Version 1 (May 13, 2008)

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AKARI FTS Toolkit Manual
Version 1
Hidenori Takahashi1 , Yoko Okada2 , Akiko Yasuda2 ,Hiroshi Matsuo3 , Mitsunobu Kawada4 , Noriko
Murakami5 , and Chris Pearson6,7
1 Gunma Astronomical Observatory
2 Institute of Space and Astronautical Science (ISAS), JAXA
3 National Astronomical Observatory of Japan
4 Nagoya University
5 Bisei Astronomical Observatory
6 CCLRC Rutherford Appleton Laboratory
7 University of Lethbridge

May 13, 2008

Version 1 (May 13, 2008)
Date
5 December 2007
6 December 2007
29 December 2007
7 January 200814 January 2008
23 April 2008
12 May 2008

i
Revision
Version 0.9
Version 0.91
Version 0.92
Version 0.93
Version 0.94
Version 0.95
Version 1

Comments
First Draft Hidenori Takahashi
Updated Format Chris Pearson
Updated Yoko Okada
Updated Chris Pearson
Updated Yoko Okada
Updated Yoko Okada
Updated Yoko Okada

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AKARI FTS Toolkit ManualContents
1 Data Preparation

2

2 fts part1
2.1 Details of GUI processes . . . . . . . . . . . . . . . . . . . . .
2.1.1 check ramp curve corr . . . . . . . . . . . . . . . . . .
2.1.2 check reset bad . . . . . . . . . . . . . . . . . . . . . .
2.1.3 rm glitch . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.4 check drv cb . . . . . . . . . . . . . . . . . . . . . . .
2.1.5 check all cb . . . . . . . . . . . . . . . . . . . . . . . .
2.1.6 check raw spec . . . . . . . . . . . . . . . . . . . . . .
2.2 options for fts part1 . . . . . . . . . . . . . . . . . . . . . . .
2.2.1 plotch . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.2 rampcorr . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.3 rampbﬂg . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.4 addname . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.5 vifbadf . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.6 mcal . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.7 pixﬂg . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.8 sigmaclip . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.9 setcbp . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Contents of the save ﬁle . . . . . . . . . . . . . . . . . . . . .

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3 FTS tools
23
3.1 fts checkrawspec . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2 fts part1 output . . . . . . . . . . . . . . . . . . . . . . . . . 23

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About this Document
This document explains how to analyze AKARI Fourier Transform Spectrometer (FTS) data. The analysis procedure consists of two main steps.
The ﬁrst processing step, f ts part1, carries out the Fourier transformationof the interferogram obtained from the time series data (TSD) to provide
the spectral information. The second processing step carries out the ﬂux
and wavelength calibrations on each channel. Since the latter calibration
part is still under development, only the former part, f ts part1 is describedin this document. Calibration part will be released in a later version.
All procedures are based on the IDL programming language. In thisdocument, it is assumed that the FIS IDL procedures and IDL itself arealready installed and running in your environment. More information on
the basics of the AKARI data ﬂow, FIS analysis tools, and strategy fordata processing using the FTS can be found in the FIS Instrument Data
User Manual (IDUM). The deﬁnition of the FIS channel numbering follow
Figures 2.1.6 or 3.2.9 in the FIS IDUM.
In the following sections, processing with many iterative steps will be
described:
1. Data preparation,
2. fts part1,
3. FTS tools

Deﬁnition of words
GB
OPD
TSD
ZPD

Green Box
optical path diﬀerencetime series data
zero path diﬀerence
centerburst

The standard FIS pipeline tool.
The format of the raw data.
The position where the optical path diﬀerenceis zero.
Same as ZPD, though also used for the whole
structure in interferogram around ZPD.

