Methods and apparatus for measuring gas flux

Patent metadata

Field	Value
Publication number	US-10060942-B2
Application number	US-201213441319-A
Country	US
Kind code	B2
Filing date	Apr 6, 2012
Priority date	Apr 6, 2012
Publication date	Aug 28, 2018
Grant date	Aug 28, 2018

Abstract

Systems and methods for measuring turbulent gas flux using high-speed vertical wind speed measurements (e.g., on the order of 5-10 Hz or more frequently) and low-speed gas content measurements (e.g., on the order of 5 Hz or less frequently), without the need for the sophisticated and expensive high-speed hardware to separate gas samples (e.g., into accumulation bags) according to updrafts and downdrafts. A time series of high-speed vertical wind speed data is used as a guide to distinguish between updrafts and downdrafts. When vertical wind speed is upward (updraft), the low-speed gas content is recorded into a data structure in one location, or marked with one flag. When vertical wind speed is downward (downdraft), the low-speed gas content is recorded into a different location, or marked with a different flag. Eddy Accumulation or Relaxed Eddy Accumulation computations can be performed using the stored gas content data to determine gas flux.

First claim

What is claimed is:

1. A method of measuring gas flux in a gas flux measurement system comprising a control system communicably coupled with a wind speed measurement device that samples wind speed at a wind speed sampling rate of greater than 5 Hz and a gas analyzer, the method comprising the steps, implemented by the control system of:
obtaining vertical wind speed data from the wind speed measurement device, the vertical wind speed data including a plurality of vertical wind speed measurements (W) obtained by the wind speed measurement device over a period of time at a wind speed sampling rate of greater than 5 Hz;
storing the plurality of vertical wind speed measurements (W) to a memory unit of the control system, wherein each of the plurality of wind speed measurements (W) includes a vertical wind speed data value sampled at each time interval corresponding to the wind speed sampling rate;
applying a coordinate rotation procedure to the vertical wind speed data to remove or reduce horizontal wind speed components;
obtaining gas content data from a gas analyzer positioned proximal to the wind speed measurement device, the gas content data including a plurality of gas content measurements obtained by the gas analyzer over said period of time simultaneously with the wind speed measurement device obtaining the vertical wind speed data and at an effective gas content sampling rate of 0.01 Hz to 5 Hz, wherein the gas content data is obtained by the gas analyzer without using bags or valves to collect gas prior to the gas content measurements being obtained;
storing the plurality of gas content measurements to the memory unit, wherein each of the plurality of gas content measurements includes a gas content data value sampled at each time interval corresponding to the gas content sampling rate;
aligning the plurality of vertical wind speed measurements with the plurality of gas content measurements based on time;
determining, from the plurality of vertical wind speed measurements (W), updraft time periods when the wind speed has an upward component and downdraft time periods when the wind speed has a downward component;
identifying, for each of the updraft time periods and the downdraft time periods, one or more gas content measurements corresponding to said time period;
determining an average or integrated gas content value (C↑) for the updraft time periods and an average or integrated gas content value (C↓) for the downdraft time periods;
determining a gas flux (F) using the values C↑ and C↓; and
storing the gas flux (F) to the memory unit.

2. The method of claim 1 , wherein the gas flux (F) is determined using an equation of the form:
F=βσ W ( C↑−C ↓)

wherein σ W is a standard deviation of W, or other similar statistical parameter describing variation, and wherein β is an empirical value.

3. The method of claim 2 , wherein β has a value of between about 0.4 and about 0.8.

4. The method of claim 1 , further including determining an average or integrated wind speed value (W↑) for the updraft time periods and an average or integrated wind speed value (W↓) for the downdraft time periods.

