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Advances in Instrumentation for Micrometeorological Studies
This document discusses various instruments used for micrometeorological studies. It begins by defining micrometeorology and its importance. It then describes different scales in meteorology from macro to micro. Various instrumentation approaches like flux gradient, Bowen ratio energy balance, and eddy covariance methods are mentioned. Specific instruments are then discussed in detail including ventilated psychrometer, soil heat flux plates, porometer, quantum sensor, sunfleck ceptometer, leaf area meter, infrared thermometer, and photosynthesis system. Case studies on their applications in India and Nigeria are provided. The document concludes by discussing the global FLUXNET network for measuring ecosystem carbon, water, and energy fluxes using the eddy covariance method.
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Advances in Instrumentation for Micrometeorological Studies
- 1. Abhilash Singh Dept. ofAgricultural Meteorology CCSHAU, Hisar Advances in Instrumentation for Micrometeorological Studies
- 2. Introduction :- micrometeorology dealswith atmospheric processes near the earth's surface providing increased knowledge of the mechanisms controlling our environment. It has increased our understanding of the response of crop plants to their physical environment permitting us to develop improved agronomic practices aimed at achieving more efficient use of water and more economical production of crops. Rather than absolute values, fast fluctuations are to be measured. Therefore fast response and more accurate instruments are required.
- 3. Name of the Scale TimeSpan Horizontal spread (km) Vertical Height (km) Examples A. Macroscale (i) Planetary Scale Weeks or Years 5000 - 10000 More than 1 Westerlies , Trade winds (ii) Synoptic Scale Days to weeks 100- 5000 More than 1 Cyclone, Anti cyclones B. Mesoscale Minutes to days 1-100 Up to 1 Thunderstorm , land breeze C. Microscale Seconds to minutes 1 Up to 10 meters Turbulance, Eddies
- 4. Approaches Flux gradient Bowen RatioEnergy Balance method Eddy covariance method
- 5. Ventilated Psychrometer Itis used to measure temperature and humidity profiles in crop. Delta T psychrometer –uses thermocouple sensors one acting as dry bulb and other wet bulb thermometer . Sensors are ventilated by a miniature fan and shielded from solar radiations, rains etc. by brass coating. The wet bulb is provided with a wick wetted in distilled water. Fan evaporates water and wet bulb depression is produced. Output is connected to data-logger.
- 6. Soil heat fluxplates It is typically used for energy-balance or Bowen- ratio flux systems. A differential thermopile (copper-constantan) is connected between the top and bottom portions of the sensing plates to measure temperature gradients across the plate. Most heat flux sensors are based on the principle of thermopile—a number of thermocouples connected in series. A single thermocouple will generate an output voltage that is proportional to the temperature difference between the joints. Using more thermocouples in series will enhance the output signal.
- 7. Steady state Porometer It can measure leaf resistance, conductance, RH, Temperature, pressure, light and transpiration rate. Water loss from a leaf is determined by maintaining constant vapour density in a cuvette that is in contact with transpiring leaf. This is achieved by pumping dry air into the cuvette at an appropriate measured rate so that humidity observed by leaf matches the ambient humidity. After enclosing the leaf in cuvette an equilibrium is be established. So due to transpiration, the outgoing humidity must be greater than the inlet humidity. Reading should be taken after 15-25 seconds, if left too long , the stomata will start to adapt to new conditions.
- 8. Quantum Sensor Quantumsensors are used to measure radiation that drives photosynthesis. During photosynthesis, plants use energy in the region of the electromagnetic spectrum from 400-700 nm. The radiation in this range, referred as Photosynthetically Active Radiation (PAR). It can be measured in energy units (watts m-2) or as Photosynthetic Photon Flux Density (PPFD), which has units of quanta (photons) per unit time per unit surface area. The unit most commonly used is micromoles of quanta per second per square meter (µmol` s-1 m-2) .
- 9. Sunfleck Ceptometer Itconsists of a long, light sensitive probe with photodiode sensors . It has two main modes of operation. The first measures average Photo synthetically Active Radiations (PAR) & second measures the sun flecks in plant canopies. Sunflecks are the bright areas under the canopy where direct beam of solar radiation penetrates without attenuation by the canopy. The fraction of the ground covered by sunflecks is a useful measurement for determining canopy cover.
