Underwater Terrain-Aided Navigation Based on Multibeam Bathymetric Sonar Images

Underwater terrain-aided navigation is used to complement the traditional inertial navigation employed by autonomous underwater vehicles during lengthy missions. It can provide fixed estimations by matching real-time depth data with a digital terrain map, This study presents the concept of using image processing techniques in the underwater terrain matching process. A traditional gray-scale histogram of an image is enriched by incorporation with spatial information in pixels. Edge comer pixels are then defined and used to construct an edge comer histogram, which employs as a template to scan the digital terrain map and estimate the fixes of the vehicle by searching the correlation peak. Simulations are performed to investigate the robustness of the proposed method, particularly in relation to its sensitivity to background noise, the scale of real-time images, and the travel direction of the vehicle. At an image resolution of 1 m2/pixel, the accuracy of localization is more than 10 meters.

Dual sensitivity of spiropyran-functionalized carbon dots for full color conversions

Multicolor phosphors that respond rapidly to external stimuli are highly desirable for many applications, including lighting,optical displays and sensors. Herein, spiropyran(SP)-functionalized carbon dots(CDs) were synthesized with a broad-spectrum output that were responsive to both ultraviolet(UV)/visible light and pH. The SP-CDs possessed strong ester linkages between the UV-absorbing/blue-emitting CDs and blue-absorbing/red-emitting surface SP groups, allowing efficient F?rster resonance energy transfer(FRET) between the donor and acceptor. UV irradiation or acid addition cause the SP ring opening to merocyanine(MC) or protonated MCH+forms, respectively, together with the formation of sheet-like aggregates. These processes enhanced the red emissions by the SP groups and attenuated blue emissions from the CDs. These changes were fully reversible under visible light or basic conditions, respectively, allowing dynamic regulation of the fluorescence properties(emission colors from blue to red, photoluminescence(PL) intensity) under photoirradiation on the timescale of minutes. As proof-of concept, we demonstrate that the emission properties of the SP-CDs can be used to construct UV and pH sensing materials as well as light emitting diode(LED) with different colors.