Limb Figure Development Plan & Status

Team Coordinator: Rick Bogart

After a teleconference among Jeff, Xania, Luiz, and myself and discussions with staff members at Stanford I have come up with a tentative list of the problems to be solved and tasks to be accomplished over the next 4 months.

The Limb-Figure Analysis processing is conceptually simple: the time-smoothed values of flat-fielded intensity in the selected limb annuluspixels need to be extracted from the Low Rate Telemetry (LRT) data stream, the values may need to be corrected for any known deficiences in the on-board flat-fielding, and a limb location and figure need to be fit to the intensities using the functional fit:

Ic(r,theta,t) = Ic0 (r) * [1 + f(t)] * [1 + g(theta, t)],

and the functions f() and g() temporally (and g() spatially) Fourier analyzed. This apparent simplicity conceals a substantial complexity, primarily because the Limb Figure Analysis will be the first pipeline to be developed using the Structure Program data stream and tabulated (as opposed to image) data therefrom. There are numerous interface issues to be dealt with in the data description, affecting operations as well as analysis. These include the specification of the mask to be used on board, recovery of mask information, and organization of a data set which does not have a uniform coordinate basis. Rock Bush, Katie Scott, and Jim Aloise are involved respectively in the operations, the LRT data extraction, and the data description.

There is no realistic hope of obtaining useful MDI data in the LRT stream from the ground. This is because the dataset is averaged over 25 minutes, but there is no decent pointing in the solar light feed to the simulator instrument at Lockheed. The solar limb will move a very large amount relative to the width of the annulus in times very short compared to the integration time. We will get simulated LRT data frames, but it will be very difficult to even verify that the selected mask pixels are in the correct location, and impossible to use the data for downstreaming tests. Thus, we will have to substitute proxy data for the Level 0 (raw data extracted from telemetry) before doing flat-fielding and limb-fitting. This can be done by applying the presumed onboard mask to full images, possibly whole-disk images from a High-Rate Telemetry (HRT) stream from MDI, but preferably the 4-days' of Ca-K data we have from the High-L Helioseismometer (HLH). Lyle Bacon has simulators for the onboard processing that can be applied to proxy data, and Luiz Sa and I are familiar with the HLH data. From this point on, there may be useful data for Xania Scheick to work on the limb-fitting and analysis programs. Of course it is also necessary for information on flat-fielding procedures, which Luiz and Xania will also presumably be dealing with, to be fed back through Rock to the onboard processing environment.

1. Operations (Rock Bush)
   • The manner of specifying the limb mask to be used by the IP and changes thereto need to be defined.
   • The limb masks need to be defined as functions of time.
   • The defined method of describing the limb mask used by the IP (presumably the DPC's) needs to be implemented.
   • The flat-fielding corrections must be implemented in the IP Structure Program.

2. Level 0 Processing (Katie Scott)
   • The limb figure data need to be extracted from the LRT stream.
   • The format for raw (level 0) limb-figure data needs to be defined; the data stream must include not only the data themselves, but information on the mask used and other key ancillary data, such as S/C roll angle.

3. Level 1 Processing (Luiz Sa)
   • Develop procedure for flat-fielding and updating onboard flat-field

4. Level 2 Processing (Xania Scheick)
   • Implement and test limb-fitting algorithms, using proxy data

5. Test Data (Lyle Bacon)
   • Structure Program equivalent tables of the limb pixels (proxies) need to be created from HLH data

This page last reviewed and revised 4 May 1995

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