- 10. Portable Leaf AreaMeter Non-destructive leaf area measurement in the field can be done so that leaf area can be monitored without damaging the plants. It allows precise evaluation of plant canopy development throughout the growing season. It displays and stores individual leaf area, accumulated area, leaf length, average width, maximum width. It has resolution of 1 mm 2 . The major components are the scanning head and the readout console. Area data are recorded by the readout console as the scanning head is passed over the leaf.
- 11. Infrared Thermometer Infrared(IR) thermometers measure reflected infrared radiations having wavelength longer than visible light that can be correlated to a specific surface temperature of the object being measured. Anything above absolute zero (-273.15 degrees Celsius or 0 degrees Kelvin) emit radiation. Based on Stephen – Boltzmann‘s law E = 𝝈 T 4 (For Black Body) E = 𝝈 ε T 4 (For Grey Body) Range - - 30 to 100 0C Response Time - less than one second Accuracy up to 0.10 C Uses : – It is used to measure the Plant canopy temperature . Indices like CWSI (Crop Water Stress Index) have been developed which are used in irrigation planning.
- 12. Parameter Industrial QualityConsumer Quality Operating range -18 to 100 0c -10 to 50 0c Measurement Range 0 to 50 0c -33 to 220 0c The I-Q IRT sensors used in the study have a cost of∼$300 USD and the C-Q IRT sensors used were purchased for ∼$30 USD.
- 13. Portable Photosynthesis System The instrument makes rapid, simultaneous measurements of photosynthesis rates and stomatal conductance. It is based on the principle of Infra red gas analysis. During photosynthesis CO2 is consumed while in respiration it is released. Reference tube contains a known concentration of CO2 and a sample tube contains air of which CO2 concentration is to be measured. In the reference tube known amount of IR is depleted due to absorption by CO2 while in sample tube depletion is corresponding to CO2 concentration to be measured. On the basis of difference in concentration of CO2 between the two samples, the rate of photosynthesis is measured.
- 14. • Study area-Orissa , India (Thakur et al. 2013)
- 15. Effect of cultivationpractices and N levels on photosynthetic rate of flag and fourth leaf, measured at milk grain (MG) and late ripening (LR) stage of rice crop. Treatments Flag leaf Fourth leaf Photosynthetic rate (µmol m-2 s-1) Photosynthetic rate (µmol m-2 s-1) MG LR MG LR Cultivation practices System of rice intensification (SRI) 17.4 13.5 11.9 10.0 Transplanted flooded rice (TFR) 12.0 8.6 9.3 6.0 Nitrogen levels N0 11.0 7.5 9.3 6.2 N60 14.0 10.7 10.5 7.8 N90 16.4 12.6 10.9 8.7 N120 17.5 13.3 11.7 9.3
- 16. The Bowen(1926) introduced a relationship between sensible heat (𝑯 𝒔 ) and latent heat (𝑯𝒍 ), known as the Bowen ratio, β , is expressed in the form β = 𝑯 𝒔 𝑯𝒍 = ϒ 𝜟𝑻 𝜟𝒆 It is a micrometeorological technique often used for estimating the surface energy fluxes ( i.e. latent heat, sensible heat fluxes) This method uses time averaged measurements of temperature and humidity profiles in the surface boundary layer for the estimation of these fluxes. The surface energy budget is given by, 𝑹 𝒏=𝑯𝒔 + 𝑯𝒍 + G + Δs Bowen ratio energy balance (BREB)
- 17. Bowen Ratio System Air temperature is measured at two heights with chromel–constantan thermocouples wire. Soil heat flux is measured by heat flux plates which are buried in the soil at a fixed depth of between 5 to 10 cm to reduce errors due to vapour transport of heat. Vapour concentration is measured with a krypton hygrometer.
