Eddy Flux Measurements
turbulent fluxes eddy covariance method measurement techniqes
Olaf Kolle IMPRS core course
Atmosphere & Ocean 2016
2 Eddy-Covariance Instrumentation Index of contents
Index of Contents
1. Turbulent Fluxes and Eddy Covariance Method
2. History of Eddy-Covariance Measurements and Instrumentation
3. Modern Instruments and Data Acquisition
4. Power Supply Issues
5. Examples of Station Setups of MPI-BGC
6. Additional Sources of Information
3 Eddy-Covariance Instrumentation Turbulent Fluxes
Turbulent Fluxes and Eddy Covariance Method
Eddy Covariance Measurements Why is it widely used?
Biosphere-Atmosphere-Exchange Eddy Covariance (EC) as a meteorological tool
to determine energy, trace gas and momentum exchange between
ecosystems and the atmosphere for continuous flux measurements → long term observation to obtain fluxes with a high temporal resolution and without disturbance of the environment
4 Eddy-Covariance Instrumentation Turbulent Fluxes
Turbulent Fluxes and Eddy Covariance Method
Eddy Covariance Measurements Why is it widely used?
Some key questions and applications
how do ecosystems react on • global warming (e.g. permafrost areas) • increasing atmospheric CO2 concentrations (e.g. growth rates)
how are energy exchange, hydrological cycle, trace gas exchange modified by land use change
selective manipulation experiments comparison of adjacent ecosystems within same climate gain long term data for global databases gain data for model development and validation
5 Eddy-Covariance Instrumentation Turbulent Fluxes
Turbulent Fluxes and Eddy Covariance Method
Eddy Covariance Measurements Where to apply?
→ Atmospheric Boundary Layer (ABL) Definition: The part of the troposphere that is directly influenced by the presence of the
earth’s surface and which responds to surface forcings with a timescale of about 1 hour or less (Stull, 1988)
However: Given enough time or space, the entire atmosphere will adjust to surface
conditions (boundary conditions) But:
Surface conditions change too rapidly for the entire atmosphere to adjust. Changes arise from diurnal cycle of energy exchange at the surface.
6 Eddy-Covariance Instrumentation Turbulent Fluxes
Turbulent Fluxes and Eddy Covariance Method
Vertical integration:
Fzcwdz
tc hh
=∂
∂+
∂∂
∫∫00
'' Fcwcwdztc
h
h
=−+∂∂
⇒ ∫ 00
''''
cSzcw
tc
=∂
∂+
∂∂ ''
''cwFF S +=
total flux = storage flux + turbulent flux
Eddy Covariance Measurements Theory and equations
uc
vc
wc
7 Eddy-Covariance Instrumentation Turbulent Fluxes
Turbulent Fluxes and Eddy Covariance Method
Example for turbulent time series Vertical wind velocity and CO2 concentration
8 Eddy-Covariance Instrumentation Turbulent Fluxes
Turbulent Fluxes and Eddy Covariance Method
Example for turbulent time series Vertical wind velocity and CO2 concentration
( ) ( ) ''''11),cov(11
cwcwn
ccwwn
cwn
jjjj
n
jj ==−⋅−= ∑∑
==
9 Eddy-Covariance Instrumentation Turbulent Fluxes
Turbulent Fluxes and Eddy Covariance Method
Eddy Covariance Measurements Assumptions
Both variables must be measured at the same point in space and time (how?) Horizontal homogeneity (advection? → footprint analysis)
Steady state conditions (quality test)
10 Eddy-Covariance Instrumentation Turbulent Fluxes
Turbulent Fluxes and Eddy Covariance Method
Eddy Covariance Measurements Instruments
All variables have to be measured fast enough to catch all flux contributing fluctuations within the entire frequency range For wind components and temperature: Sonic anemometer-thermometer For trace gases: Fast responding gas analyzer
11 Eddy-Covariance Instrumentation History
History of Eddy-Covariance Measurements and Instrumentation
• First instruments to measure turbulent wind field in boundary layer appeared 1944 – Interest of military in flow patterns of missiles – Theoretical meteorologists interested in wind velocity spectra (Kolmogorov) – Similarity theory (Monin and Obukhov) – Assumption of constant flux in surface layer
