Apparatus and method for assessing volumetric moisture content and controlling an irrigator

1. An apparatus for assessing at least one property of a target soil, the apparatus comprising:

a microwave signal generator arranged to generate a first microwave signal, wherein the generated first microwave signal is a fixed frequency microwave signal;

a detector;

a probe comprising an electrical conductor exhibiting a first end and a second end removed from said first end, said probe arranged to be embedded in the target soil; and

a coupler arranged to couple a first portion of the generated first microwave signal as a second microwave signal to the first end of said probe, and to couple a second portion of the generated first microwave signal as a microwave reference signal to a reference input of said detector, said second microwave signal exiting the second end of said probe as a third microwave signal, the second end of said probe carrying the third microwave signal connected to an input of said detector;

said detector arranged to square each of said third microwave signal and said microwave reference signal and to output a phase difference signal indicative of the phase difference between the squared third microwave signal and the squared microwave reference signal; and

a control circuitry coupled to the output of said detector and arranged to output an irrigation control signal responsive to said phase difference signal with the probe embedded in the target soil at present, said phase difference signal with the probe embedded in the target soil when the target soil is dry, and the phase difference signal with the probe embedded in the target soil when the target soil is saturated,

said control circuitry is further arranged to:

calculate a volumetric moisture content of the target soil responsive to the phase difference signal for the target soil at present with the probe embedded in the target soil, the phase difference signal when the target soil is dry with the probe embedded in the target soil,

and the phase difference signal when the target soil is saturated with the probe embedded in the target soil,

wherein the irrigation control signal is responsive to the calculated volumetric moisture content,

wherein the volumetric moisture content (VMC) is calculated in accordance with:

V

⁢

⁢

M

⁢

⁢

C

=

(

ΔΦ

⁢

⁢

m

Δ

⁢

⁢

Φ

⁢

⁢

f

-

ΔΦ

⁢

⁢

d

ΔΦ

⁢

⁢

f

)

/

(

ΔΦ

⁢

⁢

s

ΔΦ

⁢

⁢

f

-

1

)

,

where ΔΦm is the phase difference for the target soil at present, ΔΦf is the phase difference for ambient air, ΔΦd is the phase difference for the target soil when dry, and ΔΦs is the phase difference for the target soil when saturated.

2. The apparatus of claim 1 , wherein said irrigation control signal is coupled to an irrigation system and arranged to alternately enable and disable irrigation responsive to said irrigation control signal.

3. The apparatus of claim 1 , wherein the fixed frequency of said generated first microwave signal is approximately 900 Megahertz.

4. The apparatus of claim 1 , further comprising a low frequency signal generator arranged to output a first low frequency signal, the first low frequency signal coupled to an input of the coupler, and wherein:

said coupler is further arranged to couple a first portion of the first low frequency signal as a second low frequency signal to the first end of said probe, and to couple a second portion of the first low frequency signal as a low frequency reference signal to the reference input of said detector, said second low frequency signal exiting the second end of said probe as a third low frequency signal, the second end of said probe carrying the third low frequency signal to the input of said detector;

said detector is further arranged to square said third low frequency signal and said low frequency reference signal and to output an amplitude difference signal indicative of the phase difference between the squared third low frequency signal and the squared low frequency reference signal; and

wherein said control circuitry is arranged to assess the salinity of the target soil responsive to the amplitude difference signal with the probe embedded in the target soil.

5. The apparatus of claim 4 , wherein said control circuitry is further arranged to output the irrigation control signal responsive to a condition of said amplitude difference signal so as to flush the target soil.

6. The apparatus of claim 4 , wherein the low frequency first signal is in the range of 12.5-25 Megahertz.

7. The apparatus of claim 1 , wherein said control circuitry is arranged to output the irrigation control signal so as to maintain the phase difference between the phase difference when the target soil is dry and the phase difference when the target soil is saturated.

8. A method of assessing at least one property of a target soil, the method comprising:

providing a probe constituted of an electrical conductor exhibiting a first end and a second end removed from said first end, said probe arranged to be embedded in the target soil;

generating a first microwave signal, said generated first microwave signal having a fixed frequency;

coupling a first portion of the generated first microwave signal as a second microwave signal to the first end of said provided probe, said second microwave signal exiting the second end of said probe as a third microwave signal;

coupling a second portion of the generated microwave first signal as a reference microwave signal;

squaring each of the third microwave signal and the reference microwave signal;

determining a dry phase difference between the squared third microwave signal and the squared reference microwave signal with the probe embedded in the target soil when the target soil is dry;

