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.

1. Abhilash Singh
Dept. of Agricultural Meteorology
CCSHAU, Hisar
Advances in Instrumentation for
Micrometeorological Studies

2. Introduction :-
micrometeorology deals with 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
Time Span
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 Ratio Energy Balance method
Eddy covariance method

5. Ventilated Psychrometer
 It is 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 flux plates
 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
 Quantum sensors 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
 It consists 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 Area Meter
 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 Quality Consumer 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 cultivation practices 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 estimation of 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 novel instrument for monitoring
the micrometeorology of rice canopies
(Fukuoka et.al. 2012)

21. MINCER – Micrometeorological Instrument
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. Eddy Covariance Method

23. Sensors and Instruments
3D Sonic Anemometer (wind Velocity)
Krypton Hygrometer (vapour density)
Thin wire Thermopile
(temperature)
Solid State pressure Sensor
IRGA
Data Processing and Control Unit

24.  Sonic anemometers use 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
 The LI-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
 krypton hygrometer 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
 Data collection 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 New Tool 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 April 2014, 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
These instruments 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 micrometeorological instruments
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. Thank you.