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AKARI FTS Toolkit Manual

Data Preparation

Suppose the ﬁle name of the raw observations data set (TSD) as input base+“ﬁts.gz”.
Before running the f ts part1 processing step, it is required to separate thetarget observation data from the calibration data, etc., in the raw data set.
The task is performed by the following simple IDL command:FISDR> fts mk obj mcal acal,input base+‘ﬁts.gz’ [,/noobj] [,/nomcal][,/noacal] [,/nodark]
Just type f ts mk obj mcal acal to display the usage. f ts mk obj mcal acal
makes several subsets from the TSD ﬁts ﬁle of one pointed observation.
Output ﬁles have extra characters between input base and ‘ﬁts.gz’, which
represent the contents of the subset. “obj” means the celestial object data,“mcal” means the internal calibration light source data, “dark” means dark
data, and “acal” means the cal-A lamp data. “dark1”, “dark2”, and “dark3”
refer to the dark data before the observation, between the observation of theinternal calibration lamp and the celestial object, and after the observation,
respectively. “acal b” and “acal a” are the cal-A lamp data before and after
the observation, respectively. If only selected subsets are required, options
can be set to omit the unneeded subsets, e.g. setting the /nomcal option
will omit the “mcal” data subset.
Either of input base+‘obj.ﬁts.gz’ or input base+‘mcal.ﬁts.gz’ becomesthe input for the f ts part1 procedure.

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fts part1

The f ts part1 process carries out the Fourier transformation of the timeseries data (TSD) to obtain spectral information. The processing steps are
given below. During the processing, there will be several GUIs for checkingof data, ﬂagging and corrections. Additional optional parameters used at
the startup of f ts part1 are summarized in section 2.2[Raw data]
1. ADU to voltage conversion (GB pipeline tool)
2. Ramp curve correction (GB pipeline tool with correction table optimized for FTS observations)
Correct for non-linearity of the ramp curve.
GUI : check ramp curve corr
• Quality check of the ramp curve correction.
3. Diﬀerentiation (GB pipeline tool)[Interferogram + DC component]
4. Separate into individual scans
5. Remove reset anomaly
GUI : check reset bad• Removal of any data aﬀected by resets.
6. Remove glitches
GUI : rm glitch• Masking glitches by eye if necessary.
7. Subtract DC component

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AKARI FTS Toolkit Manual
8. Interpolation of bad data
Replace any bad data by the median of other scans. Since the ﬁrst scanin SED mode is aﬀected by an irregular drive pattern at the starting
point, we ignore the ﬁrst scan when calculating the median in the SED
mode.
9. Determine the zero path diﬀerence (ZPD) in a speciﬁc channel
Since the value of the position sensor is correct only relatively, the
ZPD must be determined. The present toolkit determines the ZPD
that minimizes the squared imaginary part integrated over the eﬀective
wavenumber.
GUI : check drv cb• Check the estimated ZPD for the every scan in a speciﬁc channel
and tune parameters to reject incorrect estimates.
10. Determine the ZPD in all channels
It is assumed that the relative deviation of the ZPD between diﬀerent
scans is the same for all channels. And the ZPD of all the channels
are estimated in this step.
GUI : check all cb• Check the estimated ZPD for all channels and tune parameters
to reject incorrect estimates.
11. Discrete Fourier Transform
Apply Discrete Fourier Transform using the output of the position sensor and the determined ZPD in the previous steps to the interferogramof each and every scan.
12. Average the spectra
After applying Fourier transforms, the average spectrum is taken.
GUI : check raw spec
• Check the Fourier transformed spectra for all channels.
[Raw spectra] (ﬁnal output of the f ts part1)

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To start the process, from IDL command line, input the following command
FISDR> fts part1, input base+‘obj.ﬁts.gz’ [,plotch = integer][,rampcorr = 1,2,3 or string] [,/mcal] [,/sigmaclip]
Just type fts part1 to display the usage. Refer to Section 2.2 for a detailed
description of the available options. The rampcorr option (see 2.2.2) is used
to select the appropriate ramp curve correction table. It is not necessary
to specify rampcorr except for very bright objects, and in most cases thedefault correction table is used. The plotch option (see 2.2.1) is used to selecta speciﬁc channel used for the adjustment of the ZPD. For observations ofpoint or small extended sources it is necessary to set the channel in which thesource is detected as plotch. For large extended sources, it is not necessary
to specify plotch, and the default channels (channel 23 for SW and 7 for
LW) will be used. The mcal option (see 2.2.6) should be used when the user
process the data of the internal calibration lamp. The sigmaclip option (see2.2.8) is for automatic glitch removal. We recommend to use this option,otherwise the user will have to remove all glitches manually by eye. The
following sub-section describes the details of GUI processes.

