Classification of CryoSat-2 Radar Echoes - Towards an Interdisciplinary Approach in Earth System Science - page 137

Classification of CryoSat-2 Radar Echoes

Robert Ricker, Stefan Hendricks, Veit Helm and R ü diger Gerdes

Abstract Sea-ice thickness at global scale is an important variable in the polar
climate system. Only satellite altimeters such as onboard the CryoSat-2 mission
allow us to obtain sea-ice thickness on hemispherical scale. Accurate CryoSat-2
altimeter range measurements provide surface elevations which have to be refer-
enced to the local sea level to obtain sea-ice freeboard that can be converted into
sea-ice thickness assuming hydrostatic equilibrium. The local sea-surface height is
determined by careful detection of leads in the ice surface using the speci

c

characteristics of the radar signal. Off-nadir re cantly

affect the range retracking and hence bias the surface elevations of leads and sea ice.
This can

fl ections from leads can signi

finally lead to a negative freeboard and hence also affects the thickness and
volume retrieval. We present a method for the classi cation of CryoSat-2 radar

echoes to correctly discriminate between valid and off-nadir biased echoes. We
apply our classi

cation to a CryoSat-2 track from December 15 where 50 leads over
a distance of 2,300 km are identi ed. Overall 22 % of the surface elevations are

associated with biased radar echoes.