IDL Spectral Line Data Reduction at Green Bank

This web page is intended for observers at the NRAO Green Bank site, running IDL in the Linux computing environment. The following steps will present GBT data taken towards Orion A at 43 to 46 GHz. It is expected that the observer will modify their data configuration files and write their own IDL procedures for special processing of their observations.

After the observer has completed their data reduction, the observer is requested to submit (ie copy) their observing procedures to a public account at the Green Bank site. (Put your contributions in: /home/astro-util/idlUser -- Thanks!)

Demonstration

Within the GB computing environment type the following:

Step	Type	Note
1	mkdir ~/idl	Create directory for your IDL work, later many files will be created
2	cd ~/idl	Go to the new directory
3	/opt/local/bin/rt_idl	Start up the IDL development environment, windows will appear
		The latest GBT Spectra will appear!
4	demoOrion	At the IDL prompt, type demoOrion, to start the demo
5	-ENTER-	Hit Enter at the IDL prompt to step though the data

Step Details

Steps 1, 2 and 3

The IDL package written by Tom Bania provides the basic functionality of common packages (ie GET,# ; SHOW). This functionality is implemented in IDL procedures and the first steps define the location of the version of these procedures the observer will use. A unix script will search for the latests spectra in the default GBT output data directory.

Step 4

Step 5

Notes on the GB IDL

• data - Directory containing the observer pre-selected data
• figs - Directory output postscript figures (from PRINTON and PRINTOFF)
• saves - Directory containing saved versions of the IDL environment.

GB IDL Command Summary

The GBT observations are organized in scans, and "sdfits" puts the scan data in FITS records The GB IDL environment works with data records (rec below) that are loaded into one of 10 special buffers. In addition, the special buffers may be copied to a storage area NSAVE for later use. The special 10 buffers have defined functions:

• !b[0] -- working buffer: everything invokes what is in here
• !b[1] -- BMODEL and GMODEL buffer
• !b[2] -- copy of !b[0] during BASE and GAUSS
• !b[3] -- ACCUM buffer
• !b[4] -- AVE buffer: copy of last AVE
• !b[5] -- ON buffer: copy of ON scan
• !b[6] -- OFF buffer: copy of OFF scan
• !b[7] -- PSW buffer: copy of (ON-OFF)/OFF
• !b[8] -- SMOOTH buffer: copy before any smoothing operation.
• !b[9] -- SHOW buffer: copy of latest SHOW
• !b[10] -- SHOW buffer: copy of latest RESHOW; used by REFRESH
• !b[11] -- SHOW buffer: copy of previous RESHOW
• !b[12] -- SHOW buffer: copy of previous RESHOW
• !b[13] -- SHOW buffer: copy of previous RESHOW
• !b[14] -- SHOW buffer: copy of previous RESHOW
• !b[15] -- SHOW buffer: copy of previous RESHOW
• !b[16] -- SHOW buffer: copy of previous RESHOW

Each IDL procedure is contained in a file in directory /home/astro-util/idl/gb_macros. A list of commands is provided below:

Command	Function
accum	Add buffer 0 to accumulation
addem,rec_array	Add array of records to Stack
add,rec	Add record to Stack
ave	Compute weighte averages of accumulation
avgstk	Accumulate and average stack records
bbb,nfit	Fit Polynomial Baseline of order nfit
bb,nfit	Fit Polynomial Baseline of order nfit
bmark	Mark baseline region on the plot
boxcar,nch	Box car smooth by nch
b	Fit polynomial baseline, used previous nfit,regions
bsearch,nmax	Baseline fit up to order nmax
cat	List the contents of the stack
ccc,xpos,ypos	Return xpos,ypos cursor positions
chan	Flag plotting channels on X axis
clearset	Initials Select Variables to default
clrstk	Empty the record stack
comment,msg	Write 44 character messag to history
copy,bin,bout	Copy buffer bin to buffer bout
curoff	Turn off cursor input for scaling
curon	Turn on cursor input for scaling
curx	Set Plot X region using cursor (forces Cursor on)
curxy	Set Plot X-Y region using cursor (forces Cursor on)
cury	Set Plot Y region using cursor (forces Cursor on)
dcoff	Flag NO subtract mean baseline for display
dcon	Flag automatic subtrack mean baseline
dcsub	Subtract mean baseline from buffer 0
demoOrion	Steps Observer through a demo of Orion A data
demoHe3	Steps Observer through a demo of Helioum 3 data
display,array	Display 2-d array
disp,n,m	Show buffer n and overplot buffer m
div,n,m	Divid buffer n by m, output to buffer 0
fetch,recon	Get recon, compute recoff andsubtract
files	Print files currently used by GB IDL
fixx,xmin,xmax	Set Plot X range with input values
fixxy,xmin,xmax,ymin,ymax	Set Plot X-Y ranges with input values
fixy,ymin,ymax	Set Plot Y range with input values
flagoff	Turn Flag off for plot display option
flagon	Turn Flag on for plot display option
flag,ch	Set channel for vertical line at x-ch
flg_id,ch,lab,clr	Draw vertical flag at x=ch, label=lab, clr=color
freex	Flag full X range on next SHOW
freexy	Flag full X and Y ranges on next SHOW
freey	Flag full Y range on next SHOW
freq	Set x axis labeling to frequency
gauss	Prompt observer for gaussian fitting parameters
gbtrestore	Restore all GB IDL values from previous gbtsave
gbtsave	Save all GB IDL values from a session
gbt_win	Create plot window taylored to GBT Data reduction
gbt_xwin	Create IDL window for data reduction
getns,ns	Restore save region ns
getoff,rec	Copy rec into buffers 0 and 6
geton,rec	Copy rec into buffers 0 and 5
get,rec	Copy rec into buffer 0
gg,ngauss	Fit ngauus Gaussians to the data
g	Tuned gaussian fitting program
hdr,rec	Prints data header for rec
hline,val	Draw horizontal line at y=val
info	Print information about data in buffer 0
keys	Display the current GBT realtime data selection Keywords
killwin	Kill the GB IDL Plot window
list,start,stop	Print summary of records loaded int GB IDL
look	Fetch data from records on stack, plot with DC offset subtracted
make_gbt	Create and Fill the gbt data structure with records
make_nsave	Create NSAVE file for storing the GBT data structures
mask,dsig,index	Display regions
mediansub,halfWidth	Subtrack median of halfWidth wide from buffer 0
minus,m,n	Subtract buffer m from n and put in buffer 0
mk	Convert Y axis scale from Kelvins to milli-Kelvins
molecule	Show all known molecular lines on current plot
mult,m,n	Multiply buffer m by and put in buffer 0
nroff	Turn off Flag for baseline fit marks
nron	Turn on Flag for baseline fit marks
nrset,n	Set n baseline regions with values nreg=[.,.]
nslog	Summarize NSAVE data records
nsoff	Turn NSAVE write protection off
nson	Turn NSAVE write protection on
ortho_fit,xx,yy,nfit,cfit,rms	Orthogonal polynomial fit
plthdr	Anotate the plot with header values
plus,n,m	Add buffer n and m, put output in buffer 0
printoff,prt	Turn off postscript command logging, send to printer prt
printon,fname	Write postscript print commands to file fname
procs	Print list of all compiled procedures
psplot,fname	Prints postscript file fname to default printer
ps,sig_rec,ref_rec	Power Spectrum TSys*(Sig-Rec)/Rec
putns,ns	Save spectrum in buffer 0 to NSAVE area ns
realTimeSetup	Initiates real-time data display
rec_info,rec	Prints summary of GBT data rec
recombAll	Show H, He and C recombination lines on current plot
recombC	Show C recombination lines on current plot
recombH	Show H recombination lines on current plot
recombHe	Show Helium recombination lines on current plot
recombN	Show Nitrogen recombination lines on current plot
recombO	Show Oxygen recombination lines on current plot
refresh,n	Re-plot previous n plots, useful with printon/off
reshow	overplots the contents of buffer 0 on plot
rms_mask	Calculates the RMS of data in baseline REGIONS
rms,sigma,xmin,xmax	Calculates RMS sigma in between xmin,xmax
sampler,iSampler	GBT Scan sampler (polarization/frequency) band to RT select
scale,fact	Scale buffer 0 by fact
scan,number	GBT Scan number in current project to select
sd_hdr,rec	Print single dish record header for rec
sd_to_gbt,in,out	Convert single dish record to gbt_data record
select	Load record number stack with record numbers matching request
set	Prompt for scan selection critera
setBandWidth	Set maximum bandwidth for all Banks/Samplers
setline	Prompt observer for line ID for SELECT search
setplot,device	Set plot device/file name
setrec,recmin,recmax	Set record range for a SELECT search
setscan,scan	Set scan Number for SELECT search
setsource,src	Set soruce name for a SELECT search
setsrc,src	Set source name for a SELECT search
settype	Prompt for scan type of a SELECT search
settyp,typ	Sets scan type for SELECT search on data
setx,xmin,xmax	Set X min and max for plot
setxy,xmin,ymin,xmax,ymax	Set X, Y plot ranges
sety,ymin,ymax	Set Y min and max for plot
show	Show buffer 0 contents; result of last calculation
showAllInts	Show all integrations for the current scan
showLatest	Show latest spectra for most recent scan
smooth	Gaussian smooth by fixed width
smo,n	Smooth buffer 0 with FWHM=n channels
srcvloff	Turn off display of source velocity line
srcvlon	Flag display of source velocity line
srcvl,ch	Draw vertical line at x=ch on plot
state,iStates	GBT Scan state numbers to select
syms,no,scale,ifl	Create IDL symbol on the plot
tagid	Write 32 character line ID to buffer 0
tagpol	Write 4 character polarization ID to buffer 0
tagtype	Write 32 character anotation string to buffer 0
tellstk	Print list of stack recond numbers
track,scans	Reduce Track observations of a scanlist
unmk	Convert MilliKelvin Y scale to Kevlin scal
velo	Set flag for X axis velocity plots
xroll	Set X-range to inner 90 % of the data
zline	Draw line at Y=0 on the plot
zloff	Turn off the zero line
zlon	Turn on the zero line

Future Developments

One primary development direction for GB IDL is implimentation of a data browser, for selecting of data to be reduced in IDL. Keep tuned to this web page for new developments!