The ionosphere refers to the upper regions of the atmosphere (90 to 1000 km). This region is highly ionized, that is, it has a high density of free electrons (negative charges) and positively charged ions. It has practical importance because, among other functions, it enables HF radio propagation to distant places on the earth. The ionization of neutral atoms is mainly due to the extreme ultraviolet light radiation from the sun. Consequently, the ionosphere exhibits diurnal changes (day / night), seasonal changes (summer / winter) and is strongly affected by solar activity (11-year cycle, solar flares, ...). Knowledge of the characteristics of the ionosphere is required to establish radio communication links over large distances around the globe. We present in this paper the use of opportunistic HF waves in order to obtain information on the state and variation of the ionosphere. Once HF signals are identified, the knowledge of their characteristic (power, signal path, …) will allow us to study the state and the behavior of the ionosphere. The work of this paper is a first step in a research project that aims for environmental monitoring for ionospheric propagation.