NATIONAL RADIO ASTRONOMY OBSERVATORY

MEMORANDUM

DATE:

TO: Roger Norrod

FROM: Ron Maddalena

SUBJECT: Time line for holographic measurements on the 140-ft with GBT systems

Before we attempt holographic measurements on the GBT it might be prudent of us to try to test on the 140-ft as much as is possible of the GBT hardware and software. But, before we attempt holography on the 140-ft we need to test and develop some subsystems.

Holography depends upon the ability to make on-the-fly maps with high pointing accuracy and repeatability. It also depends upon holographic data analysis software and the holography frontend and backend. The project can be divided into the following subexperiments:

1. Pointing accuracy and repeatability

The aim of this experiment is to determine the accuracy and repeatability of the pointing measurements, to test for any "software hysteresis," and to compare the results to that obtained previously with the ModComp system. The test can be eliminated if previous GBT tests on the 140-ft can be used to determine the pointing accuracy and repeatability.

a. Hardware requirements:

• GBT Cassegrain system (probably X-band).
• GBT DCR.
• GBT L.O. (can be replaced with 140-ft L.O. system if necessary).
• GBT I.F. system (can be replaced with 140-ft I.F. system if necessary since this system has not yet been successfully tested on the telescope ).
• 140-ft telescope.
 

b. Software requirements:

• GBT M&C -- mostly the same software that R. Fisher and M. McKinnon have used for previous GBT tests.
• Aips++ -- mostly the same software that R. Fisher and M. McKinnon have used for previous GBT tests.
 

c. Personnel:

• Hardware engineer (M. Stennes, W. Grammer, R. Norrod).
• Software assistance (M. McKinnon, R. Fisher, P. Shannon, R. Maddalena).
 

d. Time line:

• A minimum amount of development work needed.
• End of July 1996 (some time already tentatively scheduled on the 140-ft).
• Requires one day of 140-ft time (plus a few hours of overhead).
• Minimum work needed for data processing.

2. Large-scale pointing accuracy

The experiment is designed to determine how the pointing changes over large angles, to test GBT M&C's coordinate conversions, and to compare the results to that obtained previously with the ModComp system. This is best accomplished with an all-sky pointing measurement set.

a. Hardware requirements:

The same as 1.a.

b. Software requirements:

• The same as 1.b.
• GBT M&C -- Creation of a basic, developmental 'catalog' and 'scheduling' file to be used by GBT M&C for simplifying data acquisition. What the files look like, how they will be used, etc. is not yet been determined but will require some design work.
• Aips++ -- Creation of an automated data analysis package for streamlining the processing of hundreds of pointing measurements. This builds on the tools used in 1.b above.
• Aips++ -- Creation of an all-sky pointing algorithm (this is desirable but not necessary as long as we have a way of generating ASCII files that mimics the output of existing 140-ft pointing programs).

c.. Personnel:

• The same as 1.c.
• Assistance by R. Fisher and H. Liszt to design the 'catalog' and 'scheduling' files.
• Design and creation of an all-sky pointing algorithm within Aips++ by P. Shannon and B. Garwood.

d. Time line:

• Test 1 above first must be accomplished successfully.
• Requires about four weeks of heavy development work.
• End of July 1996 (observing time has been tentatively scheduled but this might be a very ambitious deadline; M. McKinnon will need to know soon if this deadline cannot be met so that he can reschedule the telescope).
• Three days of 140-ft time plus overhead; can follow immediately after test 1.
• Requires afterwards a few weeks of data reduction.
 

3. On-the-fly mapping

The experiment is designed to test whether the GBT M&C system can generate an on-the-fly map with sufficient accuracy for holographic measurements. This can be accomplished by mapping a typical celestial point-source and also mapping a hard-edged source like the moon.

a. Hardware requirements:

The same as 1.a.

b. Software requirements:

• The same as 1.b (much of this has been tested before or can be built out of existing systems).
• GBT M&C -- Ability to map a 'moving' target like the moon.
• Aips++ -- Two-dimensional mapping algorithms.

c. Personnel:

• The same as 1.c.
• J. Brandt to develop ability to track the moon.
 

d. Time line:

• Can proceed after test 1 but probably should wait until after the successful completion of test 2.
• Requires some development work.
• Late August or September 1996 (or July if we are REALLY lucky).
• One to two days of 140-ft observing (plus overhead).
• Requires one to two weeks of data processing time.
 

4. Holography

To test whether the GBT systems can successfully complete a holographic map of a telescope and to compare the resulting maps with those generated previously of the 140-ft with the ModComp and UniPops system.

a. Hardware required:

• GBT/140-ft prime-focus holography receiver.
• GBT holography backend.
• GBT L.O. (can be replaced with 140-ft L.O. system if necessary).
• GBT I.F. system (can be replaced with 140-ft I.F. system if necessary since this system has not yet been successfully tested on the telescope ).
• 140-ft telescope.

b. Software required:

• The same as 1.b, 2.b, and 3.b.
• GBT M&C -- Macro for starting, stopping, and pausing a holographic mapping set. Includes pointing, focus determination (maybe), starting from a designated point within a map.
• Aips++ -- Ability to generate an ASCII table of telescope positions and data so that the data can be read and processed by the UniPops suite of holographic data reduction software.
• Aips++ -- Holographic data reduction (need not be completed as long as it is available soon afterwards and as long as we can feed the data into UniPops's suite of holographic data reduction software).
 

c. Personnel:

• The same as 1.c, 2.c, and 3.c.
• Holography frontend and backend engineers.
 

d. Time line:

• Should only happen after the successful completion of tests 1, 2, and 3.
• Requires about four to eight weeks for development work.
• Late November or December 1996 (at least two months after the completion of test 3).
• About five days of 140-ft observing time.
• About two to four weeks of data processing.