3. Modeling the Atmosphere

The pwv_atm module provides models for the atmospheric transmission due to precipitable water vapor at Kitt Peak National Observatory. These models can be retrieved by providing either a datetime and airmass value or a PWV column density along line of sight.

3.1. Transmission for Datetime

Modeling the atmospheric transmission function for a given datetime requires SuomiNet data to be available on the local machine. See the Updating Data section for more details.

To find the atmospheric transmission for a given datetime, use the trans_for_date function.

pwv_kpno.pwv_atm.trans_for_date(date, airmass)[source]

Return a model for the atmospheric transmission function due to PWV

For a given datetime and airmass, return a model for the atmospheric transmission function due to precipitable water vapor at Kitt Peak National Observatory.

Parameters:
  • date (datetime.datetime) – The datetime of the desired model
  • airmass (float) – The airmass of the desired model
Returns:

The modeled transmission function as an astropy table

3.1.1. Examples:

For an airmass of 1.2, the transmission function at 2013-12-15 05:35:00 is given by:

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>>> from datetime import datetime
>>> from pwv_kpno import pwv_atm
>>> import pytz
>>>
>>> obsv_date = datetime(year=2013,
>>>                      month=12,
>>>                      day=15,
>>>                      hour=5,
>>>                      minute=35,
>>>                      tzinfo=pytz.utc)
>>>
>>> pwv_atm.trans_for_date(date=obsv_date, airmass=1.2)

  wavelength  transmission
   Angstrom
  ---------- --------------
      3000.0 0.999999991637
      3001.0 0.999999991629
      3002.0 0.999999991621
         ...            ...

3.2. Transmission for PWV

Instead of relying on SuomiNet measurements, users can also retrieve the modeled transmission function by directly specifying a PWV column density. This can be done using the trans_for_pwv method.

pwv_kpno.pwv_atm.trans_for_pwv(pwv)[source]

Return the atmospheric transmission due a given PWV concentration in mm

For a given precipitable water vapor concentration, return the modeled atmospheric transmission function.

Parameters:pwv (int, float) – A PWV concentration in mm
Returns:The modeled transmission function as an astropy table

3.2.1. Examples:

For a 13.5 mm PWV column density along line of sight, the transmission function is given by:

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>>> from pwv_kpno import pwv_atm
>>> pwv_atm.trans_for_pwv(13.5)

  wavelength  transmission
   Angstrom
  ---------- --------------
      3000.0 0.999999922781
      3001.0 0.999999922702
      3002.0 0.999999922625