Photoacoustic imaging-based in situ biofouling monitoring in underwater optical windows-A novel approach

The accuracy of optical instruments is inevitably affected by marine biofouling as their optical windows become obscured in seawater. The continuous removal of biofouling imposes a substantial energy burden on the offshore instruments. Therefore, monitoring biofouling and selecting an appropriate time for biofouling removal is essential. However, an efficient in situ monitoring strategy for biofouling in underwater optical windows is currently lacking. To address these challenges, we conducted exploratory research on a new technology based on photoacoustic imaging for the in situ monitoring of marine biofouling in optical windows. First, poly methyl methacrylate coupons were hung and immersed in the coastal waters of Qingdao for varying durations during the sea trials. Evident photoacoustic signals from the biofouling attached to the surfaces of the coupons were collected by means of photoacoustic experimental platform. Two-dimensional photoacoustic images were reconstructed using photoacoustic microscopy. On comparing the optical and photoacoustic images of biofouling, photoacoustic images can more effectively reflect the degree of biological fouling. Finally, the optical and photoacoustic images of coupons subjected to ultrasonic treatment were compared and analyzed to further review the feasibility of fouling monitoring based on photoacoustic technology. These findings provide new insights into in situ detection of marine biofouling.