Dynamics of Water Movement near Boundaries of the Vadose Zone

Processes at boundaries of the unsaturated soil water zone were investigated: At the upper boundary evaporation at the soil-atmosphere interface, and at the lower boundary the dynamic capillary fringe. For studying the upper boundary, an evaporation experiment at the representative elementary volume (REV) scale was considered and modelled numerically. A model with a diffusive boundary layer and a 1D Richards' description including vapour transport fitted well to experimental data. It showed a boundary layer dominated regime in the wet range and a regime where dynamics is controlled by soil hydraulic properties in the dry range. The model could successfully be used to determine soil hydraulic properties from the corresponding evaporation experiment by inverse modelling using a Monte-Carlo Levenberg-Marquardt approach. For the lower boundary, light transmission and NIR imaging spectroscopy methods were developed and employed to measure the micro- and macroscopic water distribution in response to transient boundary conditions in a semi-2D sand medium in a Hele-Shaw cell with high temporal and spacial resolution. The analysis showed that coupled multi-phase and dynamic non-equillibrium effects are essential to understand water movement in dynamic capillary fringes, and sub-REV processes play an important role in the dynamics

Technical Note: Comparison of storage strategies of sea surface microlayer samples

The sea surface microlayer (SML) is an important biogeochemical system whose physico-chemical analysis often necessitates some degree of sample storage. However, many SML components degrade with time so the development of optimal storage protocols is paramount. We here briefly review some commonly used treatment and storage protocols. Using freshwater and saline SML samples from a river estuary, we investigated temporal changes in surfactant activity (SA) and the absorbance and fluorescence of chromophoric dissolved organic matter (CDOM) over four weeks, following selected sample treatment and storage protocols. Some variability in the effectiveness of individual protocols most likely reflects sample provenance. None of the various protocols examined performed any better than dark storage at 4 °C without pre-treatment. We therefore recommend storing samples refrigerated in the dark

A new method to determine multi-angular reflectance factor from lightweight multispectral cameras with sky sensor in a target-less workflow applicable to UAV

A new physically based method to estimate hemispheric-directional reflectance factor (HDRF) from lightweight multispectral cameras that have a downwelling irradiance sensor is presented. It combines radiometry with photogrammetric computer vision to derive geometrically and radiometrically accurate data purely from the images, without requiring reflectance targets or any other additional information apart from the imagery. The sky sensor orientation is initially computed using photogrammetric computer vision and revised with a non-linear regression comprising radiometric and photogrammetry-derived information. It works for both clear sky and overcast conditions. A ground-based test acquisition of a Spectralon target observed from different viewing directions and with different sun positions using a typical multispectral sensor configuration for clear sky and overcast showed that both the overall value and the directionality of the reflectance factor as reported in the literature were well retrieved. An RMSE of 3% for clear sky and up to 5% for overcast sky was observed