TMC Five-Point Calibration Scan

This guide provides instructions for performing a five-point calibration scan with TMC.

The procedure is intended for operators, to establish pointing calibration solutions that will later be applied during science observations.

Overview

A five-point calibration scan requires the resources must be assigned to the subarray and subarray must be online and available to accept commands.

The calibration scan sequence includes:

• One pointing scan (reference) using the full configuration.

• Four offset scans using partial configuration.

Together, these five scans provide data to derive calibration solutions and calibration solutions are available for science observations.

Step-by-Step Procedure

1. Confirm Subarray state

   • Verify that the TMC Subarray Node is online, reachable, and available.

   • If not, assign resources and configure until available.

2. Perform five calibration scans

   The calibration requires five consecutive configuration + scan cycles:

   • One scan using a full configuration.

   • Four offset scans, each using a partial configuration that only changes the pointing offsets. All other subarray configuration parameters remain unchanged.

   For each cycle:

   • Send the appropriate Configure command (full or partial).

   • Send a Scan command.

   • Observe the state transitions: READY → SCANNING → READY.

   Note

   The procedure is the same regardless of whether the configuration is full or partial (offset scans). The difference lies only in the pointing offsets provided.

   Example offsets for partial configurations

   JSON file (example)	Offset details
   partial_configuration_1.json	CA offset = 0.0, IE offset = +5.0 arcsec
   partial_configuration_2.json	CA offset = 0.0, IE offset = −5.0 arcsec
   partial_configuration_3.json	CA offset = +5.0 arcsec, IE offset = 0.0
   partial_configuration_4.json	CA offset = −5.0 arcsec, IE offset = 0.0

3. Validate pointing

   After each scan, verify that the dishes have updated their actualPointing values and that no errors were reported in the command results.

   The Dish Leaf Node exposes this attribute, which can be monitored to verify that the commanded pointing offsets are correctly applied.

4. (Optional) Apply calibration for science scans

   Once all five calibration scans are complete:

   • Send a Configure_mid.json command with the science configuration.

   • TMC automatically fetch the calibration solutions from SDP using the addresses defined in receive_address_mid.json.

   • Confirm that calibration solutions are applied to the dishes.

   Note

   Applying calibration via Configure is a standard step before starting science observations. It is mentioned here only to highlight that the solutions obtained from the five-point scan will be applied at this stage.

Troubleshooting Calibration Issues

If one of the calibration steps fails:

• Check observation state transitions

  • Confirm the Subarray moves to SCANNING during each scan and returns to READY.

• Inspect Dish Leaf Nodes

  • Check the actualPointing attribute to confirm that commanded offsets are applied.

• Verify JSON payloads

  • Ensure offsets are correct and "partial_configuration": true is included.

• Check calibration availability

  • Confirm that SDP publishes calibration data at the expected addresses.

JSON Interface References

• TMC Configure schema

• Example partial configurations (for reference/testing):

  partial_configuration_1.json

  {
      "interface": "https://schema.skao.int/ska-tmc-configure/2.2",
      "transaction_id": "txn-....-00002",
      "pointing": {
          "target": {
              "ca_offset_arcsec": 0.0,
              "ie_offset_arcsec": 5.0
          }
      },
      "tmc": {
          "partial_configuration": true
      }
  }
  

  partial_configuration_2.json

  {
      "interface": "https://schema.skao.int/ska-tmc-configure/2.2",
      "transaction_id": "txn-....-00003",
      "pointing": {
          "target": {
              "ca_offset_arcsec": 0.0,
              "ie_offset_arcsec": -5.0
          }
      },
      "tmc": {
          "partial_configuration": true
      }
  }
  

  partial_configuration_3.json

  {
      "interface": "https://schema.skao.int/ska-tmc-configure/2.2",
      "transaction_id": "txn-....-00004",
      "pointing": {
          "target": {
              "ca_offset_arcsec": 5.0,
              "ie_offset_arcsec": 0.0
          }
      },
      "tmc": {
          "partial_configuration": true
      }
  }
  

  partial_configuration_4.json

  {
      "interface": "https://schema.skao.int/ska-tmc-configure/2.2",
      "transaction_id": "txn-....-00005",
      "pointing": {
          "target": {
              "ca_offset_arcsec": -5.0,
              "ie_offset_arcsec": 0.0
          }
      },
      "tmc": {
          "partial_configuration": true
      }
  }
  

• receive_address_mid.json (used mainly for testing)