No abstract

The vortex electromagnetic (EM) wave carrying orbital angular momentum (OAM) offers a new degree of freedom for synthetic aperture radar (SAR) imaging. Because vortex EM waves have helical wavefronts, the vortex EM wave-based SAR echo contains the three-dimensional (3D) information of the target. In this paper, an OAM-based synthetic aperture radar interferometry (InSAR) technique is proposed to obtain 3D target information accurately without the existence of baseline. First, a vortex EM waves' SAR imaging model is established, and an improved range-Doppler algorithm is proposed correspondingly. Subsequently, the scheme of the OAM-based InSAR without the physical baseline is proposed. Compared with the conventional InSAR, the OAM-based InSAR can avoid the baseline decorrelation and reduce the requirement of the platform. Besides, the processing procedure of the OAM-based InSAR is simplified, which avoids the image registration and the interferogram flattening. The simulation results demonstrate the effectiveness of the proposed technique. Besides, the height estimation accuracy of the OAM-based InSAR was analyzed, in terms of interferometric phase error and OAM mode error. The height estimation accuracy can be improved by increasing the OAM mode difference appropriately. The OAM, which is completely independent of time, frequency, and polarization, offers a new scheme for the InSAR. INDEX TERMS Vortex electromagnetic wave, orbital angular momentum, SAR, InSAR.

Adsorption to dissolved organic matter (DOM) may significantly decrease the freely dissolved concentration of many hydrophobic organic compounds and, hence, result in reduced bioavailability to aquatic organisms. Here, the suitability of using triolein-embedded cellulose acetate membrane (TECAM) as a biomimetic surrogate to assess the bioavailability of organochlorine pesticides (OCPs) in water in the presence of DOM was explored. The accumulation of OCPs was measured in TECAM and pelagic Japanese medaka (Oryzias latipes) in the laboratory after 12 h exposure to water containing different levels of Aldrich humic acid. Further, OCP uptake by TECAM and medaka in real aqueous environments was evaluated after 30 d exposures in two sites. Laboratory results showed that OCP uptake by medaka consistently decreased with increasing levels of humic acid in the range of 0-15 mg C/L in sample solutions. This tendency was closely mimicked by OCP accumulation in TECAM under the same conditions. Field results showed that TECAM accumulated similar OCP patterns as medaka (r 2 ) 0.92 for site 1 and r 2 )0.94 for site 2), although comparison of the in-field eight OCP concentrations in TECAM to those in medaka yielded approximately a factor of 3 (on a wet weight basis). These results suggest that the TECAM method can be used as a simple and useful tool to predict the bioavailability and bioaccumulation potential of poorly biotransformed organic compounds in pelagic fish in aqueous environment.