The
purpose of this document is to provide a practical guide to using the
SPIRE
Photometer Simulator (SPS). It will explain how to install, and use the
SPS to
generate SPIRE data timelines. A guide to the use of the SPS custom pipeline
is then provided, which allows simple calibrated
maps to be generated from the SPS output.
The assumptions and limitations of each module are also
explained.
It is intended that this document will grow and become more useful following feedback from SPS users. As a result I would welcome any comments users might have, especially with regard any aspect of this guide which people might find confusing, or inaccurate. This document does not contain a detailed explanation of how the SPS works, or the models it uses. For this information you should consult the official SPS document V2.31 (SPIRE-UCF-NOT-003094).
SPIRE, the spectral and photometric imaging
receiver, is
one of three instruments on-board the European Space Agency's (ESA) Herschel
space observatory. It
contains a three-band submillimetre camera and
an imaging Fourier transform spectrometer (FTS), and uses arrays of
hexagonally
packed feedhorn-coupled bolometric detectors operating at a temperature
of 300
mK. The photometer has a field of view (FoV) of 4 x 8 arcminutes,
observed
simultaneously in spectral bands centred approximately at 250, 350 and
500 μm.
The angular resolution is determined by the telescope diffraction
limit, with
full-width-half-maximum (FWHM) beam widths of approximately 18, 25 and
36
arcseconds at 250, 350 and 500 μm respectively. Maximising the
aperture
efficiency of the feedhorns requires an aperture corresponding to an
angle of
2λ/D on the sky, where λ is the wavelength and D is the
telescope diameter.
Consequently, the detector beams have an angular separation of
approximately
twice the FWHM beam size on the sky.
The ultimate purpose of the SPS is to
produce
simulated SPIRE photometer data (both science and housekeeping),
derived from a
realistic physical model of the instrument. This model can be used to
“observe”
a simulated astronomical sky, using any of the allowed photometer
observing
functions (POFs). The sensitivity results should be
compatible with
the photometer sensitivity model (
The
SPS comes as a zip file containing all files required for operation,
including
the SPS custom pipeline and calibration files. The initial value of the
variables in the SPS will be set to the default nominal values. To
install the
SPS extract the data from the zip file to your choice of location. Once
this is
done you’ll need to edit your IDL “start up” file to
include the SPS
installation directory location in the IDL “!path”
parameter.
Adding the following lines, and changing the
‘your_path_here’ string to
your
chosen installation directory, will set up all of the required SPS
paths. NB: This code is platform independent. For more information on
startup files see Appendix I.
To run the SPS you also require the IDL astronomy library routines. If this library is not already installed on your system then you can download it from here. Once downloaded you will need to unpack the library and place it in your root SPS directory. If you wish to place the library in a different location, then you will need to add this location to the IDL !path parameter in your startup file.
The simplest way to use the
SPS is via the GUI. This can be started by typing sps_gui at the IDL command prompt and pressing
enter. This
should bring up the main SPS console, shown in below.
The
GUI contains 13
buttons in total, one for each of the modules down the left hand side,
and
three additional buttons for set-up and running of the simulation code.
Pressing any of the module buttons will bring up the parameter window
for
that module. Here you will be able to enter the various different
parameters required for your simulation. The units, and where
appropriate the default values, are given for each parameter in
brackets at the end of the parameter label.
The CORE
button, like the module buttons, will bring up a parameter window. This
window allows you to set up all of the parameters required for the
operation of the SPS, but that do not actually represent any component
of the real physical system. For example this is where you would
specify the file name for the output data, and the time step used
within the simulator.
Finally there are the Begin Simulation
and the Quit buttons, which start the simulation and exit the
GUI respectively.
For detailed information on the parameters
in each module parameter window see the Modules
section
To
run the SPS you must have
a fully licensed version of IDL, and approximately 1-2GB of free hard
disk
space. The true amount of space needed varies depending on the length
in time of the desired simulation, and selected output options.
