July 30th, 2010


Proximal Soil Sensing (PSS) deals with the measurement of soil properties at close range or in contact with the soil. A number of techniques are available, or currently being researched for PSS application. Each technique is capable of measuring different soil attributes either directly or indirectly (i.e. correlative),invasive or noninvasive and through active or passive techniques. Sensors are capable of deployment on mobile platforms (on-the-go vehicle based applications for mapping) or static application (e.g. continuous monitoring with wireless telemetry).

The following is a list of PSS techniques currently in use or under research. The techniques are classified by operational wavelengths (for EM) , resistivity, electrochemical or mechanical methods.

Descriptions of each technique, including the measured soil attributes and development status are available (pop-up). – Note: The technique information is currently being updated and expanded.


Gamma rays are high frequency (10^20 to 10^24 Hz) with quantum energies between 124keV and 1MeV. Gamma ray techniques can be active or passive and are based on the moderation of the gamma ray photons (absorption and scattering) through interaction with the soil. This category also include neutron techniques.



Inelastic Neutron Scattering (INS)

Thermalised Neutron Methods (TNM) / Neutron Probes (NP)

Cosmic Ray Neutrons (CRN)



X-Rays occur in the EM spectrum at a frequency range between 10^17 to 10^20 Hz and quantum energies between 124eV and 124keV. Within this range they are classified as 'hard' (short wavelength, high energy) or 'soft' (long wavelength, low energy). X-Rays can be used for soil elemental or mineralogical analysis.

X-Ray Flourescence (XRF)

X-Ray Diffraction (XRD)



These techniques are based on diffuse reflectance (or atomic emission) spectroscopy and offer a soil measurements that are rapid, relatively low cost, safe, non invasive and offer simultaneous measurement of multiple soil properties. The EM frequency range is from 10^12 Hz (MIR) to 10^15 Hz (UV).

Mid-Infrared (MIR)

Near-Infrared (NIR)

Visible (Vis) / Ultraviolet (UV)

Laser Induced Breakdown Spectroscopy (LIBS)



The microwave region occurs in the EM spectrum at frequencies between 3×10^9 and 3×10^11 Hz with quantum energies between approximately 12.4µeV and 12.4meV. Microwave is used for remote and proximal sensing and is typically based on soil emissivity or microwave attenuation changes under changing water content.



Radio Wave

Radio waves cover the EM spectrum at frequencies less than 3×10^9 Hz and energies less than 12.4µeV. There is a large range of techniques used for PSS in this band.

Time Domain Reflectometry (TDR)

Frequency Domain Reflectometry (FDR)


Ground Penetrating Radar (GPR)

Nuclear Magnetic Resonance (NMR)

Electromagnetic Induction (EMI)


Electrical Resistivity

Resistivity methods are electrical techniques characterised by direct electrode contact with the soil.

Contact Electrodes




Electrochemical methods are based on electrochemical sensors e.g. Ion Selective Electrodes (ISEs) and allow direct soil chemical measurements through a range of techniques.

Electrochemical (ECh)



Mechanical techniques are based on physical interaction between the sensor and soil.

Tillage sensors




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