Add a blend method to create temporal RGB from MultiScene

satpy/multiscene/__init__.py

@@ -1,4 +1,4 @@
 """Functions and classes related to MultiScene functionality."""
 
-from ._blend_funcs import stack, timeseries  # noqa
+from ._blend_funcs import stack, temporal_rgb, timeseries  # noqa
 from ._multiscene import MultiScene  # noqa

satpy/multiscene/_blend_funcs.py

@@ -178,3 +178,20 @@ def timeseries(datasets):
     res = xr.concat(expanded_ds, dim="time")
     res.attrs = combine_metadata(*[x.attrs for x in expanded_ds])
     return res
+
+
+def temporal_rgb(
+        data_arrays: Sequence[xr.DataArray],
+) -> xr.DataArray:
+    """Combine a series of datasets as a temporal RGB.
+
+    The first dataset is used as the Red component of the new composite, the second as Green and the third as Blue.
+    All the other datasets are discarded.
+    """
+    from satpy.composites import GenericCompositor
+
+    compositor = GenericCompositor("temporal_composite")
+    composite = compositor((data_arrays[0], data_arrays[1], data_arrays[2]))
+    composite.attrs = data_arrays[2].attrs
+
+    return composite

satpy/multiscene/_multiscene.py

@@ -338,7 +338,7 @@ def blend(
         then assigns those datasets to the blended scene.
 
         Blending functions provided in this module are :func:`stack`
-        (the default) and :func:`timeseries`, but the Python built-in
+        (the default), :func:`timeseries`, and :func:`temporal_rgb`, but the Python built-in
         function :func:`sum` also works and may be appropriate for
         some types of data.
 

satpy/tests/multiscene_tests/test_blend.py

@@ -234,7 +234,6 @@ def test_blend_two_scenes_bad_blend_type(self, multi_scene_and_weights, groups):
 
         simple_groups = {DataQuery(name='CloudType'): groups[DataQuery(name='CloudType')]}
         multi_scene.group(simple_groups)
-
         weights = [weights[0][0], weights[1][0]]
         stack_func = partial(stack, weights=weights, blend_type="i_dont_exist")
         with pytest.raises(ValueError):
@@ -390,3 +389,46 @@ def _check_stacked_metadata(data_arr: xr.DataArray, exp_name: str) -> None:
     assert 'sensor' not in data_arr.attrs
     assert 'platform_name' not in data_arr.attrs
     assert 'long_name' not in data_arr.attrs
+
+
+class TestTemporalRGB:
+    """Test the temporal RGB blending method."""
+
+    @pytest.fixture
+    def nominal_data(self):
+        """Return the input arrays for the nominal use case."""
+        da1 = xr.DataArray([1, 0, 0], attrs={'start_time': datetime(2023, 5, 22, 9, 0, 0)})
+        da2 = xr.DataArray([0, 1, 0], attrs={'start_time': datetime(2023, 5, 22, 10, 0, 0)})
+        da3 = xr.DataArray([0, 0, 1], attrs={'start_time': datetime(2023, 5, 22, 11, 0, 0)})
+
+        return [da1, da2, da3]
+
+    @pytest.fixture
+    def expected_result(self):
+        """Return the expected result arrays."""
+        return [[1, 0, 0], [0, 1, 0], [0, 0, 1]]
+
+    @staticmethod
+    def _assert_results(res, expected_start_time, expected_result):
+        assert res.attrs['start_time'] == expected_start_time
+        np.testing.assert_equal(res.data[0, :], expected_result[0])
+        np.testing.assert_equal(res.data[1, :], expected_result[1])
+        np.testing.assert_equal(res.data[2, :], expected_result[2])
+
+    def test_nominal(self, nominal_data, expected_result):
+        """Test that nominal usage with 3 datasets works."""
+        from satpy.multiscene import temporal_rgb
+
+        res = temporal_rgb(nominal_data)
+
+        self._assert_results(res, nominal_data[-1].attrs['start_time'], expected_result)
+
+    def test_extra_datasets(self, nominal_data, expected_result):
+        """Test that only the first three arrays affect the usage."""
+        from satpy.multiscene import temporal_rgb
+
+        da4 = xr.DataArray([0, 0, 1], attrs={'start_time': datetime(2023, 5, 22, 12, 0, 0)})
+
+        res = temporal_rgb(nominal_data + [da4,])
+
+        self._assert_results(res, nominal_data[-1].attrs['start_time'], expected_result)