• Advances in meteorology and the evolution of sonic anemometry • First instruments capable to measure trace gas concentrations virtually without delay
Radiation in the atmosphere Kondratyev Academic Press, 1969 - 911 Pages
12 Eddy-Covariance Instrumentation History
The Kansas and Minnesota Experiments
From: Energy and Water Cycles in the Climate System Ehrhard Raschke, Daniela Jacob Springer Science & Business Media, 29.06.2013 - 467 Pages
13 Eddy-Covariance Instrumentation History
Fast Hygrometers
• Lyman-α-Hygrometer
– Emission by hydrogen at 121.56nm – Absorption by water vapour in short open path – Model 220 Lyman-alpha Hygrometer by
Campbell Scientific (1978)
From: United States Geological Survey Water-supply Paper (1990)
Energy Balance Station (IMK, Karlsruhe, now KIT)
14 Eddy-Covariance Instrumentation History
Fast Hygrometers
Summary
Commercial instruments in the early 1990s
15 Eddy-Covariance Instrumentation History
Fast Gas Analyzers for CO2 or CO2 and H2O
• Closed path non-dispersive infrared gas analyzers by LICOR – LI-6251: only CO2, purely analog board (discontinued) – LI-6252: only CO2, analog/digital board (discontinued) – LI-6262: CO2 and H2O, analog/digital board (discontinued)
• Open path infrared gas analyzer by ADC – OP-2: only CO2 and H2O, analog/digital board (discontinued) OP-2 Instruction Manual
16 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Sonic Anemometers
• CSAT3 (Campbell Scientific, USA)
– preferred direction – sampling rate up to 60 Hz – 4 analog outputs @ 12 Bit – no analog inputs – SDM interface – RS232 interface – no heating
• Gill R3/50, R3, HS (Gill, UK)
– omnidirectional (R3) or preferred direction (HS) – sampling rate up to 50/100 Hz – 8 analog outputs @ 14 Bit – 6 analog inputs @ 14 Bit, 50/100 Hz – RS422/RS232 interface – no heating
17 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Sonic Anemometers
• Gill Windmaster and Windmaster Pro (Gill, UK)
– omnidirectional – sampling rate up to 20/32 Hz – 4 analog outputs @ 12/14 Bit – 2/4 analog inputs @ 12/14 Bit – RS422/RS485/RS232 interface – no heating
• Young Sonic Anemometer 81000V (Young, USA)
– omnidirectional – sampling rate up to 32 Hz – 4 analog outputs @ 12 Bit – 4 analog inputs @ 12 Bit – RS485/RS232 interface – no heating
18 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Sonic Anemometers
• Metek USA-1 (Metek, Germany) – omnidirectional – sampling rate up to 50 Hz – 4 analog outputs @ 12 Bit – 6 analog inputs @ 16 Bit – RS422/RS232 interface – with heating – internal data processing possible – new versions available
• Ultrasonic Anemometer 3D (Thies, Germany)
– omnidirectional – sampling rate typ. 285 Hz, output rate up to 1000 Hz – 3 analog outputs @ 16 Bit – 3 analog inputs @ 16 Bit – RS485/RS422 interface – with heating – internal data processing possible
19 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Sonic Anemometers
From: Practical Handbook of Tower Flux Observation
3D propeller anemometer (Young, USA)
other sonic anemometers
20 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (closed path)
• LI-7000 (Licor, USA)
– closed path, IR for CO2 and H2O – sample cell volume: 10.86 cm3
– 4 analog outputs @ 14 Bit (300 Hz update) – output rate up to 20 Hz (max. frequency response) – RS232 – Power consumption: 15 W to 40 W
• EC155 (Campbell Scientific, USA) – closed path, IR for CO2 and H2O – sample cell volume: 5.9 cm3
– sampling rate 100 Hz, output rate up to 25 Hz – 2 analog outputs @ 16 Bit (150 Hz update) – RS485, SDM, USB
21 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (closed path)
• G1301-f, G2301-f, G2311-f (Picarro, USA)
– Cavity Ring-Down Spectroscopy (CRDS) for CO2, CH4, H2O – sample cell volume: ? cm3
