An error is a difference between the measured value and its true value, expressed
in relative or absolute terms. The total error in measurement is a combination of
errors such as errors due to an improper exposure, exposure to a contaminant
influence (e.g. a temperature sensor exposed to a radiative source), electronic noise,
uncertainty or fluctuation in calibration or improper protrusion of the device in the
environment or signal loss during the transmission process.
When checking the magnitude of a combination of errors, dependence or
independence of errors should be considered. In the case of independence, the
square root of the sum of squares of individual errors must be less than the sum of
the absolute values of the individual errors (Shaw 1995).
A1.3 Temperature Measurements
Environmental temperature is a fundamental variable for the study of environmental
physical processes in the constant flux layer, insofar that as aforementioned
temperature profiles are essential factors for the dynamics of atmospheric processes.
The physical fundamentals underlying temperature measurement are based on
electric, expansion or thermodynamic principles. Temperature is an intensive
property common to all points of a microsystem and delivering a sensation of heat
or cold located in its boundaries. The temperature measurement is common in
everyday procedures such as meteorological previsions, control, and regulation in
rooms and apartments, healthcare amongst many other practical situations. The
principles of measuring air temperature and sensible heat fluxes by sonic
anemometry were presented in Chap. 3.
Thermometers are very common instruments for measuring temperatures of
microsystems, by recording e.g. the variation of volume of a gas or liquid with
temperature. The air temperature measured by a thermometer is the result of its
energy budget determined by the heat exchanges between the environment and the
device through the processes of radiation, convection, and conduction. The usual
rational is the use of a substance with a property which changes with temperature in
a regular way. This process can be evaluated through a linear relationship such as:
tðxÞ ¼ ax þ b
ðA1:16Þ
where t is the temperature of the used substance with the property x varying with
that temperature. The constants a and b are dependent on the used substance and
can be calculated specifying two points in the temperature scale. Thermometers of
alcohol and mercury are based on this principle. As air temperature increases the
liquid swells and the dilatation is recorded in a small tube connected with the liquid
reservoir. For thermographs, the liquid reservoirs are connected to mechanical
devices for data recording which allow the continuous recording of temperature
evolution. The bimetallic thermometers operative principle is based on the fact the
distinct metals show different expansion coefficients. Two strips of distinct metals
are joined and as they are heated or cooled the differential expansion causes a
318
Annex A1: Instrumentation in Environmental Physics
in relative or absolute terms. The total error in measurement is a combination of
errors such as errors due to an improper exposure, exposure to a contaminant
influence (e.g. a temperature sensor exposed to a radiative source), electronic noise,
uncertainty or fluctuation in calibration or improper protrusion of the device in the
environment or signal loss during the transmission process.
When checking the magnitude of a combination of errors, dependence or
independence of errors should be considered. In the case of independence, the
square root of the sum of squares of individual errors must be less than the sum of
the absolute values of the individual errors (Shaw 1995).
A1.3 Temperature Measurements
Environmental temperature is a fundamental variable for the study of environmental
physical processes in the constant flux layer, insofar that as aforementioned
temperature profiles are essential factors for the dynamics of atmospheric processes.
The physical fundamentals underlying temperature measurement are based on
electric, expansion or thermodynamic principles. Temperature is an intensive
property common to all points of a microsystem and delivering a sensation of heat
or cold located in its boundaries. The temperature measurement is common in
everyday procedures such as meteorological previsions, control, and regulation in
rooms and apartments, healthcare amongst many other practical situations. The
principles of measuring air temperature and sensible heat fluxes by sonic
anemometry were presented in Chap. 3.
Thermometers are very common instruments for measuring temperatures of
microsystems, by recording e.g. the variation of volume of a gas or liquid with
temperature. The air temperature measured by a thermometer is the result of its
energy budget determined by the heat exchanges between the environment and the
device through the processes of radiation, convection, and conduction. The usual
rational is the use of a substance with a property which changes with temperature in
a regular way. This process can be evaluated through a linear relationship such as:
tðxÞ ¼ ax þ b
ðA1:16Þ
where t is the temperature of the used substance with the property x varying with
that temperature. The constants a and b are dependent on the used substance and
can be calculated specifying two points in the temperature scale. Thermometers of
alcohol and mercury are based on this principle. As air temperature increases the
liquid swells and the dilatation is recorded in a small tube connected with the liquid
reservoir. For thermographs, the liquid reservoirs are connected to mechanical
devices for data recording which allow the continuous recording of temperature
evolution. The bimetallic thermometers operative principle is based on the fact the
distinct metals show different expansion coefficients. Two strips of distinct metals
are joined and as they are heated or cooled the differential expansion causes a
318
Annex A1: Instrumentation in Environmental Physics