Deep learning-based water quality estimation and anomaly detection using Landsat-8/Sentinel-2 virtual constellation and cloud computing

ABSTRACT

Monitoring of inland water quality is of significant importance due to the increase in water quality related issues, especially within the Midwestern United States. Traditional monitoring techniques, although highly accurate, are vastly insufficient in terms of spatial and temporal coverage. Using a virtual constellation by harmonizing Landsat-8 and Sentinel-2 data a high temporal frequency dataset can be created at a relatively fine spatial scale. In this study, we apply a novel deep learning method for the estimation of blue-green algae (BGA), chlorophyll-α (Chl), fluorescent dissolved organic matter (fDOM), dissolved oxygen (DO), specific conductance (SC), and turbidity. The developed model is evaluated against previously studied machine learning methods and found to outperform multiple linear regression (MLR), support vector machine regression (SVR), and extreme learning machine regression (ELR) generating R² of 0.91 for BGA, 0.88, 0.89, 0.93, 0.87, and 0.84 for Chl, DO, SC, and turbidity respectfully. This model is then applied to all available data ranging from 2013–2018 and time series for each variable were generated for four selected waterbodies. We then use the Empirical Data Analytics (EDA) anomaly detection method on the time series to identify abnormal data points. Upon further analysis, the EDA method successfully identifies abnormal events in water quality. Our results also demonstrate strong correlation between non-optically active variables such as SC with Chl and fDOM. The framework developed in this study represents an efficient and accurate empirical method for inland water quality monitoring at the regional scale.     

The northern Walker Lane refraction experiment: Pn arrivals and the northern Sierra Nevada root

In May 2002, we collected a new crustal refraction profile from Battle Mountain, Nevada across western Nevada, the Reno area, Lake Tahoe, and the northern Sierra Nevada Mountains to Auburn, CA. Mine blasts and earthquakes were recorded by 199 Texan instruments extending across this more than 450-km-long transect. The use of large mine blasts and the ultra-portable Texan recorders kept the field costs of this profile to less than US$10,000. The seismic sources at the eastern end were mining blasts at Barrick's GoldStrike mine. The GoldStrike mine produced several ripple-fired blasts using 8000–44,000 kg of ANFO each, a daily occurrence. First arrivals from the larger GoldStrike blasts are obvious to distances of 300 km in the raw records. First arrivals from a quarry blast west of the survey near Watsonville, CA, located by the Northern California Seismic Network with a magnitude of 2.2, can be picked across the recording array to distances of 600 km. The Watsonville blast provides a western source, nearly reversing the GoldStrike blasts. A small earthquake near Bridgeport, CA. also produced pickable P-wave arrivals across the transect, providing fan-shot data. Arrivals from M5 events in the Mariana and Kuril Islands also appear in the records. This refraction survey observes an unexpectedly deep crustal root under the northern Sierra Nevada range, over 50 km in thickness and possibly centered west of the topographic crest. Pn delays of 4–6 s support this interpretation. At Battle Mountain, Nevada, we observe anomalously thin crust over a limited region perhaps only 150 km wide, with a Moho depth of 19–23 km. Pn crossover distances of less than 80 km support this anomaly, which is surrounded by observations of more normal, 30-km-thick crust. A 10-km-thick and high-velocity lower-crustal “pillow” is an alternative hypothesis, but unlikely due to the lack of volcanics west of Battle Mountain. Large mine and quarry blasts prove very effective crustal refraction sources when recorded with a dense receiver array, even over distances exceeding 600 km. New elastic synthetic seismogram modeling suggests that Pn can be strong as a first arrival, easing the modeling and interpretation of crustal refraction data. Fast eikonal computations of first-arrival time can match pickable Pn arrival times.     

Probabilistic assessment of travel times in groundwater modeling

A Monte Carlo approach is described for the quantification of uncertainty on travel time estimates. A real (non synthetic) and exhaustive data set of natural genesis is used for reference. Using an approach based on binary indicators, constraint interval data are easily accommodated in the modeling process. It is shown how the incorporation of imprecise data can reduce drastically the uncertainty in the estimates. It is also shown that unrealistic results are obtained when a deterministic modeling is carried out using a kriging estimate of the transmissivity field. Problems related with using sequential indicator simulation for the generation of fields incorporating constraint interval data are discussed. The final results consists of 95% probability intervals of arrival times at selected control planes reflecting the original uncertainty on the transmissivity maps.     

Anisotropy of magnetic susceptibility data bearing on the transport direction of mid-tertiary regional ignimbrites,Candelaria Hills area,West-Central Nevada

