Chapter 17
Applications of Passive and Active
Microwave Sensors to the Study of
Weather Systems over the Ocean
Kristina B. Katsaros
Departement d'Oceanographie Spatiale
IFREMER, B.P. 70,
29280 Plouzane
France
17.1 Introduction
Microwave remote sensing of storms over the ocean from satellites allows special features to be
observed that are not obtainable with visible or infrared instruments. Most frequencies in use
by both passive and active systems are not affected by the small ice particles in cirrus clouds, so
the blocking by these large ice shields that occurs in the visible or infrared is avoided. Emitted
microwave radiation penetrates the clouds and can reach the satellite sensor all the way from
the sea surface at some frequencies. At other frequencies the brightness temperature observed
at the satellite represents the emission by water vapor, cloud liquid water or precipitation in the
column. The roughness of the sea surface affects the emissivity!, and accordingly the intensity
of the emitted radiation is an indicator of the surface wind speed (ifthere is no rain). Likewise
the back-scattering of radar signals by a roughened sea surface corresponds to the surface wind
speed. These features of passive and active microwave radiation have been used to study cloud
systems and cyclonic storms from tropical regions to polar latitudes. Applications of data from
the Special Sensor Microwave/Imager on the U.S. Defense Meteorological Satellites and from
the scatterometer on the European Remote Sensing Satellite-1 will be discussed. Resolution of
the various parameters vary from 15 to 50 km, and are thus rather coarse compared to visible
and infrared data. What they provide is different in nature. Features include: Subtropical
Stratus Clouds
* Estimates of cloud liquid water content can be obtained, albeit with rather large uncertainties.
linstead of" emissivity" often the term" emittance" is used.
NATO ASI Series. Vol. 145
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
Cl Springer-Verlag Berlin HeideJberg 1996
Applications of Passive and Active
Microwave Sensors to the Study of
Weather Systems over the Ocean
Kristina B. Katsaros
Departement d'Oceanographie Spatiale
IFREMER, B.P. 70,
29280 Plouzane
France
17.1 Introduction
Microwave remote sensing of storms over the ocean from satellites allows special features to be
observed that are not obtainable with visible or infrared instruments. Most frequencies in use
by both passive and active systems are not affected by the small ice particles in cirrus clouds, so
the blocking by these large ice shields that occurs in the visible or infrared is avoided. Emitted
microwave radiation penetrates the clouds and can reach the satellite sensor all the way from
the sea surface at some frequencies. At other frequencies the brightness temperature observed
at the satellite represents the emission by water vapor, cloud liquid water or precipitation in the
column. The roughness of the sea surface affects the emissivity!, and accordingly the intensity
of the emitted radiation is an indicator of the surface wind speed (ifthere is no rain). Likewise
the back-scattering of radar signals by a roughened sea surface corresponds to the surface wind
speed. These features of passive and active microwave radiation have been used to study cloud
systems and cyclonic storms from tropical regions to polar latitudes. Applications of data from
the Special Sensor Microwave/Imager on the U.S. Defense Meteorological Satellites and from
the scatterometer on the European Remote Sensing Satellite-1 will be discussed. Resolution of
the various parameters vary from 15 to 50 km, and are thus rather coarse compared to visible
and infrared data. What they provide is different in nature. Features include: Subtropical
Stratus Clouds
* Estimates of cloud liquid water content can be obtained, albeit with rather large uncertainties.
linstead of" emissivity" often the term" emittance" is used.
NATO ASI Series. Vol. 145
Radiation and Water in the Climate System:
Remote Measurements
Edited by Ehrhard Raschke
Cl Springer-Verlag Berlin HeideJberg 1996