Add reference for Gueymard 93 relative airmass model

docs/sphinx/source/whatsnew/v0.12.1.rst

@@ -0,0 +1,33 @@
+.. _whatsnew_01201:
+
+
+v0.12.1 (XXXX, 2025)
+------------------------
+
+Breaking Changes
+~~~~~~~~~~~~~~~~
+
+
+Bug fixes
+~~~~~~~~~
+
+
+Enhancements
+~~~~~~~~~~~~
+
+
+Documentation
+~~~~~~~~~~~~~
+* Add a supporting reference to :py:func:`pvlib.atmosphere.get_relative_airmass` (:issue:`2390`, :pull:`2424`)
+
+Testing
+~~~~~~~
+
+
+Maintenance
+~~~~~~~~~~~
+
+
+Contributors
+~~~~~~~~~~~~
+* Cliff Hansen (:ghuser:`cwhanse`)

pvlib/atmosphere.py

@@ -147,20 +147,13 @@ def get_relative_airmass(zenith, model='kastenyoung1989'):
 
         * 'simple' - secant(apparent zenith angle) -
           Note that this gives -Inf at zenith=90
-        * 'kasten1966' - See reference [1] -
-          requires apparent sun zenith
-        * 'youngirvine1967' - See reference [2] -
-          requires true sun zenith
-        * 'kastenyoung1989' (default) - See reference [3] -
-          requires apparent sun zenith
-        * 'gueymard1993' - See reference [4] -
-          requires apparent sun zenith
-        * 'young1994' - See reference [5] -
-          requires true sun zenith
-        * 'pickering2002' - See reference [6] -
-          requires apparent sun zenith
-        * 'gueymard2003' - See references [7] and [8] -
-          requires apparent sun zenith
+        * 'kasten1966' - See [1]_ - requires apparent sun zenith
+        * 'youngirvine1967' - See [2]_ - requires true sun zenith
+        * 'kastenyoung1989' (default) - See [3]_ - requires apparent sun zenith
+        * 'gueymard1993' - See [4]_, [5]_ - requires apparent sun zenith
+        * 'young1994' - See [6]_ - requires true sun zenith
+        * 'pickering2002' - See [7]_ - requires apparent sun zenith
+        * 'gueymard2003' - See [8]_, [9]_ - requires apparent sun zenith
 
     Returns
     -------
@@ -174,6 +167,8 @@ def get_relative_airmass(zenith, model='kastenyoung1989'):
     other models use true (not refraction-adjusted) zenith angle. Apparent
     zenith angles should be calculated at sea level.
 
+    Comparison among several models is reported in [10]_.
+
     References
     ----------
     .. [1] Fritz Kasten. "A New Table and Approximation Formula for the
@@ -191,24 +186,29 @@ def get_relative_airmass(zenith, model='kastenyoung1989'):
        clear sky solar irradiance models using theoretical and measured
        data," Solar Energy, vol. 51, pp. 121-138, 1993.
 
-    .. [5] A. T. Young, "AIR-MASS AND REFRACTION," Applied Optics, vol. 33,
+    .. [5] C. Gueymard, "Development and performance assessment of a clear
+       sky spectral radiation model,” in Proc. of the 22nd ASES Conference,
+       Solar ’93, 1993, pp. 433–438.
+
+    .. [6] A. T. Young, "AIR-MASS AND REFRACTION," Applied Optics, vol. 33,
        pp. 1108-1110, Feb 1994.
 
-    .. [6] Keith A. Pickering. "The Ancient Star Catalog". DIO 12:1, 20,
+    .. [7] Keith A. Pickering. "The Ancient Star Catalog". DIO 12:1, 20,
 
-    .. [7] C. Gueymard, "Direct solar transmittance and irradiance
+    .. [8] C. Gueymard, "Direct solar transmittance and irradiance
        predictions with broadband models. Part I: detailed theoretical
        performance assessment". Solar Energy, vol 74, pp. 355-379, 2003.
        :doi:`10.1016/S0038-092X(03)00195-6`
 
-    .. [8] C. Gueymard (2019). Clear-Sky Radiation Models and Aerosol Effects.
+    .. [9] C. Gueymard (2019). Clear-Sky Radiation Models and Aerosol Effects.
        In: Polo, J., Martín-Pomares, L., Sanfilippo, A. (eds) Solar Resources
        Mapping. Green Energy and Technology. Springer, Cham.
        :doi:`10.1007/978-3-319-97484-2_5`
 
-    .. [9] Matthew J. Reno, Clifford W. Hansen and Joshua S. Stein, "Global
+    .. [10] Matthew J. Reno, Clifford W. Hansen and Joshua S. Stein, "Global
        Horizontal Irradiance Clear Sky Models: Implementation and Analysis"
        Sandia Report, (2012).
+
     '''
 
     # set zenith values greater than 90 to nans
@@ -236,7 +236,7 @@ def get_relative_airmass(zenith, model='kastenyoung1989'):
               (np.cos(zenith_rad) ** 3 +
               0.149864*(np.cos(zenith_rad) ** 2) +
               0.0102963*(np.cos(zenith_rad)) + 0.000303978))
-    elif 'gueymard1993' == model:
+    elif 'gueymard1993' == model:  # [4], Eq. 22 and [5], Eq. 3b
         am = (1.0 / (np.cos(zenith_rad) +
               0.00176759*(z)*((94.37515 - z) ** - 1.21563)))
     elif 'gueymard2003' == model: