text: # Sylvia Dee <sylvia_dee@brown.edu>
  # PRYSM
  # PSM for Lacustrine Sedimentary Archives
  # SENSOR MODEL: GDGT-based measurements, e.g. TEX86, MBT5e
  # Function 'gdgt_sensor'
  # Modified 03/8/2016 <sylvia_dee@brown.edu>
  #====================================================================
  def gdgt_sensor(LST,MAAT,beta=(1/50),model='TEX86-loomis'):
  	'''
  	 SENSOR SUB-MODEL for GDGT proxy data
  
  	 INPUTS: 
  	 LST:    LAKE SURFACE TEMPERATURE (C)
  	 MAAT:   MEAN ANNUAL AIR TEMPERATURE (C)
  	 beta:   User-Specified transfer fucntion of LST to TEX/GDGT
  	 model:  Published calibrations for GDGTs. Options:
  	 			- Tierney et al., 2008 = 'TEX86-tierney'
  	 			- Loomis et al., 2012 = 'TEX86-loomis'
  	 			- Russell et al., 2018 = 'MBT' (for MBT-5Me calibrations with air temperature)
  
  	 More recent calibration studies have put forward univariate calibrations for 
  	 brGDGTs in lakes with mean annual air temperatures, specifically for MBT 
  	 indices which use only 5-methyl isomers MBT'_5ME.
        
       OUTPUT: pseudoproxy timeseries (monthly)
  	'''
  
  	if model=='beta':
  		pseudoproxy= beta*LST
  	elif model=='TEX86-tierney':
  		pseudoproxy= (LST+3.4992)/38.874 #tierney2008northern
  	elif model=='TEX86-loomis':
  		pseudoproxy= (LST+10.92)/54.88 #loomis2012calibration
  	elif model=='MBT':
  		pseudoproxy=(MAAT + 1.21)/32.42 #russell2018distributions
  
  	return pseudoproxy