Vis-NIR equipped soil penetrometer
Soil penetrometers capable of measuring soil reflectance along the direction of insertion of the penetrometer are provided. The penetrometer can house an array of sensors, such as, for example, a Vis-NIR reflectance sensor, a load cell, a displacement sensor, and a moisture sensor. The reflectance data collected using the penetrometer can allow the interpretation and quantification of soil constituents and contaminants at high vertical resolution, such as 3 cm or more.
1. A soil penetrometer, comprising:
a conical tip capable of penetrating into a soil sample;
a tubular housing connected to the conical tip at one end;
a tubular connector attached to the tubular housing at one end; and
a tubular extension rod capable of being detachably connected to the connector at the end opposite to the tubular housing and detachably connected to another device or a combination of devices at the end opposite to the connector,
wherein the tubular housing comprises:
a transparent window built into the wall thereof; and
an optical module comprising a light-emitting device, a mirror capable of reflecting light generated by the light-emitting device, and a fiber optic sensor, wherein the sensor is positioned in the vicinity of the transparent window to receive signals reflected by the soil sample and transmits the signal to a spectrometer, and
wherein the conical tip is hollow.
2. The penetrometer according to claim 1 , wherein the connector encloses one or more sensing devices.
3. The penetrometer according to claim 2 , comprising a moisture sensor enclosed in the connector.
4. The penetrometer according to claim 1 , wherein the light-emitting device is a lamp.
5. The penetrometer according to claim 1 , wherein the transparent window comprises sapphire.
6. The penetrometer according to claim 1 , wherein the detecting end of the optic fiber is positioned with respect to the plane parallel to the transparent window at an angle between about 40 degrees and about 55 degrees that allows optimal spectral collection by the optic fiber.
7. The penetrometer according to claim 6 , wherein the end of the optic fiber opposite to the detecting end extends through the connector and the extension rod and is connected to a Vis-NIR spectrometer.
8. The penetrometer according to claim 1 , wherein the hollow conical tip accommodates a sensing device or a combination of devices therein.
9. The penetrometer according to claim 8 , wherein the sensing device is a capacitance sensor.
10. The penetrometer according to claim 1 , wherein the optical module is enclosed in the tubular housing, and the tubular housing comprises aluminum.
11. The penetrometer according to claim 1 , wherein the conical tip, the tubular housing, the connector, and the extension rod each comprises stainless steel.
12. The penetrometer according to claim 1 , wherein the end of the extension rod opposite to the connector is connected to a device selected from soil sampling equipment, soil coring equipment, a load cell, a displacement sensor, a time-domain reflectometer, and a combination thereof.
13. The penetrometer according to claim 1 , wherein the optical fiber is configured in different geometries with respect to the plane parallel to the transparent window to obtain different signal-to-noise ratios.
14. The penetrometer according to claim 1 , which is field-portable.
15. A method of measuring soil reflectance, comprising:
providing a soil penetrometer, comprising:
a conical tip capable of penetrating into a soil sample, the tip comprising at least one sensing device;
a tubular housing connected to the conical tip at one end;
a tubular connector attached to the tubular housing at one end, the connector comprising a built-in moisture sensor; and
a tubular extension rod capable of being detachably connected to the connector at the end opposite to the tubular housing and detachably connected to another device or a combination of devices selected from soil sampling equipment, soil coring equipment, a load cell, a displacement sensor, and a time-domain reflectometer, at the end opposite to the connector,
wherein the tubular housing comprises:
a transparent window built into the wall thereof; and
an optical module comprising a light-emitting device, a mirror capable of reflecting light generated by the light-emitting device, and a fiber optic sensor, wherein the sensor is positioned in the vicinity of the transparent window to receive signals reflected by the soil sample and transmits the signal to a Vis-NIR spectrometer;
providing a soil sample; and
measuring the soil reflectance at a given depth within the sample,
wherein the soil reflectance is measured continuously as the penetrometer is inserted into the soil sample.