An instrument measures electrical properties of relatively dry soils to determine their liquid water and/or ice contents. Designed as a prototype of instruments for measuring the liquid-water and ice contents of lunar and planetary soils, the apparatus could also be utilized for similar purposes in research and agriculture involving terrestrial desert soils and sands, and perhaps for measuring ice buildup on aircraft surfaces.

Figure 1. The Water/Ice Detection Instrument relies on an electrical properties probe using a two-probe pair. In use, the free end is pushed into the ground to place the electrodes in contact with the soil.
This instrument is an improved version of the apparatus described in “Measuring Low Concentrations of Liquid Water and Ice in Soil” (NPO- 41822), NASA Tech Briefs, Vol. 33, No. 2 (February 2009), page 22. The designs of both versions are based on the fact that the electrical behavior of a typical soil sample is well approximated by a network of resistors and capacitors in which resistances decrease and capacitances increase (and the magnitude and phase angle of impedance changes accordingly) with increasing water content. The previous version included an impedance spectrometer and a jar into which a sample of soil was placed. Four stainless-steel screws at the bottom of the jar were used as electrodes of a four-point impedance probe connected to the spectrometer.

Figure 2. Phase Angle Versus Frequency was measured in the “empty” case (nothing in contact with the electrodes) and at various temperatures with electrodes in contact with (a) dry silica sand and (b) silica sand moistened with 0.1 weight percent of a 0.1 M aqueous solution of KCl.
The present instrument does not include a sample jar and can be operated without acquiring or handling samples. Its impedance probe consists of a compact assembly of electrodes housed near the tip of a cylinder. The electrodes protrude slightly from the cylinder (see Figure 1). In preparation for measurements, the cylinder is simply pushed into the ground to bring the soil into contact with the electrodes.

A typical measurement run takes several seconds. Typically, the magnitude and phase angle of impedance are measured as function of frequency from 20 Hz to 500 kHz. Figure 2 presents some results of test measurements performed at temperatures from –25 to +65 °C on dry and moist silica sand. From these and other measurement results, it was concluded that, in the aforementioned temperature range, the instrument can detect the presence of water or ice at a concentration as low 0.1 weight percent and can measure the concentration above 0.5 weight percent.

This work was done by Martin Buehler, Keith Chin, Didier Keymeulen, Timothy McCann, Suresh Seshadri, and Robert Anderson of Caltech for NASA’s Jet Propulsion Laboratory.

NPO-44261

Topics:
Icing and ice detection Physical Sciences Safety testing and procedures Soils Test equipment and instrumentation Water
This Brief includes a Technical Support Package (TSP).
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Improved Instrument for Detecting Water and Ice in Soil

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NASA Tech Briefs Magazine

This article first appeared in the March, 2009 issue of NASA Tech Briefs Magazine (Vol. 33 No. 3).

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Overview

The document outlines NASA's Technical Support Package NPO-44261, which presents an improved instrument designed for detecting water and ice in soil, particularly on lunar and planetary surfaces. Developed by NASA's Jet Propulsion Laboratory, this innovative solution addresses the need for a reliable water/ice monitor that can be deployed in various configurations, such as within the wall of a drill or integrated into the tread of a rover.

The core of the proposed solution is the Electrical Properties Probe (EPP), which consists of two electrodes that slightly protrude from a cylindrical body. This design allows the probe to make direct contact with regolith, enabling the characterization of soil properties through impedance spectroscopy. The EPP is capable of measuring several key parameters: the presence of water or ice, the conductivity of these substances, and the dielectric constant of the regolith. These measurements are obtained by analyzing the sample's impedance and phase angle across a frequency range of 20 Hz to 500 kHz.

The EPP is designed to operate effectively over a temperature range from 25 °C to -65 °C, making it suitable for the harsh conditions found on other planetary bodies. The instrument has demonstrated the ability to detect water/ice content in silica sand ranging from 0.05% to 10%, with an accuracy of a few percent. Ongoing analysis aims to refine the accuracy of these measurements further.

The novelty of this project lies in its simplicity and rapid deployment capabilities, as the EPP requires no sample handling, making it an efficient tool for in-situ analysis. By providing real-time data on water and ice content, the EPP can significantly enhance exception-based monitoring during exploration missions.

The document also emphasizes the broader implications of this technology, suggesting potential applications beyond aerospace, including scientific research and commercial ventures. For further inquiries or assistance, the document provides contact information for NASA's Innovative Technology Assets Management at JPL.

In summary, the Technical Support Package NPO-44261 details a groundbreaking instrument that enhances our ability to detect and analyze water and ice in extraterrestrial soils, contributing to our understanding of planetary environments and supporting future exploration efforts.