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1. chinaXiv:201904.00091 [pdf]

Dynamics of infiltration rate and Field-Saturated soil hydraulic conductivity in a Wastewater-Irrigated cropland

Siyi Zhang; Isaac Hopkins; Li Guo; Henry Lin
Subjects: Geosciences >> Geography

The maintenance of a soil’s infiltration rate (IR) and field-saturated hydraulic conductivity (Kfs) is crucial for the long-term sustainable functioning of wastewater-irrigated lands. However, an effective procedure for reliably measuring in situ soil Kfs remains elusive. To address this issue, this study investigated the DualHead Infiltrometer (DHI), a novel instrument for automatically determining IR and Kfs, and compared it with a traditional Double-Ring Infiltrometer (DRI) under various field conditions. In the initial phase, we optimized the procedure and settings for the DHIs in a cropland that has been spray-irrigated with secondary-treated wastewater for decades in central Pennsylvania. Results showed that our optimized procedure, which used a single, long pressure cycle, yielded more robust measurements of IR than the originally recommended sequence of two short pressure cycles. The values of Kfs measured by the DHIs with optimized settings were similar to those measured by DRIs under many (but not all) field conditions, due to their differences in infiltration surface areas, operational procedures, length of infiltration time, and soil spatiotemporal variability. Viscosity-corrected Kfs on the irrigated cropland was 123.8±94.0 mm h-1, higher than that on the adjacent non-irrigated cropland (103.2±94.6 mm h-1), but the difference was not statistically significant, owing to the high degree of soil spatiotemporal variability and our limited number of measurements. Nevertheless, the higher Kfs values measured on irrigated cropland reflect observed changes in soil structure (e.g., soil pore characteristics) that have resulted from decades of irrigation. Seasonal variations in Kfs values existed between winter and summer conditions, but IRs during all seasons remained much higher than the current spray-irrigation rate (4.25 mm h-1), suggesting that the soil is still capable of handling the routine irrigation, even during winter. However, the coefficients of variation exceeded 67.0% across the field sites investigated and the time periods covered by our measurements were limited. As this specific site is permitted to discharge treated wastewater year-round, caution must still be exercised to ensure that soil Kfs remains high enough to prevent runoff generation, especially during winter frozen conditions.

submitted time 2019-09-06 Hits24403Downloads1654 Comment 0

2. chinaXiv:201711.02398 [pdf]

International UTC TAI comparison based on BDS PPP

Yulong Ge; Baoqi Sun; WeiJin Qin; Mingjun Ouyang; Xuhai Yang
Subjects: Geosciences >> Other Disciplines of Geosciences

The BeiDou navigation satellite system (BDS) developed by China, and provided official service for Asia-pacific region freely since 2012. With development of BDS, BDS-based time transfer has become an important research direction in BDS’s application fields. At present, the main method of BDS-based time transfer is BDS Common View (BDS CV), which can reach nanoseconds magnitude. Hence, we investigate the performance time transfer based on BDS precise point positioning (PPP) toward UTC/TAI compute. In this contribution, we focus on UTC/TAI comparison based on BDS PPP by using developed quad-constellation GNSS software, which called National Time System Center’s (NTSC) Bernese. And a long-term data analysis is presented. The experiments include two parts: (1) The reliability of the software and multi-GNSS products; (2) The performance of the BDS PPP toward International UTC/TAI comparison. The experimental results reveal that the accuracy of NTSC’s Bernese GPS PPP can reach about 0.1 ns relative to BIPM TAI PPP solutions. Compared with BIPM TAI PPP solutions, the accuracy of GPS PPP solutions can achieve about 0.2 ns by using multi-GNSS precise products, such as GBM, COM. For BDS PPP solutions, the solutions of GPS PPP are regarded as reference values. It is demonstrated that the accuracy of time transfer based on BDS PPP can reach better 1 ns toward UTC/TAI comparison for the statistics of 30 days-arc solutions, while 0.1 ns magnitude can be achieved for the statistics of daily solutions due to the influence of the day boundary discontinuity. Moreover, four different processing strategies of BDS PPP which include tropospheric delay fixed, tropospheric delay and coordinates fixed, coordinates fixed, and BDS-only are tested. Results show that the comparable accuracy can be achieved for four processing strategies. Hence, one can conclude that the time transfer based on BDS-only PPP show a good performance toward UTC/TAI computation.

submitted time 2018-01-07 Hits9086Downloads2040 Comment 0

3. chinaXiv:201710.00069 [pdf]

基于MODIS云参数的卷云反射率计算研究

赵凤美; 戴聪明; 魏合理
Subjects: Geosciences >> Atmospheric Sciences

卷云反射率是天气、气候和地球能量平衡研究中关注的重要参数。卷云反射率的快速算法在遥感反演卷云特性参数中具有重要应用。依据卷云反射率随卷云光学厚度、有效尺度、太阳天顶角、观测天顶角、相对方位角等参数的变化,利用离散坐标法(DISORT)计算卷云反射率,预先建立卷云反射率随相关参数变化的快速查找表,以此建立了卷云反射率的快速算法。将MODIS卫星探测的卷云光学厚度、太阳天顶角、观测天顶角、相对方位角等因素作为输入参数,计算得到了卷云反射率,比较了计算的卷云反射率和MODIS实际测量的卷云反射率值,相关系数达到0.94,平均偏差小于18.5%,说明了卷云快速算法计算合理可行。

submitted time 2017-11-01 Hits4503Downloads1407 Comment 0

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