Hyperspectral reflectance sensing provides a rapid and cost-effective technique for assessing the suitability of groundwater for irrigation by monitoring real-time changes in its quality at a large scale. In this study, we assessed the quality of 15 groundwater samples from El Fayoum depression in the Western Desert (WD) and 25 groundwater samples from the Central Nile Delta (CND) in Egypt using a traditional approach of the physiochemical parameters, irrigation water quality indicators (IWQIs), and hydrochemical facies. The spectral reflectance data of the water surface was used to build new simple reflectance indices (SRIs), and the performance of these indices for assessing IWQIs was compared with those by partial least square regression (PLSR) that was based on all SRIs or the full-spectrum ranges. Generally, the groundwater of the CND was fresher and more suitable for irrigation purposes than those of the WD. Based on the six IWQIs, ~6.7–60.0% and 85.0–100.0% of the groundwater samples of the WD and CND, respectively, were categorized as highly suitable for irrigation purposes. Based on hydrochemical facies, Na-Cl and Ca-HCO3 were dominant in the WD and CND, respectively, as well as the alkali earth metals (Na+ + K+), which significantly exceeded the alkaline earth metals (Ca2+ + Mg2+) in the WD, with the reverse for the CND. Most developed SRIs had a moderate, weak, and moderate to strong relationship with physiochemical parameters and IWQIs in the WD, CND, and across both regions, respectively. The PLSR models based on all SRIs provided a more accurate estimation of IWQIs in calibration and validation datasets than those based on full-spectrum ranges, and both PLSR models provided better estimation than the individual SRIs. These findings support the feasibility of using ground reflectance measurements as a fast and low-cost tool for the assessment and management of groundwater for irrigation in arid and semiarid regions.

中文翻译：

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结合水文地球化学表征和高光谱反射工具来评估埃及两种地下水资源的质量和适宜性

高光谱反射传感提供了一种快速且具有成本效益的技术，可通过大规模监测地下水质量的实时变化来评估地下水是否适合灌溉。在这项研究中，我们使用物理化学参数、灌溉水质指标的传统方法评估了西部沙漠 (WD) El Fayoum 洼地的 15 个地下水样品和埃及中部尼罗河三角洲 (CND) 的 25 个地下水样品的质量(IWQI) 和水化学相。水面的光谱反射数据被用来建立新的简单反射指数（SRI），并将这些指数评估 IWQI 的性能与基于所有 SRI 或基于全部 SRI 的偏最小二乘回归（PLSR）的性能进行比较。 - 频谱范围。一般来说，CND的地下水比WD的地下水更新鲜，更适合灌溉。根据六个 IWQI，WD 和 CND 的地下水样本分别有约 6.7-60.0% 和 85.0-100.0% 被归类为非常适合灌溉目的。基于水化学相，Na-Cl和Ca-HCO3分别在WD和CND中占主导地位，以及碱土金属（Na+ + K+），其显着超过WD中的碱土金属（Ca2+ + Mg2+） , 而 CND 则相反。大多数发达的 SRI 分别与 WD、CND 和这两个地区的理化参数和 IWQI 具有中度、弱和中到强的关系。与基于全谱范围的模型相比，基于所有 SRI 的 PLSR 模型在校准和验证数据集中提供了更准确的 IWQI 估计，并且两种 PLSR 模型都提供了比单个 SRI 更好的估计。这些发现支持使用地面反射率测量作为评估和管理干旱和半干旱地区灌溉地下水的快速、低成本工具的可行性。