-- active surface, Zernickes on, FEM on; dynamic corrections on.

-- active surface, Zernickes on, FEM on (femA59wM95bG.fef); dynamic corrections on.

It seems amusing to compare the 3 K-band gain curves. Using the fitted coefficients, and plotting the smoothed curves rather than the observed points, the gain curve comparison is shown in Figure 9 as the three curves. One can see that the March 2002 curve is strangely lumpy. Apparently the surface was improved between 2002 and 2005 and resulted in the much smoother gain curves of 2005 and 2008. The addition of the Zernicke terms in 2008 gives a much flatter gain curve.

It seems amusing to compare the 3 K-band gain curves. Using the fitted coefficients, and plotting the smoothed curves rather than the observed points, the gain curve comparison is shown in Figure 9 as the three curves. One can see that the March 2002 curve is strangely lumpy. Apparently the FEM surface model was improved between 2002 and 2005 and resulted in the much smoother gain curves of 2005 and 2008. The addition of the Zernike terms in late 2006 gives the much flatter gain curve seen in the 2008 data.

• Summary results

• Summary results for K-band gain curve

• Pointing Offsets and such

It seems amusing to compare the 3 K-band gain curves. Using the fitted coefficients, and plotting the smoothed curves rather than the observed points, the gain curve comparison is shown in Figure 10 as the three curves.

It seems amusing to compare the 3 K-band gain curves. Using the fitted coefficients, and plotting the smoothed curves rather than the observed points, the gain curve comparison is shown in Figure 9 as the three curves.

• Fig 9: Comparison of K-band gain curves:
  

Pointing Offsets and such

%META:FILEATTACHMENT{name="gcurves.jpg" attr="" comment="Fig 9: Comparison of K-band gain curves" date="1219844350" path="gcurves.jpg" size="275553" user="FrankGhigo" version="1.1"}%

Figure 5a shows the corrected data and the fitted curves versus elevation, and Figure 5B versus airmass.

Figure 5 shows the corrected data and the fitted curves versus airmass.

• Fig 5: Tsys vs Airmass, adjusted Tcals:
  

The Gains are plotted in Figure 5 versus elevation, and also shown are fits of a quadratic function of the form:

The Gains are plotted in Figure 6 versus elevation, and also shown are fits of a quadratic function of the form:

The resulting gains are 1.87 and 2.02 K/Jy at LCP and RCP, respectively. But these values seem unreasonably high, as compared with earlier measurements.

• Figure 5: Gains(K/Jy) and fitted curves:
  

The resulting gains are 1.92 and 1.95 K/Jy at LCP and RCP, respectively, using the adjusted Tcals (5.376,4.201). But these values seem unreasonably high, as compared with earlier measurements.

• Fig 6: Gains(K/Jy) and fitted curves:
  

• or G = 1.74 K/Jy.

• or G = 1.745 K/Jy.

Note that G=1.74 is about what was measured in the previous gain measurements of December 2005.

Note that G=1.745 is about what was measured in the previous gain measurements of December 2005.

Another contributor to the discrepancy is a possible error in the opacity. The

If we assume the peak efficiency has not changed, then we can do a further adjustment of the Tcals as follows:

• Tcal(LCP) = 4.965 K
• Tcal(RCP) = 3.825 K

Recalculate Tsys and Tant using the new Tcals.

Pol	Trcvr (K)	Tatm (K)	τ	rms (K)	Tcal (K)	max Gain(K/Jy	rms gain (K/Jy)
LCP	20.00	272.4	0.0892	1.34	4.965	1.745	0.036
RCP	20.00	272.4	0.0871	1.35	3.825	1.745	0.048

The new plot for Tsys vs airmass is Figure 7.

Quadratic function fit coefficients

coefficient	value	1 sigma error
A0	0.9097	0.0111
A1	4.345e-3	5.61e-4
A2	-5.225e-5	6.38e-6

The new plot for Gain vs elevation is Figure 8.
• Fig 7: Tsys vs Airmass, using final adjusted Tcals:
  
• Fig 8: Gains vs elevation for the final adjusted Tcals:
  

Gain Curve Comparisons

%META:FILEATTACHMENT{name="TPTCSPNT_080408_gains.jpg" attr="" comment="Figure 5: Gains(K/Jy) and fitted curves" date="1208197295" path="TPTCSPNT_080408_gains.jpg" size="90052" user="FrankGhigo" version="1.1"}%