The SPS was developed on a Windows XP platform, and has been tested on
LINUX and Mac OS X installations. The run times are shown below for the
example simulations
described in this document for all three platforms.
| System
Platform and Specification |
Duration of
Observation (min.) |
Run Time
(min.) |
Memory Used (MB) | Output file size (MB) |
| Windows (Core Duo T7200 2 GHz, 2 GB RAM) |
15 |
7 |
331 | ~22 |
The SPS output a files can be
either IDL save format
(*.xdr) or FITS format, depending on the user selection. These files
contain
the structures used within the simulator (see the SPS document for
information).
When restored all parameters used within the simulator should be
available.
Each parameter will be stored within its associated module structure,
e.g.
telescope pointing is in the obsfun module, detector offsets
are in the
optics module, BSM pointing is in the BSM module etc.
For a simple way to read
in simulator output in to IDL use read_SPS_data.pro contained within
the
'OtherPros' folder. Once loaded, the structures, and parameters
contained
therein, can be accessed in the normal way, e.g. to plot the telescope
pointing
time line you would require the DirZ and DirY
parameters:
IDL> plot, obsfun.DirZ, obsfun.DirY
This
section takes the user through an example simulation, from initial
setting up of the SPS, to running the code, and reducing the output
data using the SPS custom pipeline. This example
simulates two orthogonal POF 5 scan map observations of the same region.
The simplest way to produce a map from these output data is to use the SPS custom pipeline. To do this simply type sps_pipe at the IDL command prompt. This will bring up a file selection window. Highlight both output files and press enter to start the data reduction. During reduction of these data an intermediate calibrated version of the original simulator output file will be produced, and place in the same location as the original data file. Once complete the pipeline will output three files for each simulation, one for each waveband. There this demonstration simulation will produce six maps, one in each waveband and scan direction. Additional output maps such as weights maps, and coverage maps can also be output via the inclusion of keywords when calling the sps_pipe command. For information on these options see the map-making section of the SPS custom pipeline.
The output
maps are shown
in the figure below: the output from the three wavebands are shown
across the page running from 250 to 500 um, and the horizontal and
vertical scans outputs are shown in each column.
In addition to the required
pipeline routines,
there are two additional routines included in the SPS distribution.
They are located in the 'OtherPros' directory within the main SPS
installation directory. These routines are read_SPS_data.pro, and
convolve_map.pr
read_SPS_data: This routine simply loads the data from a simulation output file. The routine is called from the IDL command line, and any of the 11 data structures used by the simulator can be loaded by setting the appropriate keywords, e.g.:
IDL>
read_SPS_data, 'file', obsfun=obsfun, sampling=sampling
This call would load the
observatory functions
and detector sampling data structures (containing the telescope
pointing and sampled detector timelines respectively) from the 'file'
(NB: file must be a string containing both the file name and file
path). Any number of structures can be loaded at once, and the full
list of keywords is given in the example call below:
IDL> read_SPS_data, 'file', core=core, sky=sky, obsfun=obsfun, bsm=bsm, optics=optics, thermal=thermal, background=background, astropower_astropower, detectors=detectors, sampling=sampling, hk=hk
convolve_map: The convolve map routine
generates a SPIRE
beam convolved version of an input map. This provides the noiseless
convolved map for comparison with the simulated output map. This
routine is called from the IDL command line, andwill produce one
convolved map per call. The calling sequence is:
IDL> convolve_map, file, PSW=PSW, PMW=PMW, PLW=PLW,
Jy_per_beam=Jy_per_beam
The core module does not represent a real physical part of the SPIRE photometer. Instead it contains all of the parameter information relating to the operation of the SPS. The core GUI window contains 11 fields, one for each variable. The first two variables deal with simulator internal operations, while the remaining 9 select the simulator output options. The function of each parameter is explained below. The units, and nominal values where appropriate, for each parameter are also shown in brackets after the parameter name.
