I suggest you to simply design and manufacture a portable rainfall simulator as closest as possible to your research needs (weight, elevation, rainfall intensity range, raindrop size distribution, etc.).
I can help you step by step to buy a suitable water motor-pomp, nozzles, stand and holders, pipes and etc. and finally to build your own rainfall simulator.
We have just converted a cornell sprinkle infiltrometer. It applies water over a 20 cm diameter area but applies it very evenly.The inside version is mounted at 1.5 meters which we use for determining aggregate stability. The field version we mount at 5 cm height and at 1.5 meters on large PVC pipe to compare infiltration whilst inducing crusting
Marcus its a novel effort for conceptualization. Me tried a similar field version where a 3 meter high portable rainfall simulation system used in conjunction of a portable water supply / regulatory source on live orchards..but the issue remains to match the simulated rains closer to the range of natural rains ( depths, intensities, durations) at particular location of simulation...
Matching rate, depth and duration is easily as you can control the application rate via the bubble tower. Where it doesnt work is if you want to vary the size or velocity of the droplets.