Minor changes towards issue 3135 (IMAP-Lo goodtimes)

[vineetbansal]

Change Summary

Overview

Minor changes in support for issue #3135

File changes

• imap_processing/lo/l1b/lo_l1b.py - increased precision for MET data - was causing issues when cross-checking against IMAP-Lo team's offline pipeline algorithm. Also made the code tolerant if we end up adding new species (besides 'O') in the future. Using existing constants when we can (added one new one - N_SPIN_ANGLE_BINS.

Testing

[Copilot]

Pull request overview

This PR makes small IMAP-Lo L1B “goodtimes”/background-rate processing updates to (1) increase MET precision for cross-checking against the IMAP-Lo team’s offline pipeline and (2) reduce brittleness when additional ion species are added in the future by replacing hard-coded dimensions and making some lookups more tolerant.

Changes:

• Replace hard-coded ESA/spin-bin dimensions in selected arrays with shared LO constants (and introduce N_SPIN_ANGLE_BINS).
• Make histogram species handling more tolerant when a species’ *_counts variable is absent (fallback to zeros).
• Increase gt_start_met / gt_end_met precision to float64 and relax attribute schema checking for background-rate variables.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
imap_processing/lo/l1b/lo_l1b.py	Updates array shapes to use constants, adds missing-species tolerance, increases MET precision, and changes how bgrates vars/attrs are collected.
imap_processing/lo/constants.py	Adds N_SPIN_ANGLE_BINS constant (60) to centralize spin-angle bin sizing.

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[tmplummer]

I didn't catch this before, but no epoch variable in the bgrates dataset? I'm pretty sure that will not be tolerated by SPDF.

[vineetbansal]

fixed

[tmplummer]

Suggested change

	lib_bgrates_ds = l1b_backgrounds_and_goodtimes_ds[background_rate_fields]
	lib_bgrates_ds.attrs = attr_mgr_l1b.get_global_attributes("imap_lo_l1b_bgrates")
	return lib_bgrates_ds, l1b_goodtimes_ds
	l1b_bgrates_ds = l1b_backgrounds_and_goodtimes_ds[background_rate_fields]
	l1b_bgrates_ds.attrs = attr_mgr_l1b.get_global_attributes("imap_lo_l1b_bgrates")
	return l1b_bgrates_ds, l1b_goodtimes_ds

[vineetbansal]

@tmplummer - not sure what I was smoking before, but fixed now.

[tmplummer]

It looks like a few of the changes inside of if statements are not getting exercised in unit testing. Is there any way you can add coverage for those?

          if bg_rate == 0.0:
-             bg_rate = bg_rate_anti_ram_nominal / c.BG_RATE_FLOOR_DIVISOR[elem]
+             bg_rate = bg_rate_anti_ram_nominal / c.BG_RATE_FLOOR_DIVISOR.get(elem, 1)
              sigma_bg_rate = bg_rate
          if sigma_bg_rate == 0.0:
              sigma_bg_rate = bg_rate

[tmplummer]

Thanks for adding the test coverage