Merge branch '20-add-a-first-model-for-measurement-readout-noise' into 'master'

Resolve "Add a first model for measurement/readout noise"

Closes #20

See merge request !31

lisainstrument/instrument.py

@@ -45,6 +45,7 @@ class Instrument:
                  clock_freqquaddrifts=None, clockinv_tolerance=1E-10, clockinv_maxiter=5,
                  # Optical pathlength noises
                  backlink_asds=3E-12, backlink_fknees=2E-3, testmass_asds=2.4E-15, testmass_fknees=0.4E-3,
+                 oms_asds=(6.35E-12, 1.25E-11, 1.42E-12, 3.38E-12, 3.32E-12, 7.90E-12), oms_fknees=2E-3,
                  # Pseudo-ranging
                  ranging_biases=0, ranging_asds=3E-9,
                  # Physics simulation sampling and filtering
@@ -80,7 +81,10 @@ class Instrument:
             backlink_asds: dictionary of amplitude spectral densities for backlink noise [m/sqrt(Hz)]
             backlink_fknees: dictionary of cutoff frequencied for backlink noise [Hz]
             testmass_asds: dictionary of amplitude spectral densities for test-mass noise [ms^(-2)/sqrt(Hz)]
-            testmass_fknees: dictionary of cutoff frequencied for test-mass noise [Hz]
+            testmass_fknees: dictionary of cutoff frequencies for test-mass noise [Hz]
+            oms_asds: tuple of dictionaries of amplitude spectral densities for OMS noise [m/sqrt(Hz)],
+                ordered as (isc_carrier, isc_usb, tm_carrier, tm_usb, ref_carrier, ref_usb)
+            oms_fknees: dictionary of cutoff frequencies for OMS noise
             ranging_biases: dictionary of ranging noise bias [s]
             ranging_asds: dictionary of ranging noise amplitude spectral densities [s/sqrt(Hz)]
             physics_upsampling: ratio of sampling frequencies for physics vs. measurement simulation
@@ -163,11 +167,18 @@ class Instrument:
         self.ranging_biases = ForEachMOSA(ranging_biases)
         self.ranging_asds = ForEachMOSA(ranging_asds)
 
-        # Backlink and test-mass acceleration noise
+        # Backlink, OMS and test-mass acceleration noise
         self.backlink_asds = ForEachMOSA(backlink_asds)
         self.backlink_fknees = ForEachMOSA(backlink_fknees)
         self.testmass_asds = ForEachMOSA(testmass_asds)
         self.testmass_fknees = ForEachMOSA(testmass_fknees)
+        self.oms_isc_carrier_asds = ForEachMOSA(oms_asds[0])
+        self.oms_isc_usb_asds = ForEachMOSA(oms_asds[1])
+        self.oms_tm_carrier_asds = ForEachMOSA(oms_asds[2])
+        self.oms_tm_usb_asds = ForEachMOSA(oms_asds[3])
+        self.oms_ref_carrier_asds = ForEachMOSA(oms_asds[4])
+        self.oms_ref_usb_asds = ForEachMOSA(oms_asds[5])
+        self.oms_fknees = ForEachMOSA(oms_fknees)
 
         # Frequency plan
         if offsets_freqs is not None:
@@ -391,6 +402,12 @@ class Instrument:
         """Turn off all optical pathlength noises."""
         self.backlink_asds = ForEachMOSA(0)
         self.testmass_asds = ForEachMOSA(0)
+        self.oms_isc_carrier_asds = ForEachMOSA(0)
+        self.oms_isc_usb_asds = ForEachMOSA(0)
+        self.oms_tm_carrier_asds = ForEachMOSA(0)
+        self.oms_tm_usb_asds = ForEachMOSA(0)
+        self.oms_ref_carrier_asds = ForEachMOSA(0)
+        self.oms_ref_usb_asds = ForEachMOSA(0)
 
     def disable_ranging_noises(self):
         """Turn off all pseudo-ranging noises."""
@@ -541,7 +558,8 @@ class Instrument:
 
         logger.debug("Computing inter-spacecraft carrier beatnote fluctuations on TPS")
         self.tps_isc_carrier_fluctuations = \
-            self.distant_isc_carrier_fluctuations - self.local_isc_carrier_fluctuations
+            self.distant_isc_carrier_fluctuations - self.local_isc_carrier_fluctuations \
+            + self.central_freq * self.oms_isc_carrier_noises
 
         logger.debug("Computing inter-spacecraft upper sideband beatnote offsets on TPS")
         self.tps_isc_usb_offsets = \
@@ -549,7 +567,8 @@ class Instrument:
 
         logger.debug("Computing inter-spacecraft upper sideband beatnote fluctuations on TPS")
         self.tps_isc_usb_fluctuations = \
-            self.distant_isc_usb_fluctuations - self.local_isc_usb_fluctuations
+            self.distant_isc_usb_fluctuations - self.local_isc_usb_fluctuations \
+            + self.central_freq * self.oms_isc_usb_noises
 
