Table of Contents

OTF mapping

During On The Fly (OTF) mapping, the data are recorded continuously while the telescope is scanning across the field. A common Off position is used for each row. Compared with point by point mapping, OTF mapping can be twice or more times as fast.

Setting up an OTF map is fairly complex. Plan your observations in advance! A simple example is presented. For a full discussion of the considerations involved, please consult with the CSO staff.

Planning

The (interrelated) parameters of an OTF map are:

Observing

The UIP OTF_MAP command has a plethora of options. Only some will be discussed:

Caveats

Example

Here's an example of OTF mapping of CS near the Galactic center.

! tune receiver
! cs4-3 195.954217 GHz - frequency from Lovas catalog
! tune line in lsb so usb image avoids atmospheric water line at 183 GHz
lo cs4-3 /lsb /if 5.5 
! alternate syntax if line name is not in the catalog
lo /freq 195.9542 /lsb /if 5.5

! set up spectrometer
! 11 sec integration time = sqrt (cells/row) * integration per cell = sqrt (30) * 2 sec
spec 11 /ffts1w 5.5 /res /display kilauea:1

! track source
obs sgra*

! do six submaps, 3 x 2
! although illustrated as a loop, it is probably best to do this manually
for ii 1 to 3
 for jj 1 to 2

! offsets for submaps
! offset = cell size  submap dimension * submap offset from center = (20 arcsec) * (30 cells) * index
rao /field 20*30*(ii-2)
deco /field 20*30*(jj-0.5)

! otf submap, roughly 45 min total
! submap size: 10 x 10 arcmin 
! scan speed: 10 arcsec/sec
! => 2 sec integration per cell
! => 60 sec scan (row) length
! ramp time: 5 sec  - may need some adjustment
! cell size: 20 x 20 arcsec - roughly Nyquist sampling at 200 GHz
! zig: alternate scan direction w->e, e->w, etc.
! cal: every 10 rows, about every 15 min
! pause: 10 sec after cal
! designated off position in catalog: sgra*:off_position
otf 0 0 10 5 20 20 /dimension 30 30 /zig /cal 10 /pause 10 /designated_off 

! end loops
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