3rd ACS Workshop

and advanced course

ESO Garching Headquarter,

January 15-19, 2006

Atmospheric Transmission at Microwaves (ATM) C++ implementation within ALMA TelCal Subsystem

Juan R. Pardo1

(1) Consejo superior de Investigaciones Científicas (Spain)

1. Physical model to implement (described last Monday)

2. Current C++ implementation

3. Architecture and design review

1. Physical model to implement: Atmospheric Refractivity at ALMA frequencies

Chajnantor zenith transmission for 0.5 mm H2O / Water lines / Oxygen lines / ozone lines / H2O-foreign / N2-N2 + N2-O2 + O2-O2

1a. Imaginary Part (absorption)

1b. Real Part (phase delay)

1a. ALMA needs related to this component

• Able to Guess atmospheric T, P, gas profiles from available site data (Tground, Pground, local humidity, complementary soundings)

• Given an atmospheric profile is known, then able to obtain:

• Atmospheric opacities sorted out by component (dry, wet, individual molecules, continuum-like terms, etc..).

• Phase delays sorted out by component, but specially those related to H2O.

• Simulate atmospheric brightness temperatures along a given propagation path (the easy-to-get observable)

• Inversion capabilities. Given atmospheric brightness temperatures can be measured, then it should be able to:

• Retrieve atmospheric parameters (mainly the H2O column).

• Retrieve hardware implementation parameters such as the coupling to the sky of water vapor radiometers.

• Use the retrieved information to provide correction parameters at the frequencies of the current astronomical observation.

At a

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• Starting point: Fortran code developed during 20 years.

• Contract with ESO to develop ATM for alma.

• Fortran library created to encapsulate "fundamental" physics of the problem.

• C++ interface developed specifically for ALMA needs.

• Updated via CVS (TelCal subsystem)

• Doxygen documented.

• Test examples provided using real FTS and WVR data.

• Work done within the TelCal working group.

2. C++ implimentation history

ATM_telluric

INI_singlefreq

RT_telluric

ATM_st76

ATM_rwat

ABS_h2o ABS_o2 ABS_co ABS_o3_161618

ABS_h2o_v2 ABS_o2_vib ABS_n2o ABS_o3_161816

ABS_hdo ABS_16o17o ABS_o3 ABS_o3_nu1

ABS_hh17o ABS_16o18o ABS_o3_161617 ABS_o3_nu2

ABS_hh18o ABS_cont ABS_o3_161716 ABS_o3_nu3

INTERFACE LEVEL DEEP LEVEL(LIBRARY) I/O Parameters

Ground Temperature

Tropospheric Lapse Rate

Ground Pressure

Rel. humidity (ground)

Water vapor scale height

Primary pressure step

Pressure step factor

Altitude of site

Top of atmospheric profile

1st guess of water vapor column

Layer thickness (NPP)

Number of atmospheric layers, NPP

Layer pressure (NPP)

Layer temperature (NPP)

Layer water vapor (NPP)

Layer_O3 (NPP)

Layer CO (NPP)

Layer N2O (NPP)

User

Frequency

ABSORPTION COEFS.

kh2o_lines (NPP)

kh2o_cont (NPP)

ko2_lines (NPP)

kdry_cont (NPP)

kminor_gas (NPP)

PHASE FACTORS

total_dispersive_phase (NPP)

total_nondisp_phase (NPP)

kabs (NPP)

DATA_xx_lines DATA_xx_index

xx all species

Air mass

Bgr. Temp.

Atmospheric radiance

Other sources to obtain

atmospheric parameters

Applications: INV_telluric for WVR and FTS data (available in current release)

3. Architecture and design review: Old ATM fortran code

Class AtmProfile: Profiles of physical conditions & chemical abundances

Class AbsorptionPhaseProfile: Profiles of refractive index for an array of frequencies

Class WaterVaporRadiometer: Water Vapor Radiometer system in place for phase correction

Class SkyStatus: Relevant atmospheric information for antenna operations

3. Architecture and design review: Basic C++ structure: Collaboration diagram between the most important classes

3. Architecture and design review: Comments

Class SpectralGrid: replicates essentially what would a Class of the receiver or autocorrelator components.

Class Temperautre Class Pressure Class NumberDensity, Class Length...

Classes for the physical parameters relevant to ATM have been created within this component with a namespace atm to avoid confussion. Interfaces with other components need to take this into account.

Standard classes for this physical parameters within the whole software?

Let's have a look to the documentation

3. Architecture and design review: Tests Using real atmospheric transmission curves measured with a Fourier Transform Spectrometer

Taking an average Precipitable Water Vapor amount of 0.5 mm, we have:

23 mk/μm 60 mk/μm 173 mk/μm

3. Architecture and design review: Tests 183 GHz water vapor radiometry (preferred method for phase correction

in ALMA)

GOES-10 Water vapor 350 m opacity meter

a

Observing Frequency: 230.5 GHz, PWV to phase conversion factor: 1.944 deg/m

Time since the beginning of the observation (min) on Nov. 25, 2001

3. Architecture and design review: Tests 183 GHz water vapor radiometry with actual phase correction