Abstract
<p>57 synthetic aperture radar (SAR) images were collected over the Mid-Atlantic Bight (MAB) during the Shallow Water 2006 experiment (SW06). The dependence of internal wave (IW) signature occurrences and types in SAR images on the wind conditions is studied. A defined signature mode parameter (S sub m ) quantifies the signature of the IW intensity profile in relation to the mean backscatter in the image background to determine different IW types (single positive, single negative and double sign). The statistical results show that moderate wind speeds of 4-7 m/s are favorable for imaging IWs by SAR, whereas very few IW signatures are observed when the wind speed is higher than 10 m/s and lower than 2 m/s. Many S sub m values are larger than 1 (positive signature) even when the angles between the wind direction and IW propagation direction (theta sub Wind-IW) are less than in the MAB, which does not agree with the result of da Silva et al. (2002). An advanced radar imaging model has been run for different wind conditions, radar look directions and IW amplitudes. The model results indicate that the proportion of S sub m values larger than 1, when theta sub Wind-IW < 90 degree , increases with IW amplitudes. In general, relating IW signature types mainly to the wind direction is an oversimplification without considering other factors such as look directions and IW amplitudes. An IW interaction pattern has been studied on the basis of two sequential images from ERS2 and ENVISAT with a time lag of 28 minutes and temperature and current measurements from moorings. Phase velocities of the pattern can be derived by two-dimensional cross correlation of two images or in-situ measurements. In this pattern, the IW packet with a larger amplitude shifts less while the one with a smaller amplitude shifts more due to the interaction. The strong intensity in the interaction zone implies an amplitude increase. The intensity changes in the same IW packet after the interaction implies the energy exchange. All the characteristics agree well with the dynamics of the two-soliton pattern with a negative phase shift, according to Peterson and van Groesen (2000).</p>