Calculate pressure depth uncertainty

[PennyHow]

Moved and modified from #122. Uncertainty propagation through the pressure depth calculation is not tracked, but should be in the future. Perhaps with uncertainty arrays that accompany the z_pt_cor and z_pt outputs (i.e. z_pt_cor_unc and z_pt_unc)

pypromice/src/pypromice/process/L0toL1.py

Lines 206 to 250 in c5613a9

	def getPressDepth(z_pt, p, pt_antifreeze, pt_z_factor, pt_z_coef, pt_z_p_coef):
	'''Adjust pressure depth and calculate pressure transducer depth based on
	pressure transducer fluid density
	Parameters
	----------
	z_pt : xr.Dataarray
	Pressure transducer height (corrected for offset)
	p : xr.Dataarray
	Air pressure
	pt_antifreeze : float
	Pressure transducer anti-freeze percentage for fluid density
	correction
	pt_z_factor : float
	Pressure transducer factor
	pt_z_coef : float
	Pressure transducer coefficient
	pt_z_p_coef : float
	Pressure transducer coefficient
	Returns
	-------
	z_pt_cor : xr.Dataarray
	Pressure transducer height corrected
	z_pt : xr.Dataarray
	Pressure transducer depth
	'''
	# Calculate pressure transducer fluid density
	if pt_antifreeze == 50: #TODO: Implement function w/ reference (analytical or from LUT)
	rho_af = 1092 #TODO: Track uncertainty
	elif pt_antifreeze == 100:
	rho_af = 1145
	else:
	rho_af = np.nan
	print('ERROR: Incorrect metadata: "pt_antifreeze" = ' +
	f'{pt_antifreeze}. Antifreeze mix only supported at 50% or 100%')
	# assert(False)
	# Correct pressure depth
	z_pt_cor = z_pt * pt_z_coef * pt_z_factor * 998.0 / rho_af + 100 * (pt_z_p_coef - p) / (rho_af * 9.81)
	# Calculate pressure transducer depth
	z_pt = z_pt * pt_z_coef * pt_z_factor * 998.0 / rho_af
	return z_pt_cor, z_pt