In many cases, the sources of jetlike Herbig-Haro objects are optically invisible, embedded objects which are usually detected at infrared wavelengths. The jets become visible only at distance of 10 16 -10 17 cm from the source, where they emerge from the molecular cloud core that surrounds the central object. High spatial resolution images indicate that close to the position where the jets appear, their width is a decreasing function of distance from the source. We have simulated a string of lineary aligned emitting knots that emerges from a stratified medium. For this configuration, we compute the single scattering of photons in order to obtain intensity maps of the scattered+direct light that reaches the observer