Gordon's 7-steps to HESSI Calibration

Gordon's 7-steps to HESSI Calibration


dataseq.doc  3/18/99

HESSI IMAGING DATA PROCESSING SEQUENCE

This writeup describes an idealized sequence of steps in handling HESSI imaging data, from the initial listing of individual events through the calibrated data set that forms the input to the
imaging algorithms themselves.

It is assumed that fast rate mode is NOT applicable.
Field lengths are based on the minimum feasible rather than the most convenient.
Implementation could combine steps or separate tasks within steps.
Note that the implementation could be optimized to either minimize maximum width of list or to
minimize redundant calculations for anticipated loops over energy, subcollimator, harmonic, map-center, etc.   The listing below does neither.

STEP 0:	INPUT LEVEL-0 PACKETS

Select a time range.
Input level-0 event data packets for the selected time range.


STEP 1:	SCORE CREATION

Select an energy range and a subcollimator.  
Form a score, listing individual events satisfying these criteria. 

Attribute of each event:	Time 			4-bytes  	(64 bus resolution) 


STEP 2:	TIME-BINNING

Select time-binning parameterization.
Group events in the score into time-bins with predetermined widths.
 (Special case: Each time-bin = 64 bus.)
There should be one entry per time bin,  EVEN IF THERE WERE NO EVENTS !!

Attribute of each time-bin. 	Time 			4-bytes  	(64 bus resolution) 
Number of events	4-bytes	(counts)

 
STEP 3:	ASPECT ASSOCIATION

Associate an aspect solution with each time-bin.

			Time 			4-bytes  	(64 bus resolution) 
	Number of events	4-bytes	(counts)
				Pitch offset		2-bytes	(microradians)
				Yaw offset		2-bytes	(microradians)
				Roll angle		4-bytes	(microradians)
	


STEP 4:	LIVE-TIME ASSOCIATION

Associate a live-time measure with each time-bin.
The actual time of the time-bin can be dropped.  It is no longer needed, and in any case, can be reconstructed.

Attribute of each time bin:	Number of events	4-bytes	(counts)
				Live-time measure	2-bytes	(binary fraction)
				Pitch offset		2-bytes	(microradians)
				Yaw offset		2-bytes	(microradians)
				Roll			4-bytes	(microradians)


STEP 5:	ASSOCIATE GRID CALIBRATION 

Select a map center, relative to sun center.
Select desired harmonic of grid response.
Determine the grid response matrix parameters associated with each time bin.  (This is assumed to include source-location independent factors such as detector efficiency.)
Combine the throughput and modulation efficiency into a Modulation Sensitivity. 

Attribute of each time bin:	Number of events	4-bytes	(counts)
				Live-time measure	2-bytes	(binary fraction)
				Pitch offset		2-bytes	(microradians)
				Yaw offset		2-bytes	(microradians)
				Roll			4-bytes	(microradians)
				Modulation sensitivity 2-bytes		(TBD)
				Modulation phase	2-bytes	(TBD)


STEP 6:	DETERMINE PHASE CALIBRATION

Combine map center, modulation phase, pitch and yaw offsets into a phase offset.

				Number of events	4-bytes	(counts)
				Live-time measure	2-bytes	(binary fraction)
				Roll			4-bytes	(microradians)
				Modulation sensitivity 2-bytes		(TBD)
				Phase offset		2-bytes	(TBD)


STEP 7:	ITERATE FOR BACK-PROJECTION OR MEM-SATO.

Repeat STEPs 1 through 6 with other subcollimator/harmonic choices.
The result constitutes the calibrated input to backprojection or HXT-style MEM.



 STEP 8:	CALCULATION OF VISIBILITIES

Choose a visibility strategy.
Combine output of STEP 6 into a set of visibilities.
	
			Calibrated amplitude		4-bytes	
Statistical error in amplitude	4-bytes
Calibrated phase		2-bytes
Statistical error in phase.	2-bytes
UV Position angle		2-bytes
	
This provides the visibility input to Fourier-based imaging algorithms.