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Overlap moments separation and sum

The overlap moments (L1L2 from LEEA and H1H2 from HEEA) are moments from the coincident energy ranges of the two sensors. Their raw format is slightly different to other data series we encounter because the data is tagged every half-spin. This means that, for LEEA say, L1 is data taken in the first half of the spin and L2 is data taken in the second half of the spin. In order to get this into a concurrent format, we must separate L1 and L2 and sum them. The result of this will be a data sequence which sums over the whole spin.

Some care must be taken at this stage. An identifier (the spin mode) indicates whether the data record comes from the first half or second half of the spin (note that these tags indicate the start of data, i.e. L1 is the start of the spin, and L2 is exactly halfway through the spin). With this information we can create a mask to subset the data sequence into two child sequences - one containing just the L1 data, and the other just the L2 data. We decide as a convention that all our data are to be spin-centred, that is, the time-tag will be placed half-way through a spin interval. L2 is already at this position, so we shift the L1 tags half a spin spacing (2 seconds) forward in time. Now the tags line up, we can simply add matching L1 and L2 tags together. This gives us the final L1+L2 sequence which conforms to all the other PEACE data we have. Note that gaps (intervals greater than 4 seconds without tags), are removed.

Figure 5.1: The specific energy level to be used is determined by the operating mode (LAR, MAR or HAR), the bin index and whether we wish to use the lower or upper edge of the bin. In the above example, level 04, the difference between operating modes can have an effect of several eV. At the low energy end of the integration this can have a non-negligible effect on the corrected moments.

Image levels


next up previous contents
Next: Gain correction factors Up: Calibration Previous: Energy look-up tables   Contents
Steve Schwartz 2005-03-26