determining a saturated phase difference between the squared third microwave signal and the squared reference microwave signal with the probe embedded in the target soil when the target soil is saturated;

determining a present phase difference between the squared third microwave signal and the squared reference microwave signal for the target soil at present with the probe embedded in the target soil; and

outputting an irrigation control signal responsive to said determined present phase difference, said determined dry phase difference and said determined saturated phase difference; and

calculating a volumetric moisture content of the target soil responsive to the said determined present phase difference, said determined dry phase difference and said determined saturated phase difference,

wherein the output irrigation control signal is output responsive to the calculated volumetric moisture content,

determining an ambient phase difference between the squared third microwave signal and the squared reference microwave signal when the provided probe is in ambient air,

wherein the volumetric moisture content (VMC) is calculated in accordance with

V

⁢

⁢

M

⁢

⁢

C

=

(

ΔΦ

⁢

⁢

m

Δ

⁢

⁢

Φ

⁢

⁢

f

-

ΔΦ

⁢

⁢

d

ΔΦ

⁢

⁢

f

)

/

(

ΔΦ

⁢

⁢

s

ΔΦ

⁢

⁢

f

-

1

)

,

where ΔΦm is said determined present phase difference, ΔΦf is said determined ambient phase difference, ΔΦd is said determined dry phase difference, and ΔΦs is said determined saturated phase difference.

9. The method of claim 8 , further comprising:

alternately enabling and disabling irrigation responsive to said output irrigation control signal.

10. The method of claim 8 , wherein said fixed frequency is approximately 900 Megahertz.

11. The method of claim 8 , further comprising:

generating a first low frequency;

coupling a first portion of the generated first low frequency signal as a second low frequency signal to the first end of said provided probe, said second low frequency signal exiting the second end of said probe as a third low frequency signal;

coupling a second portion of the generated first low frequency signal as a reference signal;

squaring said third low frequency signal;

squaring said low frequency reference signal;

determining an amplitude difference between the squared third low frequency signal and the squared low frequency reference signal; and

assessing the salinity of the target soil responsive to the determined amplitude difference with the provided probe embedded in the target soil.

12. The method of claim 11 , further comprising:

outputting the irrigation control signal further responsive to a condition of said determined amplitude difference so as to flush the target soil.

13. The method of claim 11 , wherein the low frequency first signal is in the range of 12.5-25 Megahertz.

14. The method of claim 8 , wherein said outputting of the irrigation control signal is arranged so as to maintain said determined present phase difference between said determined dry phase difference and said determined saturated phase difference.

15. An apparatus for assessing at least one property of a target soil, the apparatus comprising:

a microwave signal generator arranged to generate a first microwave signal, wherein the generated first microwave signal is a fixed frequency microwave signal;

detector;

a probe comprising an electrical conductor exhibiting a first end and a second end removed from said first end, said probe arranged to be embedded in the target soil; and

a coupler arranged to couple a first portion of the generated first microwave signal as a second microwave signal to the first end of said probe, and to couple a second portion of the generated first microwave signal as a microwave reference signal to a reference input of said detector, said second microwave signal exiting the second end of said probe as a third microwave signal, the second end of said probe carrying the third microwave signal connected to an input of said detector;

said detector arranged to output a phase difference signal indicative of the phase difference between the third microwave signal and the microwave reference signal; and

a control circuitry coupled to the output of said detector and arranged to output an irrigation control signal responsive to said phase difference signal with the probe embedded in the target soil at present, said phase difference signal with the probe embedded in the target soil when the target soil is dry, and the phase difference signal with the probe embedded in the target soil when the target soil is saturated,

wherein said control circuitry is further arranged to calculate a volumetric moisture content of the target soil responsive to the phase difference signal detected for the target soil at present, the phase difference signal detected when the target soil is dry and the phase difference signal detected when the target soil is saturated, wherein the volumetric moisture content (VMC) is calculated in accordance with:

V

⁢

⁢

M

⁢

⁢

C

=

(

ΔΦ

⁢

⁢

m

Δ

⁢

⁢

Φ

⁢

⁢

f

-

ΔΦ

⁢

⁢

d

ΔΦ

⁢

⁢

f

)

/

(

ΔΦ

⁢

⁢

s

ΔΦ

⁢

⁢

f

-

1

)

,

where ΔΦm is the phase difference for the target soil at present, ΔΦf is the phase difference for ambient air, Δ 101 d is the phase difference for the target soil when dry, and Δ 101 s is the phase difference for the target soil when saturated,

and wherein the irrigation control signal is responsive to the calculated volumetric moisture content.