2.1

Details of GUI processes

2.1.1

check ramp curve corr

The standard FIS pipeline tool (Green Box) is used to correct for any nonlinearity of the ramp curves (see FIS Instrument Data Users Manual Section
4.1.2). The correction table optimized for FTS observations has been prepared in the toolkit and used for nominal FTS observations. For very brighttargets whose brightness exceeds the range of the correction table, a correction table should be made from the data itself, setting rampcorr=1. In thiscase, see Section 2.2.2 for detailed explanations of this option.
This process opens a window ‘check ramp curve corr’ as shown in Figure 1 which has three panels; the lower left panel shows the raw integrated
time series data, the lower right panel shows the relation of the ramp curve
correction (white: measured, red: corrected), and the upper panel displays
the derivative of the raw data and ramp curve corrected data of the selectedchannel. One should check on the upper panel whether the corrected interferogram (blue) is ﬂat, except for the centerburst, compared to the original

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data (white). In general the correction is smaller for the LW band than the
SW band. The display range can be changed by using the [range] button.
When it is acceptable, click [ok] to progress to the next step. If somethingis unsatisfactory or wrong you may have to quit and start again using a
diﬀerent option.

Figure 1: Window for the ”check ramp curve corr” process. The white andblue lines in the upper panel represent the interferograms before and after
correction respectively.

2.1.2

check reset bad

This step removes reset anomalies. During this step, the ‘check reset bad’window can be viewed, as shown in Figure 2.
Using this GUI, user should examine the data to ensure that the reset
periods are properly ﬂagged out. Flagged data itself have the value ‘-999’
and reach far below the window. If the ﬂag is not properly set, there will be
periodic glitches before or after the reset as shown in Figure 2. Normally,
the reset anomalies can be ﬂagged using the default parameters. If periodic
glitches as exempliﬁed in Figure 2 are found, check the ramp curve correction

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ﬁrst, since an improper ramp curve correction can produce such periodic
glitches. Note that at this stage of the processing, the user does not haveto care about glitches between the resets (i.e. aperiodic, random glitches),since these will be dealt with in the next step of the processing.
Two parameters may be changed to mask any anomalous data related
to resets. The ﬁrst is used to select the pre-reset data points and the otherrefers to the post-reset data points. After tuning the [before reset] and [after
reset] sliders of the “reset anomaly range”, click [do again] to set the newparameters (e.g. as shown in Figure 3). The reset parameters are common
to all channels and scans. The [range], [channel], and “plot scan range”
sliders can be used to look at all data. Click [ok] when ﬁnished.
2.1.3

rm glitch

The ‘rm glitch’ window is shown in Figure 4. Here you should ﬂag all
individual data aﬀected by glitches by eyes. If sigmaclip option is set, σclipping glitch removal has been made before this GUI process, and ﬂagged
data points are shown as pink points. If the clipped data points are notvalid, break this process and run f ts part1 without sigmaclip option. Use[range], [channel], and “plot scan range” sliders to check all the data. Any
glitch near the centerburst will aﬀect largely on the resultant spectra andshould be removed.
For ﬂagging, select the data to be masked with the “selected data range”
slider and click [mask data] (Figure 5). Click [save] to create the ﬂag ﬁle.
Click ‘ok’ to save ﬂags and move to the next step. Flagging glitches for
all the channels often takes long time. The user can break this procedure
with the [quit] button after clicking [save], and restart f ts part1 with the‘vifbadf’ option (see Section 2.2).
2.1.4

