Arena

File:Venus-Atmosphere.png

Venus's Middle and Lower Atmospheres

So the game takes place in the atmosphere above Venus.

• Ground radius: 6,051.8 km
• Scale height: 15.9 km
• Surface gravity: 0.91 G
• Surface pressure: 92 bar
• Surface visibility: ~3 km
• Kármán line: ~165 km

ExponentialHeightFog - basically need one setting for below the upper cloud layer (BCL) and one for above the upper cloud layer (ACL) ... or maybe we need to modify it as we change altitude through C++ ... I am not entirely clear yet except that the exponential height fog is much more realistic than what we used to do ... we should not be able to see the ground above ~3 km? Should not be able to see the lower cloud layer until what altitude?

Tune the 50 km layer so large structures are readable at 5–10 km, with the far horizon fading out by 15–25 km.

Modern reviews place the lower cloud layer at about 47.5–50.5 km, and probe data show a sharp increase in extinction just below 50 km, with the lower cloud layer having visible optical depth around 6–12 in some measurements.

Exponential Height Fog and Altitude Adjustments

The exponential height fog represents how atmospheric density changes with altitude. To achieve specific visibility targets at different heights:

• Start by setting the fog density at the surface level. Adjust this until you achieve, for example, 3 kilometers of visibility near the ground.

• Next, adjust the height falloff parameter. This controls how rapidly the fog thins out as you go higher. Tune the falloff until you achieve about 10 kilometers of visibility at around 50 kilometers altitude.

• If the natural exponential transition isn’t layered enough for your needs—for instance, if you want certain altitudes to be foggier or clearer—then you can dynamically adjust density or falloff at different altitude ranges. By tweaking fog parameters in steps, you can approximate a layered atmospheric profile.

Static Directional Light (Sun)

In our scenario, Venus’s day is extremely long. Over the course of a gameplay session, the sun’s movement would be imperceptible. Thus, we treat the sun’s directional light as static.

• The sun’s light itself is pure white; any color shift we perceive (like yellow) is due to atmospheric scattering. On Venus, the color of sunlight will be handled by the Sky Atmosphere actor, which manages how light is scattered through the planet’s atmosphere.

• Keeping the sun static simplifies computations. With a stationary sun, lighting can be baked for efficiency, and clouds can still cast shadows without needing constant updates.

Sky Atmosphere Settings

These settings approximate Venus’s dense CO₂ atmosphere and upper haze. They intentionally exclude the sulfuric acid cloud decks (handled separately).

All color values are linear RGB (0–1).

Planet Setup

• Ground Radius: 6052000 (meters)
• Atmosphere Height: 100000 (meters)

Rayleigh Scattering (molecular scattering - weak on Venus)

• Rayleigh Scattering Color:
  • R: 0.02
  • G: 0.03
  • B: 0.04

• Rayleigh Scattering Scale: 0.15

• Rayleigh Exponential Distribution: 8000

Notes:

• Venus has much weaker blue-sky behavior than Earth.
• Keep this low to avoid Earth-like blue tint.

Mie Scattering (dominant haze / aerosol scattering)

• Mie Scattering Color:
  • R: 0.85
  • G: 0.65
  • B: 0.45

• Mie Scattering Scale: 8.0

• Mie Anisotropy: 0.80

• Mie Exponential Distribution: 12000

Notes:

• This is the MOST IMPORTANT parameter group.
• High scale + strong forward scattering creates:
  • bright glow toward the sun
  • washed-out horizon
  • Venus “golden haze”

Absorption (gas absorption - subtle but important)

• Absorption Color:
  • R: 0.35
  • G: 0.18
  • B: 0.08

• Absorption Scale: 0.6

Notes:

• Adds slight brown/orange attenuation
• Prevents overly bright or “milky white” atmosphere

Aerial Perspective

• Aerial Perspective View Distance Scale: 0.25
• Aerial Perspective Start Depth: 0.0

Notes:

• Lower value = thicker perceived atmosphere
• This helps maintain strong distance fade even at altitude

Multi Scattering

• Multi Scattering Factor: 1.0

Notes:

• Keep enabled — Venus relies heavily on multiple scattering
• This is what removes shadows and creates uniform brightness

Ground Albedo

• Ground Albedo Color:
  • R: 0.25
  • G: 0.20
  • B: 0.15

Notes:

• Subtle contribution only
• Prevents unrealistic light bounce