Inverse estimation of drifting-object outflows using actual observation data |
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| Authors: | Shin’ichiro Kako Atsuhiko Isobe Satoquo Seino Azusa Kojima |
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| Institution: | 1.Center for Marine Environmental Studies,Ehime University,Matsuyama,Japan;2.Urban and Environmental Engineering, Faculty of Engineering,Kyushu University,Fukuoka,Japan;3.Japan Environmental Action Network,Tokyo,Japan |
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| Abstract: | The present study attempts to establish a scientifically reliable method capable of computing the drifting-object sources
and their outflows. First, the temporal variability of the drifting-object amount is investigated every two months on a beach
west of Japan, where various source regions are anticipated because of spatiotemporally variable northeastward ocean currents
over the East China Sea. Next, in order to specify drifting-object sources, two-way particle tracking model (PTM) experiments
are carried out using simulated ocean currents and leeway drift estimated from QuikSCAT/Seawinds wind data. Finally, an inverse
method with a Lagrange multiplier is applied to estimate drifting-object outflows at each source on the basis of the two-way
PTM results and beach surveys. Accuracy of object-source identification using the two-way PTM is validated by comparing disposable-lighter
sources suggested by phone numbers printed on the lighter surface with those computed by the model. In order to examine the
reliability of the inverse estimation, the number of plastic-bottle caps found in actual beach surveys is compared with that
computed using a forward in-time PTM during the same period of actual beach surveys, over which the outflows obtained using
the inverse method are given at each source in the model. |
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