Water content in the upper 1 meter of the Martian regolith, estimated from FREND experiment data

This dataset contains a raw map of neutron suppression and a smoothed map of water content in the upper meter of the Martian subsurface derived from FREND instrument data, between latitudes 50° north and south. FREND is a high resolution neutron telescope onboard ExoMars’ TGO orbiter (see Mitrofanov, I. et al. Fine Resolution Epithermal Neutron Detector (FREND) Onboard the ExoMars Trace Gas Orbiter. Space Sci Rev 214, 86 (2018). https://doi.org/10.1007/s11214-018-0522-5). Neutron Suppression is defined as ratio between neutron count rate (counts per second) at each pixel and a reference count rate (average count rate over Solis Planum area between -115° and -65° longitude and -55° and -15° latitude). It is a dimensionless parameter, showing how much the neutron flux is suppressed relative to the reference Solis Planum area, known to be one of the driest on Mars with water equivalent hydrogen (WEH) estimated as 2.78 weight percent (wt%, see Boynton, W.V. et al. Concentration of H, Si, Cl, K, Fe, and Th in the low- and mid-latitude regions of Mars. Journal of Geophysical Research 112, (2007) E12S99. https://doi.org/10.1029/2007JE002887). Statistical errors are given in each pixel. Map of neutron suppression can be used to locate regions of high or low water content. Map of water is derived from the neutron suppression map in the following way: neutron suppression map is smoothed with a gaussian 12° (full width half maximum) filter, considering statistical errors in each pixel. Transition from smoothed neutron suppression values to WEH values is done through numerical modeling of all physical process from neutron emission from the Martian regolith to detection of neutrons by FREND instrument, depending on the WEH content in the regolith. Map of water contains three values for each pixel: minimum, mean and maximum WEH in wt%: mean values are derived from neutron suppression map, maximum and minimum values correspond to plus and minus error of the neutron suppression. These three values represent the range of WEH in each pixel within 1 error margin of neutron suppression values.本数据集包含基于ExoMars微量气体轨道器（Trace Gas Orbiter, TGO）搭载的高分辨率中能中子探测器（Fine Resolution Epithermal Neutron Detector, FREND）仪器数据生成的火星地下表层（0~1米深度）中子抑制原始图与含水量平滑图，覆盖南北纬50°区间。FREND是一款高分辨率中子望远镜，详见Mitrofanov I. 等人发表于《空间科学评论》214卷第86页（2018年）的论文《Fine Resolution Epithermal Neutron Detector (FREND) Onboard the ExoMars Trace Gas Orbiter》，DOI: 10.1007/s11214-018-0522-5。中子抑制值定义为每个像素的中子计数率（每秒计数）与参考计数率的比值，其中参考计数率取自索利斯平原（Solis Planum）区域（经度-115°至-65°、纬度-55°至-15°）的平均计数率。该参数为无量纲量，用于表征中子通量相较于已知火星最干旱区域之一的索利斯平原的抑制程度；索利斯平原的水等效氢（Water Equivalent Hydrogen, WEH）含量经估算为2.78重量百分比（wt%），详见Boynton W.V. 等人发表于《地球物理学研究杂志》112卷E12S99（2007年）的论文《Concentration of H, Si, Cl, K, Fe, and Th in the low- and mid-latitude regions of Mars》，DOI: 10.1029/2007JE002887。每个像素均标注了统计误差。中子抑制图可用于定位含水量偏高或偏低的区域。含水量图由中子抑制图推导而来，具体步骤如下：首先对中子抑制图施加高斯12°（半高全宽）滤波以进行平滑处理，过程中考虑每个像素的统计误差；随后通过数值模拟完成平滑后中子抑制值到WEH值的转换，该模拟涵盖了从火星风化层中子产生到FREND仪器探测中子的全部物理过程，且模拟结果依赖于风化层的WEH含量。含水量图为每个像素提供三个数值：重量百分比（wt%）形式的最小、平均与最大WEH含量，其中平均值由中子抑制图推导得到，最大值与最小值分别对应中子抑制值的正负误差范围。这三个数值表征了每个像素的WEH含量在中子抑制值1倍误差范围内的波动区间。