check drv cb

The next step is “check drv cb” (Figure 6). In this process, the zero path
diﬀerence (ZPD) position is identiﬁed (i.e. the position of the centerburst)
from the interferograms of a speciﬁc channel (set by plotch option). This
processing step is important to obtain proper spectra.
The lower right panel of Figure 6 shows the interferogram. The x-axis is
the relative optical path diﬀerence (hereafter opd). Initially, the tool applies
the Fourier transform assuming that each data point is the ZPD, estimatesthe integration of the squared imaginary part over the wavenumber (lower
left panel of Figure 6), and determines the ZPD as the position where this

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Figure 2: Window for the ”check reset bad” processing step. Note that thedata just before reset overshoots above the mean level of the interferogram.
The value of ﬂagged data is -999, and apparent overshoots the bottom of
the window represent -999.

Figure 3: The overshot data seen in the previous ﬁgure are removed using
the reset anomaly range.

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Figure 4: Window for the ”rm glitch” processing step. The glitch at theposition corresponding to sample number 1841 (shown by the ”blue” point)
is selected using the ”selected data range” slider.

Figure 5: After selecting the glitch data as in the previous ﬁgure, click “maskdata”. After replot by clicking any of the sliders, the removed data point
turns pink.

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integration is a minimum. The determined ZPD is shown as a white (forward
scan case) or yellow (backward scan case)line in the lower right panel andthe red point in the lower left panel. Using the “zero-path position” slider,
you can select the data point and check the interferogram (blue line in thelower right panel), the integration of the squared imaginary part (blue pointin the lower left panel) and the spectra itself under the assumption that
this point is ZPD (upper left panel; red represents the real part and blue
represents the imaginary part). You can select the scan number using the“scan” slider. The upper right panel shows the derived ZPD for each scan.
At this stage, it is necessary to check whether the ZPDs in all the scans
have been estimated correctly. Though the deﬁnition of the ZPD is the opd
where the integration of the squared imaginary part is a minimum, local
minima next to the real ZPD may have smaller values in the case of datawith low S/N or data aﬀected by strong transient eﬀects. There are twocheck points that can prove useful. The ﬁrst is whether the interferogramis a positive peak or a negative peak at the ZPD (see white or yellow lines
in the lower right panel of Figure 6). For celestial data taken in the SWband and internal calibration data with LW, the interferogram should exhibit a negative peak at the ZPD. For celestial data taken in the LW bandand internal calibration data with SW, the interferogram should exhibit apositive peak at the ZPD. The second check point regards the upper rightpanel. Since the ZPD does not change signiﬁcantly between scans, the upper
right panel should appear almost constant (except for the ﬁrst scan). If you
discover any large discrepancy (over 0.002 cm) between scans as exempliﬁed
in Figure 6, the determined ZPDs in some scans are probably not correct.
If the determined ZPDs are acceptable, click [ok] to ﬁnish this procedure.
If not, tune the ZPD using four sliders at the bottom of the window, which
cover the range of the opd used to determine the ZPD. For example in
Figure 6, improper positions of opd > −0.002 cm are selected as the ZPD inseveral backward scans (see upper right panel). Moving the lower right slider(maximum for backward scan) to −0.002 and clicking [do again], produces
the window shown in Figure 7 (after a short wait). Note that the newly
determined ZPDs seem to be correct for all the scans. This process should
be repeated until the ZPDs for all the scans are acceptable.
2.1.5

check all cb

The next step is ”check all cb” (Figure 8) and is used to check whether
the ZPD is reliable for all the channels. The window is similar to the“check drv cb” window, except for the upper right panel, in which the ZPDVersion 1 (May 13, 2008)

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Figure 6: Window of ”check drive cb” in the case of LW channel 7 of acelestial object. The red point in the lower left panel shows the selected
opd, where the integration of the square of the imaginary part is a minimum.
However, this is in the negative peak of interferogram as shown in the lower
right panel, whereas the interferogram of celestial objects observed in the
LW band should be the positive peak at ZPD. It can also be found that therelative optical path diﬀerence of this scan (= 3) is not in agreement withthat of the majority of other scans in the upper right panel.

