Merge pull request #35 from james-m-osborn/master

added seeing to cn2 in atmos conversions

aotools/turbulence/atmos_conversions.py

@@ -15,6 +15,21 @@ def cn2_to_seeing(cn2,lamda=500.E-9):
     seeing = r0_to_seeing(r0,lamda)
     return seeing
 
+def seeing_to_cn2(seeing,lamda=500.E-9):
+    """
+    Calculates the integrated Cn2 value from the seeing
+
+    Parameters:
+        seeing (float): seeing in arcseconds
+        lamda : wavelength
+
+    Returns:
+        integrated Cn2 value in m^2/3
+    """
+    r0 = seeing_to_r0(seeing,lamda)
+    cn2 = r0_to_cn2(r0,lamda)
+    return cn2
+
 def cn2_to_r0(cn2,lamda=500.E-9):
     """
     Calculates r0 from the integrated Cn2 value
@@ -29,6 +44,20 @@ def cn2_to_r0(cn2,lamda=500.E-9):
     r0=(0.423*(2*numpy.pi/lamda)**2*cn2)**(-3./5.)
     return r0
 
+def r0_to_cn2(r0,lamda=500.E-9):
+    """
+    Calculates integrated Cn2 value from r0
+
+    Parameters:
+        r0 (float): r0 in cm
+        lamda : wavelength
+
+    Returns:
+        cn2 (float): integrated Cn2 value in m^2/3
+    """
+    cn2 = r0**(-5./3.)/(0.423*(2*numpy.pi/lamda)**2)
+    return cn2
+
 def r0_to_seeing(r0,lamda=500.E-9):
     """
     Calculates the seeing angle from r0
@@ -42,6 +71,19 @@ def r0_to_seeing(r0,lamda=500.E-9):
     """
     return (0.98*lamda/r0)*180.*3600./numpy.pi
 
+def seeing_to_r0(seeing,lamda=500.E-9):
+    """
+    Calculates r0 from seeing
+
+    Parameters:
+        seeing (float): seeing angle in arcseconds
+        lamda : wavelength
+
+    Returns:
+        r0 (float): Freid's parameter in cm
+    """
+    return 0.98*lamda/(seeing*numpy.pi/(180.*3600.))
+
 def coherenceTime(cn2,v,lamda=500.E-9):
     """
     Calculates the coherence time from profiles of the Cn2 and wind velocity

test/test_atmos_conversions.py

@@ -21,12 +21,23 @@ def test_r0_to_seeing():
 
 
 def test_conversion_consistency():
+    """
+    Test internal consistency of conversion by comparing with intermediate steps
+    """
     cn2 = 5e-13
     r0 = atmos_conversions.cn2_to_r0(cn2)
     seeing_1 = atmos_conversions.r0_to_seeing(r0)
     seeing_2 = atmos_conversions.cn2_to_seeing(cn2)
     assert seeing_1 == seeing_2
 
+def test_conversion_consistency_inverse():
+    """
+    Test that the conversions invert correctly
+    """
+    seeing1 = 1.0
+    cn2 = atmos_conversions.seeing_to_cn2(seeing1)
+    seeing2 = atmos_conversions.cn2_to_seeing(cn2)
+    assert seeing1 == seeing2
 
 def test_coherenceTime():
     cn2 = numpy.array((5e-13, 1e-14))