Number of Runs: This
parameter defines the number of times the simulator will run. This
parameter is used to allow multiple simulations to be performed in a
batch mode. For information of batch simulations see the section on multiple simulations.The sky module allows the user to specify the input sky for a simulation. Three equally sized input files are required in fits format, one for each photometer band. The resolution of the input skies must be the same in all three bands, and should be small with respect to the smallest beam (18 arcsec). Details for each parameter are given below. The units, and nominal values where appropriate, for each parameter are also shown in brackets after the parameter name.
Sky resolution (2 arcsec/pixel):
This parameter defines the resolution of the input sky map. The
resolution is taken to be the same for each photometer band. The pixel
size should be small with respect to the smallest SPIRE beam size (18
arcsec), and must be an integer value. The pixels are assumed to be
square, with the value specified being the scale along one size of the
pixel.The
observatory function module allows to user to define the type of
observing function to be simulated, and it's required parameter inputs.
It also provides a visual representation of the observing pattern
plotted on top of the unconvolved input map.
There are two versions of this parameters window, a common user mode,
and an expert mode. The common user mode provides access to
HSPOT style observing parameter options, while the expert mode
allows the user a far wider selection of options. It should be noted
however that only the common user observing options will be
available for use in the real system. It is recommended the most users
use the common user mode options. The expert options
can be accessed by using the /expert keyword when calling the sps_gui
from the command prompt.
The
user defined parameters for the common user mode are described
below, and the units, and
nominal values where appropriate, for each parameter are also shown in
brackets after the parameter name. Since a description of the expert
mode parameters is of limited interest to the majority of readers,
this information has been place in Appendix II.
Observing Function:
The observing function is an integer number which defines which
observing function is to be simulated. It was found that only three of
the original six observing functions were required. These are defined
in Table 1 below. The number
2, 3, or 5 specified here should be the value input to the parameters
window to achieve each observing mode.
| Observation | HSPOT name | Photometer Observing Function (POF) Number |
| Point source photometry | Point source | 2 |
| Field (jiggle) mapping | Small map | 3 |
| Scan mapping | Large map | 5 |
Table 1: Definition of the available
observing modes
Map centre position in RA (h:m:s, or deg.): This parameter specifies the centre of the observation in right ascension (RA). The input value be specified as either h:m:s or degree specified as a decimal.
Map centre position in DEC (h:m:s, or deg.): This parameter specifies the centre of the observation in declination (DEC). The input value be specified as either h:m:s or degree specified as a decimal.
POF 2,3: Number of repetitions: This parameter
specifies the number of repeat POF 2/3 maps to be performed.
POF 2,3: Nod operation (1): Flag to turn telescope nodding on (1) and off (0).
POF 5: Line length (arcmin): This parameter simply specifies the length of the on map scan line. Additional data will be taken at each end of this scan line associated with the telescope turn around.
POF 5: Map height (arcmin): This
parameter defines the height of the on map in arcminutes.
POF 5: Scan rate (Nominal = 0, Fast = 1): This
parameter specifies the telescope scanning rate in a POF 5 observation.
This parameter can have values of 0 and 1, corresponding to the nominal
(30"/s) and fast (60"/s) scanning speeds as defined in HSPOT. Note that the nominal
scanning speed is equal to the 'slow' speed when using parallel mode.
POF 5: Scan direction (A, B, PA, PB):
This parameter specifies the scanning 'magic'
angle of the array on the sky. The 'A' and 'B' options are equivalent
to those stated in HSPOT. There is no option to perform the 'A and B'
option; instead two separate simulated observations must be performed,
one scanning at each angle. The 'PA' and 'PB' option sets up the same
'A' and 'B' scans but for parallel mode.
Number of repetitions: This parameter
specifies the number of repetitions required for this particular
observing run. All repetitions will be simulated before moving on to
the next simulation run (when more than one run is requested). The
output file name for a given run will be suffiexed with the repetition
number. See section 3.1 for
addtional information
Rotation of bolometer array on the sky (0.0): This
parameter
applies a rotation to the bolometer array on the sky. When this
parameter is adjusted the scan pattern also changes equivalently to
maintain the correct scanning angle (direction) defined abive.
