Chapter 7
Interpretation of SAR Signatures of the Sea
Surface: A Multi-sensor Approach
Leonid M. Mitnik and Vyacheslav A. Dubina
7.1 Introduction
During the last decade, satellite microwave sensors such as multichannel scanning
radiometers, scatterometers and altimeters have provided extensive time series of
upper ocean data. When combined with longer time series from visible and infrared
(IR) sensors, the picture of the complexity of upper ocean and coastal zone processes, and of air-sea-ice interaction, is broadened significantly. Large-scale ocean
processes are becoming better understood, leading researchers and modellers to
probe further into mesoscale processes (up to 200 km) where significant energy
exchanges and air-sea-ice interactions are occurring. Meandering currents are a
dominant feature of many open ocean and coastal waters and often appear in patterns
of Sea Surface Temperature (SST) and Chlorophyll a (chl-a) concentration in visible
and thermal images acquired by satellite sensors. Furthermore, these currents often
develop sharp fronts and eddies that affect wind-wave-current interactions, leading
to both wave refraction and small scale surface roughness anomalies. These in turn,
provide distinct expressions in both high resolution visible and Synthetic Aperture
Radar (SAR) images (Johannessen et al., 2006). SAR backscatter signals come from
the sea surface roughness with wavelengths which are approximately similar to the
SAR wavelength (between a few to a few of tens centimeter). The roughness is controlled by local wind, wave-current interaction, as well as by the presence of surface
active films or grease ice.
In the early 2000s, the unique and detailed ocean surface information in SAR
imagery from ERS-2, RADARSAT-1, Envisat ASAR and recently launched ALOS,
TerraSAR-X, COSMO-SkyMed, and RADARSAT-2 has been used successfully
with other ocean sensors, buoy and ship data, and regional wind/wave models to
improve our understanding of coastal and open ocean processes on these scales.
Sombining SAR images with those collected by the MODIS spectroradiometer,
L.M. Mitnik (B)
Satellite Oceanography Department, V.I. Il’ichev Pacific Oceanological Institute, Far Eastern
Branch of the Russian Academy of Sciences, Vladivostok 690041, Russia
e-mail: mitnik@poi.dvo.ru
113
V. Barale et al. (eds.), Oceanography from Space,
DOI 10.1007/978-90-481-8681-5_7, C
Springer Science+Business Media B.V. 2010
Interpretation of SAR Signatures of the Sea
Surface: A Multi-sensor Approach
Leonid M. Mitnik and Vyacheslav A. Dubina
7.1 Introduction
During the last decade, satellite microwave sensors such as multichannel scanning
radiometers, scatterometers and altimeters have provided extensive time series of
upper ocean data. When combined with longer time series from visible and infrared
(IR) sensors, the picture of the complexity of upper ocean and coastal zone processes, and of air-sea-ice interaction, is broadened significantly. Large-scale ocean
processes are becoming better understood, leading researchers and modellers to
probe further into mesoscale processes (up to 200 km) where significant energy
exchanges and air-sea-ice interactions are occurring. Meandering currents are a
dominant feature of many open ocean and coastal waters and often appear in patterns
of Sea Surface Temperature (SST) and Chlorophyll a (chl-a) concentration in visible
and thermal images acquired by satellite sensors. Furthermore, these currents often
develop sharp fronts and eddies that affect wind-wave-current interactions, leading
to both wave refraction and small scale surface roughness anomalies. These in turn,
provide distinct expressions in both high resolution visible and Synthetic Aperture
Radar (SAR) images (Johannessen et al., 2006). SAR backscatter signals come from
the sea surface roughness with wavelengths which are approximately similar to the
SAR wavelength (between a few to a few of tens centimeter). The roughness is controlled by local wind, wave-current interaction, as well as by the presence of surface
active films or grease ice.
In the early 2000s, the unique and detailed ocean surface information in SAR
imagery from ERS-2, RADARSAT-1, Envisat ASAR and recently launched ALOS,
TerraSAR-X, COSMO-SkyMed, and RADARSAT-2 has been used successfully
with other ocean sensors, buoy and ship data, and regional wind/wave models to
improve our understanding of coastal and open ocean processes on these scales.
Sombining SAR images with those collected by the MODIS spectroradiometer,
L.M. Mitnik (B)
Satellite Oceanography Department, V.I. Il’ichev Pacific Oceanological Institute, Far Eastern
Branch of the Russian Academy of Sciences, Vladivostok 690041, Russia
e-mail: mitnik@poi.dvo.ru
113
V. Barale et al. (eds.), Oceanography from Space,
DOI 10.1007/978-90-481-8681-5_7, C
Springer Science+Business Media B.V. 2010