Ship Technology
-- Ship Technology --
Real-Time Remote Sensing for Ice Navigation
Caren Garrity, Dan Lubin and Rn O. Ramseier
AOS-94 explored areas never before studied by surface ships. An investiga-
tion of historical ice conditions indicated that we could expect an average of
83 11% ice concentration along the planned route to the North Pole. A
major advantage of this expedition was the installation onboard the Polar Sea
of a TeraScan receiver and processing system developed by SeaSpace Corpora-
tion. The system was capable of real-time reception and processing of imagery
from the advanced very high resolution radiometer (AVHRR) on NOAA satel-
lites as well as the special sensor microwave imager (SSM/I) data from the
Defense Meteorological Satellite Program (DMSP) satellites.
sensors are useful for real-time weather information. Their usefulness for moni-
toring ice motion on this voyage was extremely limited due to the nearly con-
stant cloud cover and considerable fog. During AOS-94, 5.3% of the transit days
to the North Pole were nearly cloud free, and 17 days were free from fog. To be
useful for ice navigation, a satellite sensor needs to "see" through clouds and fog.
Three SSM/I algorithms were used to map sea ice during AOS-94: NASA
Team (NASA, U.S.), AES (Canadian Atmospheric Environment Service) and
85 GHz (Scripps, U.S.). The former two algorithms provide coarser-resolution
ice maps by combining the lower-frequency channels of the satellite sensor (19
and 37 GHz). Previous comparisons of these are summarized, including an
error analysis, in Steffen et al. (1992). The 85-GHz ice concentration maps
have twice the resolution (12.5 km), and the new 85-GHz algorithm is summar-
ized in Lomax et al. (1995). The reported error for derived total ice concentra-
tions during the winter is approximately 9% for the NASA Team and AES
algorithms. This error is due to signature uncertainty and the uncertainty in
atmospheric parameters, including instrument noise effects. As a result of this
experiment the 85-GHz algorithm has been evaluated (Lubin et al. 1996)
While AOS-94 was useful for comparing the ice concentrations derived
from the three algorithms, it is difficult to "validate" the sea ice algorithms,
since observing ice from the bridge of a ship is somewhat qualitative and the
visibility is limited to a small area. The visibility was estimated to be from 0.05 to
Caren Garrity and Rn Ramseier are with the Microwave GroupOttawa River, Inc., in Dunrobin, Ontario,
Canada. Dan Lubin is with the California Space Institute at the University of CaliforniaSan Diego in La Jolla,
California, U.S.A.
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