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R. P. Davies-Jones and N. B. Ward

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R. W. Saunders, N. R. Ward, C. F. England, and G. E. Hunt

TIROS–N Advanced Very High Resolution Radiometer (AVHRR) imagery has been used to study the temperature structure of the sea surface around the British Isles. We have combined the satellite imagery from both TIROS–N, METEOSAT, and conventional synoptic data to obtain a calibration for both 11 μm infrared channels, which gave sea surface temperatures accurate to ± 1 K. The changes in the sea surface temperature around the British Isles for 12 July 1979 are shown well by the satellite data. In particular, we have made a study of an anomalously warm patch in the North Sea that appeared at local noon over an area where the surface winds were weak, inhibiting surface mixing.

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C. P. Gommenginger, N. P. Ward, G. J. Fisher, I. S. Robinson, and S. R. Boxall

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The capabilities for quantitative measurements of the ocean backscatter at low grazing angles of a conventional low-budget X-band marine radar associated with a commercial digital capture board are investigated. Details are given of the external and internal calibration methods designed to determine the system’s transfer function. This work reveals that the accurate system transfer function can be determined only by calibrating the composite system in one single step. Results of an absolute calibration attempt using buoy-based corner reflectors in very calm weather conditions are presented. The dynamic range is deduced and found to span over a 50-dB range well suited to describe the ocean backscatter coefficient values expected at low grazing angles. The analysis of the overall error budget and system stability provides a theoretical estimate of the system’s relative radiometric resolution. The marine radar system is found to produce backscatter coefficient images with a relative error typically of the order of 1 dB. When averaging over several antenna rotations, the error reduces further down to 0.6 dB, where it compares favorably with the performance of traditional research radar systems. It is concluded that despite the inexpensive nature of these instruments, marine radar systems represent a tool that is effective in routinely providing reliable quantitative measurements of the sea surface roughness, which may serve to complement the synoptic views offered commonly by satellite or airborne radars.

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J. Boutin, Y. Chao, W. E. Asher, T. Delcroix, R. Drucker, K. Drushka, N. Kolodziejczyk, T. Lee, N. Reul, G. Reverdin, J. Schanze, A. Soloviev, L. Yu, J. Anderson, L. Brucker, E. Dinnat, A. Santos-Garcia, W. L. Jones, C. Maes, T. Meissner, W. Tang, N. Vinogradova, and B. Ward

Abstract

Remote sensing of salinity using satellite-mounted microwave radiometers provides new perspectives for studying ocean dynamics and the global hydrological cycle. Calibration and validation of these measurements is challenging because satellite and in situ methods measure salinity differently. Microwave radiometers measure the salinity in the top few centimeters of the ocean, whereas most in situ observations are reported below a depth of a few meters. Additionally, satellites measure salinity as a spatial average over an area of about 100 × 100 km2. In contrast, in situ sensors provide pointwise measurements at the location of the sensor. Thus, the presence of vertical gradients in, and horizontal variability of, sea surface salinity complicates comparison of satellite and in situ measurements. This paper synthesizes present knowledge of the magnitude and the processes that contribute to the formation and evolution of vertical and horizontal variability in near-surface salinity. Rainfall, freshwater plumes, and evaporation can generate vertical gradients of salinity, and in some cases these gradients can be large enough to affect validation of satellite measurements. Similarly, mesoscale to submesoscale processes can lead to horizontal variability that can also affect comparisons of satellite data to in situ data. Comparisons between satellite and in situ salinity measurements must take into account both vertical stratification and horizontal variability.

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Janet Barlow, Martin Best, Sylvia I. Bohnenstengel, Peter Clark, Sue Grimmond, Humphrey Lean, Andreas Christen, Stefan Emeis, Martial Haeffelin, Ian N. Harman, Aude Lemonsu, Alberto Martilli, Eric Pardyjak, Mathias W Rotach, Susan Ballard, Ian Boutle, Andy Brown, Xiaoming Cai, Matteo Carpentieri, Omduth Coceal, Ben Crawford, Silvana Di Sabatino, Junxia Dou, Daniel R. Drew, John M. Edwards, Joachim Fallmann, Krzysztof Fortuniak, Jemma Gornall, Tobias Gronemeier, Christos H. Halios, Denise Hertwig, Kohin Hirano, Albert A. M. Holtslag, Zhiwen Luo, Gerald Mills, Makoto Nakayoshi, Kathy Pain, K. Heinke Schlünzen, Stefan Smith, Lionel Soulhac, Gert-Jan Steeneveld, Ting Sun, Natalie E Theeuwes, David Thomson, James A. Voogt, Helen C. Ward, Zheng-Tong Xie, and Jian Zhong
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