Thin Sea-Ice Thickness as Inferred from Passive Microwave and In Situ Observations

Since microwave radiometric signals from sea-ice strongly reflect physical conditions of a layer near the ice surface, a relationship of brightness temperature with thickness is possible especially during the early stages of ice growth. Sea ice is most saline during formation stage and as the salinity decreases with time while at the same time the thickness of the sea ice increases, a corresponding change in the dielectric properties and hence the brightness temperature may occur. This study examines the extent to which the relationships of thickness with brightness temperature (and with emissivity) hold for thin sea-ice, approximately less than 0.2 -0.3 m, using near concurrent measurements of sea-ice thickness in the Sea of Okhotsk from a ship and passive microwave brightness temperature data from an over-flying aircraft. The results show that the brightness temperature and emissivity increase with ice thickness for the frequency range of 10-37 GHz. The relationship is more pronounced at lower frequencies and at the horizontal polarization. We also established an empirical relationship between ice thickness and salinity in the layer near the ice surface from a field experiment, which qualitatively support the idea that changes in the near-surface brine characteristics contribute to the observed thickness-brightness temperature/emissivity relationship. Our results suggest that for thin ice, passive microwave radiometric signals contain, ice thickness information which can be utilized in polar process studies

Physical and Radiative Characteristics and Long Term Variability of the Okhotsk Sea Ice Cover

Much of what we know about the large scale characteristics of the Okhotsk Sea ice cover comes from ice concentration maps derived from passive microwave data. To understand what these satellite data represents in a highly divergent and rapidly changing environment like the Okhotsk Sea, we analyzed concurrent satellite, aircraft, and ship data and characterized the sea ice cover at different scales from meters to tens of kilometers. Through comparative analysis of surface features using co-registered data from visible, infrared and microwave channels we evaluated how the general radiative and physical characteristics of the ice cover changes as well as quantify the distribution of different ice types in the region. Ice concentration maps from AMSR-E using the standard sets of channels, and also only the 89 GHz channel for optimal resolution, are compared with aircraft and high resolution visible data and while the standard set provides consistent results, the 89 GHz provides the means to observe mesoscale patterns and some unique features of the ice cover. Analysis of MODIS data reveals that thick ice types represents about 37% of the ice cover indicating that young and new ice represent a large fraction of the lice cover that averages about 90% ice concentration, according to passive microwave data. A rapid decline of -9% and -12 % per decade is observed suggesting warming signals but further studies are required because of aforementioned characteristics and because the length of the ice season is decreasing by only 2 to 4 days per decade

Physical and Radiative Characteristic and Long-term Variability of the Okhotsk Sea Ice Cover

Much of what we know about the large scale characteristics of the Okhotsk Sea ice cover has been provided by ice concentration maps derived from passive microwave data. To understand what satellite data represent in a highly divergent and rapidly changing environment like the Okhotsk Sea, we take advantage of concurrent satellite, aircraft, and ship data acquired on 7 February and characterized the sea ice cover at different scales from meters to hundreds of kilometers. Through comparative analysis of surface features using co-registered data from visible, infrared and microwave channels we evaluated the general radiative and physical characteristics of the ice cover as well as quantify the distribution of different ice types in the region. Ice concentration maps from AMSR-E using the standard sets of channels, and also only the 89 GHz channel for optimal resolution, are compared with aircraft and high resolution visible data and while the standard set provides consistent results, the 89 GHz provides the means to observe mesoscale patterns and some unique features of the ice cover. Analysis of MODIS data reveals that thick ice types represents about 37% of the ice cover indicating that young and new ice types represent a large fraction of the ice cover that averages about 90% ice concentration according to passive microwave data. These results are used to interpret historical data that indicate that the Okhotsk Sea ice extent and area are declining at a rapid rate of about -9% and -12 % per decade, respectively

Characteristics of sea ice floe size distribution in the seasonal ice zone

The size distribution of sea ice floes was observed by coordinated Landsat imagery and video monitoring conducted from an icebreaker and a helicopter for an area 38 km × 26 km in seasonal sea ice in the southern Sea of Okhotsk in February 2003. The combination of imagery on several scales allowed measurements of ice floes over three orders of magnitude, from 1 m to 1.5 km. Two different regimes were observed: floes larger than about 40 m have a power-law number density with an exponent of −1.87, in the lower range of earlier results. Below 40 m, the power law exponent is −1.15. The cause of these two different regimes is hypothesized to lie in the effects of swell on floes of different sizes and thicknesses. The importance of the floe size distribution for lateral melting is elucidated.An edited version of this paper was published by AGU Copyright 2006, American Geophysical Union,Geophysical Research Letters , vol.3

VALIDATION OF AMSR-E ICE CONCENTRATION & THICKNESS IN THE OKHOTSK SEA

The data from aircraft and ship campaigns in February 2003 in conjunction with high resolution satellite images for validating sea ice concentrations and thickness derived from AMSR-E brightness temperatures are presented. Patrol Vessel "SOYA" conducted time series observations of sea ice parameters such as ice type, floe size, snow thickness, density, grain size on sea ice and ice surface temperature, and salinity. Surface data by ship were used to interpret aircraft microwave (PSR) and visible channel data obtained by the high resolution Landsat-7 and MODIS images. The latter data were utilized to interpret the ice concentration derived from AMSR-E. The co-registered images of aircraft PSR, Landsat-7 and MODIS data exhibit good coherence in signatures. In highly consolidated ice cover, the ice concentrations were in good agreement within 5 to 10% in ice concentration. However, in highly divergent areas, the derived ice concentration has a negative bias due to the dominant presence of new ice. The new ice has relatively lower emmissivity than first year ice which is snow cover and is affected with waves and wetness by flooding. The relationship between the thickness and brightness temperature of sea ice was obtained in detai