城市是車輛、住宅、商業、工業匯聚之地，溫室氣體排放量大。

渦度協方差方法，為準確測量這種復雜“生態系統”的溫室氣體排放提供了可能。

LI-COR渦度協方差通量測量系統

圖片來源/大阪府立大學http://atmenv.envi.osakafu-u.ac.jp/

這些測量數據，可在評估城市溫室氣體排放現狀、優化交通組織、規劃城市發展、制定減排政策等方面發揮重要作用。

為幫助廣大通量研究工作者深入了解這一新興科研領域，5月13日，LI-COR應用科學家George Burba和Dave Johnson，就這一主題和大家分享了通量測量系統知識和相關案例。

該講座主要內容包括：

● 直接測量方法提供精準城市溫室氣體排放數據

● 渦度協方差通量測量系統的組成

● 城市生態系統溫室氣體排放研究案例

下面是視頻回放和Q&A整理（后附ppt）

Q&A整理
 

Q1 Derrick Lai: Hi Dave, thanks for your sharing and love the virtual background of Hong Kong!  In high-density and heterogeneous cities with high rises like Hong Kong, what is your suggestion of making reliable eddy covariance flux measurements? Would we be making measurements in the roughness sublayer only, instead of in the constant flux layer as the EC method assumes?  Thanks.

Derrick Lai：Dave您好！謝謝您的分享。像香港這種“高密度”城市，下墊面復雜，您能否講一下如何使用渦度協方差測量方法進行可信的通量觀測呢？我們是應該在粗糙亞層（the Roughness Sublayer）測量，還是應該在EC方法中提到的常通量層（the Constant Flux Layer）呢？
 

A1 James Kathilankal: I guess it depends upon your experiment, to cover the entire city you probably have to be on top of the highest building, but you could study sections of the city by installing on the tallest building in a particular area. This is a challenge with urban ecosystems, the lack of homogeneity

James Kathilankal：我覺得這取決于您具體的實驗目的。如果您的研究區域是整個城市，儀器的安裝高度應該位于城市最高建筑物的上方；如果您研究城市中的某些區域，儀器安裝在特定區域最高建筑物的頂部即可。由于城市下墊面異質性大，這對于測量來說，確實是個挑戰。
 

Q2 Derrick Lai: Thanks, James.  In natural ecosystems, we have to put the sensor at a height of < 1.5 times the canopy height. In the urban ecosystem, say with a mean building height of 100 m, are we measuring the flux properly by placing the sensor at only 1-2 m above the building top?

Derrick Lai：謝謝您的回答。在自然生態系統中，我們一般把通量測量儀器架設在大約1.5倍冠層高度的地方。而在城市生態系統中，比如建筑物的平均高度為100m，我們如果把儀器安裝在建筑物頂部1-2m的地方，貌似不太合適？
 

A2 James Kathilankal: Choosing the tallest building will help as at that point the building can be considered as part of the tower and when you measure at such heights, some of these requirements can be relaxed as we are measuring much larger eddies which move slowly that what you will find in short ecosystems

James Kathilankal：選取最高的建筑物來架設儀器是合理的，這個建筑物可被認為是通量觀測塔的一部分。對儀器的安裝高度要求可適當放寬，儀器可測量到更多大的渦旋運動（Larger Eddies）。（編者按：理想情況下應該安裝在建筑物平均高度1.5倍的地方，然而實現起來會很麻煩。）
 

Q3 Yingqi Zheng: Wind directions at a 30-minute scale measured by the ultrasonic anemometer, after correction, show great discrepancies from those measured by other devices. Would this cause error in estimating footprint?

Yingqi Zheng：使用超聲風速儀測量得到的30min的風向數據，和氣象站的風向數據差異較大。這是否會影響Footprint計算呢？
 

A3 James Kathilankal: ultrasonic measurements will have some discrepancies, but you can get a better temporal resolution from this data, and using diagnostics from the anemometer you can filter out unrealistic values..so average values tend to agree well with slow measuring sensors

James Kathilankal：超聲風速儀的數據（高時間分辨率的風向數據）會和慢速傳感器的測量數據存在一定差異。使用診斷值，您可以把不可信的數據濾掉。理論上，經過這種數據處理，兩者應保持較好的一致性。
 

Q4 Chaerin Park: Thank you for the good presentation. In the presentation, you mentioned that there is software that can analyze whether the observed co2 flux data originated in a specific area, is this software made by li-cor? Can all the co2 flux data observed through li-cor equipment be analyzed using this software?

Chaerin Park: 謝謝精彩的講座內容。您提到有軟件可分析通量數據的來源。請問這個軟件是LI-COR研發的嗎？所有使用LI-COR儀器獲取的數據，都可以使用這個軟件來做這種分析嗎？
 

A4 James Kathilankal: The software which is used is the Tovi software (beta version). Flux footprint modeling can be used to allocate fluxes, but this is more for getting average values.

James Kathilankal: 這個軟件是Tovi，該軟件由LI-COR自主研發。您可使用其中的Footprint模型來進行這種分析。另外，您可登陸https://www.licor.com/tovi/了解有關這個軟件的更多詳細信息（編者按：該軟件可免費試用30天）。