From 55972aeef1ff0cb4fb4ad1a4497466a88eaec837 Mon Sep 17 00:00:00 2001
From: Chunxiao Li <lcx366@126.com>
Date: Fri, 22 Jan 2021 15:31:55 +0800
Subject: [PATCH] new script about coesa76

---
 pyatmos/standardatmos/coesa76.py | 85 ++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 pyatmos/standardatmos/coesa76.py

diff --git a/pyatmos/standardatmos/coesa76.py b/pyatmos/standardatmos/coesa76.py
new file mode 100644
index 0000000..2ee1a50
--- /dev/null
+++ b/pyatmos/standardatmos/coesa76.py
@@ -0,0 +1,85 @@
+'''
+Because of the interest of aerospace engineers and atmospheric scientists in 
+conditions at much higher altitudes than those of the U.S. Standard Atmosphere 
+1976(USSA 1976), members of the U.S. Committee on Extension to the Standard 
+Atmosphere(COESA 1976) agreed to extend it to 1000 km.
+'''
+
+import numpy as np
+from pkg_resources import resource_filename
+
+from  .ussa76 import ussa76
+from ..utils import Const
+from ..utils.utils import alt_conver,check_altitude
+
+def coesa76(alts, alt_type='geometric'):
+    '''
+    Implements the U.S. Committee on Extension to the Standard Atmosphere(COESA 1976).
+
+    Usage:
+    [rhos, Ts, Ps] = coesa76(h)
+
+    Inputs:
+    alts -> [float list/array] geometric or geopotentail altitudes, [km]
+
+    Outputs:
+    rhos -> [float array] densities at a set of given altitudes, [kg/m^3]
+    Ts -> [float] temperatures ..., [K]
+    Ps -> [float] pressures ..., [Pa]
+    
+    Note: the geometric altitudes should be in [-0.610,1000] km, otherwise the output will be extrapolated for those input altitudes.
+
+    Reference: 
+        U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C. 
+        http://www.braeunig.us/space/atmmodel.htm#USSA1976
+        https://docs.poliastro.space/en/stable/index.html
+    '''
+
+    # Base altitude for the COESA 1976, [km].
+    zb = np.array([86, 91, 100, 110, 120, 150, 200, 300, 500, 750, np.inf])
+
+    # load the coefficients used to approximate density and pressure above 86km 
+    data_path = resource_filename('pyatmos', 'data/')
+    data = np.load(data_path+'coesa76_coeffs.npz')
+    rho_coeffs,p_coeffs = data['rho'],data['p']
+
+    r0 = Const.r0 # volumetric radius for the Earth, [km] 
+
+    # Get geometric and geopotential altitudes
+    zs,hs = alt_conver(alts, alt_type)
+
+    # Test if altitudes are inside valid range
+    check_altitude(zs,(-0.611,1e3),'warning')  
+
+    inds = np.zeros_like(zs,dtype=int)
+    rhos,Ts,Ps = np.zeros((3,len(zs)))
+
+    j = 0
+    for z,h in zip(zs,hs):
+
+        if z <= zb[0]: 
+            rho,T,P,Cs,eta,Kc = ussa76(h)
+        else:
+            if z > zb[0] and z <= zb[1]:
+                T = 186.8673
+            elif z > zb[1] and z <= zb[3]:
+                T = 263.1905 - 76.3232 * np.sqrt(1 - ((z - 91) / 19.9429) ** 2)
+            elif z > zb[3] and z <= zb[4]:
+                T = 240 + 12 * (z - 110)
+            else:
+                epsilon = (z - 120) * (r0 + 120) / (r0 + z)
+                T = 1e3 - 640 * np.exp(-0.01875 * epsilon)  
+
+            ind = np.where((z - zb) >= 0)[0][-1]
+
+            # A 4th order polynomial is used to approximate density and pressure.  
+            # This is directly taken from: http://www.braeunig.us/space/atmmodel.htm
+            poly_rho = np.poly1d(rho_coeffs[ind])
+            poly_p = np.poly1d(p_coeffs[ind])
+            rho = np.exp(poly_rho(z))
+            P = np.exp(poly_p(z))
+
+        rhos[j],Ts[j],Ps[j] = rho,T,P
+        j += 1    
+ 
+    return rhos,Ts,Ps             
\ No newline at end of file