Subtraction of a low order polynomial
Singular-value decomposition ( 97JMR286-124 )
Time-domain convolution filter ( 89JMR425-84 , 93JMRA88-104 , 93JMRA338-103 , 95JMRB40-106 )
Shaped-notch filter ( 95JMRB93-109 )
Use of Wavelet transforms ( 97JMR1-128 , 00JMR189-144 , 97JMR20-124 and 02JMR19-156 )
Indirect Covariance