Airborne scatterometers: investigating ocean backscatter under low- and high-wind conditions

Attempting to understand and predict weather on a local and global basis has challenged both the scientific and engineering communities. One key parameter in understanding the weather is the ocean surface wind vector because of its role in the energy exchange at the air-sea surface. scatterometers, radars that measure the reflectivity of a target offer a tool with which to remotely monitor these winds from tower-, aircraft-, and satellite-based platforms. This paper introduces three current airborne scatterometer systems, and presents data collected by these instruments under low-, moderate-, and high-wind conditions. The paper focuses on airborne scatterometers because of their ability to resolve submesoscale variations in wind fields. Discrepancies between existing theory and the observations are noted and the concerns in measuring low-wind speeds discussed. Finally, the application of using this technology for estimating the surface-wind vector during a hurricane is demonstrated. >

[1]  P. Black,et al.  SEASAT scatterometer detection of gale force winds near tropical cyclones , 1983 .

[2]  W. Plant.  A two-scale model of short wind-generated waves and scatterometry , 1986 .

[3]  S. Durden,et al.  A physical radar cross-section model for a wind-driven sea with swell , 1985, IEEE Journal of Oceanic Engineering.

[4]  W. Timothy Liu,et al.  Determination of surface stress by Seasat-SASS - A case study with JASIN data , 1981 .

[5]  David G. Long,et al.  Spaceborne radar measurement of wind velocity over the ocean-an overview of the NSCAT scatterometer system , 1991, Proc. IEEE.

[6]  W. Linwood Jones,et al.  Radar backscatter from the ocean: Dependence on surface friction velocity , 1978 .

[7]  W. Linwood Jones,et al.  The Seasat-A satellite scatterometer - The geophysical evaluation of remotely sensed wind vectors over the ocean , 1982 .

[8]  J. Wright.  A new model for sea clutter , 1968 .

[9]  Werner Alpers,et al.  Tower‐based measurements of the ocean C band radar backscattering cross section , 1989 .

[10]  A.K. Fung,et al.  Radar determination of winds at sea , 1979, Proceedings of the IEEE.

[11]  R. Moore,et al.  Radar sea return and the radscat satellite anemometer , 1972 .

[12]  C. Cox.  Statistics of the sea surface derived from sun glitter , 1954 .

[13]  David E. Weissman,et al.  Dependence of the microwave radar cross section on ocean surface variables: Comparison of measurements and theory using data from the Frontal Air-Sea Interaction Experiment , 1990 .

[14]  A. Fung,et al.  A backscattering model for ocean surface , 1992, IEEE Trans. Geosci. Remote. Sens..

[15]  S. Rice.  Reflection of electromagnetic waves from slightly rough surfaces , 1951 .

[16]  Richard K. Moore,et al.  Worldwide Oceanic Wind and Wave Predictions Using a Satellite Radar-Radiometer , 1970 .

[17]  M. Donelan,et al.  Radar scattering and equilibrium ranges in wind‐generated waves with application to scatterometry , 1987 .

[18]  L. Schroeder,et al.  AAFE RADSCAT 13.9-GHz measurements and analysis: Wind-speed signature of the ocean , 1985, IEEE Journal of Oceanic Engineering.

[19]  G. Bradley.  Remote sensing of ocean winds using a radar scatterometer , 1971 .

[20]  John C. Daley.  Wind dependence of radar sea return , 1973 .

[21]  N. E. Huang,et al.  Riding the crest : a tale of two wave experiments , 1991 .

[22]  Werner Alpers,et al.  Airborne measurements of the ocean radar cross section at 5.3 GHz as a function of wind speed , 1986 .

[23]  Kenneth L. Davidson,et al.  Ocean Radar Backscatter Relationship with Near-Surface Winds: A Case Study during FASINEX , 1989 .

[24]  William J. Plant,et al.  A wave tank study of the dependence of X band cross sections on wind speed and water temperature , 1992 .

[25]  H. Masuko,et al.  Measurement of microwave backscattering signatures of the ocean surface using X band and Ka band airborne scatterometers , 1986 .

[26]  G. Valenzuela.  Theories for the interaction of electromagnetic and oceanic waves — A review , 1978 .

[27]  William J. Plant,et al.  The dependence of X band microwave sea return on atmospheric stability and sea state , 1985 .

[28]  W. Grantham,et al.  The SeaSat-A satellite scatterometer , 1977 .

[29]  J. Young,et al.  Active microwave measurement from space of sea-surface winds , 1977, IEEE Journal of Oceanic Engineering.

[30]  C. R. Grant,et al.  Back Scattering from Water and Land at Centimeter and Millimeter Wavelengths , 1957, Proceedings of the IRE.

[31]  I. Ostrovsky,et al.  Very high frequency radiowave scattering by a disturbed sea surface Part I: Scattering from a slightly disturbed boundary , 1968 .

[32]  W. Plant,et al.  Relating The Microwave Radar Cross Section To The Sea Surface Stress: Developing A New Model Function , 1991, OCEANS 91 Proceedings.

[33]  F. J. Wentz,et al.  A model function for ocean radar cross sections at 14.6 GHz , 1984 .

[34]  A. K. Fung,et al.  A scattering model for perfectly conducting random surfaces. I - Model development. II - Range of validity , 1987 .

[35]  W. L. Jones,et al.  Aircraft measurements of the microwave scattering signature of the ocean , 1977 .

[36]  Comparison of Seasat scatterometer winds with tropical Pacific observations , 1990 .

[37]  M. C. Colton,et al.  Dependence of radar backscatter on the energetics of the air-sea interface , 1990, 10th Annual International Symposium on Geoscience and Remote Sensing.

[38]  G. Geernaert,et al.  On the wind power law and atmospheric stability effects in ocean scatterometry , 1992 .