Aplicação de uma rede de sensores sem fios como instrumento de medição de teor água de uma cultura agrícola

Abstract

This text presents the results of a research for development of a measuring method of agricultural crop water content, which utilizes radio signals employed in the communication of a wireless sensor network (WSN), which has application in precision agriculture. A WSN installed in a crop field may function autonomously for more than a year taking soil, weather and plant measurements, and transmitting these data towards a collecting point (or access point). In this kind of application, data are transmitted over radio waves (RF) passing throw a number of nodes of the network (called sensor nodes) until they reach the access point. RFdata transmission requires attention to communication quality, because RF signals spread along their way, besides being attenuated by vegetation. As long as plants moisture and the amount of vegetation in the way of RF propagation directly influence the attenuation, its measurement can be used to obtain information about plant status. The proposal of this work is to utilize the RF signal attenuation measurement of a WSN to estimate vegetation water content of an agricultural crop, as corn and soy. A number of such measurements have to be made, employing a set of pairs of sensor nodes, which are deployed in a region of the agricultural field, considered uniform, in order to obtain a mean value that represents the desired characteristic of the vegetation present in that region. Many works were developed in past decades employing monolitc systems based on radars, which used microwave signalintensity measurements to estimate the water content of agricultural crops. Differently of that, in this work it is used a distributed measurement system based in a wireless sensor network, which had been deployed in an agricultural crop field in order to collect a variety of data. The vegetation water content measuring is made without need of additional sensors, resulting in no additional cost. The text presents the theoretical formulation relating vegetation water content to the attenuation of radio waves. A propagation model is presented, as well as a measuring model of vegetation water content employing the information of the receivedsignal intensity of the communications between the WSN nodes. Several experiments were conducted in corn crop fields, in which the obtained results confirmed the proposal viability.