CYGNSS Level 3 Climate Data Record Version 1.1

This dataset contains the Version 1.1 CYGNSS Level 3 Climate Data Record which provides the average wind speed and mean square slope (MSS) on a 0.2x0.2 degree latitude by longitude equirectangular grid obtained from the Delay Doppler Mapping Instrument aboard the CYGNSS satellite constellation. The Level 2 Delay Doppler Map (DDM) data are used in the direct processing of the average wind speed and MSS data that are binned on the Level 3 grid. A subset of DDM data used in the direct processing of the average wind speed and MSS is co-located inside of the Level 2 data files. A single netCDF-4 data file is produced for each day of operation with an approximate 1 to 2 month latency. The reported sample locations are determined by the specular points corresponding to the Delay Doppler Maps (DDMs). The Version 1.1 CDR is a collection of reanalysis products derived from the SDR v3.0 Level 1 data (https://doi.org/10.5067/CYGNS-L1X30 ). Calibration accuracy and long term stability are improved relative to SDR v3.0 (https://doi.org/10.5067/CYGNS-L3X30 ) using the same trackwise correction algorithm as was used by CDR v1.0 (https://doi.org/10.5067/CYGNS-L3C10 ), which was derived from SDR v2.1 Level 1 data (https://doi.org/10.5067/CYGNS-L1X21 ). Details of the algorithm are provided in the Trackwise Corrected CDR Algorithm Theoretical Basis Document. CDR Level 2 and 3 products (ocean surface wind speed, mean square slope, and latent and sensible heat flux) are generated from the CDR L1 data using the v3.0 SDR data processing algorithms. These products also exhibit improved calibration accuracy and stability over SDR v3.0. Trackwise correction is applied to the two primary CYGNSS L1 science data products, the normalized bistatic radar cross section (NBRCS) and the leading edge slope of the Doppler-integrated delay waveform (LES). The correction compensates for small errors in the Level 1 calibration, due e.g. to uncertainties in the GPS transmitting antenna gain patterns and the CYGNSS receiving antenna gain patterns. CDR v1.1 does not include a Young Seas with Limited Fetch (YSLF) wind speed product and investigators requiring wind speed measurements in and near the inner core of tropical cyclones should use the SDR v3.0 YSLF wind speed product. A YSLF wind speed product is omitted because the trackwise correction algorithm, which constrains the average value of the L1 data using MERRA-2 reanalysis wind speeds, is inherently biased toward fully developed sea state conditions. The constraint improves wind speed retrieval performance in fully developed seas but produces underestimates in YSLF conditions. It should also be noted that the trackwise correction algorithm cannot be successfully applied to all SDR v3.0 L1 data so there is also some loss of samples that were present in SDR v3.0.

本数据集包含CYGNSS卫星星座搭载的延迟多普勒映射仪所获得的1.1版本三级气候数据记录，该记录提供了在0.2x0.2度经纬度等距圆柱网格上的平均风速和均方斜率（MSS）。二级延迟多普勒图（DDM）数据被用于直接处理平均风速和MSS数据，这些数据按照三级网格进行分类。在二级数据文件内部，用于直接处理平均风速和MSS的DDM数据子集与二级数据共同定位。针对每日常规运行，生成一个单网CDF-4数据文件，具有大约1至2个月的延迟。报告的样本位置由对应于延迟多普勒图（DDMs）的镜面点确定。1.1版本的CDR是一系列由SDR v3.0一级数据（https://doi.org/10.5067/CYGNS-L1X30）派生出的再分析产品。与SDR v3.0相比，该版本的校准精度和长期稳定性得到提升，采用了与CDR v1.0（https://doi.org/10.5067/CYGNS-L3C10）相同的轨迹校正算法，后者源自SDR v2.1一级数据（https://doi.org/10.5067/CYGNS-L1X21）。算法的详细信息可在轨迹校正CDR算法理论依据文档中找到。CDR二级和三级产品（海洋表面风速、均方斜率以及潜热和感热通量）是通过使用v3.0 SDR数据处理算法从CDR L1数据生成的。这些产品相对于SDR v3.0也显示出改进的校准精度和稳定性。轨迹校正被应用于两个主要的CYGNSS L1科学数据产品，即归一化双基地雷达散射截面（NBRCS）和多普勒积分延迟波形的前沿斜率（LES）。该校正补偿了一级校准中的微小误差，例如，由于GPS发射天线增益模式的不确定性以及CYGNSS接收天线增益模式的不确定性。CDR v1.1不包含有限风fetch的青年海域（YSLF）风速产品，需要在内核区域及其附近进行风速测量的研究人员应使用SDR v3.0 YSLF风速产品。省略YSLF风速产品的原因在于，轨迹校正算法通过使用MERRA-2再分析风速来限制L1数据的平均值，从而具有固有的偏向于充分发展的海况条件。这种限制提高了充分发展海况下的风速检索性能，但在YSLF条件下会产生低估。还应指出，轨迹校正算法无法成功应用于所有SDR v3.0 L1数据，因此也造成了一些样本的损失，这些样本原本存在于SDR v3.0中。