TOVS GLA MONTHLY GRIDS from TIROSN V01 (TOVSAMTN) at GES DISC

This dataset (TOVSAMTN) contains the TIROS Operational Vertical Sounder (TOVS) level 3 geophysical parameters derived using data from TIROSN and the physical retrieval method of Susskind et al. (1984) and processed by the Satellite Data Utilization Office of the Goddard Laboratory for Atmospheres at NASA/GSFC. This method, which is hydrodynamic model- and a priori data-dependent, is designated as the so-called Path A scheme by the TOVS Pathfinder Science Working Group. The 20 channel High resolution Infrared Radiation Sounder 2 (HIRS2) and the 4 channel Microwave Sounding Unit (MSU) aboard the NOAA-xx series of Polar Orbiting Satellites are used to produce global fields of the 3-dimensional temperature-moisture structure of the atmosphere. In addition to profiles of temperature and moisture, the HIRS2/MSU data are used to derive important quantities such as land and sea surface temperature, outgoing longwave radiation, cloud fraction, cloudtop height, total ozone overburden and precipitation estimates.

The Path A system steps through an interactive forecast-retrieval-analysis cycle. In each 6 hour synoptic period, a 2nd order General Circulation Model (Takacs et al., 1994) is used to generate the 6 hour forecast fields of temperature and humidity. These global fields are used as the first guess for all soundings occuring within a 6 hour time window centered upon the forecast time. These retrievals are then assimilated with all available insitu measurements (such as radiosonde and ship reports) in the 6 hour interval using an Optimal Interpolation (OI) analysis scheme developed by the Data Assimilation Office of the Goddard Laboratory for Atmospheres. This analysis is then used to specify the initial conditions for the next 6 hour forecast, thus completing the cycle.

The retrieval algorithm itself is a physical method based on the iterative relaxation technique originally proposed by Chahine (1968). The basic approach consists of modifying the temperature profile from the previous iteration by an amount proportional to the difference between the observed brightness temperatures and the brightness temperatures computed from the trial parameters using the full radiative transfer equation applied at the observed satellite zenith angle. For the case of the temperature profile, the updated layer mean temperatures are given as a linear combination of multichannel brightness temperature differences with the coefficients given by the channel weighting functions. Constraints are imposed upon the solution in order to ensure stability and convergence of the iterative process. For more details see Susskind et al (1984).

There are 6 level 3 data product files, each of which is in the HDF format and each representative of a different averaging time period. All files contain the same number of geophysical parameter arrays stored as HDF Scientific Data Sets (SDSs). The time periods include daily, 5 day (pentad) and monthly, with the AM and PM portions of the orbits treated separately. All data are mapped to a 1 degree longitude by 1 degree latitude global grid.

本数据集（TOVSAMTN）包含采用TIROSN数据及Susskind等（1984）提出的物理反演方法获取的泰罗斯业务垂直探测器（TIROS Operational Vertical Sounder，TOVS）三级地球物理参数，经美国国家航空航天局戈达德航天飞行中心（NASA/GSFC）戈达德大气实验室卫星数据应用办公室处理完成。该方法依赖流体动力学模式与先验数据，被TOVS探路者科学工作组指定为所谓的路径A方案。搭载于NOAA系列极轨卫星的20通道高分辨率红外辐射探测器2（High resolution Infrared Radiation Sounder 2，HIRS2）与4通道微波探测单元（Microwave Sounding Unit，MSU）可用于生成大气三维温湿结构的全球场。除温度与湿度廓线外，HIRS2/MSU数据还可用于反演海表与陆表温度、向外长波辐射、云量、云顶高度、总臭氧柱总量及降水估算值等重要物理量。
路径A系统遵循交互式预报-反演-分析循环流程。每个6小时天气时段内，采用二阶环流模式（Takacs等，1994）生成温度与湿度的6小时预报场。这些全球场将作为以预报时刻为中心的6小时时间窗口内所有探测资料的初始猜测场。随后利用戈达德大气实验室数据同化办公室开发的最优插值（Optimal Interpolation，OI）分析方案，将上述反演结果与该6小时时段内所有可用的原位观测资料（如无线电探空仪观测、船舶报告）进行同化。该分析结果将作为下一个6小时预报的初始条件，从而完成整个循环流程。
本反演算法本身是基于Chahine（1968）最初提出的迭代松弛法的物理反演方法。其基本思路为：根据观测亮温与由试验参数结合观测卫星天顶角、通过全辐射传输方程计算得到的亮温之间的差值，按比例修正前一次迭代得到的温度廓线。对于温度廓线而言，更新后的层平均温度可表示为多通道亮温差的线性组合，其系数由通道权重函数给出。为保证迭代过程的稳定性与收敛性，需对解施加约束条件。更多细节可参见Susskind等（1984）的相关研究。
本数据集共包含6个三级数据产品文件，均采用HDF格式，分别对应不同的平均时长时段。所有文件均包含相同数量的地球物理参数阵列，以HDF科学数据集（Scientific Data Sets，SDSs）格式存储。时段涵盖日尺度、5日（pentad，候）尺度以及月尺度，且轨道的上午（AM）与下午（PM）时段分开处理。所有数据均被投影到1°经度×1°纬度的全球网格上。