Methods and apparatus for measuring gas flux
Inventors
Burba, George G. • McDermitt, Dayle • Lin, Xiaomao • Xu, Liukang • Johnson, Dave
Assignees
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Publication Number
US-10060942-B2
Publication Date
2018-08-28
Expiration Date
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.
Core Innovation
The invention measures gas flux in a gas flux measurement system by using vertical wind speed data from a wind speed measurement device sampled at a wind speed sampling rate of greater than 5 Hz and gas content data from a gas analyzer positioned proximal to the wind speed measurement device. The gas content data is obtained simultaneously with the vertical wind speed data at an effective gas content sampling rate of 0.01 Hz to 5 Hz, without using bags or valves to collect gas prior to the gas content measurements being obtained. The method stores the vertical wind speed measurements and the gas content measurements to a memory unit while each measurement includes a data value sampled at each time interval corresponding to its sampling rate.
A coordinate rotation procedure is applied to the vertical wind speed data to remove or reduce horizontal wind speed components. The vertical wind speed measurements are aligned with the gas content measurements based on time, and updraft time periods and downdraft time periods are determined from the vertical wind speed measurements by identifying whether the wind speed has an upward component or a downward component. For each updraft and downdraft time period, one or more gas content measurements corresponding to that time period are identified, and average or integrated gas content values are determined for updraft and downdraft periods.
The gas flux is then determined using the updraft and downdraft values, and the gas flux is stored to the memory unit. In the described system, a control module including a processor receives the vertical wind speed data and the gas content data, performs the coordinate rotation, aligns the measurements based on time, identifies updraft and downdraft time periods, selects corresponding gas content measurements, determines average or integrated gas content values for those periods, determines gas flux from the updraft and downdraft values, and stores the resulting gas flux to the memory unit.
Claims Coverage
The document contains two independent claims, covering both a method and a system for measuring gas flux using coordinated high-rate vertical wind speed data and lower-rate gas content data, separation of updraft and downdraft periods, and computation of gas flux from updraft and downdraft gas content values. The independent claims emphasize eliminating bags or valves for gas content collection while aligning wind and gas data based on time and applying coordinate rotation to vertical wind speed data.
High-rate vertical wind speed sampling with coordinate rotation
Obtaining vertical wind speed data including a plurality of vertical wind speed measurements over a period of time at a wind speed sampling rate of greater than 5 Hz; applying a coordinate rotation procedure to remove or reduce horizontal wind speed components.
Proximal gas analyzer with low-rate gas content sampling without bags or valves
Obtaining gas content data from a gas analyzer positioned proximal to the wind speed measurement device, 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.
Time alignment and updraft/downdraft period identification for corresponding gas content
Aligning the plurality of vertical wind speed measurements with the plurality of gas content measurements based on time; determining 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 updraft time period and downdraft time period, one or more gas content measurements corresponding to said time period.
Gas flux determination from updraft and downdraft gas content values
Determining an average or integrated gas content value for the updraft time periods and an average or integrated gas content value for the downdraft time periods; determining a gas flux using the values; and storing the gas flux to the memory unit.
Across the independent claims, the claimed coverage is centered on coordinated data acquisition, coordinate rotation, time alignment, separation into updraft and downdraft periods, and determining gas flux from average or integrated gas content values for those periods. The system claim mirrors these functional steps using a control module with a processor and a memory unit.
Stated Advantages
Documented Applications
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