– 7 analog outputs @ ? Bit (? Hz update) – max. frequency response: 10 Hz (8 l/min to > 11 l/min) – RS232, Ethernet, USB – Power consumption: < 600 W (with pump)
CRDS principle
22 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (closed path)
• Models 911-0010 and 911-0011 (Los Gatos, USA)
– Integrated-Cavity Output Spectroscopy (ICOS) for CO2, CH4, H2O – sample cell volume: 408 cm3
– 3 analog outputs @ ? Bit (? Hz update) – max. frequency response: 10 Hz to 20 Hz (> 20 l/min) – RS232, Ethernet, USB – Power consumption: 150 W (without pump)
LGR’s Off-Axis Integrated-Cavity Output Spectroscopy (Off-Axis ICOS)
23 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (closed path)
• TGA200A (Campbell Scientific, USA)
– tunable-diode laser absorption spectroscopy (TDLAS) for CO2 isotopes, N2O, CH4 – sample cell volume: 200 cm3
– measurement rate: 500 Hz – max. frequency response: 10 Hz (15 l/min) – Ethernet, RS232, SDM – Power consumption: ~100 W (without pump)
24 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (enclosed path)
• LI-7200 (Licor, USA)
– non-dispersive infrared gas analyzer for CO2 and H2O – sample cell volume: 16 cm3
– maximum bandwidth: 20 Hz (digital processing) – max. frequency response: 10 Hz (15 l/min) – 6 analog outputs @ 16 Bit – 4 analog inputs @ 16 Bit – Ethernet (in/out), RS232 (max. 20 Hz), SDM (max. 50 Hz) – USB storage possible – Power consumption: 12 W (30 W during warmup)
25 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (open path)
• LI-7500, LI-7500A (Licor, USA)
– non-dispersive infrared gas analyzer for CO2 and H2O – maximum bandwidth: 20 Hz (digital processing) – 2 analog outputs @ 16 Bit, update rate 300 Hz – RS232 (max. 20 Hz), SDM (max. 40 Hz) – Power consumption: 10 W (30 W during warmup)
26 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (open path)
• EC150 (Campbell Scientific, USA)
– non-dispersive infrared gas analyzer for CO2 and H2O – measurement rate: 100 Hz – maximum bandwidth: 25 Hz (digital processing) – 2 analog outputs @ 16 Bit, update rate 100 Hz – RS485 (max. 50 Hz), SDM , USB (max. 50 Hz) – Power consumption: 5 W
27 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (open path)
• LI-7700 (Licor, USA) – Wavelength Modulation Spectroscopy (WMS) @ 1.6µm for CH4
– measurement rate: 1000 Hz – maximum bandwidth: 20 Hz (digital processing) – 4 analog inputs @ 16 Bit – 3 thermocouple inputs – Ethernet – Power consumption: 8 W
Laser beam makes 60 passes = 30 m
28 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (comparison)
Closed Path Instruments
• Several peripheral devices (pump, chemicals or zero gas, tubing, filters)
• Signal drift due to contamination of sample cell (more in humid conditions)
• Loss of information in the high frequency range due to signal smearing inside tubing and insufficient response time of analyser → spectral correction
29 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (comparison)
Closed Path Instruments
• Time lag between turbulence signals and concentration data
• Factory repairs (cell, source, detector) • Regular and intense maintenance
(calibration, filters, cleaning of hoses) • High power consumption of system • Rather high running costs
30 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (comparison)
Open Path Instruments
• No peripheral devices required • Easy setup • Less maintenance • Small drift (calibration every 6 months) • Fast sensor response, no time lag • Lower power consumption of system • Lower running costs
--- but ---
31 Eddy-Covariance Instrumentation Modern Instruments
Present-Day Gas Analyzers (comparison)
Open Path Instruments
• Very sensitive to rain, fog and dew • Large ‘correction’ of flux data required due to density
fluctuations: Webb-Pearman-Leuning (WPL) correction (Webb et al., 1980) Sensible heat flux corrects latent heat flux and both correct the CO2 flux.
