Seamless Transition from LRM to SAR in the Arctic Ocean

Conventional altimetry from ERS-1/ERS-2 and ENVISAT provides LRM altimetry in the Arctic Ocean since 1991 which have enabled us to derive a continuous record within the ESA sea level CCI initiative for 20 years up to latitude 82. With the launch of SAR altimery onboard Cryosat-2 and with the availability of SARAL/ALtiKA Ka band altimetry two new sensors providing accurate the sea level mapping in the Arctic Ocean has been available since 2010. Extending the sea level time series derived with LRM altimetry with SAR sea level time series in the Arctic Ocean is far from trivial. The first results from studies indicate that the difference in spatio-temporal coverage of the two sensors and the possibility to discriminate sea level within leads using SAR gives a spatially varying bias between the two sensors depending on ice concentration. Another problem for the combination of the time series is the fact that Cryosat-2 does not carry a radiometer. Subsequently care has to be taken to which corrections are applied to the LRM and SAR altimetry datasets, respectively. Our initial finding is that spatial averaged
data (and the related timeserie) from Cryosat-2 is lower than the corresponding time series for ENVISAT in the overlapping period during 2010 and 2011. Trying to integrate and extend the sea level time series in the Arctic Ocean with SARAL/AltiKa since 2013 has the further complication that the Ka band vs the Ku band altimeter has different scattering positions in the icecolumn. In this presentation we will present our results to compute and quantify the inter-satellite biases between ENVISAT Cryosat-2 and SARAL/AltiKa in the icecovered parts of the Arctic Ocean.