Ku- and Ka-band polarimetric radar backscatter of Arctic sea ice between October 2019 and September 2020

• Main Authors: Stroeve, Julienne, Nandan, Vishnu, Tonboe, Rasmus, Hendricks, Stefan, Ricker, Robert, Spreen, Gunnar
• Format: Dataset
• Language: English
• Published: UK Polar Data Centre, Natural Environment Research Council, UK Research & Innovation 2020
• Subjects: "EARTH SCIENCE","CRYOSPHERE","SEA ICE","ICE DEPTH/THICKNESS"; "EARTH SCIENCE","CRYOSPHERE","SEA ICE","ICE FLOES"; "EARTH SCIENCE","CRYOSPHERE","SEA ICE","SNOW DEPTH"; "EARTH SCIENCE","OCEANS","SEA ICE","ICE DEPTH/THICKNESS"; "EARTH SCIENCE","OCEANS","SEA ICE","ICE FLOES"; "EARTH SCIENCE","OCEANS","SEA ICE","SNOW DEPTH"; Arctic; MOSAiC; backscatter; polarimetry; radar; scatterometry; sea ice; snow; Canada; Sea ice
• Online Access: https://dx.doi.org/10.5285/5fb5fbde-7797-44fa-afa6-4553b122fdef; https://data.bas.ac.uk/full-record.php?id=GB/NERC/BAS/PDC/01437

This data set provides processed Ku- and Ka-band fully-polarimetric backscatter and derived polarimetric parameters from hourly scans, acquired using the KuKa radar, during Legs 1, 2, 4 and 5 of the 2019-2020 MOSAiC International Arctic Drift Expedition. Scans were acquired during winter (Legs 1 and 2), advanced melt (leg 4) and freeze-up (Leg 5) seasons, from various Remote Sensing (RS) sites, located in the MOSAiC ice floe. The first deployment of the KuKa radar was on 18 October 2019 at RS1 site and the radar was retreated (due to ice break up) on 18th November. The radar was redeployed on 29th November at RS2 site until 13th December when cracks were observed at the site and the instrument was turned off and moved to a safe location. The radar was redeployed at RS3 site and started measuring again on 21st December 2019 until 31st January 2020, after which the radar was taken off the RS site to conduct maintenance. The radar was not operational during Leg 3. During Leg 4, the radar was operational between 25th June and 19th July 2020, and later retreated back to the ship, for deployment in Leg 5. The radar was deployed on 24th August 2020 and operational until the end of the MOSAiC expedition. The dataset was collected by MOSAiC Team ICE participants and processed by Vishnu Nandan at the University of Manitoba, Canada. This work was funded in part through NERC grant NE/S002510/1, the Canada 150 Chair Program and the European Space Agency PO 5001027396. The authors thank Marine Environmental Observation, Prediction and Response Network (MEOPAR) Postdoctoral Fellowship grant to Vishnu Nandan. The authors also thank the crew of R/V Polarstern and all scientific members of the MOSAiC expedition for their support in field logistics and field data collection. : During data acquisition, the KuKa radar acquires data on a series of six signal states: the four transmit polarization combinations (VV, HH, HV and VH), a calibration loop signal and a noise signal. Each data block consists of these six signals and are processed separately for each frequency. Data are processed into range profiles of the complex received voltage, through fast fourier transform (FFT). The range profiles for each polarization combination are power-averaged in azimuth for each incidence angle. Both the Ka- and Ku-band scatterometer beam scans at the programmed incidence angle, moving across the azimuth within a prescribed azimuthal angular width. The system then moves up to the next incidence angle, at 5 degree increments, and scans the next elevation line along the same azimuthal angular width. A new file is generated each time the positioner begins a scan. The footprint of the KuKa radar during one complete scan is a function Ku- and Ka-band antenna beamwidth, and the system geometry, with the footprint increasing in area, as incidence angle increases. The raw Ku- and Ka-band radar data are stored in the KuKa radar system as .dat files, and needs to be manually downloaded from the radar's internal data drive. The radar processing IDL program is used to process the raw files and converts them into readable output data. The IDL code ingests the raw data and is post-processed using the calibration file, to derive the second-order covariance matrix, and fully-polarimetric backscatter (VV, HH, HV and VH; in dB scale). This procedure is done across the entire azimuthal angular width, for every incidence angle. The output data also contains the polarimetric parameters such as the co-polarized phase difference (in degrees) and co-polarized correlation coefficient, derived along with the polarimetric backscatter from the average covariance matrix (derived from the complex scattering matrix), of all azimuthal data blocks, within every incidence angle scan line. Using the polarimetric backscatter, user can derive other parameters such as the co-polarized and cross-polarized ratios. The output file also contains the date and time information (in UTC) and the geographical coordinates (latitude and longitude) at the time of data acquisition. The radar also records the actual incidence angle (accounting for the angle offsets) for every scan and records them in the output file. During the IDL processing, the user will be able to see the power-range and polarization signature plots for every incidence angle step, and can be saved by modifying the IDL script. The user can also modify the configuration .txt files to change the processing routine. The final processed files can be imported into any text reading program such as notepad, wordpad or excel to use the data for analysis. : KuKa radar : An experiment was done to investigate the response of the internal calibration loop in comparison to the KuKa radar's response when a metal plate was placed on the surface. This serves as a vertical height reference for the Ku- and Ka-band radar returns, and demonstrates the response of the system to a flat, highly-scattering surface. The metal plate and calibration loop data are consistent and in good agreement with each other, which indicates that the shape of the return including internal reflections are well characterized in the calibration data. For more details, refer to https://doi.org/10.5194/tc-2020-151.