%META:FILEATTACHMENT{name="TPTCSPNT_080408_gains.jpg" attr="h" comment="Figure 5: Gains(K/Jy) and fitted curves" date="1208197295" path="TPTCSPNT_080408_gains.jpg" size="90052" user="FrankGhigo" version="1.1"}% %META:FILEATTACHMENT{name="tsys_amass_newtcals.gif" attr="" comment="Fig 5: Tsys vs Airmass, adjusted Tcals" date="1219779751" path="tsys_amass_newtcals.gif" size="34277" user="FrankGhigo" version="1.1"}% %META:FILEATTACHMENT{name="gains_newtcals.jpg" attr="" comment="Fig 6: Gains(K/Jy) and fitted curves" date="1219780380" path="gains_newtcals.jpg" size="120860" user="FrankGhigo" version="1.1"}% %META:FILEATTACHMENT{name="tsys_amass_newtcals2.jpg" attr="" comment="Fig 7: Tsys vs Airmass, final adjusted Tcals" date="1219784493" path="tsys_amass_newtcals2.jpg" size="108031" user="FrankGhigo" version="1.1"}% %META:FILEATTACHMENT{name="gains_newtcals2.jpg" attr="" comment="Fig 8: Gains, final adjusted Tcals" date="1219784559" path="gains_newtcals2.jpg" size="116272" user="FrankGhigo" version="1.1"}%

The resulting gains are 1.87 and 2.02 K/Jy at LCP and RCP, respectively. But these values seem unreasonably high.

The resulting gains are 1.87 and 2.02 K/Jy at LCP and RCP, respectively. But these values seem unreasonably high, as compared with earlier measurements.

Observing from about 00:45 to 12:00 UT.

The results of the fitting, and the assumed Tcals, are listed in Table 1.

• The results of the fitting, and the assumed Tcals, are listed in Table 1.

More Discussion of Tsys and Opacity.

Pol	Trcvr (K)	Tatm (K)	τ	rms (K)	Tcal (K)
LCP	20.01	272.4	0.1013	1.42	5.376
RCP	20.01	272.4	0.1013	1.41	4.201

• Figure 5: Gains(K/Jy) and fitted curves:
  

%META:FILEATTACHMENT{name="TPTCSPNT_080408_gains.jpg" attr="" comment="Figure 5: Gains(K/Jy) and fitted curves" date="1208197295" path="TPTCSPNT_080408_gains.jpg" size="90052" user="FrankGhigo" version="1.1"}%

The gain, G, relates to aperture efficiency, η as follows:

• G (K/Jy) = Ta'/S = Ag η / 2k = 2.845 η
• Ag is the geometric area of the telescope,
• Ta' = Tant * exp(τA) ; (where A is the airmass).

The main factors contributing to the aperture efficiency are the pattern illumination efficiency, ηpat, which is about 70% for the GBT feeds, and the surface efficiency, ηsurf, due to surface irregularities. The surface efficiency is given by the Ruze formula:

• ηsurf = exp{ -(4*π s / λ)^2 }
• s is the rms surface irregularity.

Earlier calibrations have yielded s=390 microns, which would imply that

• ηsurf = 0.8762 at 22.236 GHz.

• η = 0.61
• or G = 1.74 K/Jy.

Note that G=1.74 is about what was measured in the previous gain measurements of December 2005. Since that time the surface model has improved due to the addition of the Zernicke polynomial terms. This would result in flattening out the gain curve, but is not expected to increase the peak in the gain curve by a significant amount. A measured G=2.0 implies that there are no surface errors, i.e., s=0.

Have the TCals changed??

Using the calibrator flux informatino from

Using the calibrator flux information from

Gaussian profiles were fitted to each cross scan. After each two azimuth scans, the pointing LPC is updated so that the elevation scans should go through the peak. Thus we used the peaks of the fits to the elevation scans to determine the antenna temperatures (Tant). The Tant is corrected for atmospheric absorption and divided by the source flux density to obtain the gain, G, in Kelvin/Jansky.

• G = Tant * exp(τA) / S(Jy)

The Gains are plotted in Figure 5 versus elevation, and also shown are fits of a quadratic function of the form:

• G(z) = Gmax * (A0 + A1*z + A2*z^2 )
  where z = the zenith distance = 90 - elevation.

The resulting gains are 1.87 and 2.02 K/Jy at LCP and RCP, respectively. But these values seem unreasonably high.

Predicted Gain

Using the calibrator flux informatino from http://www.vla.nrao.edu/astro/calib/manual/baars.html we obtain the following for our observed calibrators:

Weather conditions were mostly clear, but becoming foggy or light overcast.

Observing Log

--config

22.236 GHz center with 320 MHz bandwidth, dual beam; tracking feed 1.

-- quadrant detectors running, but QD temps files not updating.

