WARNING: UserWH2O doesn't have anything to do with the actual atmosphere being modeled. But somewhat mysteriously, some variables scale with it, and others do not, and you better know which, since its not documented (except here, to my knowledge)

  • [Wet|Dry]Opacity from SkyStatus is scaled to userWH20.
  • [Wet|Dry]Opacity directly from the RefractiveIndexProfile is not.
  • CASA's python interface to ATM uses the latter, so you'll probably get the results you expect to get. (SkyStatus and RefractiveIndexProfile are C++ objects used in the code - if you don't know much about Object Oriented Programming, don't worry, you don't really need to know what's hapenning under the hood, but if you're a developer you certainly want to understand how this works.)

So far so good, since SkyStatus is (as far as we can tell) designed for experiments like WVR phase correction, where one has a prediction of WH2O to compare with the real WH2O.

Here's a plot of WetOpacity taken from the RefractiveIndexProfile, and taken from SkyStatus, just setting userWH20:

userh2o skyopac.png

However, things rapidly get less intuitive: All of the following come from SkyStatus: path wetpath.png
  • As far as I can tell, most of the other opacity/path variables go with the real atmosphere ,not the userWH20: getAbs[CO|H20|N20|Dry][Lines|Cont], get[CO|H20|N20Dry][Opacity|PathLength] (I've checked about a third of them).
  • TebbSky scales with userWH2O.
  • SkyBackgroundTemperature is the CMB 2.73K, so it does not.

On a different note, since you can't apparently initialize an atmosphere to have the PWV that you want, you have to pick the right humidity to get a specific PWV. Ever wonder how PWV relates to % humidity:? Here's the plot, with all the other atmo parameters left at their defaults: The proportionality constant is Ground WH20 [mm] = 0.07838 +/- 0.00018 times humidity in %

hum gh2o.png

-- RemyIndebetouw - 2009-07-29

Topic attachments
I Attachment Action SizeSorted ascending Date Who Comment
hum_gh2o.pngpng hum_gh2o.png manage 23 K 2009-07-29 - 12:01 RemyIndebetouw  
path_wetpath.pngpng path_wetpath.png manage 28 K 2009-07-30 - 09:55 RemyIndebetouw  
userh2o_skyopac.pngpng userh2o_skyopac.png manage 32 K 2009-07-29 - 15:28 RemyIndebetouw  
This topic: ALMA > WebHome > AlmaSci > AlmImcal > SimulatorCookbook > AtmIssues
Topic revision: 2009-07-30, RemyIndebetouw
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