@Override
    public void write(JmeExporter ex) throws IOException {
        super.write(ex);
        OutputCapsule oc = ex.getCapsule(this);
        oc.write(fogColor, "fogColor", ColorRGBA.White.clone());
        oc.write(fogDensity, "fogDensity", 0.7f);
        oc.write(fogDistance, "fogDistance", 1000);
    }
the distance of the fog. the higher the value the distant the fog looks

@param fogDistance the desired distance (in world units, default=1000)
jme3-effects/src/main/java/com/jme3/post/filters/FogFilter.java