DOI: 10.1594/pangaea.909683
title: ASI3 northern hemisphere swath brightness temperatures and gridded sea ice concentration

description: Since the launch of the AMSR series satellites in 2002, brightness temperatures are observed at 89 GHz with a much improved spatial resolution at about 5 km. Ice concentration retrieval using measurements at this frequency can therefore reveal more detailed features such as leads. Brightness temperatures at 89 GHz are however more prone to atmospheric and surface influences from water vapor, liquid water path, wind and surface temperature, which leads to erroneous sea ice retrieval. We improve an 89 GHz sea ice retrieval method, the ARTIST Sea Ice (ASI) algorithm, by correcting the observed brightness temperatures for atmospheric influences before they are input to the algorithm. A new retrieval algorithm named ASI3 is developed based on the weather corrected brightness temperatures and newly identified open water (80 K) and sea ice (14 K) tie points.The most influencing component of this correction scheme is including liquid clouds, the largest weather influence contributor. The correction is carried out by simulating brightness temperatures through a radiative transfer model and geophysical data retrieved by an optimal estimation method. -----------------------------This data set contains the ASI3 swath weather corrected brightness temperatures and the ASI3 daily gridded sea ice concentration in the northern hemisphere above latitude 50N.The corrected brightness temperatures are based on the AMSR-E Level 2A spatially resampled data at the resolution of 18.7 GHz channel (21km).The sea ice concentration data are derived from the corrected 89 GHz brightness temperatures, gridded to polar stereographic projection at 6.25km resolution.Each swath corrected brightness temperature file is packaged with geolocation coordinates.The coordinates of the daily gridded ice concentration are packaged in one standalone file.File information- Format Data are in HDF5 format. The geolocaton data fields are in H5T_IEEE_F32LE format. All the other data fields are in H5T_IEEE_F64LE.- File Naming Convention 1. Corrected swath brightness temperature files ASI2_200601110038_oem_clwon_asiwf_10c.hdf5 ASI2_yyyymmddhhmm_atm_clwswitch_cin_oemver.hdf5 yyyy: four-digit year mm: two-digit month dd: two-digit day hh: hour, listed in UTC time, of first scan in the AMSR-E swath mm: minutes, listed in UTC time, of first scan in the AMSR-E swath atm: atmospheric data used for the weather correction. The ASI3 algorithm uses Optimal Estimation Method (OEM) data set. clwswitch: clwon or clwoff, switch for cloud liquid water correction. cin: input ice concentration for the weather correction. The ASI3 algorithm uses ASI ice concentration with relaxed open water filter. oemver: version of the input OEM data. 10c means OEM uses the lowest ten channels of AMSR-E measurements. 2. Gridded ice concentration files asi3_sic_20060302_oem_asiwf_clwon_10c.hdf5 asi3_sic_yyyymmdd_atm_cin_clwswitch_oemver.hdf5 The file name variables have the same meaning as in the brightness temperatures files.3. Coordinates of the gridded ice concentration data nsidc_coord_arctic_6.25km.h5Detailed data fields description 1. Corrected swath brightness temperature files - low resolution data group: 'low_res_swath' major parameters: - latlo: latitude of the low resolution swath of AMSR-E - lonlo: longitude of the low resolution swath of AMSR-E - v6c, h6c, v10c, h10, v18c, h18c, v23c, h23c, v36c, h36c, v89c, h89c: corrected brightness temperatures (unit: kelvin). v denotes vertical polarization, h horizontal. supporting parameters for ASI3 ice concentration retrieval: - gr23: gradient ratio of 23V and 18V. gr23=(TB_v23 - TB_v18)/(TB_v23 + TB_v18). - gr36: gradient ratio of 36V and 18V. gr36=(TB_v36 - TB_v18)/(TB_v36 + TB_v18). - pr18: polarization ration of 18V and 18H. pr18=(TB_v18 - TB_h18)/(TB_v18 + TB_h18). - gr23c, gr36c, pr18c: same as gr23, gr36 and pr18 but based on the weather corrected brightness temperatures. - bba: Bootstrap ice concentration. Data range is zero to one. - high resolution data group: 'hi_res_swath' major parameters: - lathi: latitude of the high resolution swath of AMSR-E - lonhi: longitude of the high resolution swath of AMSR-E - v89b, h89b: original AMSR-E brightness temperature of 89 GHz scan B. - v89chi, h89chi: weather corrected brightness temperature of 89 GHz scan B. supporting parameters for ASI3 ice concentration retrieval: - gr23hi, gr36hi, pr18hi: based on original AMSR-E brightness temperatures, resampled to high resolution swath. - gr23chi, gr36chi, pr18chi: based on corrected AMSR-E brightness temperatures, resampled to high resolution swath. - bbahi: Bootstrap ice concentration resampled to high resolution swath. 2. Gridded ice concentration files 1439x1439 array containing gridded ice concentration data. Data range is zero to one. Land pixels are set to NaN. Landmask is extended by 50 km towards ocean. Ice concentrations are retrieved above latitude 50 degrees north. - ASI: the original ASI ice concentration with all standard weather filters turned on. - ASI3: ASI3 ice concentration data based on the corrected brightness temperatures at 89 GHz. 3. Coordinates file of the gridded ice concentration data - latitude: 1439x1439 array - longitude: 1439x1439 array