Oversampled Maps and Scans - PHT32

For AOT PHT32 the integration time per raster point depends not only on the integration time entered by the user but also on the size of the map, the oversampling factor, the value for the MAXIMUM_UNSATURATED_SURFACE_BRIGHTNESS (MUSB), and minimum spacecraft dwell time per raster point (Section 6.3.3). The size of the map is given by the number of raster points and raster legs. In combination with the oversampling factor the size of the map determines the coverage factor. In Table 9 values for the coverage factor are listed for a number of typical map sizes.

Table 9: The coverage factors for the AOT PHT32 depending on the oversampling factor for a number of raster points/legs combinations. Listed are the numbers required to achieve these coverage factors in the inner region of the scan or map.
 

The MUSB is used in combination with the detector responsivity to determine the minimum time per chopper plateau. As there are a fixed number of chopper plateaus per C100 and C200 array, and since there must be at least one chopper sweep per raster point, the integration time is forced to last 32, 64, or even 128 sec per raster point for low surface brightness maps. In Table 10 the minimum integration times per raster point for four different filters are listed as a function of MUSB. We have used the detector responsivities as of August 1, 1996.

Table 10: Minimum integration times per raster point as a function of map surface brightness for four different filters, MUSB stands for AOT input parameter ``maximum unsaturated surface brightness''. Beware: the values in this table depend on detector responsivity which may be subject to change.  

The integration time entered by the observer relates to the integration time per raster point as follows:

• the time per chopper plateau is given by divided by the coverage factor
  

• the time per raster point is given by the time per chopper plateau multiplied by the number of chopper plateaus (13 for C100 and 7 for C200)
  

• if this time is smaller than the in Table 10 then the minimum integration time per raster point should be used
  

• or if this time is smaller than the minimum raster point dwell time of 12 sec, the integration time per raster point of 12 sec should be used