- 18. Bowen ratio estimationof surface energy fluxes in a humid tropical agricultural site, Ile-Ife, Nigeria (Oladosu et al. 2007)
- 19. Date and day no Air temp 0C Rainfall Rn (Wm-2 ) Hs ( Wm-2 ) HL ( Wm-2 ) G ( Wm-2 ) Observation 25/2/04 (56) 32-48 Heavy short lived 420 3 times of HL 100 26/2/04 57 30-46 In evening 600 200 300 50-80 & -120 evening 27/2/04 58 450 180 400 Clear sky more evaporation 28/2/04 59 150 250 Intense solar heating 29/2/04 60 35 220 280 Surface was dry
- 20. MINCER: A novelinstrument for monitoring the micrometeorology of rice canopies (Fukuoka et.al. 2012)
- 21. MINCER – MicrometeorologicalInstrument for the Near Canopy Environment of Rice (1) Air inlet; (2) double-hulled PVC pipe (3) single-hulled PVC pipe (4) solar-powered ventilator with rechargeable batteries (5) air outlet (6) tripod (7) data logger that records temperature and relative humidity.
- 22.
- 23. Sensors and Instruments 3DSonic Anemometer (wind Velocity) Krypton Hygrometer (vapour density) Thin wire Thermopile (temperature) Solid State pressure Sensor IRGA Data Processing and Control Unit
- 24. Sonic anemometersuse ultrasonic sound waves to measure wind velocity. They measure wind speed based on the time of flight of sonic pulses between pairs of transducers. The spatial resolution is given by the path length between transducers, which is typically 10 to 20 cm. Sonic anemometers can take measurements with very fine temporal resolution, 20 Hz or better, which makes them well suited for turbulence measurements. The lack of moving parts makes them appropriate for long term use in exposed automated weather stations 3D Sonic Anemometer
- 25. Gas Analyzer TheLI-820 CO2 Analyser is a low maintenance, economical gas analyser designed for continuous monitoring applications. Wide CO2 Measurement Range : 0-20,000 ppm Wide Operating Temperature: -20° to +45°C Low Noise Compact, lightweight design with low power consumption
- 26. Krypton Hygrometer kryptonhygrometer is used for measuring water vapour fluctuations in the air. The KH20 sensor uses a krypton lamp that emits two absorption lines : major line at 123.58 nm and minor line at 116.49 nm. Both of these lines are absorbed by water vapour, and a small amount of the minor line is absorbed by oxygen.
- 27. Thin wire Thermopile Thermocouple wire products are used for precise temperature measurement in temperature ranges from 200°C to 1300°C.
- 28. Differential Pressure Sensor Differential pressure sensors measurements are reliably, fast and stable. The digital and analog sensors offer highest accuracy and resolution, especially at very low differential pressures.
- 29. Data Logger Datacollection Systems which compiles and stores the data and transfers the data files wirelessly or over the Internet. The device have the ability to collect and store data from various instruments, such as in automatic weather station.
- 30. Data Processing • EddyPro®is a widely used eddy covariance data processing application that computes gas and energy fluxes and many useful parameters.
- 31. FLUXNET: A NewTool to Study the Temporal and Spatial Variability of Ecosystem-Scale Carbon Dioxide, Water Vapour, and Energy Flux Densities Fluxnet is a global network of micrometeorological tower sites that use eddy covariance methods to measure the exchanges of carbon dioxide, water vapor, and energy between the biosphere and atmosphere. It serves to provide an infrastructure to compile, archive and distribute data for the scientific community. (Baldochchi et al.,2001)
- 32. As of April2014, there were about 683 tower sites globally in continuous long-term operation.
- 33. Application in meteorology FLUXNET can provide new information on how the biosphere affects the partitioning of net radiation into sensible and latent heat exchange, as quantified by the Bowen ratio.
- 34. Advantages of micrometeorological instruments Theseinstruments have higher accuracy. They give the instant results. We get the continuous time series of data and this data can be stored in these instruments for future purpose. Most of these instruments are automatic, so less labour is required.
- 35. Limitations of micrometeorologicalinstruments The pace of modernization has been slow due to economic constrains being experienced by the developing countries as the cost of these instruments is very high. Maintenance of the existing meteorological instruments has also been affected by lack of adequate funding and lack of spare parts from manufacturers who no longer produce the same instruments. Due to lack of regular maintenance of these instruments and equipment, there is lack of continuity in data sets resulting in difficulties in analysis and accuracy of the end agro-meteorological products intended for the conservation and management of natural and environmental resources.
- 36.
Editor's Notes
- #5 The various exchange processes of different fluxes such as mass, momentum, energy and evapotranspiration across the boundary between Soil-plant-atmosphere continuum are measured using these approaches.
