2/8 Normalize satellite timestamps across units

pyVPRM/VPRM.py

@@ -559,8 +559,7 @@ def sort_and_merge_by_timestamp(self, min_length_snow_period=21):
                         self.sat_imgs.sat_img["timestamps"].values
                         - np.datetime64(self.timestamp_start)
                     )
-                    / 1e9
-                    / (24 * 60 * 60),
+                    / np.timedelta64(1, "D"),
                     dtype=float,
                 )
             )

tests/test_satellite_timestamps.py

@@ -0,0 +1,65 @@
+"""Regression tests for satellite timestamp normalization."""
+
+import numpy as np
+import xarray as xr
+
+from pyVPRM.VPRM import vprm_preprocessor
+from pyVPRM.sat_managers.base_manager import satellite_data_manager
+
+
+def make_satellite_scene(scene_time, pixel_time):
+    """Build a one-pixel scene with microsecond-resolution acquisition time.
+
+    Parameters
+    ----------
+    scene_time : str
+        Scene timestamp interpreted as a NumPy datetime value.
+    pixel_time : str
+        Per-pixel acquisition timestamp interpreted at microsecond precision.
+
+    Returns
+    -------
+    pyVPRM.sat_managers.base_manager.satellite_data_manager
+        Scene containing one EVI value and its per-pixel timestamp.
+    """
+
+    dataset = xr.Dataset(
+        data_vars={
+            "evi": (("time", "y", "x"), np.ones((1, 1, 1))),
+            "timestamps": (
+                ("time", "y", "x"),
+                np.array([[[np.datetime64(pixel_time, "us")]]]),
+            ),
+        },
+        coords={
+            "time": [np.datetime64(scene_time, "us")],
+            "y": [0],
+            "x": [0],
+        },
+    )
+    return satellite_data_manager(sat_img=dataset)
+
+
+def test_sort_and_merge_normalizes_microsecond_timestamps_to_days():
+    """Convert microsecond timestamps to correct elapsed-day values.
+
+    Returns
+    -------
+    None
+        The test verifies that LOWESS receives elapsed days rather than all
+        timestamps being rounded to zero under ``datetime64[us]`` input.
+    """
+
+    preprocessor = object.__new__(vprm_preprocessor)
+    preprocessor.flux_tower_instances = None
+    preprocessor.satellite_indices = ["evi"]
+    preprocessor.sat_imgs = [
+        make_satellite_scene("2022-01-01", "2022-01-01"),
+        make_satellite_scene("2022-01-09", "2022-01-09"),
+    ]
+
+    preprocessor.sort_and_merge_by_timestamp(min_length_snow_period=None)
+
+    np.testing.assert_array_equal(
+        preprocessor.sat_imgs.sat_img["timestamps"].values[:, 0, 0], [0.0, 8.0]
+    )