In this study, the applicability of the surface image velocimeter using the far-infrared camera was examined in order to solve the
application problem of the measurement in night time, which has been pointed out in previous studies as the limit of the surface image
velocimeter. For this purpose, the accuracy evaluation of measurement of the far-infrared camera was conducted for two conditions.
Accuracy was evaluated by calculating the relative error of the results of the measurements of surface image velocimeter using the
normal video camera during the daytime that was already verified. As a result, the relative error of the surface velocimeter using the far
infrared camera was 4.3% at maximum, the average error was about 1%, and the error of the fog condition was maximum 5.2% with an
average of 2%. In conclusion, it is possible to measure with high accuracy when using far-infrared camera in a invisible environments
where the water flow can not be visualized with a general camera.