SOIL MOISTURE DATA: PECK (FIFE)

Water content measurements by gravimetric methods involve weighing a wet sample, removing the water via drying in an oven, and reweighing the sample to determine the amount of water removed. Water content then is obtained by dividing the difference between wet and dry masses by the mass of the dry sample to obtain the ratio of the mass of water to the mass of dry soil. When multiplied by 100, this becomes the percentage of water in the sample on a dry-mass (or, as often expressed, on a dry-weight) basis. Soil moisture determined using the gravimetric method was measured at 800 sites along 24 transects. These transects were over flown by the airborne Gamma Radiation System used to measure soil moisture. These data are useful for comparison of airborne and ground soil moisture data. This analysis for the airborne Gamma Radiation System, using completely independent soil moisture data showed that the root mean square error of 97 flights was 3.02 percent soil moisture, with a bias of less than 0.5 percent soil moisture (Carroll et al., 1988).重量法（gravimetric method）测定土壤含水率的流程为：先称量湿试样质量，随后通过烘箱干燥脱除样品中的水分，再次称量干样质量以得到脱除的水分总量。含水率的计算方式为：以湿样与干样的质量差值除以干样质量，得到水分质量与干土质量的比值；将该比值乘以100后，即可得到以干基质量（或常称干基重量）计的样品含水率百分比。本次研究沿24条样带共布设800个采样点，采用重量法测定了各点位的土壤含水率；用于测量土壤含水率的机载伽马辐射系统（airborne Gamma Radiation System）对上述样带开展了飞行观测。该数据集可用于机载与地面土壤含水率测量数据的对比分析。基于完全独立的土壤含水率数据对该机载伽马辐射系统开展的分析结果显示：97次飞行观测的均方根误差（root mean square error, RMSE）为3.02%，系统偏差小于0.5%（Carroll 等，1988）。