Location
The weather station at the Haarweg in Wageningen is a Special AgroMeteo-Station; the
measurements include radiation and soil temperature. The coordinates of the location are
51 58’ NB; 5 38’ OL; and is about 7 metres above the sea level.
Ede(gld)
N
Wageningen
Rhenen
Figure 1 View of the location of the weather station (circle)
0
10
20
30 m
Boundary of
observation field
N
Stevenson Screen
Small building for
measurements
Scintillometer on
a roof (2m)
Arable land
precipitation
Sun duration
3
Pasture
Soil temperatures
2
1
wind
radiation
road
ditch
pasture
pasture
Trees
Table 1 Instruments at the weather station
Data
Relative humidity
Temperature and
relative humidity
Air Pressure
Wind speed at 4
levels
Wind direction
Short wave
Radiation (global,
reflected, net)
Long wave radiation
Amount of
precipitation
Precipitation
duration
Sun duration
Soil temperature
(bare soil and grass)
Sensible heat Flux
Instruments
Hair hygrometer
Thermo-Hygrometer
Ventilated Thermo-Hygrometer
Type
Cup anemometer (4x)
Wind vane
Pyranometers
Kipp en Zonen CM11
Pyrgeometer
Precipitation meter
Mierij Meteo
Precipitation meter
Thies
Sunshine Sensor
Thermocouple
Kipp&Zonen CSD1
PT 100
Large Apenture Scintillometer
Self construction
cupanemometer
wind vane
Bare soil
Grass soil
-5 cm
-5 cm
- 10 cm
-10 cm
- 20 cm
-20 cm
Pt 100
-50 cm
-100 cm
Pt 100
Figure ?? Wind
Figure ?? Soil temperatures
Short-wave radiation
Long-wave radiation
Precipitation
duration meter
Precipitation meter (amount)
Drain slot
Figure ?? Radiation
Figure ?? Precipitation
All instruments are connected to a Campbell 23X data logger, which stands inside the small
building at the field. The sensors are measured every 5 seconds, and 10-minute averages will be
stored.
Large Aperture Scintillometer (LAS)
Sender
Receiver
Light beam
The data from the LAS are logged on a small data logger, which is inside the receiver.
Data reported and Instrumentation
Thermodynamic
Dry Bulb Temperature
The dry bulb temperature is simply the air
temperature. That means, it is a measure of the kinetic
energy of the molecules in the air. It is measured
inside a Stevenson Screen using a PT100 Resistance
Temperature Dependant Thermometer
Wet Bulb Temperature
The wet bulb temperature is the temperature air would
have if its energy were used to evaporate an amount of
water equal to the amount of water vapour it contains.
It is measured inside a Stevenson screen using a
PT100 Resistance Temperature Dependant
Thermometer surrounded by a moist wick.
Figure 2 Stevenson Screen
Pressure
Pressure is a force per unit area. Atmospheric pressure at some point is equal to the
weight of the vertical column of air above the point, per unit area. It is measured
using a sensor.
Vapour Pressure
Vapour pressure is the pressure exerted by the motion of molecules of water vapour.
It is dependent on the amount of water vapour in the air and the temperature of the
air. The vapour pressure can be derived from the wet and dry bulb temperatures.
Saturation Vapour Pressure
The saturation vapour pressure is the vapour pressure the air would have if it were
saturated. It is simply a function of temperature. A data logger derives the saturation
vapour pressure from the dry bulb temperature.
Relative Humidity
Relative humidity is the ratio of vapour pressure to saturation vapour pressure,
expressed as a percentage. It is 0% for completely dry air and 100% for saturated air.
The data logger derives relative humidity data by using the wet and dry bulb
temperatures.
Precipitation
Precipitation
Precipitation is water, in liquid or solid form, which is falling upon the surface. Thus
it includes rain, hail and snow. Typically, it is reported in units of liquid depth per
unit time. For example millimetres per hour. Precipitation is measured using two
devices.
1. Tipping Bucket Rain Gauge
(Not operational)
2. Mierij Meteo Precipitation meter (Figure??).
Precipitation will be collected in a funnel, from where it drops down
into a barrel which is communicating with a vessel. In this vessel is a
float with a magnet. The position will be determined magnetostrictive.
A signal of 4-20 mm corresponds to an amount of precipitation of 010 mm.
The instrument will reset after an amount of 10 mm is collected. The
water will drain away through a magnet valve just as possible dirt.
Note: A Precipitation duration meter will soon be operational.
Figure 3 Mierij Meteo
Precipitation Meter
Wind
Wind Speed
Wind speed is a scalar quantity specifying the magnitude of the
horizontal movement of air. An Anemometer measures wind
speed.
Wind Direction
Wind direction is a measure of the direction of the horizontal air
movement. It is the direction a wind vane is pointing, reported in
degrees clockwise from true north. Wind Direction is measured
using a Wind Vane.
Standard Deviation of Wind Direction
The standard deviation of wind direction provides an indication
of the degree to which the wind direction is changing. The data
logger derives it.
Figure 4
Cupanemometer
Radiation
Sunshine Duration
Sunshine duration is a measure of the percentage of bright
sunshine observed. It is related to the duration and intensity
of direct solar radiation as opposed to diffuse radiation and
gives an indication of the presence of cloud. It is measured
automatically using a Kipp&Zonen CSD1-sunshine sensor.
Figure 5 Kipp&Zonen
CSD1-sunshine sensor
Global Short Wave Radiation
Global short wave radiation is the incident short wave radiation and comprises the
direct and diffuse components. It is measured using a Pyranometer.
Diffuse Short Wave Radiation
Diffuse short wave radiation is the diffuse component of the incident short wave
radiation. It is measured using Pyranometer.
Figure 6
View of radiation setup with incoming
and outgoing
shortwave(1, pyranometer) and
longwave(2,pyrgeometer) instruments.
Reflected Short Wave Radiation
Reflected short wave radiation is the short wave radiation coming from the surface of
the earth. It is related directly to the global short wave radiation and the surface
albedo. Reflected radiation is measured using a pyranometer
Long Wave Radiation
Long wave radiation (radiation beyond 3 µm) is measured using a pyrgeometer.
Net (All Wave) Radiation
Net all wave radiation is the downward radiation less the upward radiation. It
includes both long and short wave radiation.
Soil
Soil Temperature
Soil temperature is simply the temperature of the soil at the surface and is measured
under bare soil and under grass using thermo sensors.
Soil Heat Flux
Soil heat flux is the rate at which heat is being conducted through the soil. It is
measured using the large apenture scintillometer.
Data Logging and Transfer
A data logger (Campbell 23X) records output from the instruments. The logger also derives
some other variables from the recorded data and calculates 10-minute averages.
Mostly also a so-called multiplexer is used to expand the amount of instruments which can be
connected to the data logger. A multiplexer can be recognized by its typical ‘clicking’ sound.
For some instruments the analogue signal will be converted to a digital signal.
The data logger is connected to a so-called line driver (Plector). In this way, the data can be
transported by a telephone line to the building of the department Meteorology and Air quality.
The data will be received by a line driver, which is connected to the RS232 port of a PC. At
the PC, macros in Visual Basic process the raw data so that they can be presented at the
website.
Sensor
Sensor
Sensor
Sensor
Sensor
Multiplexer
Data
logger
Linedriver
(plector)
Telephonewire
Linedriver
(plector)
ASCI .txt
PC
Macro’s in Excel,
using Visual basic
10-minute data are
presented at the Website
(graph)
Figure 7 Data-transfer scheme
Sensor
FAQ