Ocean Wave Information Retrieval Using Simulated Compact Polarized SAR from Radarsat-2

The main objective of this paper is to demonstrate the capability of compact polarized (CP) synthetic aperture radar (SAR) to retrieve ocean wave field parameters. Souyris’ and Nord’s algorithms are used to carry out the reconstruction of CP SAR pseudo quad-polarized data for the ocean surface under both the circular transmit linear receive (CTLR) and π/4 mode. The results show that, for the CP reconstruction, Nord’s algorithm has a better convergence ability than Souyris’. In addition, the investigation of the reconstruction accuracy shows that the CTLR mode is superior to the π/4 mode, in terms of ocean surface reconstruction. It is, therefore, concluded that the reconstructed parameters of CP CTLR mode data by Nord’s algorithm adapt to retrieve ocean wave information. The ocean wave slope spectrum and other main wave parameters are also calculated from reconstructed CP data and compared with measurements from in situ National Data Buoy Center (NDBC) matched-up buoys. Comparison of CP SAR-based wave field information with buoy outputs also shows good agreement in the case of dominate wave height, wave direction, and wave period, with biases of 0.36 m, 17.96°, and 0.88 s, respectively.

Transitional relation exploration for typical loess geomorphologic types based on slope spectrum characteristics

Based on the Chinese Geomorphologic Database at 1 : 1 000 000 scales, the distribution of the typical loess geomorphologic types (such as the loess tableland, loess ridge and loess knoll) is acquired in the Loess Plateau of China. Then, based on the SRTM (Shuttle Radar Topography Mission) digital elevation model (DEM) data and topographic analysis methods, the slope spectrums are computed for the typical loess geomorphologic types and their subtypes. Through achieving the tendency line of the slope spectrum and analysing the slope spectrum characteristics of the loess typical geomorphologic types, the transitional relationships are explored: (1) the general rule is that loess tableland transitions to loess ridge, and then to loess knoll. (2) The specific relationships for the subtypes are as follows: in loess tableland, the transition is from loess terrace to complete tableland, then to residual tableland, and finally to beam tableland. In the loess ridge, the transition is from oblique ridge to knoll ridge, and the final stage is the loess knoll.

Sea wave modelling for motion control applications

The modelling of sea environment is important in designing an effective motion control system for any marine vehicle. Inadequate representation of the components of a typical random sea might lead to poor performance of the control system. A multiple output system such as the one having components of wave elevation and slope, facilitates designing the control system taking into account the different degrees of freedom. The method of modelling the sea environment presented here, provides the basis for the design of motion control systems for multiple degree of freedom cases, which give rise to excitation forces and moments acting on the marine vehicle. The method used here models the sea environment using Gaussian white noise and shaping filter to generate a multiple output form of the random sea state. In the first step a given standard wave spectrum is approximated using a rational polynomial, the coefficients of the polynomial are obtained by least square fitting method to best match the spectrum. The established rational polynomial is then decomposed to get the transfer function of the shaping filter. The wave slope spectrum is similarly approximated using the same rational polynomial. The transfer functions of the two components of amplitude and slope, representing the filters are combined to generate a state space form. Using the white noise as input, the state space form obtains the wave elevation and slope as outputs. By performing spectral analysis using Welch method, the quality of the obtained output is checked against the targetted spectrum. The application of the simulated wave slope spectrum in a closed loop state space model is demonstrated as applied to the roll stabilization characteristics of a stationary ship using a passive tank.DOI: http://dx.doi.org/10.3329/jname.v11i1.17768

Transitional relation exploration for the typical loess geomorphologic types based on the slope spectrum characteristics

Based on the Chinese Geomorphologic Database at 1 : 1 000 000 scales, the distribution of the typical loess geomorphologic types, such as the loess tableland, loess ridge and loess knoll is acquired in the Loess Plateau of China; then, based on the SRTM 5 (shuttle radar topography mission)-DEM data and topographic analysis methods, the slope spectrums are computed for the typical loess geomorphologic types and their sub-types; through achieving the tendency line of the slope spectrum and analyzing the slope spectrum characteristics of the loess typical geomorphologic types, the transitional relationships are explored: (1) the general rule is: the loess tableland transits to 10 the loess ridge, and then transits to the loess knoll; (2) the specific relationship for the subtypes is: in the loess tableland, from the loess terrace to the complete tableland, then to the residual tableland, and finally to the beam tableland; in the loess ridge, from the oblique ridge to the knoll ridge; the final types is the loess knoll.