensors are able to monitor waves with a wavelength longer then the cut-off wavelength. The cut-off wavelength depends on the SAR sensor (resolution) and is a function of wind speed and significant wave height. In this work algorithm to retrieve sea state parameters measured by high resolution SAR data have been adapted from known C-Band SAR systems (ERS-2/ENVISAT) to the new X-Band satellite TS-X (TerraSARX). TS-X gives access to spatial resolution as fine as 1 m in Spotlight mode and high resolution variability of coastal wave fields. Images from the TS-X satellite are particularly suitable for the observation of wave behaviour in transient and shallow water (<100m water depth). By computing the 2 dimensional spectra waves can be tracked. In the second paper it is shown, how wave Refraction and shoaling can be monitored and the calculation of bottom topography can be provided. The retrieved bathymetry is compared to ETOPO1 (a 1 arc-minute global relief model of Earth's surface that integrates land topography and ocean bathymetry, source: NOAA), US Coastal Relief Model (a 3 arc-second US model integrating offshore bathymetry with land topography, source: NOAA) and sea charts from the British Admiralty. Knowledge of the water depth is one important parameter for monitoring of ship traffic and secure navigation. Planning of ship routes is an important economic factor. The knowledge about bathymetry in coastal regions or river estuaries is of high interest. Therefore, ship detection and maritime surveillance with high resolution sensors has increased, in particular in the field of maritime security and maritime safety in the last years. In the third paper first results on the combined use of TS-X ship detection, AIS (Automatic Identification System), and Satellite AIS is presented. The AIS system is an effective terrestrial method for tracking vessels in real time typically up to 40 km off the coast. The quality of TS-X images with respect to ship detection is evaluated and a first assessment of its performance for ship detection is given. Velocity of a moving ship is estimated using complex TS-X data. First results on simultaneous superposition of satellite AIS and high resolution radar images are presented.