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Figure 7: After tuning the slider, the ZPDs in all the scans are determinedcorrectly.

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for every scan is replaced by that of the channels (Figure 8). The procedureof this tool is similar to that of “check drv cb”. Since there is no need to
select forward or backward scans, only two sliders are available, instead offour. Note that the ZPD of bad channels any channels in which objects are
not detected is not trustworthy and may be ignored.

2.1.6

check raw spec

After applying Fourier transforms to the interferogram of each and every
scan, the average spectrum is taken. As ﬁnal products, spectra of complex
type are obtained. The real part corresponds to spectra with physical meaning, and the imaginary part is residual of the phase correction. Note thatthe imaginary part of the full-resolution mode data does not represent thisresidual correctly, since the Fourier transform is applied only for one-side of
the centerburst.
This step is primarily for conﬁrmation (Figure 9). The upper left andupper right panels show the averaged spectrum and the spectrum of selectedscans, respectively. The plot can be adjusted by using several available
buttons. Use the ”quit” button to ﬁnish f ts part1 processing.

2.2

options for fts part1

In this section, we explain the optional commands which are available to theuser in the f ts part1 processing step of the toolkit.
optionplotch = integer
rampcorr = 1,2,3 or string
rampbﬂg = string
addname = string
vifbadf = string/mcal
pixﬂg = integer vector/sigmaclip/setcbp

explanation
channel for the adjustment of the ZPD of each scanselect ramp curve correction table
use previously saved ramp ﬂag ﬁleadd optional characters to output ﬁles
use previously saved glitch ﬂag ﬁlerequired to process internal calibration source data
ﬂag all data on speciﬁc channels
ﬂag bad data by σ-clipping before “rm glitch” GUIestablish ZPD from driving pattern automatically

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Figure 8: Window for the ”check all cb” processing step. This window issimilar to that of ”check drv cb” except the upper right panel represents
every channel rather than every scan. Note that there is a trend to incline
on each row in the case that a large extended object is detected over several
channels.

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Figure 9: Window of ”check raw spec”. Upper left panel shows averaged
spectrum over scans (pink = real part, light blue = imaginary part). Upperright panel represents the spectrum of the selected scan.

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2.2.1

AKARI FTS Toolkit Manual
plotchThe plotch option is used to select a speciﬁc channel for the adjustmentof the ZPD of every scan, used in “check drv cb”. A channel which detects suﬃcient photons with high S/N is recommended. For large extended
sources the default channels (channel 23 for SW and channel 7 for LW) arerecommended, so it is not necessary to set this option. For point or small
extended sources, a channel in which the sources are detected should be
set: plotch = 28 or 29 and plotch = 4 or 5 for SW and LW observations,
respectively, with AOT parameters of FIS03;*;*;1, plotch = 54 or 55 andplotch = 23 for SW and LW observations, respectively, with AOT parameters of FIS03;*;*;2, and plotch = 32 or 33 (or 53) and plotch = 7 for SW
and LW observations, respectively, with AOT parameters of FIS03;*;*;0.
2.2.2

