Use of synthetic aperture radar in estimation of wave climate for coastal engineering design

Abstract

Development of Alaska's maritime resources requires design of efficient, reliable, safe facilities by coastal engineers who have a thorough knowledge of site specific wave climate: wave height, length, period, direction, and storm duration. Unfortunately, lack of wave information and validated hindcast models along the Alaskan coast often results in costly overdesigned facilities or underdesigned coastal structures which have a high risk of performance failure. To expand the nearshore wave climate availability, use of spaceborne synthetic aperture radar (SAR) data to estimate wave parameters was evaluated. SAR data were examined in raw and filtered forms, and the extracted wave climate compared to field measured data at three sites. Based on this comparison, the applications and limitations of SAR estimated parameters were established and incorporation of the information into current design practice was addressed. SAR based spectra were dominated by low frequency spectral peaks, likely due to random noise associated with SAR images, as these peaks were not present in the field measured spectra. Due to discrepancies between SAR and measured spectra, wave height, and storm duration could not be determined. Although error ranged from 12.5% to over 100% for SAR estimated wave lengths, the fact that wave lengths, although inaccurate, could be determined from SAR is promising. SAR based wave direction compared favorably to theoretical propagation directions which affirms the potential of wave parameter extraction from SAR data. However, directional field data were not available for comparison. Due to the current errors associated with SAR based wave estimations, SAR estimated wave climate cannot be incorporated into coastal design practice at this time. Research results suggest SAR data still hold great potential for estimating wave parameters. Examination of SAR based wave climate in an extensively monitored, open ocean setting would be beneficial, and the influence of environmental factors on SAR imaging of waves warrants additional investigation. Furthermore, development of a tandem SAR platform with temporal resolution on the order of seconds would be useful for wave period estimation and interferometric wave height determination. After this background research has been accomplished, another evaluation of SAR based nearshore wave climate would be worthwhile.