<p>According to the <a href="https://en.wikipedia.org/wiki/Titan_(moon)" rel="nofollow noreferrer">Wikipedia page on Titan</a>, that data was deduced from Cassini.</p>

<blockquote>
  <p>On December 21, 2008, Cassini passed directly over Ontario Lacus and observed specular reflection in radar. The strength of the reflection saturated the probe's receiver, indicating that the lake level did not vary by more than 3 mm (implying either that surface winds were minimal, or the lake's hydrocarbon fluid is viscous).</p>
</blockquote>

<p>That claim cites two sources:</p>

<p><a href="http://adsabs.harvard.edu/abs/2009GeoRL..3616201W" rel="nofollow noreferrer">newscientist.com</a> (definitely not a primary source)</p>

<p><a href="http://adsabs.harvard.edu/abs/2009GeoRL..3616201W" rel="nofollow noreferrer">Harvard ADSABS</a> which does appear to be a primary source analysis of Cassini data. However, I don't have time right now to see what peer-review made of this analysis.</p>

<blockquote>
  <p>Cassini RADAR altimetry data collected on the 49th flyby of Titan (2008 December 21) over Ontario Lacus in Titan's south polar region provides strong evidence for an extremely smooth surface, with less than 3 mm rms surface height variation over the 100m-wide Fresnel zone. Histograms of the raw radar echoes imply a mirror-like specular reflection of the transmitted signal. Such an echo is possible only if the surface is extremely flat relative to our 2.2-cm wavelength. The 3 mm upper bound follows from analyzing the strength of the specular return, which declines exponentially with increasing surface height variance. In this experiment, the strength of the echo was larger than expected, severely saturating the receiver. We developed a method to partially correct the echoes for the distortion incurred. While the implied mm-scale smoothness is not proof that the surface is liquid, it is unlikely that a solid surface is so smooth.</p>
</blockquote>

<p>From the abstract, it seems they are deriving this conclusion indirectly, but I'm not educated enough in this area to personally vouch for the methods.</p>

CC BY-SA 4.0
2018-12-20T22:12:58.010Z
That's interesting, thank you. So these describe an upper limit on roughness and are consistent with both very small waves and *no waves*, and they *don't* describe evidence that waves exist.
uhoh
CC BY-SA 4.0
2018-12-20T18:49:43.483Z
2018-12-20T18:49:43.483Z
Cody
<p>Michael Stevens from V-Sauce has a video called <a href="https://youtu.be/MwjsO6aniig?t=776" rel="nofollow noreferrer">The Mandelbrot Set</a> on a different channel. At <code>12:56</code> he says:</p>

<blockquote>
  <p>There’s a moon of Saturn that has liquid hydrocarbon lakes that literally have waves that are only like a fraction of a centimeter large, but, you could surf that, right?</p>
</blockquote>

<p>While Michael occasionally does indeed <a href="https://earthscience.stackexchange.com/q/9978/6031">say things that appear to be wrong</a> I'm guessing he got this correct.</p>

<p>How are waves a fraction of a centimeter tall measured on a moon of Saturn? How is the existence of these waves either measured or deduced?</p>

CC BY-SA 4.0
2018-12-20T11:45:19.660Z
https://www.iflscience.com/space/waves-on-saturns-moon-titan-are-just-one-centimeter-high/  and  https://www.sciencedirect.com/science/article/pii/S0012821X17303163
AtmosphericPrisonEscape
<natural-satellites><saturn><planetary-science>
How do they measure sub-centimeter wave height on a moon of Saturn?
uhoh
# How do they measure sub-centimeter wave height on a moon of Saturn?

(Asked by: username_0 on 2018-12-20)

Michael Stevens from V-Sauce has a video called [The Mandelbrot Set](https://youtu.be/MwjsO6aniig?t=776) on a different channel. At `12:56` he says:

> There’s a moon of Saturn that has liquid hydrocarbon lakes that literally have waves that are only like a fraction of a centimeter large, but, you could surf that, right?

While Michael occasionally does indeed [say things that appear to be wrong](https://earthscience.stackexchange.com/q/9978/6031) I'm guessing he got this correct.

How are waves a fraction of a centimeter tall measured on a moon of Saturn? How is the existence of these waves either measured or deduced?

**Tags:** natural-satellites, saturn, planetary-science
> **Comments:**
> **username_1**: https://www.iflscience.com/space/waves-on-saturns-moon-titan-are-just-one-centimeter-high/  and  https://www.sciencedirect.com/science/article/pii/S0012821X17303163  

---

## 1 answers

### Answer by username_2 on 2018-12-20. Score: 3 | Accepted answer

According to the [Wikipedia page on Titan](https://en.wikipedia.org/wiki/Titan_(moon)), that data was deduced from Cassini.

> On December 21, 2008, Cassini passed directly over Ontario Lacus and observed specular reflection in radar. The strength of the reflection saturated the probe's receiver, indicating that the lake level did not vary by more than 3 mm (implying either that surface winds were minimal, or the lake's hydrocarbon fluid is viscous).

That claim cites two sources:

[newscientist.com](http://adsabs.harvard.edu/abs/2009GeoRL..3616201W) (definitely not a primary source)

[Harvard ADSABS](http://adsabs.harvard.edu/abs/2009GeoRL..3616201W) which does appear to be a primary source analysis of Cassini data. However, I don't have time right now to see what peer-review made of this analysis.

> Cassini RADAR altimetry data collected on the 49th flyby of Titan (2008 December 21) over Ontario Lacus in Titan's south polar region provides strong evidence for an extremely smooth surface, with less than 3 mm rms surface height variation over the 100m-wide Fresnel zone. Histograms of the raw radar echoes imply a mirror-like specular reflection of the transmitted signal. Such an echo is possible only if the surface is extremely flat relative to our 2.2-cm wavelength. The 3 mm upper bound follows from analyzing the strength of the specular return, which declines exponentially with increasing surface height variance. In this experiment, the strength of the echo was larger than expected, severely saturating the receiver. We developed a method to partially correct the echoes for the distortion incurred. While the implied mm-scale smoothness is not proof that the surface is liquid, it is unlikely that a solid surface is so smooth.

From the abstract, it seems they are deriving this conclusion indirectly, but I'm not educated enough in this area to personally vouch for the methods.

> **Comments:**
> **username_0**: That's interesting, thank you. So these describe an upper limit on roughness and are consistent with both very small waves and *no waves*, and they *don't* describe evidence that waves exist.  

---

