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## Impact on OTF observations

For OTF observations, there are several effects to take into account.

1. We will use the average system temperature to take into account the different mixer performances.
2. Edges result in inhomogeneous noise, which depends on the exact observing setup. We here try to estimate a single noise value for the whole map. The area swept in edges are thus considered as overheads. If the total targeted area is , the receiver will then have to map . As discussed above, we can write the previous sum as a product of the targeted area times an efficiency factor, i.e.
 (38)

We thus have to remplace by in Eqs  and  to compute and . Now, if edge area is considered overheads when estimating the sensitivity, the spectra acquired in the edges will nevertheless be used to form the final image. We must thus ensure that enough time is observed on the off position when estimating the sensitivity in the position switch mode. This comes naturally if we consider the edge area as part of the submap between two off positions. This implies that the change on the total mapped area, expressed above, is the only one needed in the equations to take the edges into account.
3. A multi-pixel can cover times as fast the same area of the sky with the same sensitivity as a single-pixel of similar . Another way to look at this, is to assume that each identical (average) pixel will cover an independent part of the sky during a given observing time (i.e. ). This implies that the area seen by each pixel will be
 (39)

This finally gives
 (40)

where and are computed with
 (41)

 (42)

The times spent on and off and in the edges per pixel are then
 (43)

The algorithm to derive the time/sensitivity estimation in the case of OTF can thus be applied with the following modifications in the input parameters : , , , must be replaced by , , , .

Next: Bibliography Up: Generalization to a multi-pixel Previous: Imaging with HERA
Gildas manager 2014-07-01