HIT L0 - change epoch to center collection time

[vmartinez-cu]

This PR changes the epoch values used for science data to be the center collection time for that data. Previously, the starting time was being used.

Closes #1838

Updated Files

• imap_processing/hit/l0/decom_hit.py
  • Created an array of mean epoch values in science frames as the new epoch coordinate in the dataset

[Copilot]

Pull Request Overview

The PR updates the science data epoch values to use the center of each collection frame rather than the starting time.

• Compute mean of first and last packet times for each science frame
• Replace NumPy array accumulation with a Python list
• Assign new epoch coordinate as an xarray DataArray

Comments suppressed due to low confidence (2)

imap_processing/hit/l0/decom_hit.py:314

• [nitpick] Using "epoch" as the dimension name may conflate the index with its values; consider using a more descriptive dimension like "frame" and assign "epoch" solely as the coordinate name for clarity.

    sci_dataset.coords["epoch"] = xr.DataArray(epoch_per_science_frame, dims=["epoch"])

imap_processing/hit/l0/decom_hit.py:309

• Building the coordinate array by appending to a Python list may be less efficient; consider accumulating values in a NumPy array or converting the final list to np.array(epoch_per_science_frame) before creating the DataArray for better performance.

        epoch_per_science_frame.append(

[Copilot]

The original epoch variable is not dropped before assigning a new coordinate. Consider calling sci_dataset = sci_dataset.drop_vars("epoch") to avoid conflicts or duplicate variables.

Suggested change

	# Add new data variables to the dataset and update epoch coordinate
	# Add new data variables to the dataset and update epoch coordinate
	sci_dataset = sci_dataset.drop_vars("epoch", errors="ignore") # Drop existing epoch variable if it exists

[vmartinez-cu]

sci_dataset.coords["epoch"] = xr.DataArray(epoch_per_science_frame, dims=["epoch"]) replaces the epoch coordinate with the new values and doesn't need to be dropped first

[sdhoyt]

Nice!

[sdhoyt]

Is it possible to check the center epoch in one of your existing unit tests?