Underwater Acoustics and Depth Uncertainties In the Tropics

Acoustic velocity is known to vary with temperature, depth and salinity (TDS). Calibration of acoustic systems is required at the beginning and end (and sometimes midway) of each hydrographic operation, in order to correct for these velocity variations. Estuarine waters in the tropics were investigated employing wide combinations of temperature, depth and salinity to verify the relationships between these parameters and the acoustic velocity. A maximum error in depth of 0.2m was obtained. Consequently, in the absence of other sources of errors, acoustic systems may need to be calibrated only once in the cause of a full day bathymetric survey operation in the tropics.Se sabe que la velocidad acústica varía con la temperatura, la profundidad y la salinidad (TDS). Se requiere la calibración de los sistemas acústicos al principio y al final (y a veces a mitad de camino) de cada operación hidrográfica, para corregir estas variaciones de velocidad. Se estudia-ron las aguas de las zonas de estuarios de los trópicos, empleando amplias combinaciones de tem-peratura, profundidad y salinidad para comprobar las relaciones entre estos parámetros y la velo-cidad acústica. Se obtuvo un error máximo de 0,2 m en la profundidad. Por consiguiente, en au-sencia de otras fuentes de errores, los sistemas acústicos pueden necesitar ser calibrados sólo una vez a causa de una operación hidrográfica de un día entero de duración en los trópicos.L‘on sait que la vitesse des ondes acoustiques varie en fonction de la température, de la profondeur et de la salinité (TDS). L‘étalonnage de systèmes acoustiques est requise au début et à la fin (et parfois au milieu) de chaque opération hydrographique, afin de corriger ces variations de la vitesse. Les eaux d‘estuaires dans les zones tropicales ont été ont fait l‘objet d‘investigations à l‘aide d‘une large combinaison de températures, de profondeurs et de salinité afin de vérifier la relation entre ces paramètres et la vitesse des ondes acoustiques. Une erreur maximum de profon-deur de 0,2m a été obtenue. Par conséquent, en l‘absence d‘autres sources d‘erreurs, les systèmes acoustiques peuvent devoir être étalonnés une fois seulement pour la cause d‘une opération de levés bathymétriques d‘une journée entière dans les zones tropicales

Detecting gas flares and estimating flaring volumes at individual flow stations using MODIS data.

Gas flaring has gained global recognition as a prominent agent of pollution, leading to the establishment of the Global Gas Flaring Reduction (GGFR) initiative, which requires an objective means of monitoring flaring activity. Because auditable information on flaring activity is difficult to obtain there have recently been attempts to detect flares using satellite imagery, typically at global scales. However, to adequately assess the environmental and health impacts of flaring from local to regional scales, it is important that we have a means of acquiring information on the location of individual active flaring sites and the volume of gas combusted at these sites. In this study we developed an approach to the retrieval of such information using nighttime MODIS thermal imagery. The MODIS flare detection technique (MODET) and the MODIS flare volume estimation technique (MOVET) both exploit the absolute and contextual radiometric response of flare sites. The levels of detection accuracy and estimation error were quantified using independent observations of flare location and volume. The MODET and MOVET were applied to an archive of MODIS data spanning 2000–2014 covering the Niger Delta, Nigeria, a significant global hotspot of flaring activity. The results demonstrate the substantial spatial and temporal variability in gas flaring across the region, between states and between onshore and offshore sites. Thus, whilst the estimated total volume of gas flared in the region over the study period is large (350 Billion Cubic Metres), the heterogeneity in the flaring indicates that the impacts of such flares will be highly variable in space and time. In this context, the MODET and MOVET offer a consistent and objective means of monitoring flaring activity over an appropriate range of scales and it is now important that their robustness and transferability is tested in other oil-producing regions of the world

Contributions of gas flaring to a global air pollution hotspot:spatial and temporal variations, impacts and alleviation

Studies of environmental impacts of gas flaring in the Niger Delta are hindered by limited access to official flaring emissions records and a paucity of reliable ambient monitoring data. This study uses a combination of geospatial technologies and dispersion modelling techniques to evaluate air pollution impacts of gas flaring on human health and natural ecosystems in the region. Results indicate that gas flaring is a major contributor to air pollution across the region, with concentrations exceeding WHO limits in some locations over certain time periods. Due to the predominant south-westerly wind, concentrations are higher in some states with little flaring activity than in others with significant flaring activity. Twenty million people inhabit areas of high flare-associated air pollution, which include all of the main ecological zones of the region, indicating that flaring poses a substantial threat to human health and the environment. Model scenarios demonstrated that substantial reductions in pollution could be achieved by stopping flaring at a small number of the most active sites and by improving overall flaring efficiency

Great Britain transport, housing, and employment access datasets for small-area urban area analytics

