SOS: SKA Observation Simulator

Simulate SKA1_Mid visibility (radio observations) using CASA toolkit. Create synthetic radio sky models at arbitrary redshifts and simulate realistic interferometric observations.

Figure: UV coverage from 15 min of simulated observation with SKA1_Mid.

Features

• Radio Sky Modeling: Create synthetic radio halo models at multiple redshifts
• Cosmological Calculations: K-corrections and angular diameter distances using ΛCDM cosmology (Planck 2015)
• Visibility Simulation: Simulate interferometric measurements using CASA toolkit
• Flexible Configuration: YAML-based configuration for reproducible simulations
• Well-Tested Code: Comprehensive unit tests for all utilities
• Modern Python: Python 3.8+ with full type hints and documentation
• Clean Architecture: Modular package structure for maintainability

Requirements

• Python: 3.8 or higher
• CASA: 4.7.2 or higher (for visibility simulations)
• Dependencies: See requirements.txt

Quick Start

Installation

# Clone repository
git clone https://github.com/deepakdeo/SOS.git
cd SOS

# Install package
pip install -e .

# For development (includes testing tools)
pip install -e ".[dev]"

Basic Usage

1. Creating Model Sky Images

from sos.core.image_maker import ImageMaker, CosmologyCalculator
from sos.utils.logger import setup_logger

# Set up logging
logger = setup_logger(__name__)

# Create image maker
image_maker = ImageMaker(
    cell_size="0.01arcsec",
    image_size=7200,
    reference_frequency="9.2GHz",
)

# Create models at multiple redshifts
images = image_maker.create_model_sky(
    redshifts=[0.1, 0.5, 1.0],
    linear_size_mpc=0.5,
    reference_flux_jy=0.6,
    spectral_index=-1.6,
)

2. Using Configuration Files

from sos.config.config_loader import ConfigLoader

# Load configuration from YAML
config = ConfigLoader("config.yaml")

# Access values with dot notation
redshifts = config.get("simulation.redshifts")
spectral_index = config.get("simulation.spectral_index")

3. Simulating Visibility (in CASA)

from sos.core.visibility_sim import VisibilitySimulator

# Within CASA environment
simulator = VisibilitySimulator(
    config_file="ska_mid197_new.cfg",
    spectral_index=-1.6,
    channels=1,
)

# Simulate visibility
ms_path = simulator.simulate_visibility(
    image_path="modelsky_0.1.im",
    output_ms_path="visibility_0.1.ms",
    num_scans=1,
    scan_duration_sec=900.0,
)

Project Structure

SOS/
├── sos/                          # Main package
│   ├── __init__.py
│   ├── constants.py              # Global constants
│   ├── core/                     # Core simulation modules
│   │   ├── image_maker.py        # Sky model creation
│   │   └── visibility_sim.py     # Visibility simulation
│   ├── config/                   # Configuration management
│   │   └── config_loader.py      # YAML config handling
│   └── utils/                    # Utility functions
│       ├── coordinates.py        # RA/DEC conversions
│       ├── logger.py             # Logging setup
│       └── validators.py         # Input validation
├── tests/                        # Unit tests
├── examples/                     # Example scripts & configs
├── setup.py                      # Setup configuration
├── pyproject.toml               # Project metadata
├── requirements.txt             # Runtime dependencies
├── README.md                    # This file
└── ska_uv.png                  # Sample UV coverage

Contents

1. make_img.py : Creates toy-model radio sky based on inputs provided
2. SOS.py : Simulates SKA visibility when a radio sky and SKA configuration file is provided
3. ska_mid197.cfg : Configuration file with 197 antennas (including MeerKAT)
4. ska_mid133.cfg : Configuration file with 133 antennas (excluding MeerKAT)
5. SOSv2.py : SKA simulation for CASA versions > 4.7.2
6. ska_mid197_new.cfg : New configuration for CASA 4.7.2+ (197 antennas)
7. ska_mid133_new.cfg : New configuration for CASA 4.7.2+ (133 antennas)
8. ska_uv.png : Sample UV coverage (15-min observation)

SOS works with CASA 4.7.2 or earlier
SOSv2.py requires CASA versions > 4.7.2

Configuration

Create a config.yaml file to customize your simulation:

simulation:
  redshifts: [0.05, 0.1, 0.5, 1.0]
  spectral_index: -1.6
  channels: 1
  frequency_resolution_mhz: 50.0

source:
  linear_size_mpc: 0.5
  reference_flux_jy: 0.6
  source_type: 1  # 1=extended, 2=point, 3=mixed

image:
  cell_size: "0.01arcsec"
  image_size: 7200
  reference_frequency: "9.2GHz"

telescope:
  config_file: "ska_mid197_new.cfg"
  elevation_limit: 17.0

See examples/config_example.yaml for full configuration options.

Testing

# Run all tests
pytest

# Run with coverage
pytest --cov=sos

# Run tests in parallel
pytest -n auto

Module Overview

sos.constants

Global constants used throughout the package:

• Coordinate conversion factors
• Astronomy constants (speed of light, Planck 2015 cosmology)
• Telescope and observation defaults
• Source model parameters

sos.core.image_maker

• CosmologyCalculator: ΛCDM distance and angular size calculations
• ImageMaker: Create synthetic radio sky models

sos.core.visibility_sim

• VisibilitySimulator: Simulate interferometric visibility measurements

sos.config.config_loader

• ConfigLoader: Load and validate YAML configurations
• Nested key access with dot notation

sos.utils.coordinates

Consolidated coordinate conversion functions:

• ra_arcsec_to_hms() - RA to HH:MM:SS format
• dec_arcsec_to_dms() - DEC to ±DD:MM:SS format
• parse_ra_hms() - Parse RA string to decimal
• parse_dec_dms() - Parse DEC string to decimal

sos.utils.validators

Comprehensive input validation:

• Redshift ranges and spectral index bounds
• File existence and format checking
• Coordinate string format validation
• Image parameter validation

sos.utils.logger

Centralized logging with console and file output.

Improvements from Original

✅ Modular Architecture: Well-organized package structure
✅ No Duplication: Consolidated duplicate functions
✅ Type Hints: Full Python 3.8+ annotations
✅ Configuration Files: YAML-based configuration system
✅ Comprehensive Logging: Professional logging throughout
✅ Input Validation: Early error detection
✅ Unit Tests: 25+ comprehensive tests
✅ Better Documentation: Examples and API docs

Troubleshooting

CASA Not Found

ImportError: CASA toolkit not available

Solution: Run SOS scripts within CASA environment:

casa -c "execfile('script.py')"

Configuration File Not Found

FileNotFoundError: File not found: config.yaml

Solution: Specify full path or ensure file exists in current directory.

Coordinate Conversion Errors Check coordinate string format:

• RA: "HHhMMmSS.Ss" (e.g., "04h30m15.50s")
• DEC: "±DDdMMmSS.Ss" (e.g., "-20d30m45.50s")

Examples

See examples/ directory for complete examples:

1. example_image_maker.py - Create model images with cosmological scaling
2. example_config.py - Load and use YAML configurations
3. config_example.yaml - Complete configuration template

References

• SKA: Square Kilometre Array - https://www.skao.org/
• CASA: Common Astronomy Software Applications - https://casa.nrao.edu/

License

MIT License - See LICENSE file

Authors

• Deepak Deo
• Dr. Ruta Kale (NCRA-TIFR)

Contributing

See CONTRIBUTING.md for guidelines.

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Version 1.0 (refactored) | Updated February 2026