When i render my Houdini Ocean in Mantra PBR, the images always get very noisy towards the horizon. I just use a simple light setup with a Sky-HDRI, no other lights used in the scene. I tried to isolate what is causing the noise, but it seems like the noise is present in almost all the AOVs. I increased pixel samples to 8x8, max Ray Samples to 16, Reflection Quality to 3, i even increased the Sampling Quality in the Environment Light to 8. The Rendering times go up like crazy, to 4 hours max per frame (Res. 1920x1080) but the noisy horizon just doesn't seem to get any better.

Any Tips? Maybe someone else encountered the same problem and found a solution for it. Thanks!

It's probably an issue with the dicing quality; it's probably switching to undiced geometry too close to the camera. That seems to come up fairly often with renders of somewhat-but-not-very flat oceans.

On the Rendering > Dicing tab of the Mantra ROP, try setting the Shading Quality Multiplier to 2 and see if that makes a difference. There might also be some tweaks to the Z-Importance parameter that would be useful, but I don't remember the exact behaviour of it.

it's the part of the ocean, that's far away from the camera, at the horizon, that troubles me. the ocean close the camera works fine, so i don't think its a dicing problem. when i use z-importance, it just flattens the ocean at a certain distance from the camera and i get a straight line between diced geo and undiced geo. doesn't really help for the perspective i am using.

mawn
it's the part of the ocean, that's far away from the camera, at the horizon, that troubles me.

Yep. I'm assuming that the issue is that it's not dicing enough far away from the camera, so it might help to increase the amount of dicing by increasing the Shading Quality Multiplier to 2 or more.

If that doesn't help, it would be useful if you could post a HIP file demonstrating the issue.