JPL SMAP Level 2B CAP Sea Surface Salinity V5.0 Validated Dataset

This is the PI-produced JPL SMAP-SSS V5.0, level 2B CAP, validated sea surface salinity (SSS) and extreme winds orbital/swath product from the NASA Soil Moisture Active Passive (SMAP) observatory. It is based on the Combined Active-Passive (CAP) retrieval algorithm developed at JPL originally in the context of Aquarius/SAC-D and now extended to SMAP. JPL SMAP V5.0 SSS is based on the newly released SMAP V5 Level-1 Brightness Temperatures (TB). An enhanced calibration methodology has been applied to the brightness temperatures, which improves absolute radiometric calibration and reduces the biases between ascending and descending passes. The improved SMAP TB Level 1 TB will enhance the use of SMAP Level-1 data for other applications, such as sea surface salinity and winds. The JPL SMAP-SSS L2B CAP product includes data for a range of parameters: derived SMAP sea surface salinity, SSS uncertainty and wind speed/direction data for extreme winds, brightness temperatures for each radiometer polarization, ancillary reference surface salinity, ice concentration, wind and wave height data, quality flags, and navigation data. Each data file covers one 98-minute orbit (15 files per day). Data begins on April 1,2015 and is ongoing, with a 3 day latency in processing and availability. Observations are global in extent and provided at 25km swath grid with an approximate spatial resolution of 60 km. The SMAP satellite is in a near-polar orbit at an inclination of 98 degrees and an altitude of 685 km. It has an ascending node time of 6 pm and is sun-synchronous. With its 1000km swath, SMAP achieves global coverage in approximately 3 days, but has an exact orbit repeat cycle of 8 days. On board Instruments include a highly sensitive L-band radiometer operating at 1.41GHz and an L-band 1.26GHz radar sensor providing complementary active and passive sensing capabilities. Malfunction of the SMAP scatterometer on 7 July, 2015, has necessitated the use of collocated wind speed for the surface roughness correction required for the surface salinity retrieval.本数据集为美国国家航空航天局（National Aeronautics and Space Administration, NASA）土壤湿度主动被动（Soil Moisture Active Passive, SMAP）观测台产出的、由首席研究员（Principal Investigator, PI）主导生成的喷气推进实验室（Jet Propulsion Laboratory, JPL）SMAP-SSS V5.0级2B联合主动被动（Combined Active-Passive, CAP）产品，是经过验证的海面盐度（Sea Surface Salinity, SSS）与极端风轨幅宽产品。该数据集基于JPL最初为Aquarius/SAC-D任务开发的CAP反演算法，现已扩展适配SMAP任务。JPL SMAP V5.0级海面盐度产品以最新发布的SMAP V5级1亮度温度（Brightness Temperatures, TB）数据为基础，采用了增强型定标方法，优化了绝对辐射定标精度，同时缩减了升轨与降轨之间的系统偏差。经过改进的SMAP V5级1亮度温度数据，可进一步拓展SMAP级1数据在海面盐度、海面风场等多类场景中的应用价值。JPL SMAP-SSS L2B CAP产品涵盖多类参数：反演得到的SMAP海面盐度、海面盐度不确定度、极端风场景下的风速与风向数据、各辐射计极化通道的亮度温度、辅助参考海面盐度、海冰浓度、风浪高度数据、质量标记以及导航数据。每份数据文件覆盖一段98分钟的观测轨道（每日共15份文件），数据起始于2015年4月1日并持续更新，数据处理与发布存在3天的延迟。观测数据覆盖全球范围，以25km幅宽网格存储，空间分辨率约为60km。SMAP卫星采用近极轨轨道，轨道倾角为98度，轨道高度为685km，升交点地方时为18:00，属于太阳同步轨道。该卫星幅宽达1000km，可在约3天内完成全球覆盖，轨道重复周期为精准的8天。星载仪器包含一台工作于1.41GHz的高灵敏度L波段辐射计，以及一台工作于1.26GHz的L波段雷达传感器，可提供互补的主动与被动遥感能力。2015年7月7日，SMAP散射计发生故障，导致海面盐度反演所需的海面粗糙度校正，不得不改用匹配的同步风速数据进行替代。