Telescope absolute pointing error (3.7 arcsec): The absolute pointing error is the 1-sigma absolute error in the initial pointing of the telescope. While the nominal value for this parameter is 3.7 arcsec., in many cases it is useful to set this value to zero.
Telescope drift (0.0 arcsec/sec): The
telescope drift parameter is a 1-sigma velocity drift in a random
direction. It therefore implements a random, and constant, linear drift
throughout the observation. There is no known nominal value for this
parameter, therefore the user is recommended to use a value of 0.0 for
now.
The BSM module does not contain
any user defined parameters. The button remains on the SPS GUI console
as a place holder for possible use in future versionsof the SPS.
Parameters used to set up chopped and jiggled observations are
contained within the Observatory Functions
parameter window.
There are three user defined
parameters in the optics module, as well as in interface in which the
user can select the operational detectors. The units, and nominal values where
appropriate, for each parameter are also shown in brackets after the
parameter name.
Field distortion (1):
The parameter is a flag to tell the simulator to use the measured field
distortion in each array (1), or to assume no field distortion (0).
SPIRE FOV offset - z-axis (0 arcsec): The value
of this parameter sets the offset of the SPIRE array borsight with
respect to the telescope boresight along the z spacecraft coordinate
axis.
SPIRE FOV offset - y-axis (659 arcsec): The value of this parameter sets the offset of the SPIRE array borsight with respect to the telescope boresight along the y spacecraft coordinate axis.
The thermal module simulates
thermal variations in the SPIRE photometer system. Thermal noise as
defined here is unwanted variation in the thermal environment of SPIRE,
and does NOT relate to Johnson or
any other kind of noise processes within the detectors or read-out
electronics.
At present the in-flight thermal
environment of SPIRE is not well known, and thus the model used to
simulate the thermal time lines is relatively crude. At present a
thermal noise time line is generated with a given noise spectral
density, and 1/f noise knee frequency. This time line is then low-pass
filtered assuming an RC circuit filter profile. This represents
physically the coupling of the cooler tip to the detector arrays,
which represent a large thermal mass. The time constant is different
for each detector array, representing the different distances between
each array and the cooler tip. For more information on this modelling
see the SPS document.
At present most of the nominal
values stated here are crude estimates, chosen to produce
characteristic time lines, and should not be considered correct at this
point. As a result these parameters should not be changed without input
from a member of the instrument team.
Thermal noise (0): This
parameter turns the thermal noise on (1) and off (0). At the time of
writing this document there are no routines within either the SPIRE
pipeline or SPS custom pipeline to remove the thermal noise drift,
hence the nominal value is set to 0. This is expected to change to 1,
however, once the required routines are available.
Nominal cooler temperature
(0.3 K): This value specifies the nominal cooler (and thus also
detector array) temperature.
Thermal noise spectral density
(5e-5 KHz-1/2): This parameter defines the noise spectral
density, i.e. the noise level.
Thermal noise knee frequency
(0.1 Hz): This parameter states the 1/f noise knee frequency.
Thermal time constant in PSW
band (70.0 s): This parameter specifies the time constant used in
the low-pass RC filter for the PSW array.
Thermal time constant in PMW band (100.0 s): This parameter specifies the time constant used in the low-pass RC filter for the PMW array.
The background module defines the
background power on the detectors from the optical elements in the
system. There are only two user defined parameters in this module, both
relating to the temperature gradient across the primary mirror. The
nominal values stated here are rough estimates, and are given to allow
characterisation of this systematic affect.
Thermal gradient - z axis (0.00): This
parameter specifies the fractional temperature gradient across the
SPIRE field of view in the z telescope axis. This is the Earth-Sun
direction, hence a temperature gradient of 2% is assumed. Since no
routines are currently written to remove this affect from the data
however, a nominal value of 0.0 is used. This will change once the
require routine is present in the pipeline.
