A new algorithm for tuning of computed radiances for HIRS2/MSU

Small biases of the order of 1 C exist in brightness temperatures computed for a number of atmospheric sounding channels using radiosonde reports of atmospheric temperature humidity profile compared to those of collocated HIRS2/MSU observations on TIROS N. These biases are attributed to errors in the computed atmospheric transmittances functions. Channel dependent empirical tuning coefficients were found such that the biases in the channel brightness temperatures are removed if the transmittances used to calculate these brightness temperatures are modified. Possible shortcomings of this method are that some of the bias errors may be due to instrumental calibration problems and that the part that is computational may not be of the form assumed in the equation used. Form of tuning was implemented in the calculation which has the potential of distinguishing between calibration and calculation errors and is also computationally faster and more easily vectorizable.