Potassium Doppler-resonance lidar for the study of the mesosphere and lower thermosphere at the Arecibo Observatory

We have developed a lidar to study the temperature structure of the nighttime mesopause region over the Arecibo Observatory (18.35°N, 66.75°W) by measuring the lineshape of the fluorescence spectrum of atomic potassium that is deposited in the mesosphere and lower thermosphere (MLT) by meteors. To demonstrate how the potassium lidar can enhance MLT studies at Arecibo, we show recent results for: (1) comparisons with airglow temperature measurements; (2) simultaneous operations with stratospheric and mesospheric temperature profiling by Rayleigh lidar; (3) simultaneous observations of K, Ca⁺, and E-region electron density profiles; and (4) occurrences of sporadic K layers, and relationships to sporadic E layers.     

Physical State and Composition of Polar Stratospheric Clouds Inferred from Airborne Lidar Measurements During SESAME

The airborne lidar LEANDRE was deployed from Kiruna (Sweden) in January1995, during Phase III of the Second European Stratospheric Arctic andMid-latitude Experiment (SESAME). Polar Stratospheric Clouds (PSC) weredetected on several flights. Four lidar retrievals, on two different days, arepresented together with the thermal history of air masses, derived from 5-daybackward trajectories calculated from the TOPCAT model, using ECMWF analyses.The first PSC case was observed at the synoptic scale and at a temperatureclose to the ice frost point, with no significant depolarization, suggestingthat particles were in the liquid phase, probably liquid ternaryH₂SO₄/HNO₃/H₂Osolution forming a Type 1b cloud. Locally, on the same day, a Type II PSC (icecloud) was detected above the Scandinavian Mountains and was related tomesoscale processes. On another day, the third lidar retrieval only showedbackground aerosols signature, whereas the last one was performed at the NATequilibrium temperature and its measured depolarization ratio was consistentwith few solid state Type Ia particles, probably composed of NAT. From thethermal histories, the different behaviour of the two Type I clouds isexplained in terms of cooling rates and compositional hysteresis, driven bytemperature.     

Cloud-base distribution and cirrus properties based on micropulse lidar measurements at a site in southeastern China

The cloud fraction(CF) and cloud-base heights(CBHs), and cirrus properties, over a site in southeastern China from June 2008 to May 2009, are examined by a ground-based lidar. Results show that clouds occupied the sky 41% of the time.Significant seasonal variations in CF were found with a maximum/minimum during winter/summer and similar magnitudes of CF in spring and autumn. A distinct diurnal cycle in the overall mean CF was seen. Total, daytime, and nighttime annual mean CBHs were 3.05 ± 2.73 km, 2.46 ± 2.08 km, and 3.51 ± 3.07 km, respectively. The lowest/highest CBH occurred around noon/midnight. Cirrus clouds were present ～36.2% of the time at night with the percentage increased in summer and decreased in spring. Annual mean values for cirrus geometrical properties were 8.89 ± 1.65 km, 9.80 ± 1.70 km, 10.73 ± 1.86 km and 1.83 ± 0.91 km for the base, mid-cloud, top height, and the thickness, respectively. Seasonal variations in cirrus geometrical properties show a maximum/minimum in summer/winter for all cirrus geometrical parameters. The mean cirrus lidar ratio for all cirrus cases in our study was ～ 25 ± 17 sr, with a smooth seasonal trend. The cirrus optical depth ranged from 0.001 to 2.475, with a mean of 0.34 ± 0.33. Sub-visual, thin, and dense cirrus were observed in ～12%, 43%, and 45%of the cases, respectively. More frequent, thicker cirrus clouds occurred in summer than in any other season. The properties of cirrus cloud over the site are compared with other lidar-based retrievals of midlatitude cirrus cloud properties.     

Preparing The National Map for the 3D Elevation Program – products,process and research

The 3D Elevation Program (3DEP) is a collaborative effort among government entities, academia, and the private sector to collect high-resolution 3-dimensional data over the United States. The United States Geological Survey (USGS) is making preparations for managing, processing, and delivering petabytes of 3DEP elevation products for the Nation. In addition to the existing 1/3, 1, and 2 arc-second seamless elevation data layers of The National Map, new 3DEP products include lidar point cloud data; a standard 1-meter DEM layer; additional source datasets; and, in Alaska, 5-meter digital elevation models. A new product generation system improves the construction and publication of the seamless elevation datasets, prepares the additional 3DEP products for distribution, and automates the data management functions required to accommodate the high-volume 3DEP data collection. Major changes in geospatial data acquisition, such as high resolution lidar data, volunteered geographic information, data processing using parallel and grid computer systems, and user needs for semantic access to geospatial data and products, are driving USGS research associated with the 3DEP. To address the research requirements, a set of inter-related projects including spatiotemporal data models, data integration, geospatial semantics and ontology, high performance computing, multi-scale representation, and hydrological modeling using lidar and other 3DEP data has been developed.     

