Gayana 68(2): 355-357, 2004,

Remotly Sensed Sea Surface Temperature from Aircraft

B. H. Kwon¹, B. Benech², P. Durand³ & Y. S. Kim⁴

¹Dept. Of Environmental Atmospheric Sciences, Pukyong National University, Busan, Korea
²Centre des Recherches Atmospheriques, Lannemezan, France
³Laboratoire d'Aérologie, Toulouse, France
⁴Dept. Of Satellite Information Sciences, Pukyong National University, Busan, Korea bhkwon@mail1.pknu.ac.kr

ABSTRACT

The experiment was conducted around south of the Azores islands, in the middle eastern part of the northern-Atlantic basin. The experimental area was situated between 31°N-38°N and 21°W-28°W. The experiment was performed in order to improve our knowledge of ocean-atmosphere interactions from the local-scale to the meso-scale. The sea surface temperature remotely measured by aircraft was corrected considering the radiation flux divergence. From the descending IR flux in function of the difference between the surface temperatures measured from the ship and the aircraft (SST_shipSST_aircraft), the difference decreases when the IR flux increases. The sea surface temperature was corrected of the radiation flux divergence of the atmosphere between the sea surface and the flight level. The cloudness plays an important role in this correction. The comparison between SST of the ship and the SST of the aircraft shows a difference of 1°C on average which is affected of the descending infrared flux (0.25°C per 100 m).

Keywords: sea surface temperature, aircraft, radiation flux divergence, infrared radiation

INTRODUCTION

The experiment was conducted from June to November 1993 south of the Azores islands, in the middle eastern part of the northern-Atlantic basin. The experimental area was a 500 km by 500 km box situated between 31°N-38°N and 21°W-28°W. The experiment was performed in order to improve our knowledge of ocean-atmosphere interactions from the local-scale to the meso-scale (Eymard et al., 1996). Parameters of the surface are deduced either from the airborne measurement, or directly from the lowest flight level, supposing that this altitude is in the surface boundary layer where fluxes are constant. The evaluation of the mean and turbulent parameters adapted to 10 m of the sea level was compared to the measurement by the ship.

DETERMINATION OF THE SEA SURFACE TEMPERATURE

The brightness temperature of the sea surface along the flight trajectory was produced from the measurement of the infrared radiation by Barnes-PRT5. Alone measurement with Merlin IV was taken in account because of a temporal difference of the Barnes sensor of the ARAT. The sea surface temperature was corrected of the radiation flux divergence of the atmosphere between the sea surface and the flight level: this correction can vary in particular with the cloudy cover. The vertical decrease of the measured SST was restored by considering the emissivity. Supposed the SST is a function of the space and the time,

(1)

The apparent temperature T_a is the function of the SST, of the emissivity, of the descending IR and of the altitude:

(2)

At the surface, the radiation can be written by

(3)

At the altitude z, the atmospheric absorption decrease the radiation

(4)

If the term is measured at the altitude z, not at the surface,

(5)

(6)

Ignoring the third order terms,

where the term I is the radiation measured by the Barnes PRT5 at the flight level, the term II is to be found (unknown: el and T_l) and the term III can be evaluated statistically at the different altitudes. In the term VI el is unknown and is measured. When , the spatial variation of results in the variation of . Figure 1 shows the descending IR flux in function of the difference between the surface temperatures measured from the ship and the aircraft (SST_shipSST_aircraft): the difference decreases when the IR flux increases. In the same trajectory over the surface, supposed that the SST and el do not vary between two measurements, we can calculate el and correct the estimation of the  SST. On each segment of about 30 km, the measured SST was corrected. The histogram, in Figure 2, shows the percentage of the correction for the SST over every altitude due to the divergence of the IR flux. For the Merlin IV, the applied correction is 0.25°C per 100 m as the histogram of the Figure 6 from the different analyzed days.

Figure 1. Variation of the descending IR flux in function of the difference of the SST.

Figure 2. Histogram of the correction of the SST according to the flight level of the Merlin IV.

SUMMARY

On the ship (Suroît), the temperature of water is measured directly at 2.5 m of depth. The comparison between SST of the ship and the SST of the aircraft (Merlin IV) shows a difference of 1°C on average. This correction is affected of the descending infrared flux and can vary a few tenth of degree according to the cloudy cover. We found the good correction with related to the SST assimilated in the model ARPEGE.

ACKNOWLEDGMENTS

Sensing Meteorology, one of the Research and Development on Meteorology and Seismology funded by Korea Meteorological Administration (KMA).

REFERENCES

Eymard, L., S. Planton, P. Durand, Y. Camus, P. Y., Le Traon, L. Prieur, A. Weill, D. Hauser, B. Le Squere, J. Rolland, J. Pelon, F. Baudin, B. Bénech, J. L. Brenguier, G. Caniaux, P. De Mey, E. Dombrowski, A. Druilhet, H. Dupuis, B. Ferret, C. Flamant, P. Flamant, F. Hernandez, D. Jourdan, K. Katsaros, D. Lambert, J. M. Lefevre, P. Le Borgne, A. Marsoin, J. Tournadre, V. Trouillet, & B. Zakardjian, 1996, Study of the air-sea interactions at the mesoscale: the SEMAPHORE experiment. Ann. Geophys., 14, 986-1015.         [ Links ] [1]