32 Eddy-Covariance Instrumentation Data Acquisition
Data Acquisition
• on site system
1. pure data collection 2. data collection and processing 3. data collection, processing and visualization
4. data archiving 5. data transmission
1. pure data collection data collection can be done with data-loggers, computers or special systems
• suitable data-loggers from Campbell Scientific: CR1000, CR3000, CR5000, CR6
• computers should be selected according to power supply situation and environmental conditions (laptops, industrial computers, desktop computers)
• an example for a special system is
the LI-7550 interface box with USB-stick data storage
33 Eddy-Covariance Instrumentation Data Acquisition
Data Acquisition
2. data collection and on site processing
– customized data-logger programs with on line flux calculation from Campbell Scientific support of CSAT3, open or closed path gas analyzer and meteorological sensors – EddyMeas (MPI-BGC) running on WINDOWS® (tested up to WIN7) support of various Gill sonics, Metek USA-1, Young 81000V, CSAT3 (only when linked to datalogger) support of most gas analyzers (CH4 only partly) – SmartFlux™ (Licor Biosciences)
34 Eddy-Covariance Instrumentation Data Acquisition
Data Acquisition
3. data collection and on site processing and visualization
– EddyMeas (MPI-BGC)
– Campbell Scientific data-logger and EC-system connected to computer running RTMC software
35 Eddy-Covariance Instrumentation Data Acquisition
Data Acquisition
36 Eddy-Covariance Instrumentation Data Acquisition
Data Acquisition
• Typical measurement and data acquisition setups
analog
digital
air inlet line
37 Eddy-Covariance Instrumentation Data Acquisition
Data Acquisition
• Typical measurement and data acquisition setups
digital digital
anal
og
analog
38 Eddy-Covariance Instrumentation Data Acquisition
Data Acquisition
• Typical measurement and data acquisition setups
Can be used with SmartFlux integrated
39 Eddy-Covariance Instrumentation Data Acquisition
Data Acquisition
• Typical measurement and data acquisition setups
digital
digital (SDM) digital (SDM)
analog
air inlet line
40 Eddy-Covariance Instrumentation Data Acquisition
Data Acquisition
• Typical measurement and data acquisition setups
digital (SDM)
IRGASON
41 Eddy-Covariance Instrumentation Power Supply Issues
Power Supply Issues
• wide range of power requirements – data-logger with sonic and open path analyzer: ~ 6 W
– data-logger with sonic and closed path analyzer: ~ 12 W
– computer with sonic and enclosed path analyzer: ~ 75 W
– computer with sonic and closed path analyzer (e.g. LI-7000): ~ 120 W
– computer with sonic and closed path analyzer (e.g. Picarro): ~ 500 W
– typical setup with computer, sonic, LI-7200, vertical profile of CO2 and H2O (valve switching unit and data-logger), meteorological sensors on a data-logger, fans: ~ 180 W to 250 W
42 Eddy-Covariance Instrumentation Power Supply Issues
Power Supply Issues
• power supply systems – line power: UPS always recommended
– solar energy • Tanguro (Brasil): 1 kW & batteries (800 Ah) sufficient
• Hainich (Germany): 2.5 kW & batteries not sufficient ® generator
– fuel cell running on methanol or propane: 50 W to 100 W (lifetime ~ 5000 h)
– wind energy: not really common
– generator only (diesel, gasoline, propane): lifetime of engine 1000 h to 2000 h
– batteries only: possible for very low power consumption, regular exchange
43 Eddy-Covariance Instrumentation Power Supply Issues
Power Supply Issues
• lightning protection – very important at least for voltage spikes through power line
– instrument protection by ‘outer lightning protection’ • lightning rod: cone ® of protection
• isolated conductor must be well earthed
• isolated mounting of instruments and grounding
• tower construction as conductor also possible but not recommended
– protection of data acquisition (data-logger, computer etc.) by ‘inner lightning protection’ • each single wire protected by surge arresters (overvoltage protectors): expensive
