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Oceanography
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Sea surface effect in sea surface temperature detection
Residue analysis
We examined the dependency of the residues of eq. (2)upon various disturbance factors.
1 Difference between the brightness temperature and the buy SST
The amount of the air-sea interacting effect might be reflected to the difference between X 4 and Y because the former air-sea defect the skin temperature and the later at the 1m depth. Figure 3 is the scattered diagram of the residues versus (X 4 - Y). For the match-ups with large residues, there exists a specific dependency upon the difference. That is, large positive residues appear to small, values of (X 4 - Y) and large negative residues are to large (X 4 - Y).
2 Difference between the air temperature and the buoy SST
The air temperature (A) is measured on No. 6 buoy at 3m above the sea surface. The amount of the (A-Y) might be another quantity for estimating the amount of the air-sea interacting effects because it directly affects the sea skin temperature. Figure 4 is the scattered diagram of the residues versus (A-Y). Large positive residues appear to match-ups with smaller (A-Y) and large negative residues appear with larger (A - Y).
By considering that the standard deviation of residues is 0.50C, let say that a residue is large if its absolute value is larger than 1.0C. By restricting large residues, we took the scattered diagram of (A-Y) versus (X 4 - Y) as in figure 5. Those seem to be distributed along a straight line. That is for the match-ups with large residues, the effect of (X4 - Y) to residues can be substituted by (A - Y).
Discussion
Table 2 is the list of scenes in which the large residues appeared. From table 2m large negative residues were restricted to the daytime data in spring and summer. The strong sunshine and the high air temperature will increase the sea skin surface temperature rapidly, but the temperature at 1m depth might be slow to respond. So that the large value of (X4 - Y) might be occurred. Under the circumstance, the buoy temperature might be overestimated and large negative residues would be probable to appear.
Large positive residues were restricted to the midnight math-ups in spring, autumn or winter. In those seasons, strong radiation cooling often occurs. Then low air temperature will cool the skin temperature first, but the temperature at 1m depth is slow to respond. So that the temperatures at 1m depth might be underestimated and large positives residues are probable appear. The data suggest that to consider the air-sea effects is very important for the reliable validations.
A special buoy to observe the vertical temperature distribution near the sea surface called "Sea Surface temperature profiler buoys (SSTPB)" was developed as shown in figure 6. SSTPB has 11 temperature detectors within + 2m and measures the temperature profile every 30 minutes. Attached with frame and float as shown in figure 7, SSTPB was set neat the No. 6 buoy in Mutsu Bay (10).
July 7, 1992 was a clearly fine day. It was very calm until about 14:00 but began to blow after that, Figure 8 is the data observed and figure 9 shows the temporal changes of its vertical temperature profile. At 5:00 right after the sunrise, the profile is just straight. But there appeared about 5C difference between -0cm and -100cm at 14:00. The profile became straight again after it began to blow. On the other hand, July 4, 1992 was clearly fine but the wind was more than 7m/sec in the daytime. Them the water temperature was kept just homogeneous as shown in figures 10~11. Those show the significance of the sea surface effects in the temperature detection by the Remote Sensing. We are still continuing the observation by SSPB, and it may take several years to prove the sea surface effects more precisely.
And its scattered diagram is shown in figure 12. The standard deviation of the residues is 0.34C. which must be considerably small among the contemporarily reported results.
Conclusion
By using the observation data set in Mutsu Bay. It is shown that the air-sea interacting effects might be one of the major disturbances in the SST estimation due to the split-window method. For the selected data set , which was set up by excluding the math-ups doubted to be disturbed by the air-sea interacting effects, we got the standard deviation of residues of 0.34C.
References
Barton, I.J., 1985, Transmission model and ground-truth investigation of satellite-derived sea surface temperature, journal of climate and applied meteorology, 24, 508-516.
- Deschamps, P.Y. and Phulpin, T., 1980, Atmospheric correct of infrared measurements of sea surface temperature using channels at 3.7., 11 and 12 mm, Boundary layer Meteorology, 18, 131-143.
- Llewellyn-Jones, D.T., Minnett, P.J., Saunders, R.W. and Zavody, A.M., 1984, Satellite Multichannel infrared measurements of sea surface temperature of the N.E. Atlantic Ocean using AVHRR/2, Quarterly Journal of Royal Meteorological Society, 110, 613-631.
- Maul G.A. 1983, Zenith angle effects in multichannel infrared sea surface Remote Sensing, Remote Sensing of Environment, 13, 49-451.
- MoClain, E.P., Pichel, W.G. and Walton, C.C., 1985., Comparative performance of AVHRR-based multichannel sea surface temperatures, Journal of Geophysical Research, 90, 11, 587-11, 601.
- McMillin. L. M. and Crosby. D. S. 1984. Theory and validation of the multiple window sea surface temperature technique, Journal of Geophysical Research, 89, 3655-3661.
- Robinson, I. S. and Ward N., 1989, Comparison between satellite and ship measurements of sea surface temperature in the north-east Atlantic Ocean, International Journal of Remote Sensing, 10, 787-799
- Strong, A.E. and McClain, E.P., 1984, Improved Ocean Surface Temperature from Space, ----------- Comparisons with drifting buoys--- Bulletin American Meteorological Society, 65, 138-142.
- Yokoyama, R., and Tanba, S., 1991, Estimation of Sea surface temperature via AVHRR of NOAA-9, -------- comparison with fixed buoy data ---------------------, International Journal of Remote Sensing, 12.25134-2528.
- Yokoyama R., S. Tanba, T. Souma, "Observation System for Sea surface temperature validation Test in Mutsu Bay", 2nd International Conference on Japanese Earth Observation Programs Proceedings of PRE ISY INTERNATIONAL SYMPOSIUM. 57 ~ 68, 1991.
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