北京城市大气混合层与气溶胶垂直分布观测研究

2002年3～10月在北京大学利用微脉冲激光雷达(MPL)观测了气溶胶时空变化。提出一种反演混合层高度的方法,这种方法减小了仪器订正的误差,反演的混合层高度与探空测量结果有很好的一致性。利用该方法计算了观测期间晴天无云天气条件下的混合层高度,分析了混合层高度及其增长率的日变化、季节变化,初步研究了混合层高度和近地面气溶胶分布的相互关系,分析了表征大气扩散能力的通风系数的日变化。结果表明,利用MPL监测城市混合层是可行的和优越的。     

A report on long-term trends and variabilities in middle atmospheric temperature over Gadanki (13.5°N, 79.2°E)

The present study reports long-term variabilities and trends in the middle atmospheric temperature (March 1998–2008) derived from Rayleigh backscattered signals received by the Nd:YAG lidar system at Gadanki (13.5°N, 79.2°E). The monthly mean temperature compositely averaged for the years 1998–2008 shows maximum temperature of 270 K in the months of March–April and September at altitudes between 45 and 55 km. The altitude profile of trend coefficients estimated from the 10 years of temperature observations using regression analysis shows that there exists cooling at the rate with 1σ uncertainty of 0.12±0.1 K/year in the lower stratospheric altitudes (35–42 km) and 0.2±0.08 K/year at altitudes near 55–60 km. The trend is nearly zero (no significant cooling or warming) at altitudes 40–55 km. The regression analysis reveals the significant ENSO response in the lower stratosphere (1 K/SOI) and also in mesosphere (0.6 K/SOI). The solar cycle response shows negative maxima of 1.5 K/100F10.7 units at altitudes 36 km, 41 km and 1 K/100F10.7 units at 57 km. The response is positive at mesospheric altitude near 67 km (1.3 K/100F10.7 units). The amplitudes and phases of semiannual, annual and quasi-biennial oscillations are estimated using least squares method. The semiannual oscillation shows larger amplitudes at altitudes near 35, 45, 62 and 74 km whereas the annual oscillation peaks at 70 km. The quasi-biennial oscillations show larger amplitudes below 35 km and above 70 km. The phase profiles of semiannual and annual oscillations show downward propagation.     

Uncertainty in quantitative analyses of topographic change: error propagation and the role of thresholding

Topographic surveys inevitably contain error, introducing uncertainty into estimates of volumetric or mean change based on the differencing of repeated surveys. In the geomorphic community, uncertainty has often been framed as a problem of separating out real change from apparent change due purely to error, and addressed by removing measured change considered indistinguishable from random noise from analyses (thresholding). Thresholding is important when quantifying gross changes (i.e. total erosion or total deposition), which are systematically biased by random errors in stable parts of a landscape. However, net change estimates are not substantially influenced by those same random errors, and the use of thresholds results in inherently biased, and potentially misleading, estimates of net change and uncertainty. More generally, thresholding is unrelated to the important process of propagating uncertainty in order to place uncertainty bounds around final estimates. Error propagation methods for uncorrelated, correlated, and systematic errors are presented. Those equations demonstrate that uncertainties in modern net change analyses, as well as in gross change analyses using reasonable thresholds, are likely to be dominated by low-magnitude but highly correlated or systematic errors, even after careful attempts to reduce those errors. In contrast, random errors with little to no correlation largely cancel to negligible levels when averaged or summed. Propagated uncertainty is then typically insensitive to the precision of individual measurements, and is instead defined by the relative mean error (accuracy) over the area of interest. Given that real-world mean elevation changes in many landscape settings are often similar in magnitude to potential mean errors in repeat topographic analyses, reducing highly correlated or systematic errors will be central to obtaining accurate change estimates, while placing uncertainty bounds around those results provides essential context for their interpretation. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.     

建筑遗产数字化表型监测技术现状及发展趋势

针对多种数字化手段特点在不同类型的建筑遗产表型监测的应用问题,该文从数字化监测手段入手,结合目前在国内外各领域的应用情况及经典案例,通过对比分析几种技术手段的监测范围、特点及成果精度,总结得到各技术手段优势及所适用的监测对象。目前比较普及的技术手段有传统测量技术、摄影测量技术、三维激光扫描技术及集成多种手段的技术方法,根据监测对象特点来进行不同病害类型的监测工作,如表面破损、整体及局部的变形等。针对现阶段所存在的问题,提出未来遗产保护健康监测方面发展趋势及展望。