Interpretation of gravity and magnetic anomalies caused due to spherical bodies

Summary The method of continuation has been used to obtain the master curves for gravity and magnetic anomalies caused by spherical bodies. The procedure to calculate the depth of burial and radius of spherical bodies has been outlined.     

On absence of certain periods in the love-wave spectrum

Summary It has been noted by several observers that no Love-wave spectrum is complete in the sense that it contains all the periods. The reason for this has been sought for in the presence of a low-velocity layer.     

Student Learning of Place: Learning Progressions Can Help Fill the Gaps

This commentary is a response to Larsen and Harrington's article titled “Developing a Learning Progression for Place” (2018). The commentary includes a discussion of the benefits to other content areas that research on student learning of place can provide. The commentary also describes the coherence that learning progressions can bring to research on student learning of complex, interdisciplinary domains of study.     

Prospect for UV observations from the Moon

Space astronomy in the last 40 years has largely been done from spacecraft in low Earth orbit (LEO) for which the technology is proven and delivery mechanisms are readily available. However, new opportunities are arising with the surge in commercial aerospace missions. We describe here one such possibility: deploying a small instrument on the Moon. This can be accomplished by flying onboard the Indian entry to the Google Lunar X PRIZE competition, Team Indus mission, which is expected to deliver a nearly 30 kgs of payloads to the Moon, with a rover as its primary payload. We propose to mount a wide-field far-UV (130–180 nm) imaging telescope as a payload on the Team Indus lander. Our baseline operation is a fixed zenith pointing but with the option of a mechanism to allow observations of different attitudes. Pointing towards intermediate ecliptic latitude (50^° or above) ensures that the Sun is at least 40^° off the line of sight at all times. In this position, the telescope can cover higher galactic latitudes as well as parts of Galactic plane. The scientific objectives of such a prospective are delineated and discussed.     

Assessment of urban heat island effect for different land use–land cover from micrometeorological measurements and remote sensing data for megacity Delhi

Urban heat island intensities (UHI) have been assessed based on in situ measurements and satellite-derived observations for the megacity Delhi during a selected period in March 2010. A network of micrometeorological observational stations was set up across the city. Site selection for stations was based on dominant land use–land cover (LULC) classification. Observed UHI intensities could be classified into high, medium and low categories which overall correlated well with the LULC categories viz. dense built-up, medium dense built-up and green/open areas, respectively. Dense urban areas and highly commercial areas were observed to have highest UHI with maximum hourly magnitude peaking up to 10.7 °C and average daily maximum UHI reaching 8.3 °C. UHI obtained in the study was also compared with satellite-derived land surface temperatures (LST). UHI based on in situ ambient temperatures and satellite-derived land surface temperatures show reasonable comparison during nighttime in terms of UHI magnitude and hotspots. However, the relation was found to be poor during daytime. Further, MODIS-derived LSTs showed overestimation during daytime and underestimation during nighttime when compared with in situ skin temperature measurements. Impact of LULC was also reflected in the difference between ambient temperature and skin temperature at the observation stations as built-up canopies reported largest gradient between air and skin temperature. Also, a comparison of intra-city spatial temperature variations based UHI vis-à-vis a reference rural site temperature-based UHI indicated that UHI can be computed with respect to the station measuring lowest temperature within the urban area in the absence of a reference station in the rural area close to the study area. Comparison with maximum and average UHI of other cities of the world revealed that UHI in Delhi is comparable to other major cities of the world such as London, Tokyo and Beijing and calls for mitigation action plans.     