-- quadrant detectors etc running, but Inclinometer temperature files not updating?

Results

• Summary results
• Tsys and Opacity
• Gain Curve and Efficiency
• Pointing Offsets and such

• AZ/EL coverage for this session:
  

Summary

Tsys and Opacity

Tsys = Trcvr + Tatm{ 1 - exp(-τA)}
where the airmass A = 1/sin(elevation)

The Tsys values were calculated by the program "prepoint" which uses the GFM utilities; the noise cal injection is used to convert units to Kelvin, using previously measured calibrations of the values of Tcal. The results of the fitting, and the assumed Tcals, are listed in Table 1.

Figure 2a shows the graph of Tsys vs elevation, and the fitted curves; Figure 2b shows Tsys plotted vs airmass.

We can compare the opacity, τ, derived from this dataset, which is sort of an average over the 11 hour observing session, with the Cleo predictions, which are shown in Figure 3. The predictions show the average τ varying from about 0.08 to 0.11 over the observing period. So the τ of 0.103 derived from the Tsys data is in reasonably good agreement.

We can also compare with Cleo's prediction of the atmospheric temperature, Tatm. Figure 4 shows the Cleo predictions, in which Tatm ranges between 270 and 274K, again in not too bad agreement with the fits to the Tsys.

• Fig 2A: Tsys vs Elevation and fitted curves.:
  

• Fig 2B: Tsys vs Airmass and fitted curves.:
  

• Fig 3: Predicted Opacity, April 7-8.: The horizontal bar shows the duration of the experiment.
  

• Fig 4: Predicted atmospheric temperatures.: The horizontal bar shows the duration of the experiment.
  

Gain Curve and Efficiency

Pointing Offsets and such

%META:FILEATTACHMENT{name="coverage_080408.gif" attr="" comment="AZ/EL coverage" date="1207760675" path="coverage_080408.gif" size="57008" user="FrankGhigo" version="1.1"}% %META:FILEATTACHMENT{name="tsyss_080408.jpg" attr="" comment="Fig 2A: Tsys vs Elevation and fitted curves." date="1207771036" path="tsyss_080408.jpg" size="62370" user="FrankGhigo" version="1.1"}% %META:FILEATTACHMENT{name="tsyss_amass_080408.jpg" attr="" comment="Fig 2B: Tsys vs Airmass and fitted curves." date="1207771079" path="tsyss_amass_080408.jpg" size="56962" user="FrankGhigo" version="1.1"}% %META:FILEATTACHMENT{name="zopacity2_080408.gif" attr="" comment="Fig 3: Predicted Opacity, April 7-8." date="1207771345" path="zopacity2_080408.gif" size="15838" user="FrankGhigo" version="1.1"}% %META:FILEATTACHMENT{name="atmostemp_080408.jpg" attr="" comment="Fig 4: Predicted atmospheric temperatures." date="1207771612" path="atmostemp_080408.jpg" size="63966" user="FrankGhigo" version="1.1"}%

Start observing about 8:50 EDT; scan 1 on 3C147

Start observing about 8:50 EDT; scan 1 on 3C147 -- antenna not in scan coordinator! Start again with scan number 2.

Using scheduling block "Kgaincal_2"

Scans 2 - 301 peak/focuses on Mars and 3C147

02:01 AM -- switch to scheduling block "Kgaincal_1" (3C286 and 3C295) Scans 301 to 628. End of observing at 08:02 EDT (12:02 UT)

Altogether, 125 good peak/focus sequences.

%META:TOPICINFO{author="FrankGhigo" date="1207618320" format="1.0" version="1.1"}% %META:TOPICPARENT{name="CommissioningHistory"}%

TPTCSPNT_080408 K-band gain calibrations, April 8, 2008

The plan is to do peak/focus on 3C147 and Mars until they set, Then switch to 3C286 and 3C295 until they set about 8am tomorrow morning.

First, Galen and I went up to the receiver room to flip a switch that enabled MCB control of the KA-band receiver cals.

Start observing about 8:50 EDT;  scan 1 on 3C147

-- Tsys about 46 K; winds calm < 5 MPH at start; clear skies.; Tambient=8.5C
-- active surface, Zernickes on, FEM on; dynamic corrections on.
-- quadrant detectors running, but QD temps files not updating.
-- Cleo predicted opacity about 0.08 at start, a bump up to 0.12 sometime during the run.
-- MARS diameter April 8 is 6.66x6.62".  Tant about 3.5K

10:15 pm -- leave it with Dave

-- FrankGhigo - 08 Apr 2008