SMS	Short description	Photo
GMS	GMS consist of electrodes contained in a granular matrix that is enclosed within a gypsum solution, a membrane, and a metal case. Gypsum buffers salinity effects. A small charge is placed on the electrodes, and electrical resistance through GMS is measured. As water is used by plants or as the soil moisture decreases, water is drawn from GMS and resistance increases. Conversely, as soil moisture increases, resistance decreases.
HDS	In HDS, the air temperature in a porous block is measured before and after a small heat pulse is applied to it. The amount of heat flow from the pulse-heated point is mostly proportional to the amount of water contained within the porous material. That means a wet material will heat up slower than a dry one. This rise in air temperature (or the cooling) is measured with an accurate air temperature sensor located at the sensor tip.	[F3]
Capacitance	A capacitive does not measure moisture directly (pure water does not conduct electricity well); instead, it measures the ions that are dissolved in the moisture. These ions and their concentration can be affected by a number of factors; for example, adding fertilizer will decrease the resistance of the soil.
TDR	TDR consists of parallel rods, acting as transmission lines, where a voltage is launched along the rods and reflected back to TDR for analysis. The velocity of the voltage pulse along the rod is related to the dielectric permittivity of the soil. The velocity of the pulse for wet soils is slower than that of drier soils.
FDR	FDR uses an oscillator to propagate an electromagnetic signal through either a metal line or other wave guide. The difference between the output wave and the return wave frequency is measured to determine soil moisture.