Read the following statements.
(A) TDR stands for Time Domain Refraction.
(B) TDR is based on the estimation of dielectric constant of water.
(C) Dielectric constant of water is 80.
(D) TDR is relatively unaffected by salinity or bulk density variations.
(E) TDR measures soil moisture suction.
Choose the correct answer from the options given below.

Question

Which of the following statements is false?

Answer 1

Let's check each of the five statements about Time Domain Reflectometry (TDR) one at a time.

(A) TDR stands for Time Domain Refraction: wrong, the correct full form is Time Domain Reflectometry, named for the reflected electrical pulse the instrument times, not any refraction effect.
(B) TDR is based on the estimation of dielectric constant of water: wrong as stated, TDR estimates the apparent dielectric constant of the whole soil mass (soil, water and air together), not specifically of water, water's own dielectric constant is simply a fixed reference value used in the conversion formula.
(C) Dielectric constant of water is 80: correct, water's dielectric constant is close to 80 at ordinary soil temperatures, far above soil minerals or air, which is exactly why even small changes in water content shift the bulk reading a lot.
(D) TDR is relatively unaffected by salinity or bulk density variations: correct, this is one of the main reasons TDR is preferred over resistance based sensors, since normal shifts in salt content or compaction do not distort the reading much.
(E) TDR measures soil moisture suction: wrong, TDR reports volumetric water content, suction (tension) is a separate quantity measured with tensiometers, not TDR.

Only (C) and (D) survive this check, the other three either misstate what TDR measures or mix up terminology.

Let's summarize:

TDR measures bulk soil dielectric constant to infer water content, it does not directly give suction.
Its big practical strength is staying reliable across different salinity and bulk density conditions.

So the correct answer is option 3, (C) and (D) only.

Answer 2

Let's check each of the five statements about Time Domain Reflectometry (TDR) one at a time.

(A) TDR stands for Time Domain Refraction: wrong, the correct full form is Time Domain Reflectometry, named for the reflected electrical pulse the instrument times, not any refraction effect.
(B) TDR is based on the estimation of dielectric constant of water: wrong as stated, TDR estimates the apparent dielectric constant of the whole soil mass (soil, water and air together), not specifically of water, water's own dielectric constant is simply a fixed reference value used in the conversion formula.
(C) Dielectric constant of water is 80: correct, water's dielectric constant is close to 80 at ordinary soil temperatures, far above soil minerals or air, which is exactly why even small changes in water content shift the bulk reading a lot.
(D) TDR is relatively unaffected by salinity or bulk density variations: correct, this is one of the main reasons TDR is preferred over resistance based sensors, since normal shifts in salt content or compaction do not distort the reading much.
(E) TDR measures soil moisture suction: wrong, TDR reports volumetric water content, suction (tension) is a separate quantity measured with tensiometers, not TDR.

Only (C) and (D) survive this check, the other three either misstate what TDR measures or mix up terminology.

Let's summarize:

TDR measures bulk soil dielectric constant to infer water content, it does not directly give suction.
Its big practical strength is staying reliable across different salinity and bulk density conditions.

So the correct answer is option 3, (C) and (D) only.

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