In west-central Nevada, the Oligocene Candelaria pyroclastic sequence reaches a local thickness of up to 1.3 km, in what has been referred to as the Candelaria trough, but more generally the accumulation of ash-flow tuffs and related volcanic rocks is less than 300 m thick. Complete to near complete outcrops are scattered over about 3200 km² in the Candelaria Hills and surrounding ranges of the Southern Walker Lane structural zone. Three regionally extensive compound cooling units within the overall sequence (25.8 Ma Metallic City, 24.1 Ma Belleville, and 23.7 Ma Candelaria Junction Tuffs) have distinguishing characteristics and are the focus of study. At 106 sites, anisotropy of magnetic susceptibility (AMS) data provide an estimate of transport direction of each tuff. Inferred transport directions based on the AMS data are corrected for a modest clockwise, yet variable magnitude, vertical axis rotation that affected these rocks in late Miocene to Pliocene time, as revealed by paleomagnetic studies. The AMS data show a somewhat orderly pattern of magnetic fabrics that we interpret to define unique transport directions for the Metallic City and Candelaria Junction Tuffs. The low susceptibility and degree of anisotropy of the Belleville Tuff limits our interpretation from this pyroclastic deposit. The Metallic City and Candelaria Junction Tuffs typically show gentle, south–southeast and southeast dipping magnetic fabric imbrication, respectively, and very gently plunging magnetic lineations. These AMS fabric elements indicate the tuffs were transported to the north–northwest and northwest, respectively. The AMS fabric data from the Metallic City and Candelaria Junction Tuffs suggest relatively unrestricted flow during emplacement. Evidence across the 3,200 km² area to support more regionally controlled channelized flow into and/or flow along the east northeast–west southwest axis of the Candelaria trough is lacking. The ignimbrites clearly filled a topographic depression inferred to have formed concurrent with early, localized Basin and Range extension during pyroclastic emplacement, but based on the uniformity of AMS fabric data, we infer that the depression quickly filled and did not hinder flow across the region. Unrecognized eruptive centers for the three ignimbrites may lie buried beneath Neogene basin fill sediments south–southeast of the Candelaria Hills or concealed below younger deposits farther southeast into the Palmetto Mountains. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Revised and prepared for publication in the Bulletin of Volcanology.     

Three-dimensional decomposition method of global atmospheric circulation

By adopting the idea of three-dimensional Walker, Hadley and Rossby stream functions, the global atmospheric circulation can be considered as the sum of three stream functions from a global per- spective. Therefore, a mathematical model of three-dimensional decomposition of global atmospheric circulation is proposed and the existence and uniqueness of the model are proved. Besides, the model includes a numerical method leading to no truncation error in the discrete three-dimensional grid points. Results also show that the three-dimensional stream functions exist and are unique for a given velocity field. The mathematical model shows the generalized form of three-dimensional stream func- tions equal to the velocity field in representing the features of atmospheric motion. Besides, the vertical velocity calculated through the model can represent the main characteristics of the vertical motion. In sum, the three-dimensional decomposition of atmospheric circulation is convenient for the further in- vestigation of the features of global atmospheric motions.     

3D Surface velocity retrieval of mountain glacier using an offset tracking technique applied to ascending and descending SAR constellation data: a case study of the Yiga Glacier

COSMO-SkyMed is a constellation of four X-band high-resolution radar satellites with a minimum revisit period of 12 hours. These satellites can obtain ascending and descending synthetic aperture radar (SAR) images with very similar periods for use in the three-dimensional (3D) inversion of glacier velocities. In this paper, based on ascending and descending COSMO-SkyMed data acquired at nearly the same time, the surface velocity of the Yiga Glacier, located in the Jiali County, Tibet, China, is estimated in four directions using an offset tracking technique during the periods of 16 January to 3 February 2017 and 1 February to 19 February 2017. Through the geometrical relationships between the measurements and the SAR images, the least square method is used to retrieve the 3D components of the glacier surface velocity in the eastward, northward and upward directions. The results show that applying the offset tracking technique to COSMO-SkyMed images can be used to derive the true 3D velocity of a glacier’s surface. During the two periods, the Yiga Glacier had a stable velocity, and the maximum surface velocity, 2.4?m/d, was observed in the middle portion of the glacier, which corresponds to the location of the steepest slope.     

China's high-resolution optical remote sensing satellites and their mapping applications

Since the beginning of the twenty-first century,several countries have made great efforts to develop space remote sensing for building a high-resolution earth observation system.Under the great attention of the government and the guidance of the major scientific and techno-logical project of the high-resolution earth observation system,China has made continuous breakthroughs and progress in high-resolution remote sensing imaging technology.The development of domestic high-resolution remote sensing satellites shows a vigorous trend,and consequently,a relatively stable and perfect high-resolution earth observation system has been formed.The development of high-resolution remote sensing satellites has greatly pro-moted and enriched modern mapping technologies and methods.In this paper,the develop-ment status,along with mapping modes and applications of China's high-resolution remote sensing satellites are reviewed,and the development trend in high-resolution earth observa-tion system for global and ground control-free mapping is discussed,providing a reference for the subsequent development of high-resolution remote sensing satellites in China.     

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东部和中部型El Nino发展年对中国夏季降水的影响*

近年来随着对赤道东太平洋海温异常特征的深入认识,赤道太平洋海温变化的不同类型对气候的影响逐渐引起人们的关注。本文分析了东部和中部型El Ni?o发展年海温分布特征及其对中国夏季降水影响的差异和机理。结果表明：(1)东部型El Ni?o年的海温正距平中心发展快且强度比中部型El Ni?o年强。(2)两类El Ni?o发展年,中国夏季降水分布差异最大的是东北和华北地区,呈相反的分布,华南地区只是变化幅度不同,江淮流域降水一致偏少。(3)Walker环流分布的差异是两类El Ni?o年夏季降水分布差异的重要原因,其位于西太平洋地区下沉支的强弱以及有无上升支的分布,对西太副高和我国水汽的输送有明显影响。(4)500hPa位势高度场的遥相关波列以及高低层大气的垂直运动也是造成两类El Ni?o年中国夏季降水分布差异的重要原因。