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Äàòà èçìåíåíèÿ: Mon Nov 1 00:31:15 2004
Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 05:00:53 2007
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A1956 alfa precursor proposal: extra galactic ultra deep survey

Index:

28sep04: A1956 first use of driftchase pattern. pixel positions off at the start.
21oct05: A1956 drift chase pattern. updated position errors.

Intro:

Project a1956 is one of the alfa precursor proposals. It will do multiple drift scans (78 seconds drift, then reacquire the start of the strip) to increase the integration time of the map.

28sep04: A1956 first use of driftchase pattern. pixel positions off at the start. (top)

Project a1956 took some data on 28sep04 to test things out. It used the driftchase pattern. The drift scan lasted for 78 seconds. For one of the scans the ra/dec positions for the pixels were off at the begining of the scan (all scans were not checked). These are the values stored in crval2a,crval3a of the fits header. The plot shows the ra,dec positions (.ps) (.pdf) . These are for pixel 0 (the central beam).

Fig 1. These plots are the first 15 seconds of the drift. The top plot is the azimuth, the bottom plot is the zenith angle. The telescope continued to move for the first 5 seconds of the drift (this problem has been looked into).
Fig 2 top: This is the ra during the drift. The black line is taken from crval2a, the red line is computed from the encoder az,za,time offline in idl (wasalfacmpradec). The units are hours.
Fig 2 2nd plot: This is the difference (crval2a-idlcomputed) in arcminutes.
Fig 2 3rd plot: The declination during the drift in degrees. The black line comes from crva3a. The red line is computed from the az,za,time offline in idl.

Fig 2 bottom:

Processing: usr/a1956/posErrsep04/positions_28sep04.pro

21oct04: A1956 drift chase positions after working on pattern. (top)

Project a1956 started their observing run on 21oct04. The drift chase procedure had been worked on to correct the positioning errors seen on 28sep04. On 21oct04 5 driftchase scans were done each lasting 80 seconds. I took the ra/dec positions from the header (crval2a,crval3a) for beam 0 and compared them with ra/dec positions computed using the encoder az, za, and encoder time (interpolated to the data times in the header). The plots show the ra,dec positions (.ps) (.pdf) .

Fig 1 top. A linear fit was done to the ra values for each 80 seconds. The black lines are the ras from the header (crval's). The red lines are computed offline using the encoder values. The y axis is great circle arc seconds (i included the cosine of the dec).
Fig 1 2nd : This has the declination minus the median declination plotted for each of the 5 scans. Black comes from crvalxx while red is computed offline from the encoder values. The y axis is arc seconds.

Fig 2 3rd,4th:

The ra,dec positions from the header values crval2a,crval3a has improved. It jumps around by about +/- 7 asecs max for this data set. The az,za encoder values changed by at most 1 arcsecond, so the jumping around is a computational problem and not the telescope moving.

Processing: usr/a1956/posErrsep04/positions_21oct04.pro

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