Testing Sea Ice Motions from Sequential Passive Microwave Observations with ERS SAR and Buoy Ice Motions.

by R. Kwok, A. Schweiger, D.A. Rothrock, and C. Kottmeier

Observing the motion of sea ice from space is rather analogous to observing wind
stress over the wet oceans: both provide surface forcing for modeling ocean
dynamics.  Ice motion is also directly provides the advective component of the
equations governing the mass balance of the sea ice cover.  Thus its routine
observation from space is of great value to understanding ice and ocean
behavior.  We have estimated ice motion from sequential passive microwave
imagery: both the 85 GHz channel of SSM/I and the 37 GHz channel of SMMR.  The
method, which has been well used previously, involves finding the spatial offset
that maximizes the cross-correlation of the brightness temperature fields over
100 kilometer patches in two images separated in time.  The problems with using
passive microwave imagery arise from its rather coarse spatial resolution of 12
km for the 85 GHz and 25 km for the 37 GHz data.  The ice moves only about 10 km
per day.  The time interval between tracking images must be chosen to allow the
ice to move as far as possible without having the ice cover deform so strongly
or the appearance of the surface change so drastically that the tracker cannot
recognize the same patch of ice in its new location.  We assess the quality of
motions tracked over one day intervals and motions tracked over three days.  We
take as the "truth" motions observed by drifting buoys and by tracking high
resolution ERS SAR imagery.  We find rms errors of from 5 to 15 km in the
displacements.  Errors seem to be largest in the most dynamic regions, in
particular near the ice edge in the Barents and Greenland seas, and in zones
with high shear.  We believe a useful record of ice motion can be established
for the duration of the SMMR and SSMI sensors: that is, from 1978 into the next
millenium.

Presenter: D. A. Rothrock

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry