We study the problem of sensor node localization for a hybrid wireless sensor network deployed in a precision agriculture farm, with nodes located both underground and above-ground. We consider received signal strength measurements from unmodulated signals transmitted between neighboring sensor nodes and between satellite nodes and sensor nodes for ranging purposes. While this paper studies the network based localization of sensors, placed in multiple media, based on the measurements of received signal strengths, in a companion paper we study the same problem based on the time of arrival measurements. The localization problem is formulated with the goal of parameter estimation of the joint distribution of the ranging measurements. First, we arrive at power fading models for the two communication scenarios in our network to model the received signal strength in terms of propagation distance and hence, the participating nodes' location coordinates. We account for various signal degradation effects such as fading, reflection, transmission, and signal interference. Then, we formulate maximum likelihood optimization problems to estimate the nodes' location coordinates using the derived statistical models. We also present a sensitivity analysis of the estimates with respect to the soil complex permittivity and magnetic permeability.
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