rampcorr

The ramp curve correction table is selected by rampcorr option. By default,
the correction table in the toolkit for FTS observations, which is recommended for most data, is used. This option accepts either an integer 1, 2, 3
or a string of a ccf ﬁlename.
1 : Make a correction table using the data itself. This is required for very
bright objects.
2 : Apply correction table for survey mode data. Not recommended (testpurpose).
3 : No correction. Not recommended (test purpose).
ccf ﬁle name (string) : select speciﬁc ramp curve correction table. See below.
Processing with rampcorr=1, generates a ramp curve correction tableﬁle named “***ramptbl.ccf”. Once a correction table is made for one observation, the user can use it every time by specifying the ﬁle as rampcorr=“***ramptbl.ccf ” instead of making the correction table again.
If rampcorr = 1 is selected, the ”check ramp” monitor window appears(Figure 10). All ramp curves (far from the centerburst) used to make acorrection table are plotted in the top-left window. Unsuitable ramp curve
data should be ﬂagged in this step. A channel is selected using the [channel]
slider. There are two additional sets of sliders, ”ramp curve range” and”sample number range”. The former is used to remove a ramp curve, andthe latter is used to remove data of the same sample number from all ramps.

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When you select the “all channel” button, the same data points are simultaneously removed in all channels, whereas using the “one channel” button,
only the data in the selected channel is removed. The ﬁrst point of the ramp
curve, i.e. data with the sample number being 0, should be removed because
these data should not be included as the beginning of the ramp curve. Select the ﬁrst point with the “sample number range” slider (Figure 10), andclick [mask sample number]. The actual removal of a ramp curve follows thesame methodology of the removal of bad sample data except “ramp curve
range” is used instead of the “sample number range” sliders (Figure 11). It
is not necessary to remove bad ramp curves very ﬁnely, since most of themwill be removed automatically in the following processing.
Click [save ﬂag] to save the above processing. At any time, one may
return to the last saved position by clicking the [reset] button. Click [saveﬂag] and [ok] to move to the next procedure, the derivation of the averaged
ramp curve (Figure 12) and the production of the ramp curve correction
table.
2.2.3

rampbﬂg

This option is used to refer to a previously saved ramp ﬂag ﬁle and should
be used with the rampcorr=1 option set.
rampbﬁg = ‘*****ramp.sav’

2.2.4

addnameThis option adds optional characters to output ﬁles. The default name of
the ﬁnal IDL save ﬁle is ”ﬁlename + part1.sav”. The new characters areinserted in between the ﬁlename and part1.sav.
addname = ‘****’

2.2.5

vifbadf

If the users have previously saved ﬂagging ﬁle of glitches, the users importit for the ”rm glitch” processing by setting this option.
vifbadf = ‘*****vifbad.sav’

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Figure 10: Window for the ”check ramp” process. The data selected withthe “sample number range” sliders turn green.

Figure 11: The ramp curve selected with the “ramp curve range” sliders
turn red.

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Figure 12: Window to check the averaged ramp curve. White lines are all
the ramps with scaling and the blue line is the assumed average. Click [ok]to continue.

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2.2.6

mcal

This option should be used when processing the data of the internal calibration light source. The temperature of the internal calibration source
becomes stable only after several scans, thus the data of ﬁrst 3 scans andlast scan is discarded with this option.
/mcal

2.2.7

pixﬂg

This option is used to ﬂag all data on speciﬁc channels, e.g. saturated
channels, in addition to LW[2,3,18,33,42] and SW[1,11] which are alreadyknown to be bad channel.
pixﬂg = [6,7,31]

2.2.8

sigmaclip

Flag bad data by σ-clipping before glitch-check GUI.
/sigmaclip

2.2.9

setcbpThe ZPD is automatically established from the driving pattern with thisoption. This option should be used only for faint sources which do not havea clear centerburst and for which the ZPD can not be determined from thedata itself.
/setcbp

2.3

Contents of the save ﬁleDuring the f ts part1 processing, several ”save ﬁles” are created. Note thatthe creation of some ﬁles depend on the options employed.

