ADD: IMD Reader

[syedhamidali]

• Closes ADD: Support for India Meteorological Department (IMD) radar NetCDF format #368
• Tests added
• Changes are documented in history.md

Summary

Add a new xarray backend (IMDBackendEntrypoint, engine="imd") for reading India Meteorological Department (IMD) radar NetCDF files, which use a NetCDF4 container with an IRIS-inspired variable layout. IMD radars store one sweep per file; this PR adds:

• open_imd_datatree() — reads a single file or a list of files and assembles a multi-sweep volume as a CfRadial2-compatible DataTree
• group_imd_files() — groups a directory of mixed IMD files into per-volume file lists by filename stem
• open_imd_volumes() — batch-processes directories into a nested DataTree with vcp_NN volume nodes

Moments are mapped to CfRadial2/FM 301 names (T→DBTH, Z→DBZH, V→VRADH, W→WRADH, ZDR, HCLASS) with canonical attributes. Unit conversions are applied where needed (pulseWidth μs→s, waveLength cm→frequency Hz).

Code ported from radarx with improvements for xradar integration.

Test Data

IMD sample files (Jaipur S-band, 2 volumes × 10 sweeps) added to open-radar-data v0.7.0 under the IMD/ prefix. Requires open-radar-data>=0.7.0.

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[kmuehlbauer]

@syedhamidali Nice to see this landing in xradar! ❤️ Thank you for working through this.

It would be great to have the test data in open_radar_data to use in the test suite. The notebook need to move to myst markdown. Some dates in file headers needs adjustment, too.

[kmuehlbauer]

CI didn't kick in, I'm going to close/reopen.

[kmuehlbauer]

Had to fix the merge conflict. Now CI did run.

[kmuehlbauer]

@syedhamidali Please pin open-radar-data to >=0.7.0. We'll have to wait for conda-forge, though.

[kmuehlbauer]

@syedhamidali Thanks, follow-up here: conda-forge/open-radar-data-feedstock#21. After this get's merged, the package should be available after another hour or two.

[codecov]

Codecov Report

❌ Patch coverage is 99.11111% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.15%. Comparing base (230dbf5) to head (06a3a7a).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
xradar/io/backends/imd.py	99.10%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #367      +/-   ##
==========================================
+ Coverage   93.94%   94.15%   +0.21%     
==========================================
  Files          28       29       +1     
  Lines        6191     6416     +225     
==========================================
+ Hits         5816     6041     +225     
  Misses        375      375              

Flag	Coverage Δ
notebooktests	0.00% <0.00%> (ø)
unittests	94.15% <99.11%> (+0.21%)	⬆️

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[kmuehlbauer]

@syedhamidali Thanks, this looks really good.

[syedhamidali]

@kmuehlbauer Thank you for reviewing it!

[kmuehlbauer]

@syedhamidali Please merge at your discretion.