From 7dab9d42fee50663d761cb9640371fc2c7f47592 Mon Sep 17 00:00:00 2001
From: j-atkins <106238905+j-atkins@users.noreply.github.com>
Date: Fri, 31 Jul 2026 16:07:44 +0200
Subject: [PATCH 1/2] new method for setting initial conditions for sampling
 variables

---
 src/virtualship/instruments/base.py | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/virtualship/instruments/base.py b/src/virtualship/instruments/base.py
index ce0f8324..e4e737c5 100644
--- a/src/virtualship/instruments/base.py
+++ b/src/virtualship/instruments/base.py
@@ -155,6 +155,26 @@ def execute(self, measurements: list, out_path: str | Path) -> None:
             self.simulate(measurements, out_path)
             print("\n")
 
+    def _sample_initial(
+        self,
+        pset: parcels.ParticleSet,
+        fieldset: parcels.FieldSet,
+        sensors_config: object,
+    ) -> None:
+        """Perform initial Field sampling with ParticleSet."""
+        for sensor in sensors_config:
+            if not (sensor.enabled and sensor.sensor_type in self.sensor_kernels):
+                raise ValueError(
+                    f"Attempted to initialise sensor '{sensor.sensor_type}' but it is not enabled or not in sensor_kernels."
+                )
+
+            fs_key = sensor.meta.fs_key
+            field = getattr(fieldset, fs_key)
+            particle_vars = [pv.name for pv in sensor.meta.particle_vars]
+
+            for var in particle_vars:
+                setattr(pset, var, field[pset.t, pset.z, pset.y, pset.x])
+
     def _get_copernicus_ds(
         self,
         time_buffer: float | None,

From 1529b4afdd7f95ec23295022ad164cdf5c9f971b Mon Sep 17 00:00:00 2001
From: j-atkins <106238905+j-atkins@users.noreply.github.com>
Date: Fri, 31 Jul 2026 16:08:04 +0200
Subject: [PATCH 2/2] add initial sampling step to all (non-underway)
 instruments

---
 src/virtualship/instruments/argo_float.py | 5 +++++
 src/virtualship/instruments/ctd.py        | 3 +++
 src/virtualship/instruments/drifter.py    | 3 +++
 src/virtualship/instruments/xbt.py        | 3 +++
 4 files changed, 14 insertions(+)

diff --git a/src/virtualship/instruments/argo_float.py b/src/virtualship/instruments/argo_float.py
index 96b8e4f0..029a0aec 100644
--- a/src/virtualship/instruments/argo_float.py
+++ b/src/virtualship/instruments/argo_float.py
@@ -324,6 +324,11 @@ def simulate(self, measurements, out_path) -> None:
             drift_days=[argo.drift_days for argo in measurements],
         )
 
+        # add initial conditions to sampling variables
+        self._sample_initial(
+            argo_float_particleset, fieldset, argo_float_config.sensors
+        )
+
         # define output file for the simulation
         out_file = ParticleFile(
             path=out_path,
diff --git a/src/virtualship/instruments/ctd.py b/src/virtualship/instruments/ctd.py
index 5b8cba61..1291890d 100644
--- a/src/virtualship/instruments/ctd.py
+++ b/src/virtualship/instruments/ctd.py
@@ -209,6 +209,9 @@ def simulate(self, measurements, out_path) -> None:
             winch_speed=[WINCH_SPEED for _ in measurements],
         )
 
+        # add initial conditions to sampling variables
+        self._sample_initial(ctd_particleset, fieldset, ctd_config.sensors)
+
         # define output file for the simulation
         out_file = ParticleFile(path=out_path, outputdt=OUTPUT_DT)
 
diff --git a/src/virtualship/instruments/drifter.py b/src/virtualship/instruments/drifter.py
index 3b52dc71..fe8b3738 100644
--- a/src/virtualship/instruments/drifter.py
+++ b/src/virtualship/instruments/drifter.py
@@ -154,6 +154,9 @@ def simulate(self, measurements, out_path) -> None:
             ],
         )
 
+        # add initial conditions to sampling variables
+        self._sample_initial(drifter_particleset, fieldset, drifter_config.sensors)
+
         # define output file for the simulation
         out_file = ParticleFile(
             path=out_path,
diff --git a/src/virtualship/instruments/xbt.py b/src/virtualship/instruments/xbt.py
index 9de23092..c59e6996 100644
--- a/src/virtualship/instruments/xbt.py
+++ b/src/virtualship/instruments/xbt.py
@@ -164,6 +164,9 @@ def simulate(self, measurements, out_path) -> None:
             fall_speed=[xbt.fall_speed for xbt in measurements],
         )
 
+        # add initial conditions to sampling variables
+        self._sample_initial(xbt_particleset, fieldset, xbt_config.sensors)
+
         out_file = ParticleFile(path=out_path, outputdt=OUTPUT_DT)
 
         # build kernel list from active sensors only