         ## Measured pseudo-ranging on TPS grid (high-frequency)
 
@@ -604,7 +623,8 @@ class Instrument:
 
         logger.debug("Computing test-mass carrier beatnote fluctuations on TPS")
         self.tps_tm_carrier_fluctuations = \
-            self.adjacent_tm_carrier_fluctuations - self.local_tm_carrier_fluctuations
+            self.adjacent_tm_carrier_fluctuations - self.local_tm_carrier_fluctuations \
+            + self.central_freq * self.oms_tm_carrier_noises
 
         logger.debug("Computing test-mass upper sideband beatnote offsets on TPS")
         self.tps_tm_usb_offsets = \
@@ -612,7 +632,8 @@ class Instrument:
 
         logger.debug("Computing test-mass upper sideband beatnote fluctuations on TPS")
         self.tps_tm_usb_fluctuations = \
-            self.adjacent_tm_usb_fluctuations - self.local_tm_usb_fluctuations
+            self.adjacent_tm_usb_fluctuations - self.local_tm_usb_fluctuations \
+            + self.central_freq * self.oms_tm_usb_noises
 
         ## Reference interferometer local beams
 
@@ -656,7 +677,8 @@ class Instrument:
 
         logger.debug("Computing reference carrier beatnote fluctuations on TPS")
         self.tps_ref_carrier_fluctuations = \
-            self.adjacent_ref_carrier_fluctuations - self.local_ref_carrier_fluctuations
+            self.adjacent_ref_carrier_fluctuations - self.local_ref_carrier_fluctuations \
+            + self.central_freq * self.oms_ref_carrier_noises
 
         logger.debug("Computing reference upper sideband beatnote offsets on TPS")
         self.tps_ref_usb_offsets = \
@@ -664,7 +686,8 @@ class Instrument:
 
         logger.debug("Computing reference upper sideband beatnote fluctuations on TPS")
         self.tps_ref_usb_fluctuations = \
-            self.adjacent_ref_usb_fluctuations - self.local_ref_usb_fluctuations
+            self.adjacent_ref_usb_fluctuations - self.local_ref_usb_fluctuations \
+            + self.central_freq * self.oms_ref_usb_noises
 
         ## Sampling beatnotes and measured pseudo-ranges to THE grid
 
@@ -922,6 +945,40 @@ class Instrument:
                 self.physics_size, self.ranging_asds[mosa])
         )
 
+        ## OMS noise
+
+        logger.info("Generating OMS noise")
+
+        self.oms_isc_carrier_noises = ForEachMOSA(lambda mosa:
+            noises.oms(self.physics_fs, self.physics_size,
+                self.oms_isc_carrier_asds[mosa], self.oms_fknees[mosa])
+        )
+
+        self.oms_isc_usb_noises = ForEachMOSA(lambda mosa:
+            noises.oms(self.physics_fs, self.physics_size,
+                self.oms_isc_usb_asds[mosa], self.oms_fknees[mosa])
+        )
+
+        self.oms_tm_carrier_noises = ForEachMOSA(lambda mosa:
+            noises.oms(self.physics_fs, self.physics_size,
+                self.oms_tm_carrier_asds[mosa], self.oms_fknees[mosa])
+        )
+
+        self.oms_tm_usb_noises = ForEachMOSA(lambda mosa:
+            noises.oms(self.physics_fs, self.physics_size,
+                self.oms_tm_usb_asds[mosa], self.oms_fknees[mosa])
+        )
+
+        self.oms_ref_carrier_noises = ForEachMOSA(lambda mosa:
+            noises.oms(self.physics_fs, self.physics_size,
+                self.oms_ref_carrier_asds[mosa], self.oms_fknees[mosa])
+        )
+
+        self.oms_ref_usb_noises = ForEachMOSA(lambda mosa:
+            noises.oms(self.physics_fs, self.physics_size,
+                self.oms_ref_usb_asds[mosa], self.oms_fknees[mosa])
+        )
+
     def invert_timer_deviations(self, timer_deviations, sc):
         """Invert timer deviations of a given spacecraft.
 

lisainstrument/noises.py

@@ -204,3 +204,27 @@ def testmass(fs, size, asd=2.4E-15, fknee=0.4E-3):
         fs, size, asd, fknee)
     return red(fs, size, asd / (2 * pi * c)) \
         + infrared(fs, size, asd * fknee / (2 * pi * c))
+
+def oms(fs, size, asd, fknee):
+    """Generate optical metrology system (OMS) noise allocation [ffs].
+
+    The power spectral density in displacement is given by
+
+        S_oms(f) [m] = asd^2 [ 1 + (fknee / f)^4 ].
+
+    Multiplying by (2π f / c)^2 to express it as fractional frequency deviations,
+
+        S_oms(f) [ffd] = (2π asd / c)^2 [ f^2 + (fknee^4 / f^2) ]
+                      = (2π asd / c)^2 f^2 + (2π asd fknee^2 / c)^2 f^(-2)
+
+    Note that the level of this noise depends on the interferometer and the type of beatnote.
+
+    Warning: this corresponds to the overall allocation for the OMS noise from the Performance
+    Model. It is a collection of different noises, some of which are duplicates of standalone
+    noises we already implement in the simulation (e.g., backlink noise).
+
+    """
+    logger.debug("Generating OMS noise (fs=%s Hz, size=%s, asd=%s m/sqrt(Hz), fknee=%s Hz)",
+        fs, size, asd, fknee)
+    return violet(fs, size, 2 * pi * asd / c) \
+        + red(fs, size, 2 * pi * asd * fknee**2 / c)