This paper is concerned with an analysis of field distribution caused by sensor nodes. First, we introduce 1-ray and 2-rays models with two modification factors to estimate the field distribution in complicated natural environments. One of the two factors is an amplitude modification and the other is an distance order of propagation. By using the two factors, we can calculate field distributions in complicated fields such as random rough surface. Next we propose a algorithm for radio communication distance based on the 1-ray and 2-rays models. In the numerical examples, we show the field distribution caused by sensor nodes, using 1-ray and 2-rays models. Finally, we discuss how many sensor nodes are needed to cover the field area in order to construct sensor networks.