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

Kurzfassung

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 compared to obtained parameters from operational numerical models. One focus in the first paper was to understand the synergy of high resolution passive microwave satellite sensors and optical sensors in different scales. The combination of retrieved meteorological and oceanographical parameters, e.g. wind speed and significant wave height by satellite sensors 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 in 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 higher values of environmental parameters in extreme weather situations, which seem not to be captured well by the analyzed 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. Wind speed is the most obvious feature in SAR images over the ocean. The modulation of sea surface roughness by wind makes waves in radar images visible and a description of the variations of wave fields can be provided. Due to high resolution of Radar 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 TerraSAR-X. TerraSAR-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 TerraSAR-X satellite are particular suitable for the observation of wave behavior in transient and shallow water (<100m water depth). By computing the 2 dimensional spectra waves can be tracked. Wave Refraction and shoaling can be monitored and the calculation of bottom topography can be provided. The retrieved bathymetry is compared against depth data from other sources like ETOPO1, US Coastal Relief Model 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 this work first results on the combined use of TerraSAR-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 TerraSAR-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 TerraSAR-X data. First results on simultaneous superposition of satellite AIS and high resolution radar images are presented.