Shared Risk Observing Program

by Stephan W. Witz last modified Apr 29, 2013 by Stephan Witz

The Shared Risk Observing (SRO) program allows observers access to capabilities that can be set up via the Observation Preparation Tool and run through the dynamic scheduler (without intervention), but are not well tested. In semester 2013B this program provides a number of extended correlator capabilities:

  1. Data rates as high as 60 MB/s and integration times as short as 50msec.
  2. Use of the 3-bit samplers in any frequency band, with subbands which can be narrower than 128 MHz. All subbands within a baseband must be contiguous, and must have the same bandwidth.  Note that it makes little sense to use the 3-bit samplers for L and S bands, where the 8-bit system cover the entire available observing band with higher dynamic range and better sensitivity.
  3. Mixing 3- and 8-bit basebands (3-bit AC and 8-bit BD, or vice versa) in the same correlator configuration.
  4. More flexible Baseline Board stacking, with the ability to assign any number of Baseline Board pairs (BlBPs) to each subband, rather than only powers of two. These configurations are significantly more complex, and the observer is urged to read the section on spectral line capabilities (above) with care. Some examples of possible shared risk configurations are given below.
  5. Access to the 3-bit samplers for observations with (up to 3) subarrays.

Those proposing for Shared Risk Observing must explicitly define their correlator set-up(s) in the PST, instead of using the GOST. Those in doubt as to whether their proposed setups are Shared Risk or Resident Shared Risk are encouraged to get in touch with NRAO staff well before the proposal deadline.

 

Shared risk observations: spectral line configurations

Arbitrary Baseline Board stacking using the 8-bit samplers is allowed under the Shared Risk Observing (SRO) program for semester 2013B. The basic capabilities are given in the table above (Subband Bandwidth and Spectral Resolution Options), the difference being that the number of Baseline Board pairs assigned to a subband (nBlBP) can be any integer up to 64, rather than only a power of two. Similarly the interaction between BlBP stacking the number of independent subbands is as described above, but this interaction is more subtle and potentially confusing in the shared risk case.

To give some idea of the possibilities, the following tables give two examples of possible shared risk configurations. The SRCT display shows how the Baseline Boards are used to process the individual subbands. The cyan boxes show the Baseline Boards used to process data from baseband A0/C0, while the yellow boxes show Baseline Boards used to process data from baseband B0/D0.

Shared Risk Configuration Example #1
BasebandSubbandPol'n products Spectral channelsnBlBP
A0/C0 sb0 RR 10240 40
A0/C0 sb1 LL 768 3
A0/C0 sb2 RR,LL 2176 17
B0/D0 sb0 RR 256 1
B0/D0 sb1 RR,LL 384 3
SRCT display: Correlator configuration figure: sro1_8bit_ac40+3+17_bd1+3.png

 

 

 

Shared Risk Configuration Example #2
BasebandSubbandPol'n products Spectral channelsnBlBP
A0/C0 sb0 RR 4352 17
A0/C0 sb1 RR, LL 1152 9
B0/D0 sb0 RR,RL,LR,LL 192 3
B0/D0 sb1 RR, LL
4480 35
SRCT display: Correlator configuration figure: sro2_8bit_ac17+9_bd3+35.png

 

Note that the individual subbands can have different bandwidths, and those bandwidths may be chosen completely independently of the number of spectral channels in each subband. So for instance a subband with bandwidth 2 MHz and 1152 spectral channels would have a channel separation of 2 MHz/1152= 1.736 kHz; but the observer could equally well choose a bandwidth of 64 MHz for that subband, leading  to a channel separation of 64 MHz/1152=  55.56 kHz.

Again, can be difficult to distinguish between configurations which are available as Shared Risk Observing (SRO), and those which are only available through the Resident Shared Risk Observing (RSRO) program. If in doubt, please consult with NRAO staff.