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SMA Data Format



The SMA data format

Raw SMA data is recorded in a variety of files contained in a single directory. The data format is MIR, which is IDL tailored to work with SMA data. The data are binary so detailed file format information is required to unpack it.

The SMA has had two correlators: ASIC, and (exclusively since 2016) SWARM. ASIC had 48 spectral windows which could each have a different frequency resolution. While at different points in the array's history, ASIC has had 2GHz or 4GHz bandwidth. SWARM on the other hand is more straightforward. It has just four chunks (SWARM terminology for spectral windows) of 2GHz each, with a fixed frequency resolution of 140kHz.

To complicate matters, the transition from ASIC to SWARM was gradual, so between 2014 and 2016, data had the 48 ASIC windows in addition to a varying number of SWARM chunks.


What files are in the SMA data directory?

You can find a description of the files at What's in the SMA raw data directory?. As the data is binary, detailed formatting information is needed to unpack it.


What were the setup and sources for this dataset?

You have a few options for getting an overview of a dataset - including the correlator(s), sources and tuning. In addition to the options below you can check the observing report for non-proprietary data which is linked from the SMA Data Archive, or email smarequester@cfa.harvard.edu.

When the spectral windows/chunks are given they will be numbered as sX. The list below shows the set-ups you will encounter.

s01-s48 = ASIC only
s01-s49 = ASIC + SWARM chunk 1
s01-s50 = ASIC + SWARM chunks 1 & 2
s01-s51 = ASIC + SWARM chunk 1,2 & 3
s01-s52 = ASIC + SWARM chunk 1,2,3 & 4
s1-s4 = SWARM only


1) SMARechunker -L

[root@rtdc9 ~]$ SMARechunker -i /sma/data/science/mir_data.2015/151230_04:37:57/ -L
The file has 3450 scans
and contains data for the following chunks:
c1
s01 s02 s03 s04 s05 s06 s07 s08 s09 s10 s11 
s12 s13 s14 s15 s16 s17 s18 s19 s20 s21 s22 
s23 s24

2) whatishere

[root@rtdc9 ~]$ whatishere /sma/data/science/mir_data.2015/151230_04:37:57/
|>---------------------------------------------------------------------
LO Freq. (Rx0): 349.993 GHz
UT Start:   4.6281    UT Stop:   19.1997
Maximum baselines:    28    Max. ok baselines:    28
Minimum baselines:    28
Number of scans:    3450    Number of ok scans: 3305
Number of sources:    13
(In following list, names are truncated at 16 characters)
       #  Name           #Scans   Scan Range   Avg UTH    HA min  HA max
       1  3c84             208   (   0-1448)    9.1824    -2.53    3.72
       2  Vesta             41   (   7-  47)    4.7541     0.33    0.50
       3  3c84_LR          243   (  53-1406)    8.3812    -2.29    3.54
       4  0510+180_LR      134   ( 179-1974)    9.4365    -3.58    4.16
       5  0510+180         163   ( 189-2087)    9.3520    -3.54    4.65
       6  S255IR-SMA1     1367   ( 199-2409)   10.3135    -4.55    4.99
       7  0532+075_LR       22   ( 874- 992)    8.6516    -0.96   -0.45
       8  0532+075          43   ( 886-1112)    9.0319    -0.91    0.06
       9  0739+016_LR       33   (2090-2316)   14.1149     2.17    3.15
      10  0739+016          54   (2102-2433)   14.5137     2.22    3.65
      11  Callisto          34   (2437-3362)   15.6116    -0.26    3.45
      12  3c279_LR         408   (2470-3405)   16.9727    -1.47    2.29
      13  3c279            555   (2510-3449)   17.5277    -1.30    2.48
|>---------------------------------------------------------------------
|> No high frequency receiver data found.
|>---------------------------------------------------------------------

3) IDL select command

IDL> readdata, dir='/sma/data/science/mir_data.2015/151230_04:37:57'
IDL> select
% Compiled module: SELECT.
All Sources:   3c84 Vesta 3c84_LR 0510+180_LR 0510+180 S255IR-SMA1 0532+075_LR 0532+075 0739+016_LR 0739+016 Callisto 3c279_LR 3c279
All Baselines:  1-2 1-3 1-4 1-5 1-6 1-7 1-8 2-3 2-4 2-5 2-6 2-7 2-8 3-4 3-5 3-6 3-7 3-8 4-5 4-6 4-7 4-8 5-6 5-7 5-8 6-7 6-8 7-8
All Recs:  345
All Bands:  c1 s01 s02 s03 s04 s05 s06 s07 s08 s09 s10 s11 s12 s13 s14 s15 s16 s17 s18 s19 s20 s21 s22 s23 s24
All Sidebands :  l u
All Polarization states:  Unknown RR RL LR LL LH LV RH RV HR HL HH HV VR VL VH VV
All Integrations: 0-3448



SMA Correlators

The current SWARM correlator was introduced in 2014. Initaially its spectral windows (or chunks in SWARM terminology) were added to the 48 ASIC spectral windows. Eventually in 2016 ASIC was switched off leaving just the 4 SWARM chunks.

CORRELATOR DATES DETAILS NOTES
ASIC 2003-2016
  • 2GHz bandwidth.
  • 48 spectral windows, each of which could have a different number of channels.
  • The spectral windows are labeled s01-s48.
  • Some windows may be missing from certain data.
SWARM 2014-present
  • 4 chunks of 2GHz bandwidth each.
  • Fixed frequency resolution of 140kHz.
  • The chunks were added one at a time from 2014 onwards. Their labels were appended to the ASIC numbers as s49-s52.
  • When ASIC was turned off they were relabeled as s1-s4.
  • The data from the early days of was SWARM is test quality only and you will want to check the quality.



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