Post on 05-Jan-2016
description
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
ll A
LM
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