Last Modified: December 31, 2014
Ronald J Maddalena
Calculates
the time needed
to map,an area including overhead, based on the integration time
per beam area (e.g., the results from the Sensitivity
Calculator) and the
area to be mapped. Provides example ASTRID commands as well as
other mapping parameters. Supports the typical mapping commands
for on-the-fly (OTF) rectangular maps, OTF Daisy maps, and point
rectangular maps.
ALGORITHM DETAILS:
The algorithms used by the calculator follow those described in Mangum,
Emerson, and Greisen
(2007, A&A 474, 679) but with the incorporation of the restrictions
imposed by the the GBT's maximum slew rates and the backend's minimum
sampling time and
time resolution. The
calculated time per sample returned by the calculator always will be an
integer multiple of the backend's time resolution and will have a value
greater than the backend's minimum sampling time for the selected
mode. The calculated
slew rate is kept below the telescope's maximum. The time per row
or column will always be an integer multiple of the sample time.
And, the
number of rows or petals in the map will be integer. Since the
calculator always rounds up in its calculations, you will always get at
least the
desired time per beam area.
Because of these restrictions, the
actual time per beam area will be larger than that specified.
But, the calculator ensures that the returned
value will always be as close as possible to the user's input
value. The user should be aware that there
are a large number of situations when the hardware restrictions will
produce values for the actual time per beam that are much larger than
the desired values and, thereby, the map will take significantly longer
than one would initially expect. If such observations are
run as the calculator specifies, the map will have higher sensitivity
than was originally specified. Optionally, if the actual time per
beam or map time is much higher than you desire or can tolerate, and
your observing isn't approaching the telescope's maximum slew rate,
then using a faster-sampling mode, if one exists, might help.
The calculator warns the user whenever they will be exceeding the
telescope's maximum number of accelerations of 2 per minute but the
calculator does not
enforce this restriction. If you receive this warning, you may
need to increase values for either the time per beam or the map size,
which will increase the time needed to make the map.
Note: For map type of OTF Rectangle the calculator provides
separate
answers for RALongMap and the DecLatMap
as the overhead, row spacing, etc will
be different for the two styles of map. If you are using the Astrid
procedures of PointMapWithReference, RALongMapWithReference, or
DecLatMapWithReference, the calculator does not include the overhead or
observing time for performing the reference observations.
Created
and maintained by: Ron Maddalena and the Green
Bank Support Staff