• excellent grounding where provided (chassis of devices, shields of cables)
44 Eddy-Covariance Instrumentation Examples of Station Setups
Examples of Station Setups
Wetzstein, Thuringia, Germany • spruce forest • line power • 30 m tower • Gill R3, LI-7000, laptop • profile system • meteorology
45 Eddy-Covariance Instrumentation
Examples of Station Setups
Gebesee, Thuringia, Germany • agricultural field • line power • 3 m to 6 m telescopic tower • Gill R3, LI-7000, laptop • profile system • meteorology
Examples of Station Setups
46 Eddy-Covariance Instrumentation
Examples of Station Setups
Majadas, Extremadura, Spain • holm oak grove • line power • 2 x 15 m tower, 1 subcanopy tower • Gill R3, LI-7200, industrial computer • profile system • meteorology
Examples of Station Setups
47 Eddy-Covariance Instrumentation
Examples of Station Setups
Tanguro, Mato Grosso, Brasil • rain forest (control and burnt) • solar energy system • 2 x 36 m tower • Metek USA-1, LI-7200, laptop computer • meteorology
Examples of Station Setups
48 Eddy-Covariance Instrumentation
Examples of Station Setups
Tanguro, Mato Grosso, Brasil • soy field • solar energy system • 6 m tower • Metek USA-1, LI-7200, industrial computer • meteorology
Examples of Station Setups
49 Eddy-Covariance Instrumentation
Examples of Station Setups
Tanguro, Mato Grosso, Brasil • soy field • solar energy system • 6 m tower • Metek USA-1, LI-7200, industrial computer • meteorology
Examples of Station Setups
50 Eddy-Covariance Instrumentation
Examples of Station Setups
ZOTTO, Central Siberia, Russia • pine forest, bog • generator • 1 x 30 m tower, 1 x 10 m tower • Metek USA-1, LI-7200, Picarro,
laptop computer • profile system • meteorology
Examples of Station Setups
51 Eddy-Covariance Instrumentation
Examples of Station Setups
Cherskii, North East Siberia, Russia • tussok tundra • generator • 2 x 6 m tower (control, drained) • Metek USA-1, LI-7200, Los Gatos,
industrial computer • meteorology
Examples of Station Setups
52 Eddy-Covariance Instrumentation Communication Standards
Communication Standards
wired communication between instruments, data-loggers and computers • RS232
− old standard for serial data transmission − max. distance: 15 m to 50 m − 300 baud up to 115200 baud (baud=symbols/second): ~ 1 Mbit/s
• RS422 − longer distances: 1200 m − 10 bus sharing units − 10 Mbit/s
• RS485 − longer distances: 1200 m − 32 bus sharing units − 12 Mbit/s
• SDM (synchronous device for measurement (addressable) − max. distance: 7 m − 15 bus sharing units − > 10 Mbit/s
• SDI-12 (synchronous digital interface) − max. distance: 70 m − 1200 baud
• Ethernet − 10, 100 Mbit/s, 1, 10, 100 Gbit/s − 1 m to 50 km, copper and optical fiber
• USB (1.0, 2.0, 3.0) since 1996 − universal serial bus − 1.5 Mbit/s to 5 Gbit/s − max. distance: 5 m
53 Eddy-Covariance Instrumentation Additional Sources of Information
Additional Sources of Information
Field intercomparison of four methane gas analyzers suitable for eddy covariance flux measurements O. Peltola1, I. Mammarella1, S. Haapanala1, G. Burba2, and T. Vesala1
1Department of Physics, University of Helsinki, P.O. Box 48, Helsinki 00014, Finland 2LI-COR Biosciences, 4421 Superior Street, Lincoln, NE 68504, USA Biogeosciences, 10, 3749–3765, 2013
Practical Handbook of Tower Flux Observation The Forest Meteorology Research Group of the Forestry and Forest Products Research Institute (FFPRI) runs FFPRI FluxNet. The network carries out research on the exchange of energy, water and carbon dioxide between the atmosphere and Japanese forest ecosystems.
A Brief Practical Guide to Eddy Covariance Flux Measurements George Burba, Dan Anderson
Eddy Covariance A Practical Guide to Measurement and Data Analysis Editors: Marc Aubinet, Timo Vesala, Dario Papale
Eddy Covariance Method George Burba (Licor Biosciences)