Instrument, system and method for automated low cost atmospheric measurements

• US 20060266950A1
• Filed: 05/11/2006
• Published: 11/30/2006
• Est. Priority Date: 05/11/2005
• Status: Active Grant

• Current Assignee: University of North Texas
• Original Assignee: University of North Texas
• Inventors: Nebgen, Gilbert B., Waller, William T., Acevedo, Miguel Felipe
• Granted Patent: US 7,489,397 B2
• Time in Patent Office: Days
• US Class Current: 250/372
• CPC Class Codes: G01N 2021/3155 Measuring in two spectral ranges, e.g. UV and visible
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence
• CPC Class Codes: G01S 3/7861 Solar tracking systems

Abstract

An apparatus and method for measuring ozone in the atmosphere. The apparatus utilizes a fiber optic cable connected to a collimating lens located outdoors and a spectrometer that is located indoors. A pan-and-tilt positioning unit having a pan-axis capable of tracking an azimuth angle of the Sun, and a tilt-axis capable of tracking an elevation angle of the Sun, is utilized for automatically pointing the collimating lens directly at the Sun and taking readings for column ozone determination on any given day of the year. The apparatus and method utilizes a computer that is in electrical communication with the spectrometer and the pan-and-tilt unit.

Claims

1. ) An apparatus for measuring ozone in the atmosphere, comprising:

(a) a fiber optic cable having a first end and a second end;

(b) a collimating lens having narrow field of view coupled to the first end of the fiber optic cable, wherein light from a Sun is capable of being funneled into the fiber-optic medium and is transmitted through the fiber optic cable, wherein the narrow field of view is in the range of from about 1°

to about 45°

;

(c) a spectrometer having a ultra-violet/visible light (“

UV/VIS”

) channel coupled to the second end of the fiber optic cable;

(d) an optical bandpass filter coupled to the fiber optic cable interposing the first end and the second end of the fiber optic cable; and

(e) a pan-and-tilt positioning unit having a pan-axis capable of tracking an azimuth angle of the Sun, and a tilt-axis capable of tracking an elevation angle of the Sun, wherein pan-and-tilt positioning unit further comprises a means for mounting the collimating lens.

2. ) The apparatus of claim 1, further comprising:

a computer in electrical communication with the spectrometer and the pan-and-tilt unit, wherein the pan-axis and the tilt-axis is controlled by the computer using software through a RS232 interface.

3. ) The apparatus of claim 2, further comprising, a software architecture that utilizes a script;

a mechanism control and calculation algorithm;

file storage device; and

the spectrometer for communicating instructions and data, wherein the script communicates information to the mechanism control and calculation algorithm, and the spectrometer;

the spectrometer communicates information to the file storage device;

the mechanism control and calculation algorithm communicates information to the file storage device; and

the file storage device communicates information to the script and to the mechanism control and calculation algorithm.

4. ) The apparatus of claim 1, further comprising:

a second fiber optic cable having a first end and a second end;

a second collimating lens having narrow field of view coupled to the first end of the second fiber optic cable; and

the spectrometer having a second channel for tracking a visible-light/near infra-red (“

VIS/NIR”

) spectrum that is coupled to the second end of the second fiber optic cable.

5. ) The apparatus of claim 3, wherein the first and second collimating lenses have a narrow field of view comprising about 2.50.

6. ) The apparatus of claim 1, wherein the fiber optic cable connects the collimating lens and the spectrometer through a barrier that separates an outdoor place from an indoor place.

7. ) The apparatus of claim 1, wherein the fiber optic cable comprises a diameter of about 200 μ

m and a length up to about 20 meters.

8. ) The apparatus of claim 1, wherein the bandpass filter comprises a two-stage optical bandpass filter capable of filtering wavelengths of light that are outside the range of about 260 nm to about 340 nm.

9. ) The apparatus of claim 1, wherein the spectrometer comprises a grating having 1800 lines for detecting UV/VIS in a range of about 200-350 nm;

a 2048-element linear CCD array detector;

a 10 um entrance slit; and

optical resolution of 0.234 nm full width at half maximum (“

FWHM”

).

10. ) The apparatus of claim 1, wherein the pan-and-tilt positioning unit comprises a stepper motor driven mechanism capable of a 360°

pan axis rotation with the tilt axis range being about 111°

with a resolution of about 0.051°

per half-step for each axis that corresponds to about 49 steps across an about 2.5°

lens field of view.

11. ) The apparatus of claim 1, wherein the means for mounting the collimating lens comprises an aluminum bracket having a bend angle of about 20°

.

12. ) A method for measuring ozone in the atmosphere, comprising:

(a) initializing an outdoor pan-and-tilt positioning unit having a pan-axis capable of tracking an azimuth angle of a Sun, and a tilt-axis capable of tracking an elevation angle of the Sun, wherein the outdoor pan-and-tilt positioning unit comprises a mounted collimating lens that is coupled to an indoor spectrometer through a fiber optic cable, and the outdoor pan-and-tilt positioning unit is in electrical communication with a computer capable of controlling the pan-axis and the tilt-axis using software through an interface;

(b) using the software for calculating the azimuth angle of the Sun and the elevation of the Sun for a date, time, and location, creating a calculated azimuth angle and a calculated elevation angle of the Sun;

(c) pointing the mounted collimating lens toward the Sun by controlling the pan-axis and the tilt-axis with the computer using software through the interface, wherein mounted collimating lens is pointed toward the calculated azimuth angle and the calculated elevation angle of the Sun,

(d) fine-positioning the collimating lens toward the Sun by programing a series of fine movements of the pan-axis and the tilt-axis until the light intensity striking the collimating lens has a maximum signal of about 330 nm for a filtered spectrum of sunlight having a range of about 260-340 nm;

(e) gathering spectrometer data for calculating column ozone base upon Lambert-Beer-Bouguer Law, and calculating column ozone, forming a calculated column ozone value;

(f) averaging the calculated column ozone value for each time step (e) is completed, forming an average column ozone value;

(g) repeating step (b) at least once before proceeding to step (h); and

(h) recording the average column ozone value.

13. ) The method of claim 12, further comprising, selecting a software architecture that utilizes a script;

a mechanism control and calculation algorithm;

file storage device; and

the spectrometer for communicating instructions and data, wherein the script communicates information to the mechanism control and calculation algorithm, and the spectrometer;

the spectrometer communicates information to the file storage device;

the mechanism control and calculation algorithm communicates information to the file storage device; and

the file storage device communicates information to the script and to the mechanism control and calculation algorithm.

14. ) The method of claim 12, further comprising, selecting the collimating lens to have a narrow field of view comprising about 2.5°

.

15. ) The method of claim 12, further comprising, selecting the fiber optic cable to comprises a diameter of about 200 μ

m and a length up to about 20 meter.

16. ) The method of claim 12, further comprising, selecting a two-stage optical bandpass filter capable of filtering wavelengths of light that are outside the range of about 260 nm to about 340 nm, wherein the optical bandpass filter is installed and coupled to the fiber optic cable interposing the collimating lens and the spectrometer.

17. ) The method of claim 12, further comprising, selecting the spectrometer having a grating with 1800 lines for detecting UV/VIS in a range of about 200-350 nm;

a 2048-element linear CCD array detector;

a 10 um entrance slit; and

optical resolution of 0.234 nm full width at half maximum (“

FWHM”

).

18. ) The method of claim 12, further comprising, selecting the pan-and-tilt positioning unit having a stepper motor driven mechanism capable of a 360°

pan axis rotation with the tilt axis range being about 111°

with a resolution of about 0.051°

per half-step for each axis that corresponds to about 49 steps across an about 2.5°

lens field of view.

19. ) The method of claim 12, further comprising, selecting the means for mounting the collimating lens to be an aluminum bracket having a bend angle of about 20°

.

20. ) The method of claim 12, further comprising, selecting a closed loop positioning algorithm for determining the series of fine movements used until the light intensity striking the collimating lens has the maximum signal of about 330 nm for a filtered spectrum of sunlight.

21. ) The method of claim 12, further comprising, selecting the computer for recording the average column ozone value.