Analytical solutions for transient temperature distribution in a geothermal reservoir due to cold water injection

An analytical solution to describe the transient temperature distribution in a geothermal reservoir in response to injection of cold water is presented. The reservoir is composed of a confined aquifer, sandwiched between rocks of different thermo-geological properties. The heat transport processes considered are advection, longitudinal conduction in the geothermal aquifer, and the conductive heat transfer to the underlying and overlying rocks of different geological properties. The one-dimensional heat transfer equation has been solved using the Laplace transform with the assumption of constant density and thermal properties of both rock and fluid. Two simple solutions are derived afterwards, first neglecting the longitudinal conductive heat transport and then heat transport to confining rocks. Results show that heat loss to the confining rock layers plays a vital role in slowing down the cooling of the reservoir. The influence of some parameters, e.g. the volumetric injection rate, the longitudinal thermal conductivity and the porosity of the porous media, on the transient heat transport phenomenon is judged by observing the variation of the transient temperature distribution with different values of the parameters. The effects of injection rate and thermal conductivity have been found to be profound on the results.     

Dynamics of sea-ice biogeochemistry in the coastal Antarctica during transition from summer to winter

The seasonality of carbon dioxide partial pressure(pCO_2).air-sea CO_2 fluxes and associated environmental parameters were investigated in the Antarctic coastal waters.The in-situ survey was carried out from the austral summer till the onset of winter[January 2012,February 2010 and March 2009) in the Enderby Basin.Rapid decrease in pCO_2 was evident under the sea-ice cover in January,when both water column and sea-ice algal activity resulted in the removal of nutrients and dissolved inorganic carbon(DIC) and increase in pH.The major highlight of this study is the shift in the dominant biogeochemical factors from summer to early winter.Nutrient limitation(low Si/N),sea-ice cover,low photosynthetically active radiation(PAR),deep mixed layer and high upwelling velocity contributed towards higher pCO_2during March(early winter).CO_2 fluxes suggest that the Enderby Basin acts as a strong CO_2 sink during January(-81 mmol m~2 d~(-1)),however it acts as a weak sink of CO_2 with-2.4 and-1.7 mmol m~(-2) d~(-1)during February and March,respectively.The present work,concludes that sea ice plays a dual role towards climate change,by decreasing sea surface PCO_2 in summer and enhancing in early winter.Our observations emphasize the need to address seasonal sea-ice driven CO_2 flux dynamics in assessing Antarctic contributions to the global oceanic CO_2 budget.     

基于激光雷达的自然资源三维动态监测现状与展望

激光雷达作为一种主动的三维遥感观测技术,在不同尺度的土地、矿产、森林、草原、湿地、水、海洋等自然资源的三维动态监测中发挥着越来越重要的作用.本文将在简要介绍激光雷达技术发展现状的基础上,重点阐述激光雷达技术在各类自然资源三维动态监测中的应用现状,同时对激光雷达在自然资源调查中的应用潜力和局限性进行综合分析,最后探讨以激...     

Structural information derived from ambient noise tomography over a hydrocarbon-producing region in the Cachar fold belt,lower Assam,northeast India

Ambient noise tomography is a powerful tool that has found increasing application in reservoir analysis and imaging. The Cachar fold belt in lower Assam, northeast India encompasses several wells under active hydrocarbon production, along with several dry wells. To overcome the lack of active seismic data over the entire fold belt, a passive seismic study was carried out to image the concealed three-dimensional sub-surface structures. The data were recorded from February to November 2011 by a network of 65 wideband seismometers spanning an area of about 40 × 60 km². The data are crosscorrelated in the 2–5 s band, followed by phase-weighted stacking to estimate noise correlation functions with surface wave signatures. The traveltimes picked from the frequency-time analysis are utilized in a tomographic inversion for Rayleigh wave group velocities. The group velocity anomalies have a lateral resolution of ~ 3.5 × 5.5 km² and variations of up to $\pm 20\%$ for each period. The group velocities are in turn inverted for S-wave velocity distribution as a function of depth. The three-dimensional S-wave velocity tomograms reveal the tight anticlines and broad synclines, with high- and low-velocity zones corresponding to structural highs and lows, respectively. The structural interpretation is supported for the part of the region with producing wells and covered by active seismic data, wherein the post-stack time migrated seismic section shows anticlinal and synclinal features similar to those obtained from ambient noise tomography. The structures revealed by ambient noise tomography can help identify zones of interest to be targeted by active seismic surveys in the Cachar fold belt.