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Nature of Instrumental Data

With only a few modifications, the Hjellming memo has the following requirements on the nature of the instrumental data to be addressed by AIPS++.

1.

All data from the GI should be assumed to potentially (but not necessarily) involve full measurement of the electromagnetic field involving all four Stokes parameters

2.

Multiple frequency bands may be simultaneously observed (e.g., for observing multiple lines simultaneously or multi-frequency synthesis), with variable numbers of channels in each band

3.

Single dish and synthesis array data will be handled on an equal footing.

4.

Rapid time switching of polarizations, frequencies, and pointing centers must be allowed.

5.

Polarization measurements may be time switched if all polarization measurements are not obtained simultaneously

6.

Data combinations for different observations may have different numbers of spectral channels and channel widths which may need to be accommodated within single data sets

7.

Observations should be regarded as mosaiced by default. Mosaicing observations may have many ($\sim$1000) pointing centers

8.

Single dish observations are special cases of mosaiced data.

9.

Beam switched or multibeam systems on single dishes must be accomodated.

10.

If available from the on-line data archive, instrumental performance and meteorological data must be associated with instrumental data sets.

• Little thought has been given to this requirement as yet.

11.

Meaningful error measures or estimates should be regarded as standard in an observation.

• This will need substantial feedback to those originating data

12.

Antenna size, system temperatures, and frequency band-passes may differ widely.

13.

The integration time may vary from antenna pair to antenna pair.

14.

VLB antennas in space will require support for orbital position dependence including acceleration terms. An external emphemeris will be required.