Thermal gradient - y axis
(0.00): This parameter specifies the fractional temperature
gradient across the
SPIRE field of view in the y telescope axis. This is perpendicular to
the Earth-Sun
direction and is therefore assumed to be uniform (0.0).
The astropower module does not contain
any user defined parameters. The button remains on the SPS GUI console
as a place holder for possible use in future versions of the SPS.
The
detectors module simulates the detector response to the total
(background + astronomical) power seen by the detectors during a
observation. The photon, Johnson, and amplifier noises are also added
to
the noiseless time lines within this module if requested.
Johnson + Photon noise (1): This parameter turns
the noise generation in this module on (1) and off (0).
1/f noise (1): This
parameter selects either white noise (0) or 1/f noise (1). If the user
has selected to turn the noise off via the previous parameter, then the
value of this parameter is not used.
1/f noise knee frequency (0.1
Hz): This parameter specifies the 1/f noise knee frequency when
the operating with 1/f noise.
Real bolometer parameters (1):
This parameter allows the user to use the bolometer parameters as
measured in the instrument flight module test campaign (1), or the
design bolometer parameters (0). When using the design parameters all
detectors are assumed to be working, and to have identical values. When
operating with the measured parameters (1) the measured 1/f noise knee
frequency is used, overriding the value specified in the previous
parameter.
PSW Voltage bias (21.2 mV): This
parameter defines the RMS voltage bias across the detector for the PSW
array.
PMW Voltage bias (21.2 mV): This parameter defines the RMS voltage bias across the detector for the PMW array.
PLW Voltage bias (21.2 mV): This parameter defines the RMS voltage bias across the detector for the PLW array.
The sampling module simulates the
on-board SPIRE read-out electronics and samples the data at the
requested rate.
The data are filtered, and digitized in this process. The output data
are in ADU, and have had the appropriate offset removed (see SPS
document for details).
Sampling frequency (16 Hz): This parameter is the
detector readout sampling
frequency.
Sampling (1): This
parameter selects whether the data pass through this module (1) or not
(0). If this parameter is set to 0 then this module is by-passed and no
output is generated.
AC bias frequency (130.0 Hz): This parameter sets the detector read-out bias modulation frequency. The value of this parameter should only be changed by an expert user.
JFET harness capacitance (50e-12 F): This parameter defines the capacitance of the JFET harness. The value of this parameter should only be changed by an expert user.
Demodulator phase difference
between reference and input sources (0.0 deg.): This parameter
specifies the phase
difference between reference and input sources in the demodulator. The
value of this parameter should only be changed by an expert user.
The house keeping module creates
level-0 keeping data, in hexadecimal format, corresponding to the
chosen observing function. There are two user defined parameters in
this module.
HK sampling frequency (1 Hz): This
parameter specifies the output sampling frequency for the house keeping
data time lines.
The
author also requests that any work resulting from the use of this
simulator contain a reference to the SPS published A&A paper, along
with the acknowledgement contained on the SPS website.
Disclaimer:
This software
is available "as is", without warranty of any kind either expressed or
implied, including the implied warranties of merchantability and
fitness for a specific purpose. By using this software you are
assuming all risks and costs. In no event is the United Kingdom
Astronomy Centre, or the Science and Technology Facilities Council
liable for any damages or losses that might result from the use of this
software.
