Antenna Characterization Database

The Antenna Characterization Database describes the data files that contain the information that is used for deriving pointing/focus models.

In the proposed new system we may make use of a Python program, "peakdata.py", that was written to extract the heights and widths as fit by the GFM routines. "peakdata.py" may be found in the directory:

In the proposed new system we may take as a starting point a Python program, "peakdata.py", that was written to extract the heights and widths as fit by the GFM routines. "peakdata.py" may be found in the directory:

Thus "peakdata.py" can be developed into software that will produce the "Astronomy Data" files that are described in the "Antenna Characterization DataBase".

The plan is to generate data files for antenna pointing and dynamic corrections

The first step is to generate data files for antenna pointing and dynamic corrections

Packages for reading and writing FITS files are available both for Python, and for c/c++. Consult folks in the Green Bank software group for details.

Getting the Pointing Offsets

The heart of the pointing data is the set of offsets between the coordinates predicted by the pointing model and the coordinates actually measured for each radio source observed in pointing calibration run.

In a pointing calibration run, the telescope points to a series of known calibration sources and does a cross scan to determine the actual location of the source. A gaussian fit to each scan gives the offset, height, and width of the source.

In the proposed new system we may make use of a Python program, "peakdata.py", that was written to extract the heights and widths as fit by the GFM routines. "peakdata.py" may be found in the directory:

~ashelton/yuri/

"peakdata.py" uses the "fql" system to extract the necessary data from the DCR, Antenna, and Reveiver FITS files. It runs the gaussian fitting routines from GFM, and writes the results into an ascii file. Some additional code will be needed to write out the offsets and additional information from the Antenna files.

August 18, 2006

Introduction

The plan is to generate data files for antenna pointing and dynamic corrections from the raw data that is produced in a pointing calibration observing session. The software presently in use is written in Glish. The desire is to replace these routines with Python and to bring the system into accord with standard GBT software practices.

The precision pointing of the GBT involves two main systems:

• adjustments of the Azimuth and Elevation (position tracking).
• adjustments of the subrelector (focus tracking).

The position and focus tracking include two parts, one could be called the "static" model, the other the "dynamic" model. The Static model is a set of equations that determine the corrections to the coordinates as read by the azimuth and elevation encoders and the positioning of the subreflector, as a function of azimuth and elevation. The dynamic part uses the temperature sensors on the GBT to calculate corrections to the Az/El position and to the subreflector positioning.

The PTCS system is describe in great detail in the wiki page: PTCS project wiki pages

The data needed for deriving pointing/focus models comes from special observing sessions in which many known calibration radio sources are observed.

The initial goal of the software upgrades is to produce files of data to be input to the model fitting programs. These files are described in the wiki page:

Antenna Characterization Database

Specifications

The new software will do the following:

• Read the raw FITS files from a GBT calibration observing run.
• Produce files for the "Antenna Characterization DataBase" as described in the above-mentioned wiki page.
• The "database" files will be produced in ascii form as they are now, but consideration should be given to entering them into a real data base system such as sql.

• Future plans call for additional datasets to be used; in particular inclinometer data will be used in the future. Thus there should be some flexibility in the system for accessing more FITS files and producing more data base files than mentioned in these specifications.

FITS Files

The GBT system stores raw data as FITS files. These files are normally located in the directory : /home/gbtdata/"projectid", where "projectid" is the code name assigned to the project. For PTCS calibration projects, the project ID is typically of the form "TPTCSPNT_yymmdd".

For a general explanation of FITS file formats, one may consult

FITS Reference

And it should be noted that all the GBT FITS data files of a subset of FITS types knows as the "binary tables" format.

Each type of FITS file will be in a directory naming the type of file. Under that directory are the FITS files themselves, named for the data and time at which they were created.

This is a list of the GBT FITS file types that will be used:

%META:TOPICINFO{author="FrankGhigo" date="1155822504" format="1.0" version="1.1"}% %META:TOPICPARENT{name="Main.MyObservingIssues"}%

Preliminary Specifications for PTCS Software Upgrades

-- FrankGhigo - 17 Aug 2006