Basic Steps to Use atmosphere tool

The basic steps to use atmosphere tool are:

1. Construct atmospheric model profile to calculate transmission
2. Setup frequencies to calculate transmission
3. Get atmospheric transmission (the opacities, phase delay, path length, absorption coefficients, etc.)

Construct atmospheric model profile

Use initAtmProfile method to construct atmospheric model profile. The atmospheric model profile is composed of the layer thickness, pressure, temperature, and gas density of atmospheric component species as a function of the altitude. It can be used to calculate absorption and phase coefficients, as well as to perform forward and/or retrieval radiative transfer calculations. The atmospheric component species used in the calculation are H₂O, CO, O₃, N₂0, NO₂, O₃, and SO₂.

The atmospheric model profile can be build by defining the following values

• the altitude of the site
• the temperature, pressure and relative humidity at the ground
• the top height of atmospheric profile (maxAltitude)
• the tropospheric temperature lapse rate (dTem_dh)
• the initial step of pressure (dP) and multiplicative factor of pressure steps (dPm)
• the scale height of water vapor (h0)
• the atmospheric type ID (atmType)

The available atmospheric types are TROPICAL, MIDLATSUMMER, MIDLATWINTER, SUBARTSUMMER, and SUBARTWINTER. It controls the profile of upper layers of atmosphere. The map between atmospheric types and IDs can be listed by a method, listAtmosphereTypes.

Method initAtmProfile optionally accepts layerBoundaries and layerTemperature to construct an atmospheric model profile using user defined temperature profile of atmosphere.

It is possible to modify basic atmospheric parameters after initialization by updateAtmProfile method.

Method getBasicAtmParams prints the current parameters used to construct atmospheric model profile. Use getProfile to obtain the atmospheric model profile constructed.

Setup frequencies to calculate transmission

Use initSpectralWindow method to define frequencies (spectral windows) to compute transmission. The building blocks of spectral window are the center frequency (fCenter), band width (fWidth), and channel width (fRes). The method accepts a list of quantities for the frequencies when nbands > 1 in the method.

Use addSpectralWindow method to add more spectral windows after initialization.

There are several methods to return spectral window setttings, e.g., getSpectralWindow, getBandWidth, getChanFreq, getChanNum, getChanSep, getNumChan, getRefChan, and getRefFreq.

Get atmospheric transmission

There are three setter methods that can be invoked only after atmospheric model and spectral windows are defined, i.e., setUserWH2O, setAirMass, and setSkyBackgroundTemperature, which define the water vapor column used for radiative transfer calculations, air mass used for the radiative transfer, and balckbody temperature of the sky background (default: 2.73K), respectively.

Now it is ready to invoke getter methods to compute and obtain the transmission of the atmospheric model you defined in previous steps. Tool atmosphere computes,

• the integrated opacity along atmospheric path, e.g., getWetOpacity, getCOLinesOpacity
• the integrated path length, e.g., getN20LinesPathLength, getDispersivePathLength
• the atmospheric phase delay, e.g., getNonDispersivePhaseDelay
• the equivalent Black-body or the Rayleigh-Jeans Temperature of (a channel in) a spectral window, e.g., getTebbSky, getAverageTrjSky
• the absorption coefficient at a layer in the atmospheric profile, e.g., getAbsO3Lines, getAbsH2OCont

Please refer to descriptions in Methods for details of each method.