Inversion of temperature time series from near-surface porous sediments

An inversion technique is presented which delivers optional thermal properties and/or flow velocities from temperature time series at various positions. In contrast to inversion techniques based on analytical solutions, the described module implemented in MATLAB can be applied using general time series as input, and is not restricted to oscillating or other special conditions. Internally, the MATLAB pdepe-solver is used for the direct solution of the transport equation, and the MATLAB optimization toolbox is used for the inverse modelling. The module can be applied to calculate groundwater recharge or discharge in aquatic sediments or in the unsaturated zone, and to estimate horizontal or vertical flow velocities in groundwater. An example is presented for the latter situation, utilizing a large dataset of borehole temperature measurements from the Lake Stechlin test site in Germany.