- #13 A field comparison of industrial-quality and consumer-quality infrared thermocouple sensors monitoring a grass canopy and a cotton canopy indicated that these two types of sensors were similar over a 13–35◦C range. The measurement of temperature made with two types of sensors would not differ significantly. Based on these results we conclude that the lower cost consumer-quality infrared thermometers are suitable for use in production agricultural applications.
- #16 In order to assess N utilization in relation to photosynthetic activity, three hills with an average number of panicles were selected from each sub-plot. For each hill, 3 flag leaves and 3 fourth-leaves were selected at the milk-grain stage (111 days after germination; 22–26 April) and late-ripening stage (123 days after germination; 4–6 May) to measure the photosynthetic rate by using a portable photosynthesis system (CIRAS-2; PP Systems Ltd., Hertfordshire, UK). Measurements were taken on a clear sunny day (solar radiation>1,200μmol m−2s−1) between 10:30 and 11:00 a.m. before the mid day reduction in photosynthesis.
- #20 Conclusions- Any day that follows a previous night precipitation, the latent heat flux during the daytime was found to be greater by a factor of two or more than the sensible heat flux. For the relatively dry days however, the sensible heat flux is of the same magnitude or slightly higher when compared with the latent heat flux. Generally, for the tropical zones, during the dry seasons the sensible heat flux is larger than latent heat, but during wet seasons the reverse is the true.
- #22 as rice panicles are the organs most susceptible to heat stress it is necessary to measure the panicle temperature to understand the impairment caused by heat stress which require elaborate measurement system and time consuming work making it difficult for the researcher to obtain necessary data. as a practical alternative The air temperature around the panicle is easier to measure than the panicle temperature which is closer to the panicle temperature than the air temperature observed at weather stations which are usually distant from study sites. another problem is difficulty in supplying power to equipment because electricity is rarely available in a paddy field so to overcome these difficulties these scientists develop the MINCER which is a radiation shielded ,solar powered, force ventilated system which can provide the data of air temp and relative humidity at an affordable cost. as a result of ease of use and use and cost effectiveness of MINCER ,more than 100 units are already in operation in eight countries that are participating in MINCERnet monitoring network (Yoshimito et. al. 2012)
- #23 Very useful technique to measure and calculate turbulent fluxes in atmospheric boundary layer. This method was developed by swinbank in1951.
- #24 To compute turbulent fluxes, measured scalar variables (e.g., temperature from a sonic anemometer, density of water vapour, CO2, and CH4 from gas analysers) and 3-dimensional wind components (u, v, and w, from a sonic anemometer) are recorded in a data acquisition system. These data are subsequently processed using flux computation software. Eddy Covariance Systems provides an accurate way to measure surface-atmosphere fluxes of energy and trace gas fluxes over a variety of ecosystems, including agricultural and urban landscapes, landfills, and various water surfaces. Fluxes can be measured by instrumentation mounted on a stationary or mobile tower, floating vessel (such as a ship or buoy), or an aircraft
- #25 Measurements from pairs of transducers can be combined to yield a measurement of velocity in 1-, 2-, or 3-dimensional flow.
- #26 It is an absolute, non-dispersive infrared (NDIR) gas analyzer based upon a single path, dual wavelength infrared detection system. It can be used in a wide range of demanding environmental conditions. The optical bench can be easily cleaned by the user; which reduces down-time due to contamination, and eliminates the need for factory recalibration.
- #29 The outstanding performance of differential pressure sensors is based on the dynamic measuring principle, in which the differential pressure is determined using intrinsic flow measurement.
- #30 For example, a raw data file collected over a period of 24 hours can be as large as 200 MBEddy covariance instruments generate large amounts of data.. A system that can compress and store large data files can be very helpful in remote areas, making it possible to store several months of raw data. The central data collection hub have the ability to log the CO2 and H2O data with synchronized anemometer data.
- #34 Occurrences of negative Bowen ratios are recorded as well and are attributed to radiative cooling and the presence of water on the surface. In both instances, stable thermal stratification is associated with the downward transfer of sensible heat. The timing of leaf-out also has a distinct impact on the humidity and temperature of the planetary boundary layer and the seasonal pattern of its maximum height During the winter, the Bowen ratio is variable, and in many instances large, with H being up to 6 times greater than λE.