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[1] We present a method for extracting spatially resolved water content profiles q(x) from a two-wire time domain reflectometry (TDR) probe. The profile q(x) is represented in terms of the dielectric e r (x) and ohmic s(x) properties in the longitudinal direction of the TDR probe. We solve the inverse problem iteratively by combining a one-dimensional time domain solution of the transmission line equations and a genetic optimization method. The method is capable of finding the global optimum in a complicated error landscape without initial assumptions, except physically reasonable limits. The method utilizes both the position and the magnitude of the TDR signal. We analyze water content profiles from laboratory measurements and demonstrate that the achievable spatial resolution can be made as low as 2 cm and even smaller. The present implementation of the numerical code demonstrates the practical feasibility of spatially resolved water content profiles.

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Context. Hydrides of the most abundant heavier elements are fundamental molecules in cosmic chemistry. Some of them trace gas irradiated by UV or X-rays. Aims. We explore the abundances of major hydrides in W3 IRS5, a prototypical region of high-mass star formation. Methods. W3 IRS5 was observed by HIFI on the Herschel Space Observatory with deep integration ( 2500 s) in 8 spectral regions. Results. The target lines including CH, NH, H 3 O + , and the new molecules SH + , H 2 O + , and OH + are detected. The H 2 O + and OH + J = 1−0 lines are found mostly in absorption, but also appear to exhibit weak emission (P-Cyg-like). Emission requires high density, thus originates most likely near the protostar. This is corroborated by the absence of line shifts relative to the young stellar object (YSO). In addition, H 2 O + and OH + also contain strong absorption components at a velocity shifted relative to W3 IRS5, which are attributed to foreground clouds. Conclusions. The molecular column densities derived from observations correlate well with the predictions of a model that assumes the main emission region is in outflow walls, heated and irradiated by protostellar UV radiation.