conductivity of the conductive fluid surrounding the accelerometer . This 

 drift could be identified from calibrations over a succession of time. 



32. In 1982 Datawell made available an improved modulator printed- 

 circuit board for bringing calibrations within specification and for prevent- 

 ing further decrease in sensitivity; however, this modification was not made 

 for the 1980 FRF buoys. Datawell provided curves for correction of calibra- 

 tion sensitivity based on differences between buoy temperature during calibra- 

 tion and buoy temperature when the buoy is measuring waves in the ocean. The 

 NOAA Engineering Support Office developed a table based on the Datawell curve 

 which can be entered with the uncorrected difference error value d (Table 2) 

 and the temperature of the water during the time of the buoy operation to 

 determine the difference error correction (see tabulation below). The dif- 

 ference error correction is added to d to obtain the corrected difference 

 error D . For temperatures during buoy operation greater than the buoy tem- 

 perature during calibration (22.4°C), no correction is necessary. 



Diff . 



22.4 



20 





13 



16 



14 



12 



16 



S 



e.ee 



6.666 



9.081 



9. 



991 



0.061 



0.091 



9.666 



-9.099 



-0.002 



e.ei 



6 



669 



6.007 



0. 



003 



0.609 



0.016 



0.011 



0.911 



9.011 



e.e2 



6 



666 



0.099 







012 



0.614 



0.016 



0.018 



0.619 



0.020 



-9.63 



6 



99U 



6.909 







913 



0.016 



0.619 



0.021 



6.624 



6.02e 



-a. 64 



6 



096 



0.098 







012 



0.616 



0.026 



0.023 



0.027 



0.629 



-9.05 



9 



906 



9.99S 







911 



0.616 



6.029 



0.624 



0.628 



0.032 



-6.96 



e 



969 



9.964 



9 



910 



0.615 



0.020 



0.025 



0.030 



0.034 



-6.67 



8 



966 



6.663 



6 



669 



0.015 



0.621 



0.026 



0.031 



6.036 



-e.68 



6 



060 



6.663 







010 



8.017 



0.623 



9.029 



0.034 



6.039 



-6.69 



9 



.966 



0.606 







.013 



0.019 



6.626 



0.032 



0.038 



0.043 



-0.16 



6 



.669 



0.019 







.017 



0.024 



6.631 



0.637 



0.943 



0.049 



33. Since these error corrections are oscillation-period dependent, 

 their application requires that the wave data be decomposed into amplitude 

 coefficients or variance-spectrum coefficients for each frequency or period. 

 A less accurate but also less complicated procedure would be to apply a single 

 correction to, say, the significant wave height based on the peak spectral 

 wave period and an average water temperature estimate. For correction of 

 amplitudes or derived parameters linearly related to amplitude, a correction 

 factor F(T) can be obtained from the sum of the Datawell DW and 

 temperature-corrected difference error D by: 



19 



