Methods and systems for detecting human presence in an outdoor monitored site are disclosed. In an configuration, the method may include providing at least three transmitters for transmitting radio signals and at least three receivers for receiving radio signals. Channel state information (CSI) data is extracted from the radio signals. The CSI data include phase values and amplitude values. The CSI data is converted into an image representation map and then a surface map is generated using Machine Learning (ML) networks. The surface map is a representation of correspondence between the image representation map and a 3-dimensional (3D) surface associated with a human body.