Additional information from cables installed in a shallow, near-zero velocity pool showed significantly higher temperature differences with cable depth when compared to the cable in the higher-velocity canal flows. However, the magnitude of the DTS differences could not be fully explained by stratification alone. Corresponding thermister data showed smaller vertical differences (~0.03-0.1☌) suggesting thermal stratification was also present in the canal. In this study, DTS data show differences of 0.1-0.2☌ in temperatures as seen by cables separated vertically by 0.31 m on the sidewall and center of the channel. Calculations predict that at peak solar radiation, in combination with shallow depths and slow velocities, typical fiber-optic cable is likely to experience heating greater than the ambient water column. ![]() Thermister strings were installed at the same depths, but shielded from solar radiation and designed to record absolute water temperatures. ![]() Cables were installed in water depths from 0.05 to 0.79 m in locations of faster (center of canal) and slower (sidewall) water velocities. To confirm these calculations, a field study was conducted to test the effects of solar radiation by installing two types of fiber optic cable at multiple, uniform depths in a trapezoidal canal with constant flow determined by a controlled release from Porcupine Dam near Paradise, Utah. ![]() Given higher water velocities, substantial increases in turbidity, and/or deeper water, there should be negligible solar heating on the cable. These indicate that for clear waterbodies with low velocities and shallow depths, some heating on the cable is likely during peak daily solar radiation. Initial calculations of these affects considered: shortwave radiation as a function of time of day, water depth, and water clarity fiber optic cable dimensions and fluid velocity. ![]() Because fiber optic cables used for DTS are typically sheathed in dark materials resistant to UV deterioration, the question arises of how shortwave solar radiation penetrating a water column influences the accuracy of absolute DTS-derived temperatures. In recent years, distributed temperature sensing (DTS) has enjoyed steady increases in the number and diversity of applications.
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