INNAME Input UV data (name) INCLASS Input UV data (class) INSEQ Input UV data (seq. #) INDISK Input UV data disk drive # CHANNEL 0.0 3000.0 Freq. channel (0 for cont.) NMAPS 0.0 8. # freq chan. to map (max=8) OUTNAME Output image name (name) OUTDISK Output image disk drive # OUTSEQ -1.0 32000.0 Output seq. no. STOKES Stokes parameters (see HELP) Use 'LINE' for spectral line IMSIZE 32. 4096. Image size (X,Y) is pixels CELLSIZE 1.E-12 (X,Y) size of grid in asec SHIFT (X,Y) image shift in asec UVTAPER 0. (U,V) gaussian taper units are kilolambda UVRANGE 0. Min & max baseline (klambda) UVWTFN UV dist. weight function blank => uniform UVBOX 0. 128. Additional rows and columns used in weighting. Use 0. DOGRIDCR -1. 1. Correction for gridding? DOTV -1. 1. Use TV? > 0 -> yes. ZEROSP 0-spacing fluxes and weights XTYPE 0. 10. Conv. function type in x default spheroidal YTYPE 0. 10. Conv. function type in y default spheroidal XPARM Conv. function parms for x YPARM Conv. function parms for y GUARD -1. 0.9 x,y guard band fractional radius BADDISK Disk drive #'s to avoid

UVMAP Type: Task Use: Fourier Transform UV data from a disk file to make catalogued images. Several images can be made with one execution. Now writes REAL format output images. Adverbs: INNAME.....Input UV data file (name). Standard defaults. INCLASS....Input UV data file (class). Standard defaults. INSEQ......Input UV data file (seq. #). 0 => highest. INDISK.....Input UV data file disk drive #. 0 => any. CHANNEL....Frequency channel to map (1 relative) Use 0 for (pseudo)continuum data. NMAPS......Number of frequency channels to map. 0 => 1. Maximum = 8. OUTNAME....Output image name (name). Standard defaults. OUTDISK....The disk drive # of output images. 0 => highest with space (note: I and Beam go on same disk, Q and U go on same disk but may not be same on 0) Note: OUTCLASS='XYYY' where X=Stokes, YYY=IM001 or BM001 OUTSEQ.....Output sequence number. 0 => highest unique. STOKES.....Make images with these STOKES parameters blank =>I,B 'I' =>I,B (B=beam) 'IQU' =>I,Q,U,B 'IV' =>I,V,B 'IQUV'=>I,Q,U,V,B 'RL' =>R,L,B 'LINE'=> Spectral line I polarization 'RLIN'=> Spectral line right circular poln. 'LLIN'=> Spectral line left circular poln. IMSIZE.....(X,Y) image size in pixels. Must be a power of 2 on each side from 32X32 to 4096X2048 CELLSIZE...(X,Y) pixel separation in asec. SHIFT......(X,Y) shift of map center from phase center in asec. Map center = Phase center + shift. If X>0 & Y>0, source shifts to south-west (down & right). Units are arc sec at the initial coordinate in RA and Dec (if unrotated). UVTAPER....(U,V) gaussian taper (kilolambda) at 30 percent level UVRANGE....(Minimum,Maximum) baseline (kilolambda) in map. UVWTFN.....Weighting function of (u-v) place. blank=>Uniform; 'NA'=>Natural UVBOX......(U,V) box size for smoothing. See HELP UVBOX DOGRIDCR...Apply gridding correction in maps? > 0 => yes. DOTV.......Display UV coverage on the TV? > 0 => yes. ZEROSP.....Zero-spacing value of I,Q,U,V,Weight or R,L,-,-,Weight. XTYPE......Convolution function type in X-direction 1=Pillbox, 2=exponential, 3=Sinc, 4=Exp*Sinc, 5=Spheroidal, 6=exp*BESSJ1(x)/x. <= 0 or > 5 -> 5. YTYPE.....Convolution function type in Y-direction XPARM.....Array containing parameters for XTYPE. See HELP UVnTYPE when n=convolution type. If STOKES='RL' or 'L' and XPARM(9) = 1.0, then the Lmap is made with freq = catfreq + XPARM(10) where units are Hz (for pseudo-cont line data). YPARM.....Array containing parameters for YTYPE. GUARD.....Fraction of the x and y radius for which uv samples are not allowed. < 0 => just enough to avoid mathematical errors in the convolution. 0 => 0.3 * SQRT(taper weight at 0.3 from edge). BADDISK...Disk drive #'s to avoid for scratch files

UVMAP: Task which makes a map from UV data on disk using AP DOCUMENTOR: T.J.Cornwell NRAO/VLA RELATED PROGRAMS: UVLOD,UVSRT,APCLN,IMAGR,CALIB PURPOSE UVMAP makes dirty maps and beams from (u,v) data using a Fast Fourier Transform (FFT). The data must be in the 'XY' sorted order produced by UVSRT so that gridding requires minimum core storage. The data are then convolved onto the regularly spaced grid which is used for the Fourier transform. Maps of several Stokes parameters, and a beam, can be made with one execution. A fairly complete description of the functions performed by UVMAP is given in Lecture 2 of the Proceedings of the NRAO-VLA Workshop on Synthesis Mapping. Observers who are unfamiliar with interferometry are recommended to study this volume. COMMENTS CHANNEL, NMAPS: