Overlap correction function based on multi-angle measurements for an airborne direct-detection lidar for atmospheric sensing

We estimate the overlap function (accounting for near-field effects) for an airborne nadir-mounted lidar, based on multi-angle measurements of an atmospheric scene obtained during two flights. For each atmospheric layer, a regression on the logarithm of the range-corrected signal versus the secant of the off-nadir angle allowed evaluation of the optical depth and the backscattering coefficient multiplied by the lidar constant. These quantities allow for computation of the lidar signal unaffected by the overlap effect, and then for determination of the overlap correction function. Its evolution over time can also help to detect changes in the alignment. The method is easy to implement as long as a scanning capability is available, and it can be applied in aerosol-free or aerosol-laden conditions, the requirement being a constant and horizontally homogeneous atmosphere during the measurements. For multichannel lidars, the method can be applied separately for each channel.

Aerosols' variability and their relationship with climatic parameters over West Africa

Aerosols' influences on Earth's climate have been documented by several authors. This ranges from scattering and reflecting of shortwave radiation (direct effect) which is also regarded as the "Whitehouse Effect," to the ability to act as condensation nuclei (indirect effect) which results in cloud droplet formation. This broad summary of aerosol's effect on earth's climate has in turn affected some other weather variables either positively or negatively depending on people's perspectives. This work was done in a view to ascertaining some of these claims by determining the statistical significance of some certain aerosol's relationships with some selected weather variables. This was done over six (6) stations across the West African region to represent the climatic zones from the rainforest around the coasts to the desert of the Sahel. Data used consist of aerosol types (biomass burning, carbonaceous, dust, and PM_2.5) and climatic types (convective precipitation, wind speed, and water vapor) over a period of 30 years, with the python and ferret programs explicitly used for the graphical analyses. Climatologically, locations close to the point source seem to record more of the presence of the pollutants than the farthest ones. Results indicated that aerosols were more pronounced in the dry months of NDJF over the rainforest region depending on the latitudinal position of the location. The relationship result showed a negative correlation between convective precipitation and aerosols, except carbonaceous. But the strongest relationship can be found between water vapor and the selected aerosol types.