A towed gamma ray spectrometer, called the RESQ hose (RESQ: Radiometric Environment Survey and Quantification), has been developed to continuously map the distribution of radionuclides in the seafloor. The instrument consists of a gamma ray spectrometer in a flexible hose that is attached to a wire or tether cable. The system is towed along the seafloor by a ship, allowing the detector to maintain continuous contact with the seafloor over long distances. Since measurements of seafloor radiation requires the device to be in contact with the seafloor, the system is equipped with accelerometers, underwater microphones and depth sensors to verify that the system is in contact with the seafloor at any given time. We describe sea trials using the RESQ hose to monitor seafloor radiation off Fukushima, within 40km of the Fukushima Dai-ichi Nuclear Power Plant (F 1 NPP) during August 2012. It is expected that data obtained using the RESQ hose will significantly improve our understanding of the distribution of radionuclides into the marine environment following their discharge from F 1 NPP between March and May 2011.
A ship towed gamma ray spectrometer has been developed to continuously map the distribution of radionuclides on the seafloor following the release from the Fukushima-Daiichi Nuclear Power Plant. The device enables continuous measurement of gamma emitters such as 137Cs and 134Cs to be made over long distances. In order to geo-reference the measurements made, accurate localization of the system is necessary. In this paper, a method to determine the location of the instrument is developed based on simulations using a two phase lumped mass model of the towed system. The effects of environmental parameters such as the frictional coefficient of the seafloor, and underwater currents on the position of the towed system are assessed in order to bound uncertainty in the position estimates. We demonstrate the accuracy of the model by comparing depth measurements of the towed system with acoustic measurements of bathymetry during towed deployment at sea.
Outflow from river (river water plume) significantly influences physical and biological processes in estuarine and coastal environments. It is important to understand seasonal and spatial variability of dynamics and distribution of the river water plume. Colored dissolved organic matter (CDOM) of terrestrial origin is transported by river water. For monitoring the river water plume, it is one of useful methods to utilize the product of CDOM derived from ocean-color satellite. Moreover, as a result of the river influence, many previous studies have been published that terrestrial CDOM was inversely correlated with sea surface salinity in various coastal regions. If satellite-derived CDOM can be used as a tracer of the river plume, mapping of salinity should be possible for the plume. In the present study, we will introduce the method for deriving sea surface salinity from ocean-color satellite data in the East China Sea.