Evaluation of spatial and temporal characteristics of GNSS-derived ZTD estimates in Nigeria

Theoretical and Applied Climatology - This study presents an in-depth analysis to comprehend the spatial and temporal variability of zenith tropospheric delay (ZTD) over Nigeria during the period...     

Farmers’ choice of wetland agriculture: checking wetland loss and degradation in Lagos State, Nigeria

The issue of food security has received increasing emphasis in developing countries, particularly in the cities. The emphasis on food security has engendered agricultural expansion and encroachment on the coastal and inland wetlands in these nations. To facilitate and sustain the security of food in the developing countries local and international policies have been designed and employed; they have specifically targeted abounding food production towards ensuring human survival in the cities. However, the various ecological and socio-economic benefits derivable from the preservation of wetlands and inland valleys in these urban environments may be lost, with the transformation in the land use and cover. This study is therefore concerned with how wetland degradation and loss can be checked and mitigated, focusing on the developing countries and their cities. In this respect, the farmer’s awareness of the impacts of wetland cultivation and the role of accessibility, socio-economic and biophysical factors influencing the choice of wetland farming are examined. To this end, structured questionnaire on choice of wetland agriculture in the urban and periurban wetland areas of Lagos city was administered to the farmers. Simple frequency analysis is used to explain and interpret the data generated. The data reveals a generally low level of farmers’ awareness of the implication of wetland cultivation; it shows different categories of factors influencing the choice of wetland farming. Provision of irrigation infrastructure and improvement in living standard of the people through poverty eradication can discourage disadvantageous encroachment on wetlands in cities.     

EM telemetry assessment for horizontal drilling in part of the Tarim basin through numerical simulation

Electromagnetic telemetry is bi‐directional transmission of borehole data for effective drilling, especially in unconventional wells. In this study, numerical simulations was used to investigate the possibility of applying EM telemetry for measurement while drilling (MWD) in an ultra‐deep borehole in the Tahe region of the Tarim basin, using the drill string as an antenna excited as a gaped dipole source to quantify spatial variations of the electromagnetic field from subsurface to the surface. Results confirm that the distribution of the electric field along the drill string is sensitive to vertical variations of electric conductivity in the host rock. The simulated results show a high attenuation within the conductive formations, thereby limiting the effectiveness of EM telemetry in data transfer to the surface. In addition, the changes in thickness and resistivity of the target region affects the amplitude of the desired response.     

Development of the emerging electromagnetic methods for deep earth exploration

Three emerging techniques for surface electromagnetic (EM) exploration with high detection accuracy and large depth of investigation, namely, WEM (wireless electromagnetic method), MTEM (multi‐channel transient electromagnetic method) and SOTEM (short‐offset grounded‐wire TEM), are introduced. In detail, we proposed a newly developed sky‐wave theory in which EM wave can propagate in full space of ionosphere‐atmosphere‐lithosphere. Correspondingly, we developed the WEM recording system to measure the sky‐wave to obtain the structures down to ～10 km depth. We then introduced MTEM as a highly effective method for mineral exploration with target depth of 3km. Using self‐developed MTEM system, we presented the results obtained from mineral exploration study carried out in China. Lastly, we proposed the SOTEM method for a greater detection depth (1.5km) than traditional loop source TEM (500m) with a small offset and high resolution.