5. The method of claim 4 ,
wherein determining an average gas content value (C↑) includes:
multiplying each gas content measurement corresponding to an updraft time period by the average vertical wind speed for that updraft time period to produce updraft values;
normalizing each updraft value by the average or integrated wind speed value (W↑); and
averaging all normalized updraft values to produce the average gas content value (C↑);
wherein determining an average gas content value (C↓) includes:
multiplying each gas content measurement corresponding to a downdraft time period by the average vertical wind speed for that downdraft time period to produce downdraft values;
normalizing each downdraft value by the average or integrated wind speed value (W↓); and
averaging all normalized downdraft values to produce the average gas content value (C↓); and
wherein the gas flux (F) is determined using an equation of the form:
F=W↑C↑−W↓C ↓.

6. The method of claim 4 , wherein the gas flux (F) is determined using an equation of the form:
F=βσ W ( C↑−C ↓),

wherein σ W is a standard deviation of W, or other similar statistical parameter describing variation, and wherein β=σ W /(W↑−W↓).

7. The method of claim 4 , wherein determining average or integrated wind speed values W↑ and W↓ includes determining a total average or integrated wind speed for said period of time.

8. The method of claim 1 , wherein aligning includes applying a time delay computation to align the plurality of vertical wind speed measurements with the plurality of gas content measurements based on one or more of a physical parameter of the gas analyzer, wind speed, wind direction, and system setup configuration.

9. The method of claim 1 , wherein identifying gas content measurements corresponding to said updraft and downdraft time periods includes flagging stored gas content measurements differently in the memory unit for updraft and downdraft time periods.

10. The method of claim 1 , wherein identifying gas content measurements corresponding to said updraft and downdraft time periods includes storing, in the memory unit, gas content measurements corresponding to an updraft time period in a different column or logically separate location in a database table than gas content measurements corresponding to a downdraft time period.

11. The method of claim 1 , wherein aligning includes applying a circular correlation process to align the plurality of vertical wind speed measurements with the plurality of gas content measurements or computing time alignment from wind speed and direction and distance between devices.

12. The method of claim 1 , wherein the wind speed sampling rate is greater than 6 Hz.

13. A system for measuring gas flux; the system comprising:
a wind speed measurement device configured to obtain vertical wind speed data including a plurality of vertical wind speed measurements (W) obtained over a period of time at a wind speed sampling rate of greater than 5 Hz;
a gas analyzer positioned proximal to the wind speed measurement device, the gas analyzer configured to, simultaneously with the wind speed measurement device obtaining vertical wind speed data, obtain gas content data including a plurality of gas content measurements obtained over said period of time at an effective gas content sampling rate of 0.01 Hz to 5 Hz, wherein the gas content data is obtained without using bags or valves to collect gas prior to the gas content measurements being obtained; and
a control module, including a processor, wherein the control module is adapted to receive the vertical wind speed data and the gas content data, and store the vertical wind speed data and the gas content data to a memory unit, wherein each of the plurality of wind speed measurements (W) includes a vertical wind speed data value sampled at each time interval corresponding to the wind speed sampling rate, wherein each of the plurality of gas content measurements includes a gas content data value sampled at each time interval corresponding to the gas content sampling rate, and wherein the processor is configured to:
apply a coordinate rotation procedure to the vertical wind speed data to remove or reduce horizontal wind speed components;
align the plurality of vertical wind speed measurements with the plurality of gas content measurements based on time;
determine, from the plurality of vertical wind speed measurements (W), updraft time periods when the wind speed has an upward component and downdraft time per

Assignees

• Burba George G
• Mcdermitt Dayle
• Lin Xiaomao
• Xu Liukang
• Johnson Dave
• Li Cor Inc

Inventors

• Burba George G
• Mcdermitt Dayle
• Lin Xiaomao
• Xu Liukang
• Johnson Dave

Classifications

• A61B5/14532

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• G01N30/8624

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• G01P5/001 Primary

  Full-field flow measurement, e.g. determining flow velocity and direction in a whole region at the same time, flow visualisation · CPC title

• G01N33/0067

  by measuring the rate of variation of the concentration · CPC title

• G01N21/3504

  for analysing gases, e.g. multi-gas analysis · CPC title