Assessment of surface current measured by HF radars within a suspended kelp aquaculture zone in China

High frequency (HF) radar is one of the most important instruments measuring coastal ocean surface current. The accuracy of HF radars measured surface current has been assessed in many coastal waters. Suspended aquacultures are very common in coastal waters all over the world, providing large amounts of shellfish, fish or seaweed products. In suspended aquaculture zones, aquaculture facilities cover sea surface, and they may impact the HF radars' performance in measuring surface current. To date, it is still unknown whether HF radars can measure surface current effectively within a suspended aquaculture zone. In the present study, surface current measured by two HF radars in Rongcheng, China was assessed. Rongcheng, in the eastmost of Shandong Province, is China's largest kelp aquaculture zone. In spite of the presence of numerous suspended aquaculture facilities and kelps, first-order peaks were still notable in the Doppler spectrums of the HF radars. In addition, it seems that the facilities and kelps canopies did not degrade the surface current measurement within the kelp farms. The radar can still effectively measure the surface current within the suspended kelp aquaculture zone. The measured surface current was within typical error levels of HF radars. The surface current features within the kelp farms were well captured by the HF radars. However, the suspended kelp aquaculture weakened the echo power of HF radars probably due to the reduced wave height within the kelp farms. Thus, coastal suspended aquaculture could reduce the working range of HF radars. Yet in the present study, the impact on working range is slight, and the measured surface current is still valid and is valuable data source for understanding the circulation pattern, nutrient transporting and for the aquaculture planning.