|
Document |
Ref. |
Comments |
|
Operating Modes for
the SPIRE Instrument (Chap. 5) |
SPIRE-RAL-PRJ-000320;
Issue 3.0, 4 January 2002 |
Describes the basic
operations of chopping and nodding, and outlines the different
observing modes and their parameters. |
|
SPIRE Sensitivity
Models |
SPIRE-QMW-NOT-000642;
21 May 2007 |
Presents detailed
calculations of the instrument sensitivity in various observing modes,
and summarises the values of various telescope and instrument
parameters. Simulator results should be
basically compatible with it. |
|
Herschel/Planck
Instrument Interface Document Part A |
SCI-PT-IIDA-04624 |
Provides
information on Herschel pointing and slewing capabilities and
parameters in Section 5.12 |
|
Herschel Pointing
Modes |
SCI-PT-RS-07725;
Issue 3.0, 24 May 2002 |
Describes the
Herschel pointing modes. Note: this doc. Is also Annex 4 of the IID-A |
|
Herschel/SPIRE
Detector Control Unit Design Document |
SAp-SPIRE-FP-0063-02;
Issue 0.3, 18 February 2003 |
Describes how the
bolometer signals are processed and digitised by the DCU electronics |
|
SPIRE Filter
Specification Document |
SPIRE-QMW-PRJ-000454 Issue: 2.2, 29
October 2002 |
Summarises the
location of and requirements for the filters and dichroics. |
|
Relative
performance of filled and feedhorn-coupled focal plane architectures |
|
Presents a general
treatment of the performance of feedhorn-coupled detector arrays. |
|
The SPIRE Analogue Signal Chain |
SPIRE-UCF-DOC-002890, Issue 2, 19 July 2007 |
Describes the
analogue signal chain and photometer data processing pipeline, as
implemented in this simulator. |
|
SPIRE AOT Implementation Document |
SPIRE-RAL-DOC-002663,
draft 2, 15 January 2008 |
Describes the
definition of the various house keeping parameters throughout the
course of all observing modes. |
|
Herschel
Straylight Calculation Results |
HP-2-ASED-TN-0023, 29 September 2004 |
Report on stray
light in the Herschel telescope. |
|
SPIRE Photometer
Simulator |
SPIRE-UCF-DOC-003094, Issue 2.0 (this document) |
Describes the
modelling and architecture of the photometer simulator |
The IDL startup file is an IDL
program file
which is run each time IDL is started. A
sample IDL startup file called start_up_example.pro is located in the
SPS release. This can be edited, and used as required. This file is used to load your
personal preferences.
The startup file can be specified
in two ways,
depending on the system you are using:
Windows: In windows IDL
is accessed by the
IDL development environment (IDLDE). The startup file can be specified
by first clicking on the 'File' menu, and selecting 'Preferences'. This
will load up the preferences window. Select the 'Startup' tab from this
window, and enter the location, and name of your startup file.
Alternatively you can use the 'Browse' button to navigate to your
chosen file.
UNIX, LINUX, MAC OS: While
IDL can be used
via the IDLDE in this operating system, and the startup file selected
in the same way as in Windows, it is not generally used. The startup
file is more normally specified by setting the 'IDL_STARTUP'
environment variable in the users .cshrc, or .tcshrc file, .e.g.:
setenv IDL_STARTUP
/home/user/.idl_startup
Once the modificed .cshrc or
.tcshrc file has
been sourced, IDL will run the startup file upon initiallisation of
each IDL session.
Observing Function:
The observing function is an integer number which defines which
observing function is to be simulated. It was found that only three of
the original six observing functions were required. These are defined
in Table 1 below. The number
2, 3, or 5 specified here should be the value input to the parameters
window to achieve each observing mode.
| Observation | HSPOT name | Photometer Observing Function (POF) Number |
| Point source photometry | Point source | 2 |
| Field (jiggle) mapping | Small map | 3 |
| Scan mapping | Large map | 5 |
Table 1: Definition of the available
observing modes
Map centre position in RA (h:m:s, or deg.): This parameter specifies the centre of the observation in right ascension (RA). The input value be specified as either h:m:s or degree specified as a decimal.
Map centre position in DEC (h:m:s, or deg.): This parameter specifies the centre of the observation in declination (DEC). The input value be specified as either h:m:s or degree specified as a decimal.
Telescope absolute pointing error (3.7 arcsec): The absolute pointing error is the 1-sigma absolute error in the initial pointing of the telescope. While the nominal value for this parameter is 3.7 arcsec., in many cases it is useful to set this value to zero.