Version 1 (May 13, 2008)21*** part1.sav : ﬁnal output of fts part1*** vifbad.sav : bad ﬂag data of glitches created in ”rm glitch”***ramp.sav : bad ﬂag data of ramps created by [save] button in ”check ramp”(with option rampcorr=1)***.ramptbl.ccf : ramp curve correction table (with option rampcorr=1)***ramp*.ps : Some postscript ﬁles produced during the process of making
the ramp curve correction table (with option rampcorr=1)
Major contents of *** part1.sav• VER (STRING) : Version of fts part1• FILENAME0 (STRING) : The name of the input TSD ﬁle• DATATYPE (STRING) : ‘FIS SW’ / ‘FIS LW’• PKTID F (BYTE) : 124 (for SED mode) / 14 (for Full-resolutionmode)• RSEXT (INT = Array[2]) : Removed reset point [pre, post]• PCH (INT) : = plotch-1• RADEC A (DOUBLE = Array[2, ndet all]) : Equatorial coordinate ofeach channel calculated from AOCU. RADEC A[0, *] is RA, RADEC A[1,*] is DEC in degree. See FIS IDUM for attitude determination.
• RADEC G : Same as RADEC A but calculated from G-ADS.
• VIFBAD (INT = Array[ndata, ndrv, ndet]) : Flag of the interferogram• RANGE (DOUBLE = Array[2]) : Range of data for Fourier transform[cm]• DC (DOUBLE = Array[ndrv, ndet]) : Non-interferometric component,
which is an averaged interferogram over a scan.
• VIF (DOUBLE = Array[ndata, ndrv, ndet]) : Interferogram of eachscan and channel• VIFPOS (ODUBLE = Array[ndata, ndrv]) : Optical path diﬀerencein each scan for PCH ([cm])• WN (FLOAT = Array[nwn]) : Wavenumber [cm−1 ]22

AKARI FTS Toolkit Manual• SPEC (DOUBLE = Array[nwn, 2(average/stdv), 3(real/imaginary/phase),2(forward/backward),ndet]) : Averaged spectrum• SPECBARA (DOUBLE = Array[ndrv, nwn, 3(real/imaginary/phase),2(forward/backward), ndet]) : Spectrum of each scanndet = Number of channels for WIDE band (SW/LW = 60/45)
ndet all = Number of channels for WIDE and NARROW band (SW/LW= 100/75)
ndrv = Number of scans
ndata = Number of data per scan. For SED mode observations, the ﬁrst
half of the data corresponds to the forward scan and the last half tothe backward scan. For Full-resolution mode, the ﬁrst half of the data
corresponds to the backward scan and last half corresponds to theforward scan.
nwn = Number of wavenumber elements in the spectrum

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23

FTS tools

Two tools are provided to support the FTS data reduction. Typing without
argument will display the usage. Suppose the ﬁle name of the ﬁnal output
of fts part1 as input base+‘part1.sav’ in the following.

3.1

fts checkrawspec

The “check raw spec” window (Figure 9) is opened by this command. plotch
speciﬁes the channel to plot, though this can be changed using the GUI.
FISDR> fts checkrawspec,ﬁlename=input base+‘part1.sav’[,plotch=*]3.2

fts part1 output

This procedure makes postscript or ascii ﬁles from input base+‘part1.sav’.
FISDR> fts part1 output, input base+‘part1.sav’ [,/mcal] [,addname =string] [,/psﬁle] [,ﬁxmin = value] [,ﬁxmax = value] [,wnmin = value] [,wnmax= value] [,/txtﬁle] [,txtch = integer vector]
If the user wants to obtain a postscript ﬁle to show the raw spectra of
all the channels, set psﬁle option. Then input base+‘part1.ps’ ﬁle is created.
The minimum or maximum values of x- and y-axis can be speciﬁed for all
the channels by the options wnmin, wnmax, ﬁxmin and ﬁxmax, respectively.
If the user wants to obtain an ascii ﬁle of the raw spectra, set txtﬁleoption, then input base+‘part1.txt’ ﬁle is created. By default, the data ofall the channels are included. Data of speciﬁc channels can be extracted by
txtch option, e.g. txtch = [33,34,35].
/mcal option should be given when the user processes the data of theinternal calibration lamp. The addname option can be used to add a word
between ‘part1’ and ‘.ps’ or ‘.txt’ of output ﬁles.