Variable drifter depth

src/virtualship/instruments/drifter.py

@@ -73,8 +73,12 @@ def __init__(self, expedition, from_data):
         }
         limit_spec = {
             "spatial": False,  # no spatial limits; generate global fieldset
-            "depth_min": 1.0,  # [meters]
-            "depth_max": 1.0,  # [meters]
+            "depth_min": abs(
+                expedition.instruments_config.drifter_config.depth_meter
+            ),  # [meters]
+            "depth_max": abs(
+                expedition.instruments_config.drifter_config.depth_meter
+            ),  # [meters]
         }
 
         super().__init__(

tests/instruments/test_drifter.py

@@ -1,23 +1,46 @@
 """Test the simulation of drifters."""
 
 import datetime
+from typing import ClassVar
 
 import numpy as np
 import xarray as xr
-
 from parcels import FieldSet
+
 from virtualship.instruments.drifter import Drifter, DrifterInstrument
 from virtualship.models import Location, Spacetime
 from virtualship.models.expedition import Waypoint
 
+BASE_TIME = datetime.datetime.strptime("1950-01-01", "%Y-%m-%d")
+LIFETIME = datetime.timedelta(days=1)
 
-def test_simulate_drifters(tmpdir) -> None:
+DEPLOY_DEPTH = -1.0  # default
+
+
+def create_dummy_expedition():
     # arbitrary time offset for the dummy fieldset
-    base_time = datetime.datetime.strptime("1950-01-01", "%Y-%m-%d")
 
-    CONST_TEMPERATURE = 1.0  # constant temperature in fieldset
+    class DummyExpedition:
+        class schedule:
+            waypoints: ClassVar = [
+                Waypoint(
+                    location=Location(
+                        1, 2
+                    ),  # any location is fine for dummy, actual drifter deployment locations are defined in the test functions
+                    time=BASE_TIME,
+                ),
+            ]
+
+        class instruments_config:
+            class drifter_config:
+                lifetime = LIFETIME
+                depth_meter = DEPLOY_DEPTH
 
-    LIFETIME = datetime.timedelta(days=1)
+    return DummyExpedition()
+
+
+def test_simulate_drifters(tmpdir) -> None:
+    CONST_TEMPERATURE = 1.0  # constant temperature in fieldset
 
     v = np.full((2, 2, 2), 1.0)
     u = np.full((2, 2, 2), 1.0)
@@ -29,8 +52,8 @@ def test_simulate_drifters(tmpdir) -> None:
             "lon": np.array([0.0, 10.0]),
             "lat": np.array([0.0, 10.0]),
             "time": [
-                np.datetime64(base_time + datetime.timedelta(seconds=0)),
-                np.datetime64(base_time + datetime.timedelta(days=3)),
+                np.datetime64(BASE_TIME + datetime.timedelta(seconds=0)),
+                np.datetime64(BASE_TIME + datetime.timedelta(days=3)),
             ],
         },
     )
@@ -40,37 +63,22 @@ def test_simulate_drifters(tmpdir) -> None:
         Drifter(
             spacetime=Spacetime(
                 location=Location(latitude=0.5, longitude=0.5),
-                time=base_time + datetime.timedelta(days=0),
+                time=BASE_TIME + datetime.timedelta(days=0),
             ),
-            depth=0.0,
+            depth=DEPLOY_DEPTH,
             lifetime=datetime.timedelta(hours=2),
         ),
         Drifter(
             spacetime=Spacetime(
                 location=Location(latitude=1, longitude=1),
-                time=base_time + datetime.timedelta(hours=20),
+                time=BASE_TIME + datetime.timedelta(hours=20),
             ),
-            depth=0.0,
+            depth=DEPLOY_DEPTH,
             lifetime=None,
         ),
     ]
 
-    # dummy expedition for DrifterInstrument
-    class DummyExpedition:
-        class schedule:
-            # ruff: noqa
-            waypoints = [
-                Waypoint(
-                    location=Location(1, 2),
-                    time=base_time,
-                ),
-            ]
-
-        class instruments_config:
-            class drifter_config:
-                lifetime = LIFETIME
-
-    expedition = DummyExpedition()
+    expedition = create_dummy_expedition()
     from_data = None
 
     drifter_instrument = DrifterInstrument(expedition, from_data)
@@ -99,3 +107,83 @@ class drifter_config:
         assert np.all(temp[np.isfinite(temp)] == CONST_TEMPERATURE), (
             f"measured temperature does not match {drifter_i=}"
         )
+
+
+def test_drifter_depths(tmpdir) -> None:
+    CONST_TEMPERATURE = 1.0  # constant temperature in fieldset
+
+    v = np.full((2, 2, 2, 2), 1.0)
+    u = np.full((2, 2, 2, 2), 1.0)
+    t = np.full((2, 2, 2, 2), CONST_TEMPERATURE)
+
+    # different values at depth (random)
+    v[:, -1, :, :] = 1.0 * np.random.randint(0, 10)
+    u[:, -1, :, :] = 1.0 * np.random.randint(0, 10)
+    t[:, -1, :, :] = CONST_TEMPERATURE * np.random.randint(0, 10)
+
+    fieldset = FieldSet.from_data(
+        {"V": v, "U": u, "T": t},
+        {
+            "time": [
+                np.datetime64(BASE_TIME + datetime.timedelta(seconds=0)),
+                np.datetime64(BASE_TIME + datetime.timedelta(days=3)),
+            ],
+            "depth": np.array([-10, 0]),
+            "lat": np.array([0.0, 10.0]),
+            "lon": np.array([0.0, 10.0]),
+        },
+    )
+
+    # drifters to deploy (same time and location, but different depths)
+    drifters = [
+        Drifter(
+            spacetime=Spacetime(
+                location=Location(latitude=5.0, longitude=5.0),
+                time=BASE_TIME + datetime.timedelta(days=0),
+            ),
+            depth=DEPLOY_DEPTH,
+            lifetime=datetime.timedelta(hours=12),
+        ),
+        Drifter(
+            spacetime=Spacetime(
+                location=Location(latitude=5.0, longitude=5.0),
+                time=BASE_TIME + datetime.timedelta(days=0),
+            ),
+            depth=DEPLOY_DEPTH - 5.0,  # different drogue depth
+            lifetime=datetime.timedelta(hours=12),
+        ),
+    ]
+
+    expedition = create_dummy_expedition()
+    from_data = None
+
+    drifter_instrument = DrifterInstrument(expedition, from_data)
+    out_path = tmpdir.join("out.zarr")
+
+    drifter_instrument.load_input_data = lambda: fieldset
+    drifter_instrument.simulate(drifters, out_path)
+
+    # test if output is as expected
+    results = xr.open_zarr(out_path)
+
+    assert len(results.trajectory) == len(drifters)
+
+    drifter_surface = results.isel(trajectory=0)
+    drifter_depth = results.isel(trajectory=1)
+
+    assert drifter_surface.z[0] > drifter_depth.z[0], (
+        "Surface drifter should be at shallower depth than deeper drifter"
+    )
+
+    surface_depths = drifter_surface.z.values
+    depth_depths = drifter_depth.z.values
+    assert np.all(surface_depths[~np.isnan(surface_depths)] == surface_depths[0]), (
+        "Surface drifter depth should be constant"
+    )
+    assert np.all(depth_depths[~np.isnan(depth_depths)] == depth_depths[0]), (
+        "Depth drifter depth should be constant"
+    )
+
+    assert drifter_surface.temperature[0] != drifter_depth.temperature[0], (
+        "Surface and deeper drifter should have different temperature measurements"
+    )