Use 0. These keywords will be used with real spectral line data bases. OUTDISK : If OUTDISK = 0, the map and beam will be put on the same disk. The Q and U maps may be put on another disk. It is best to specify OUTDISK. IMSIZE,CELLSIZE : For effective CLEANing of the maps, the number of pixels per beam should be such that the pixel value immediately north or east of the beam center is no less than about 50 percent of the peak. In the gridded data (shown on the TV if DOTV=1) the furthest point from the corner should be no more than 1/4 of the full gridsize. However, if tapering is used, the outlying (u,v) points may not have any significant weight in the map. Furthermore, the CLEAN algorithm in APCLN will only CLEAN correctly a quarter of the map so that the dirty map size should be at least twice the size of the area to be CLEANed. The map should also be made large enough that no strong confusing sources are aliased by the FFT. Aliased sources or aliased sidelobes will not CLEAN properly and will limit the fluctuation level on your final map. UVMAP will make maps which have a power of two pixels on a side; between 32 and 4096 on the X-axis and between 32 and 2048 on the Y-axis. STOKES : When only the Stokes parameter I is requested, all parallel hand data are used. When multiple Stokes parameter maps are made only the records which contain all necessary correlators are included and hence only one dirty beam is necessary. When CLEANing be careful not to mix up dirty beams made with Stokes I and with other Stokes combinations. If you do not expect your source to show significant circular polarization, as is normally the case with galactic and extragalactic continuum sources, making a V map can be a useful diagnostic for calibration problems, correlator offsets, etc. The V map should be a pure noise map close to the theoretical sensitivity if your data base is well calibrated and edited. UVWTFN : The default uniform weighting option gives higher resolution than natural weighting. However, uniform weighting gives a signal to noise ratio that is about 30 percent lower. Natural weighting is therefore preferable for detection experiments. With uniform weighting the dirty beam size decreases slightly with larger maps, other parameters remaining unchanged. ZEROSP : To improve CLEANing of extended sources, the zero-spacing flux should be included in UVMAP. The weight assigned should normally be in the range 10-100 but you may need to experiment, as the optimal value depends on your (u,v) coverage. Inclusion of the zero-spacing flux will allow CLEAN to interpolate into the inner region of the (u,v) plane more accurately, provided that this flux does not exceed the average visibility at the short spacing by too much. You must also CLEAN deeply to derive the full benefit of this (see the EXPLAIN file for APCLN). Jacqueline van Gorkom claims that the only proper weight for the zero spacing flux density is the number of cells missing in the center of the uv plane as long as the zero spacing flux density doesn't greatly exceed the amount observed on the shortest baselines. UVBOX : Using UVBOX not equal to zero should, to some extent, suppress sidelobes due to unusual fluctuations in the u,v plane sampling such as occurs at the end of a long track, or in snapshots. XTYPE,YTYPE : The default convolution function Spheroidal (5) is now recommended for nearly all maps. This replaces the default function EXP*SINC (4) used prior to the 83jul15 version. SPECTRAL LINE : When making spectral line map from pseudo-continuum data the user may want to correct for the frequency difference between the channels stored in the R and L IF slots. At the moment this information is not stored in the header and so must be inserted by hand. To do this set XPARM(9) to 1.0 and set XPARM(10) to the channel spacing in HERTZ. EXECUTION TIMES : Typical execution times for running UVMAP in an otherwise empty VAX 11/780 with FPS120B array processor are : Time in minutes 4.0 * (D/500,000) **1.0 Get data 1.8 * (D/500,000) **0.5 * (M/1024) **0.3 Grid data 2.0 * (M/1024) **2.1 Do FFT 2.0 * (M/1024) **2.0 Write maps where M is the map size and D is the number of visibility points. Generally two maps (map and beam) are made with each execution. DISK SPACE : The amount of disk space allocated for the following maps is : 256 x 256 256 blocks 512 x 512 1024 blocks 1024 x1024 4096 blocks 2048 x2048 16384 blocks REFERENCES Proceedings of the NRAO-VLA Workshop on Synthesis Mapping 1982, ed. A.R.Thompson and L.R.D'Addario.