Description: The only remote sensing technique capable of obtain- ing sea-ice thickness on basin-scale are satellite altime- ter missions, such as the 2010 launched CryoSat-2. It is equipped with a Ku-Band radar altimeter, which mea- sures the height of the ice surface above the sea level. This method requires highly accurate range measure- ments. During the CryoSat Validation Experiment (Cry- oVEx) 2011 in the Lincoln Sea, Cryosat-2 underpasses were accomplished with two aircraft, which carried an airborne laser-scanner, a radar altimeter and an electro- magnetic induction device for direct sea-ice thickness re- trieval. Both aircraft flew in close formation at the same time of a CryoSat-2 overpass. This is a study about the comparison of the sea-ice freeboard and thickness dis- tribution of airborne validation and CryoSat-2 measure- ments within the multi-year sea-ice region of the Lincoln Sea in spring, with respect to the penetration of the Ku- Band signal into the snow.

Description: Large areas of the Arctic Ocean are covered with sea ice, the extent, thickness, concentration and properties of which change seasonally, interannually and on longer time scales. The Arctic Ocean is often difficult to access, making satellite remote sensing the only means to obtain information about the sea ice on a pan-Arctic scale. In order to improve the processing and interpretation of satellite data and imagery, in-situ calibration and validation are necessary. In spring 2011, measurements on first year sea ice north of Svalbard were performed during two scientific cruises with the ships KV “Svalbard” and RV “Lance” as a part of the CryoVEx 2011 project. During these cruises, detailed measurements of snow and ice thickness, freeboard, and snow density were performed on ice stations and from a helicopter. The data collected contributes to the calibration and validation of the SIRAL sensor data from the CryoSat-2 radar altimeter satellite, which measures the freeboard of sea ice for estimating its thickness. In snow pits, the stratigraphy of the snow pack was recorded. The collected data are currently being integrated with satellite data, airborne observations from helicopter that measured ice thickness using an electromagnetic induction sounder (EM-bird) and conducted aerial photography, and a Twin-Otter aircraft carrying the ESA Airborne Synthetic Aperture and Interferometric Radar Altimeter System (ASIRAS) system, the airborne radar altimeter designed to simulate the SIRAL radar on board the satellite, as well as a laser scanner. The first analysis of airborne and in- situ data indicates that the ASIRAS radar altimeter used in this experiment did not fully penetrate the snow layer on top of the sea ice. The regional sea ice characteristics for the research area are described using SAR products, obtained from the Envisat and Radarsat-2 satellites, in order to improve the interpretation and conclusions of the CryoSat-2 calibration and validation.

Description: We show first results of a combined ground based and airborne validation campaign for CryoSat-2 synthetic aperture interferometric radar altimeter (SIRAL) measurements over Austfonna, Svalbard. A decade time series of glacier facies for this ice cap interpreted from 800 MHz ground-penetrating radar data clearly show there to be considerable variation within the firn pack, which needs to be captured by CryoSat-2 if we are to correctly interpret the satellite observed surface changes. The ground based radar data were obtained with a CRESIS Ku-band FMCW radar. The radar was operated to cover the frequency band of the CryoSat-2 SIRAL and the airborne version, Airborne Synthetic Aperture and Interferometric Radar Altimeter System (ASIRAS) carried by the Danish geophysics plane. Simultaneous profiles were obtained within half a day of each other with all three radars during the spring calibration/validation campaign on the Austfonna ice cap, Svalbard. The profiles, totaling approximately 200 km, span an elevation change of 400 m from the summit down to the ablation area, and cover a range of glacier facies and surface snow conditions. The ground based KU-band radar, which clearly images the near surface layering, was supported by manual snow depth sounding, 800 MHz radar, snow pits, firn cores, and borehole videos, all of which are used to validate interpretation of the CryoSat-2 data.

Description: CryoSat-2 was launched in April 2010, as part of the European Space agency's (ESA) Earth Opportunity Programmes. The primary scientific objectives of the mission are to determine changes of the ice sheet elevation and sea ice thickness within its nominal lifetime of five years to get a better understanding of the short-term response of the Cryosphere to climate change. In order to validate the scientific data products four post-launch CryoSat Calibration/Validation Experiments (CryoVEx) were carried out since CryoSat-2’s successful launch. The CryoVEx campaigns included co-coordinated field and airborne measurements at selected validation sites in the Arctic and Antarctica. We will present first results of CryoSat-2 comparisons with GPS data acquired at the Halvfarryggen ice dome in Dronning-Maud-Land (DML), Antarctica during CryoVExANT-2010. A second comparison will be shown with airborne laser scanner data acquired during the same campaign in the Blue Ice area next to Novo runway also situated in DML. The GPS and laser scanner data will be used as reference elevation for the analysis. For our comparisons, we use CryoSat-2 level 1b and level 2 data products acquired in the SARIn mode, since the validation sites are close to the coast with surface slopes of up to one degree. Both sites have different snow/firn properties, which can be used to determine the penetration depth of the Ku-Band signal. The area around Halvfarryggen is characterised by a strong east-west gradient in snow accumulation rate, ranging from 0.5 m to 3 m firn per year. The Novo area is pure Blue Ice, covered with small patches of snow. Therefore, different backscatter mechanism will dominate the received radar signal, volume scattering at the Halvfarryggen and surface scattering in the Blue Ice area, respectively. For volume scattering, the re-tracked surface elevation is typically biased with the effective penetration depth of the radar signal. In the Blue Ice area no signal penetration is expected and the re-tracked radar elevation should resemble the GPS determined surface elevation. Apart from results with respect to penetration depth, we will get a first estimate of the accuracy of the CryoSat-2 SARIn product using interferometric phase processing which accounts for across track slopes.

Description: Sea ice thickness on basin-scale is an important variable in the polar climate system, however datasets are sparse. The only remote sensing technique capable of obtaining sea ice thickness on that scale are satellite altimeter missions, such as the ICESat and CryoSat-2. The CryoSat-2 satellite was launched in 2010 and is equipped with the Ku-Band radar altimeter SIRAL. CryoSat-2 is part of the ESA’s Living Planet Programme and was especially developed for the observation of changes in the cryosphere. This includes especially the determination of variations in sea ice thickness in the Arctic Ocean. For that purpose it is essential to validate the Cryosat-2 products. The CryoSat Validation Experiment (CryoVEx) combines field and airborne measurements in the Arctic and Antarctica in order to validate CryoSat measurements. Here we report the results from the first combined aircraft and satellite data acquisition over sea ice in the Arctic Ocean. The aircraft was equipped with ASIRAS, an airborne radar altimeter, which was built to simulate the SIRAL sensor on CryoSat-2. During the CryoVEx 2011 campaign in the Lincoln Sea several Cryosat-2 underpasses were accomplished with two aircraft. One aircraft was equipped with ASIRAS and an airborne laser scanner; the second aircraft carried an electromagnetic induction device for direct sea ice thickness retrieval and an airborne laser scanner as well. Both aircraft flew in close formation at the same time of a CryoSat-2 overpass. This is a presentation about the results from comparing sea ice freeboard distribution of laser and radar altimeter measurements with the CryoSat-2 product within the multi-year sea ice region of the Lincoln Sea in spring, with respect to the penetration of the Ku-Band signal into the snow and the effect of surface roughness on the radar range retrieval.