Dual Channel Algorithm for Retrieval of Sea Surface Temperatures from Satellite Thermal Images
Analysis of Ocean Colour Temperature Scanner (OCTS) data
The algorithm was later tested with OCTS data sets. Five scenes were selected from the Remote Sensing Technology of Japan (RESTEC) archive and they were captured by ADEOS satellite on 22 March 1997, 21 April 1997, 24 May 1997, 13 June 1997 and 21 June 1997.
Similar analyses performed earlier were carried out with OCTS data sets. Cloud free sea water pixels for bands 10, 11 and 12 were extracted for SST retrieval. The digital numbers were converted to brightness temperatures using the calibration parameters produced by NASDA. The SST values were computed using equation (1) and then
compared with the values retrieved using equation (4) below developed by NASDA (Sakaida et al. 1998).
MCSST = C0+ C1T11+
C2 (T11+ T12)+ C3 (T11- T10) (4)
+ C4 (1/cosq - 1) (T11- T12) +
C5 (1/cosq-1)(T11-T10) (4)
The coefficient C
0 To C
5 were taken from the table provided in the report. The results produced by the algorithm of equation (1) were correlated with the output from equation (4) and the RMS errors were estimated. Again with these data sets the present algorithm has shown comparable performance with the established algorithm produced by NASDA as indicted by high correlation coefficients and small RMS errors shown in table 3. The plot in Figure 3 indicate the correlation between the two considered algorithms.
Table 3. Correlation of the results using equation 1 and equation 5
| Date |
Correlation coefficient |
RMS error |
| 23 March 1997 |
0.99 |
0.43 |
| 21 April 1997 |
0.99 |
0.46 |
| 24 May 1997 |
0.99 |
0.66 |
| 13 June 1997 |
0.99 |
0.16 |
| 21 June 1997 |
0.99 |
0.43 |
Figure 3. SST from equation (1) vs. SST from NASDA MCSST for 13 June 1997 data.
Conclusion
The results of the study indicated that the performance of the developed algorithm is comparable to the established algorithms such as NOAA MCSST for retrieval of SST using AVHRR data and NASDA MCSST for application of OCTS data. However, this algorithm produced better accuracy than the NOAA MCSST for SST determination in sea water areas around Malaysia. This is due to this algorithm takes into account of the local atmospheric condition. Although coincident in-situ data were not available for comparison using OCTS data but the computed values were in order of magnitude of the local readings as given in the reference in-situ data and they are highly correlated with the NASDA MCSST computed values. The present study has indicated that it is possible to use this algorithm globally without resource to the local in-situ data for calibration. This will be verified by pursuing further research. The atmospheric profiles from radiosonde are required data for obtaining transmittance values corresponding to the scenes used and coincident SST for more accurate verification.
Acknowledgements
The authors like to thank the Universiti Sains Malaysia for funding the project involving AVHRR data, the Malaysian Meteorological Services for providing the AVHRR images and in-situ SST readings, ESCAP and NASDA for providing financial support and ADEOS OCTS data, RESTEC, our students Murali Shangkar, Jeru Iruthaya Nathan, Lee Eng Hou, Yan Wai Hong and our research officer Tadris Ahmad for their helps.
Reference
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