AWS
Surinder Kaur
HydroMet Services
 India Meteorological Department was made sole
custodian of rainfall observations in India
vide Rainfall Resolution of 1890.
Hydro met Division of IMD is providing the services in the field of
- Rainfall Monitoring
- Hydro met Design
- Hydro met Forecasting (QPF)
- National and International Co operation
- Public Awareness
Surface
Observatories
Type of Observatories
Surface Observatories
Aviation Current Weather Observatories
High Wind Speed Recording Stations
INSAT-based Data Collection Platforms
Hydrometeorological Observatories
Network
Nos.
559
71
4
100
701
Non-Departmental Raingauge Stations:
- Reporting
- Non-Reporting
3540
5039
Non-Departmental Glaciological Observatories (Non-reporting):
- Snowgauges
- Ordinary Raingauges
- Seasonal Snow Poles
Agrometeorological Observatories
Evaporation Stations
Soil Moisture Recording Stations
Dew-fall Recording Stations
Evapotranspiration Stations
Ozone Stations
Radiation Stations
21
10
6
219
222
49
80
39
6
45
Air Pollution Observatories:
- Background Pollution Observatories
- Urban Climatological Units
- Urban Climatological Observatories
Ships of the Indian Voluntary Observing Fleet
Seismological Observatories
10
2
13
203
58
Trend in South West Monsoon Rainfall
1. Annual rainfall =1182.8 mm
2. south-west monsoon rainfall
(June to Sept)= 877.2 mm(74.2%)
3. High variability in time and
space -- floods & drought
Trend in Rainfall
•Winter Season
•Pre monsoon
•Post Monsoon
•Annual
Trend in Mean Annual Temp.
Definition of AWS
An Automatic Weather Station(AWS) is
defined as a station at which instruments
generate
and
transmit/
record
observations automatically and convert it
into coded form, and send to a particular
location if required.
Purpose of Establishing AWS network
 AWS are used for increasing the number and the reliability of
surface observations. They do this by:
 Increasing the density of an existing network by providing data from new
sites and from sites which are difficult to access.
 Supplying for manned stations, data outside the normal working hours
 Increasing the reliability of measurements by the use of new technology
 Ensuring the homogeneity of networks by standardizing the measuring
techniques.
 Satisfying new observational needs and requirements
 Reducing human errors
 Lowering operational costs by reducing the number of observers
Disadvantages
The loss of the data due to sabotage
(Theft of Solar Panel, Battery etc)
The loss of the data for some of the
meterological parameters e.g Amount of
cloud, Sudden development in the
weather etc.
Types of AWS




Self Timed AWS
Pseudo Random type AWS
Alarm type AWS
Interrogative type AWS
a) Satellite based
b) Landline based
Norms of AWS site selection criteria and its
installation
1. Each AWS is established in a fenced piece of land measuring 12 m
X 15 m with good exposure conditions.
2. The norms for AWS site selection are:
 There shall be no obstruction to the transmitting antenna.
 Avoid
a. Obstructions like tall buildings, trees etc.
b. Location of the site on the edge of a slope, hillocks, cliff or inside a
valley
c. Large industrial heat sources
d. Location near high-tension power lines
e. Rooftops, Steep slopes, sheltered hollows, high vegetation, shaded
areas or swamps
f. Low places holding standing water after rains.
g. Underground obstructions like buried cables or conduits.
h. Pollution influence from surrounding farms and towns.
Exposure conditions for sensors of
meteorological parameters at AWS site
• Wind speed and direction
 The wind speed and direction sensors are required
to be installed on a mast, at a height of 10m from
ground level.
 The sensors are required to be located on the mast,
which is installed at a distance of at least ten times
the height of nearby buildings, trees or other
obstructions.
Cont.
• Air Temp & Relative Humidity
 The standard measurement height for temperature
and relative humidity sensor is 1.25 to 2m.
 The sensor is to be located at a distance of at least
four times the height of obstructions like trees,
buildings etc.
 The sensors are generally located in an open level
area that is at least 9m in diameter.
 The site enclosure should be covered by short
grass or natural earth.
 Large paved areas, bitumen surfaces in the vicinity
of at least 30m have to be avoided.
Atmospheric pressure
The Atmospheric pressure being an important
meteorological parameter, the elevation of the station to
which the station pressure relates is very important and
hence the chosen site must be located in a flat terrain.
Rainfall
The rainfall sensor (tipping bucket) is placed in an open
area as far as possible at a minimum distance of four
times the height of any obstruction.
The standard measurement height is 30 cm above
ground level.
Solar radiation
Solar radiation sensors to be mounted at a minimum
height of 3m to ensure easy leveling and cleaning.
The AWS mast should be located within a chain linked fencing enclosure over an
area of 15 metre x 12 metres which satisfies all the exposure conditions for
sensors.
A Typical AWS Station
A Typical ARG Station
Basic Concept of Telemetry
 Telemetry link consists of three sub-system
a) AWS field station: Sensors, Signal Conditioning
unit, Data Logger, UHF Transmitter, Antenna,
Power Supply unit(12V DC battery float charged
through solar panel), Weather proof housing.
b) Space unit (Data Relay Transponder): UHF
receiving antenna for 402.75 MHz, Down converter
(402.75 MHz to 28 MHz), Filter, Up-converter (28
MHz to 4506.05 MHz), Amplifier, Transmitting
Antenna
c) Receiving Earth Station: Antenna, Low noise
amplifier, Down converter, BPSK demodulator,
server for data processing.
The Telemetry System
 The changes in the capacitance/resistance of a sensor
which varies linearly with the changes in the Met.
Parameters forms the basis of observation.
 The system transmits its measurements to KALPANA
satellite located at 74oE at set time interval of an hour
on a frequency between 402.65-402.85 MHz at a power
of 3-10 Watts with a crossed YAGI antenna.
 The data along with the station identification code, start
and end signals are transmitted through antenna by the
modulation to KALPANA @ 4800 bit/sec. The length of
the message is 422 bits.
Characteristics of Sensors
 ACCURACY - Accuracy is a measure of how closely
the sensor's output matches the "true" value of the
parameter being sensed.
 PRECISION - Precision is
repeatability of the sensor.
a
measure
of
the
 RESOLUTION - The resolution of a sensor is the
smallest change in the input that is reflected in the
output. Greater resolution does not imply greater
accuracy.
Resolution and Accuracy are two
independent variables. The advantage of resolution
over accuracy is that changes in the input parameter
can be detected and tracked.
Sensors of AWS (As per WMO
requirements for AWS)
Height above which
Characteristics
it is to be installed
Air temperature 2 m
-40 ̊C to +60 ̊C, Accuracy: ± 0.2 ̊C, Resolution: 0.1 ̊C
Parameter
Relative
humidity
Atmospheric
pressure
Rainfall
2m
0% to 100%, Accuracy: ± 3%, Resolution: 1%
1.5 m
0.6 to 1 m
600-1100 hPa (100 hPa above datum value), Accuracy:
0.2 hPa, Resolution: 0.1 hPa.
Accuracy: 2% at 240 mm/hr Resolution: 0.5 mm
Wind speed
10 m
1.2 m/s
Wind direction
10 m
+5o
Soil
temperature
Soil moisture
-20 cm
Accuracy: ±0.4 ̊C
-20 cm
+5 %
No. of Stations Installed
(as on 31.12.2011)
Automatic Weather Stations
(AWS) - 667
No. of Stations Installed
(as on 31.12.2011)
Automatic Raingauge Stations
(ARG) - 557
Thank You