Telescope drift (0.0 arcsec/sec): The
telescope drift parameter is a 1-sigma velocity drift in a random
direction. It therefore implements a random, and constant, linear drift
throughout the observation. There is no known nominal value for this
parameter, therefore the user is recommended to use a value of 0.0 for
now.
POF 2,3: Chop throw (126.0 arcsec): This parameter defines the chop throw of the BSM during POF 2 and 3 observations.
POF 2,3: Chop direction wrt z axis (90 deg.): This parameter defines the chop direction, with respect to the z-spacecraft axis, during POF 2 and 3 observations.
POF 2,3: Chop frequency (2.0 Hz): This parameter defines the BSM chop frequency during POF 2 and 3 observations.
POF 2,3: Chop cycles per jiggle position (16, 4): The
parameter specifies the number of chop cycles are performed in each POF
2/3 jiggle position. The nominal values stated are for POFs 2 and 3
respectively.
POF 2,3: Nod
operation (1): Flag to turn telescope nodding on (1) and off (0).
POF 2,3: Nod throw (126.0
arcsec): This parameter specifies the angular scale between
telescope nod positions. Nominally it should be equal to the chop throw.
POF 2,3: Jiggle positions per nod cycle (8, 16): This parameter defines the number of jiggle positions per nod cycle. The nominal values stated are for POFs 2 and 3 respectively.
POF 2,3: Number of nod cycles per sub-map (2): This parameter defines the number of nod cycles per 'sub-map'. One POF 3 map is made up of 4 separate 16 point sub-maps. Therefore there are 8 nod cycles in total in a POF 3 observation. POF 2 contains no sub-maps, making the total number of nod cycles in a POF 2 observation 2.
POF 2,3: Number of repetitions: This parameter
specifies the number of repeat POF 2/3 maps to be performed.
POF 2: Grid spacing (arcsec): This
parameter applies only to the POF 2 mode, and specifies the separation
of the different chop positions within the 7 point map.
POF 5: Number of line scans: This
parameter denotes the number of line scans to be performed in a POF 5
(scan map) observation. The value stated must be an integer.
POF 5: Line separation (arcsec 348.0): This
identifies the separation between POF 5 line scans.
The separation varies depending on the scanning angle chosen. The
nominal value shown here corresponds to a scan along the diagonal axis
(the only axis allowed within HSPOT).
POF 5: Scan rate (30.0 arcsec/sec): This
parameter specifies the telescope scanning rate in a POF 5 observation.
This value corresponds to the HSPOT 'nominal' value as selected
in the SPIRE large map option window, and 'slow' in the
SPIRE/PACS parallel mode option window. For the 'fast' option in
both HSPOT windows a scan rate of 60 arcsec/sec should be selected.
POF 5: Line length (arcsec): This
parameter simply specifies the length of the on map scan line.
Additional data will be taken at each end of this scan line associated
with the telescope turn around.
POF 5: Scan direction (42.4 or -42.4 deg.):
This parameter specifies the scanning 'magic' angle of the array
on the sky. There are two nominal values, corresponding to the
two orthogonal scan direction used
when cross-scanning (required for use with MADmap). The 42.4 degree
angle corresponds to scan angle 'A' defined in the SPIRE large map mode
window in HSPOT, and -42.4 with angle 'B'.
POF 5: Telescope acceleration (3.0
arcsec/sec2): This
parameter defines the telescope acceleration and deceleration rate.
This value should be set to the nominal value in almost all cases.
POF 5: Rotation of scan pattern on the sky
(-2.6 or 87.4 deg.): This parameter
applies a rotation to the scan pattern on the sky. The nominal values
stated here correspond to the nominal scan direction values
respectively. These values will result in the telescope scanning approximately along the map RA and DEC axes, thereby observing the
majority of a square input map. This make optimal use of the input map,
and ensures that the majority of sources within the map are observed.
