Refraction.ipynb

import numpy as np
import matplotlib.pyplot as pl
%matplotlib inline

# pressure correction
P=np.array([76]) #kPa
T=np.array([0.,10.,20.,30.]) # degC
pcor=(P[0]/101.)*(283./(273+T))

pix_scale=4.96
pix_per_arcmin=60./pix_scale

dalt=2.8
alt=np.linspace(30,90,61)[::-1]
dR=np.empty(len(alt))
for i in range(0,len(alt)):
  R1=1./np.tan(np.radians(alt[i]+(7.31/(alt[i]+4.4))))
  R2=1./np.tan(np.radians(alt[i]-dalt+(7.31/(alt[i]-dalt+4.4))))
  dR[i]=(R1-R2)*pix_per_arcmin


pl.figure(1,figsize=(10,5))
pl.plot(alt,dR*pcor[0],'r-')
pl.plot(alt,dR*pcor[1],'g-')
pl.plot(alt,dR*pcor[2],'b-')
pl.plot(alt,dR*pcor[3],'k-')
pl.title('Differential Refraction Across NGTS FOV [%d kPa]' % (P[0]))
pl.xlabel('Altitude of Highest Point (deg)')
pl.ylabel('Differential Refraction (pix)')
pl.legend(('T=  0 C','T=10 C','T=20 C','T=30 C'),loc='upper left')
pl.xlim(25,90)
pl.ylim(-2.5,0)
pl.show()