Atacama Pathfinder EXperiment APEX
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Atmospheric opacity calculator


By entering the frequency (in GHz) and the amount of precipitable water vapor (PWV) you can calculate the zenith optical depth τo. Typical values for PWV would be 0.2 mm (in very good conditions), 0.5 mm (normal conditions, use this value if you do not know the time of year for your observations), and 1.0 mm in mediocre conditions. The entered frequency and the calculated τo will be transferred to the RMS and integration time calculators below. For the APEX-2a receiver the tuning range is 279-381 GHz.

Calculate τo
Freq. [200 - 1600 GHz]
PWV [mm] [0.05,0.1....3]
τo

RMS calculator
Integration time calculator
By entering the atmospheric temperature (some 10 degrees below the ground temperature at Chajnantor), the (average) elevation of the source, the receiver temperature, an on-source integration time, and the spectral resolution, the RMS (in K) can be estimated. See the observing time calculation page for details. The APEX-2a receiver temperature is about 70 K for the entire tuning range.
By entering the atmospheric temperature (some 10 degrees below the ground temperature at Chajnantor), the (average) elevation of the source, the receiver temperature, required RMS (in K), and the spectral resolution, the on-source integration time can be estimated. Also the total time is calculated assuming toff=ton and a system observing efficiency of 0.625, i.e. ttotal=(ton + toff)/0.625. The system efficiency takes into account time for telescope movements and calibrations.

Tatm (K)
Source elevation (deg)
Trec (K)
tint ON( sec)
FFTS (Number of channels)
Frequency resolution (kHz)

Vel. resolution Δv (km/s)

τo
Frequency (GHz)
Tsys (K)
Position switching σ (K)
Beam switching σ (K) (not implemented)
Frequency switching σ (K) (not implemented)

Tatm (K)  
Source elevation (deg)  
Trec (K)  
RMS (K)  
FFTS (Number of channels)  
Frequency resolution (kHz)
 

Vel. resolution Δv (km/s)

 
τo  
Frequency (GHz)  
Tsys (K)  
Position switching ton ttotal
Beam switching ton (not implemented) ttotal
Frequency switching ton (not implemented) ttotal

 

 

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Last update : March 1, 2006