diff --git a/esbo_etc/classes/IRadiant.py b/esbo_etc/classes/IRadiant.py
index a913f9c..756ad4d 100644
--- a/esbo_etc/classes/IRadiant.py
+++ b/esbo_etc/classes/IRadiant.py
@@ -9,7 +9,7 @@ class IRadiant(ABC):
     in the beam.
     """
     @abstractmethod
-    def calcSignal(self) -> Tuple[SpectralQty, str]:
+    def calcSignal(self) -> Tuple[SpectralQty, str, float]:
         """
         Calculate the signal coming from the component
 
@@ -19,6 +19,8 @@ class IRadiant(ABC):
             The emitted, reflected or transmitted signal
         size : str
             The size of the target.
+        obstruction : float
+            The obstruction factor.
         """
         pass
 
diff --git a/esbo_etc/classes/optical_component/AOpticalComponent.py b/esbo_etc/classes/optical_component/AOpticalComponent.py
index 09fbc1c..222a90f 100644
--- a/esbo_etc/classes/optical_component/AOpticalComponent.py
+++ b/esbo_etc/classes/optical_component/AOpticalComponent.py
@@ -52,7 +52,7 @@ class AOpticalComponent(IRadiant):
         self.__obstructor_temp = obstructor_temp
         self.__obstructor_emissivity = obstructor_emissivity
 
-    def calcSignal(self) -> Tuple[SpectralQty, str]:
+    def calcSignal(self) -> Tuple[SpectralQty, str, float]:
         """
         Calculate the spectral flux density of the target's signal
 
@@ -62,12 +62,15 @@ class AOpticalComponent(IRadiant):
             The spectral flux density of the target's signal
         size : str
             The size of the target.
+        obstruction : float
+            The obstruction factor.
         """
-        signal, size = self.__parent.calcSignal()
+        signal, size, obstruction = self.__parent.calcSignal()
         info("Calculating signal for class '" + self.__class__.__name__ + "'.")
         signal = self._propagate(signal) * (1 - self.__obstruction)
+        obstruction = obstruction + self.__obstruction
         debug(signal)
-        return signal, size
+        return signal, size, obstruction
 
     def calcBackground(self) -> SpectralQty:
         """
diff --git a/esbo_etc/classes/target/ATarget.py b/esbo_etc/classes/target/ATarget.py
index c614343..fd1c3cf 100644
--- a/esbo_etc/classes/target/ATarget.py
+++ b/esbo_etc/classes/target/ATarget.py
@@ -46,7 +46,7 @@ class ATarget(IRadiant):
         debug(background)
         return background
 
-    def calcSignal(self) -> Tuple[SpectralQty, str]:
+    def calcSignal(self) -> Tuple[SpectralQty, str, float]:
         """
         Calculate the spectral flux density of the target's signal
 
@@ -56,10 +56,12 @@ class ATarget(IRadiant):
             The spectral flux density of the target's signal
         size : str
             The size of the target.
+        obstruction : float
+            The obstruction factor.
         """
         info("Calculating Signal for class '" + self.__class__.__name__ + "'.")
         debug(self.__sfd)
-        return self.__sfd, self.__size
+        return self.__sfd, self.__size, 0.0
 
     @staticmethod
     @abstractmethod
diff --git a/tests/target/test_BlackBodyTarget.py b/tests/target/test_BlackBodyTarget.py
index f4b5744..5106d7b 100644
--- a/tests/target/test_BlackBodyTarget.py
+++ b/tests/target/test_BlackBodyTarget.py
@@ -13,7 +13,7 @@ class TestBlackBodyTarget(TestCase):
     def test_calcSignal(self):
         signal = SpectralQty(np.arange(400, 800, 100) << u.nm, np.array([4.91164694e-15, 5.61732017e-15, 5.22403225e-15,
                                                                          4.43017583e-15]) << u.W / (u.m ** 2 * u.nm))
-        self.assertEqual(self.target.calcSignal(), (signal, "Point"))
+        self.assertEqual(self.target.calcSignal(), (signal, "Point", 0.0))
 
     def test_calcBackground(self):
         noise = SpectralQty(np.arange(400, 800, 100) << u.nm, np.repeat(0, 4) << u.W / (u.m ** 2 * u.nm * u.sr))
diff --git a/tests/target/test_FileTarget.py b/tests/target/test_FileTarget.py
index 783b29c..9952928 100644
--- a/tests/target/test_FileTarget.py
+++ b/tests/target/test_FileTarget.py
@@ -11,8 +11,8 @@ class TestFileTarget(TestCase):
 
     def test_calcSignal(self):
         signal = SpectralQty(np.arange(200, 210, 1) << u.nm,
-                                   np.arange(1.1e-15, 2.0e-15, 1e-16) << u.W / (u.m ** 2 * u.nm))
-        self.assertEqual(self.target.calcSignal(), (signal, "Point"))
+                             np.arange(1.1e-15, 2.0e-15, 1e-16) << u.W / (u.m ** 2 * u.nm))
+        self.assertEqual(self.target.calcSignal(), (signal, "Point", 0.0))
 
     def test_calcBackground(self):
         noise = SpectralQty(np.arange(200, 210, 1) << u.nm,