This paper provides a brief description of three new forms of key datasets relevant to urban analytics studies namely: Transport, Housing and Employment Accessibility, covering Great Britain, developed by the Urban Big Data Centre (UBDC). Full details of the research related to this paper are contained in “Spatial urban data system: A cloud-enabled big data infrastructure for social and economic urban analytics” [1]. The transport Dataset contains public transport availability (PTA) indicators at both the stop/station and small-area levels (lower layer super output area (LSOA) and middle layer super output area (MSOA)). The employment dataset provides information on the number of people with access to employment within specific distances from each output area. The housing datasets contains quarterly house rent and sales prices aggregated at output area level (MSOA). The theoretical background for measuring the datasets at small area levels is also presented in this paper. Additionally, a variety of raw data used to produce some of the datasets (e.g. PTA) is also included to enable interested readers to reproduce them

Satellite survey of gas flares:development and application of a Landsat-based technique in the Niger Delta

Pollution from oil and gas exploitation in the Niger Delta has greatly endangered the natural ecosystem, with gas flaring identified as a key agent of environmental pollution in the region. Efforts to evaluate the impacts of flaring on the surrounding environment have been hampered by limited access to official information on flare locations and volumes; hence an alternative method of acquiring such information is needed. This paper describes the development and application of the Landsat Flare Detection Method (LFDM), based on the combination of the near, shortwave and thermal infrared bands of Landsat imagery. The technique was validated using a reference dataset of flare locations interpreted from aerial photographs, achieving a user accuracy of 86.67%. The LFDM was applied to a time-series of imagery (1984 to 2012 inclusive) to obtain a long term flaring history of the region; 303 flares (251 onshore and 52 offshore) were detected over the study period. The spatiotemporal distribution of these flares corresponds with known variations in oil and gas activities in the region. There was considerable variation between states in the trajectories of gas flaring activity and the proportion of onshore versus offshore flaring, which indicates substantial spatiotemporal variations in the environmental impacts of this industry. The LFDM builds upon existing methods of flare detection, which were based on moderate resolution imagery, by offering: increased precision of flare location estimates, improved objectivity, accurate identification of onshore and offshore flares and a long flaring history. The LFDM is an efficient and cost effective method which is able to provide local to regional scale information which is complementary to that derived from other remote methods of flare detection and ground-based surveys. It could thus be used for either backward (flare history) and/or forward (monitoring) surveys, especially in monitoring the country’s progress towards the recently set 30% flare reduction target by 2017

Great Britain Transport, Employment Access Datasets for small-area Urban Area Analytics

This paper provides a brief description of four new forms of key datasets relevant to urban analytics studies namely: Transport, Housing and Employment Accessibility and Education, covering Great Britain, developed by the Urban Big Data Centre (UBDC). Full details of the research related to this paper are contained in “Spatial urban data system: A cloud-enabled big data infrastructure for social and economic urban analytics”[1]The transport Dataset contains public transport availability (PTA) indicators at both the stop/station and small-area levels (lower layer super output area (LSOA) and middle layer super output area (MSOA)). The employment dataset provides information on the number of people with access to employment within specific distances from each output area. The housing datasets contains quarterly house rent and sales prices aggregated at output area level (MSOA). The education data contains secondary school (Greater Glasgow Area, Scotland) and Higher Education (Great Britain) student-level data. In addition to all educational outcomes at school stages S4-S6, the secondary school pupil data consists of age, gender, nationality and ethnic background, level of English, attendance, post-school destinations, and receipt of Gaelic education. This is augmented by individual schools’ data consisting of staffing levels, proportions of pupils’ speaking particular languages at home, religious denomination, distance travelled by students from home, and accessibility to greenspace from both the home and school neighbourhoods. The higher education (HE) dataset consists of home and term-time locations (at postcode sector level), subject studied, level and mode of study of courses, level and classification of qualification, and post-HE destination. The theoretical background for measuring the datasets at small area levels is also presented in this paper. Additionally, a variety of raw data used to produce some of the datasets (e.g. PTA) is also introduced to enable interested readers to reproduce them

FireBIRD Mission Data for Gas Flaring Analysis

German Aerospace Center (DLR) initiated the FireBIRD mission for the purpose of fire analysis. Twin satellites, TET-1 and BIROS, provide data specialized in this field. This data can be used in gas flaring analysis. Gas flaring is a process of burning the associated gas obtained during crude-oil extraction. During this process, great amounts of greenhouse gases are emitted into the atmosphere. In order to enable monitoring this process, reliable data is necessary. The paper provides an overview on existing thermal sensors which can be used in researching the subject of gas flares. The comparison discusses sensor features important to gas flaring studies. The FireBIRD mission is described and assessed for the purpose of this application. The data is compared to the existing database from the World Bank. FireBIRD proves to have potential for this application, and in some cases significant advantages over other sensors. Research in this direction will be continued in the project