HR: 0800h
AN: H21E-1061    [Abstracts]
TI: A Method for Detecting Submarine Groundwater Discharge by Thermal Infra-Red Measurement
AU: * Sairaiji, M
EM: tt36515@mail.ecc.u-tokyo.ac.jp
AF: University of Tokyo, Department of Geosystem Engineering University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AU: Tomochika, T
EM: tokunaga@geosys.t.u-tokyo.ac.jp
AF: University of Tokyo, Department of Geosystem Engineering University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AU: Mogi, K
EM: kmogi@geosys.t.u-tokyo.ac.jp
AF: University of Tokyo, Department of Geosystem Engineering University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan
AB: Submarine Groundwater Discharge (SGD) has been considered to be one of the important pathways for the transport of freshwater and dissolved constituents from land to coastal ocean. To better understand the importance of SGD, it is necessary to determine spatial distribution, flux, and chemistry of SGD. In this study, Thermal Infra-Red (TIR) survey was conducted to evaluate the ability of this technique for detecting the discharge points. The sea surface temperatures were measured by a TIR sensor with high spatial resolution (1~2cm) and with high frequency (1Hz) at the intertidal zone where groundwater discharge has been found and described. The temperature of discharged freshwater was about 14 $\deg$ C lower than that of ambient seawater because this measurement were done in August. The discharge flux was about 1.3$\sim$6.4$\times$10$^{-6}$m$^{3}$/s, and the area of discharge was about 0.64m$^{2}$. The measurements were conducted from sunset to late at night to remove the effects of sunlight on the sea surface temperature. During the half-day measurements, seawater depth changed from 0 to 1.5m caused by the tidal fluctuation, which enabled us to discuss the water depth-dependant change of sea surface temperature variation. The lower temperature region at sea surface due to the effect of SGD was observed, and the maximum temperature drops were 1.1 and 0.4 $\deg$ C where water depths were 0.5 and 1.1m, respectively. The maximum water depth where we could detect the signal by SGD was 1.3m in this study. The areas of the lower temperature region tended to decrease as the water depth increased. For example, the area of lower temperature (0.6 $\deg$ C) region was about 0.7m$^{2}$ in the case where the water depth was about 0.3m, and it reduced to be about 0.3m$^{2}$ in the case of 0.5m water depth. Using the obtained results from this study, we analyzed the required spatial resolution for TIR survey to detect the existence of the studied SGD with the sensor of which temperature resolution is 0.1 $\deg$ C, which is the standard temperature resolution for airborne TIR survey. It was concluded that the studied SGD could be detected by TIR survey with 50cm spatial resolution even though this resolution has not been achieved in the present airborne TIR survey. However, by using balloon sonde or powered paraglider, we can provide the above mentioned resolution and could use the TIR technique for capturing the spatial distribution of SGD.
DE: 1829 Groundwater hydrology
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting