System and method for determining gas optical density changes in a non-linear measurement regime

• US 7,253,903 B2
• Filed: 12/29/2004
• Issued: 08/07/2007
• Est. Priority Date: 12/29/2004
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Sachse, Glen W., Rana, Mauro
• Primary Examiner(s): Toatley, Jr.; Gregory J.
• Assistant Examiner(s): Underwood; Jarreas
• Application Number:
  US11/027,930
• Publication Number:
  US 20060139648A1
• Time in Patent Office: 951 Days
• Field of Search: 250/343, 356/364, 356/437
• US Class Current: 356/437
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427

Abstract

Each of two sensors, positioned to simultaneously detect electromagnetic radiation absorption along a path, is calibrated to define a unique response curve associated therewith that relates a change in voltage output for each sensor to a change in optical density. A ratio-of-responses curve is defined by a ratio of the response curve associated with the first sensor to the response curve associated with the second sensor. A ratio of sensor output changes is generated using outputs from the sensors. An operating point on the ratio-of-responses curve is established using the ratio of sensor output changes. The established operating point is indicative of an optical density. When the operating point is in the non-linear response region of at least one of the sensors, the operating point and optical density corresponding thereto can be used to establish an actual response of at least one of the sensors whereby the actual sensor output can be used in determining changes in the optical density.

Claims

1. A system comprising:

a gas concentration monitoring system that monitors concentration changes of a gas along a path irradiated by electromagnetic radiation, wherein a change of absorption of at least some of said electromagnetic radiation at a specific wavelength by said gas is indicative of a measure of said concentration changes of said gas along said path,

said gas concentration monitoring system including first and second sensors positioned to simultaneously detect said absorption along said path,

each of said first and second sensors being calibrated to thereby define a unique response curve associated therewith that relates a voltage output change per optical density change for each of said first and second sensors as a function of optical density,

wherein each said response curve includes a unique non-linear response region thereof, and

wherein a ratio-of-responses curve is defined by a ratio of said response curve associated with said first sensor to said response curve associated with said second sensor; and

a processor coupled to said gas concentration monitoring system for generating a ratio of sensor output changes defined as a ratio of output changes associated with said first sensor to output changes associated with said second sensor, said ratio of sensor output changes being used to establish an operating point on said ratio-of-responses curve that is indicative of an optical density wherein, when said operating point is in said non-linear response region of at least one of said first and second sensors, said operating point and said optical density corresponding thereto can be used to establish an actual response of at least one of said first and second sensors that is used in determining changes in said optical density.

2. A system as in claim 1 wherein said first sensor is a gas filter correlation radiometer and said second sensor is a differential absorption radiometer.

3. A method comprising the steps of:

providing a gas concentration monitoring system that monitors concentration of a gas along a path irradiated by electromagnetic radiation, wherein absorption of at least some of said electromagnetic radiation at a specific wavelength by said gas is indicative of a measure of said concentration of said gas along said path, said gas concentration monitoring system including first and second sensors positioned to simultaneously detect said absorption along said path;

calibrating each of said first and second sensors to thereby define a unique response curve associated therewith that relates a change in voltage output for each of said first and second sensors to a change in optical density, wherein each said response curve includes a unique non-linear response region thereof;

forming a ratio-of-responses curve defined by a ratio of said response curve associated with said first sensor to said response curve associated with said second sensor;

collecting outputs from each of said first and second sensors;

generating a ratio of sensor output changes using said outputs from each of said first and second sensors, said ratio of sensor output changes defined as a ratio of output changes associated with said first sensor to output changes associated with said second sensor;

establishing an operating point on said ratio-of-responses curve using said ratio of sensor output changes, said operating point being indicative of an optical density wherein, when said operating point is in said non-linear response region of at least one of said first and second sensors, said operating point and said optical density corresponding thereto can be used to establish an actual response of at least one of said first and second sensors that is used in determining changes in said optical density; and

utilizing said indicated optical density to monitor the concentration of said gas.