ASTM D4430-00(2010)
(Practice)Standard Practice for Determining the Operational Comparability of Meteorological Measurements
Standard Practice for Determining the Operational Comparability of Meteorological Measurements
SIGNIFICANCE AND USE
This practice provides data needed for selection of instrument systems to measure meteorological quantities and to provide an estimate of the precision of measurements made by such systems.
This practice is based on the assumption that the repeated measurement of a meteorological quantity by a sensor system will vary randomly about the true value plus an unknowable systematic difference. Given infinite resolution, these measurements will have a Gaussian distribution about the systematic difference as defined by the Central Limit Theorem. If it is known or demonstrated that this assumption is invalid for a particular quantity, conclusions based on the characteristics of a normal distribution must be avoided.
SCOPE
1.1 Sensor systems used for making meteorological measurements may be tested for laboratory accuracy in environmental chambers or wind tunnels, but natural exposure cannot be fully simulated. Atmospheric quantities are continuously variable in time and space; therefore, repeated measurements of the same quantities as required by Practice E177 to determine precision are not possible. This practice provides standard procedures for exposure, data sampling, and processing to be used with two measuring systems in determining their operational comparability (1,2).
1.2 The procedures provided produce measurement samples that can be used for statistical analysis. Comparability is defined in terms of specified statistical parameters. Other statistical parameters may be computed by methods described in other ASTM standards or statistics handbooks (3).
1.3 Where the two measuring systems are identical, that is, same make, model, and manufacturer, the operational comparability is called functional precision.
1.4 Meteorological determinations frequently require simultaneous measurements to establish the spatial distribution of atmospheric quantities or periodically repeated measurement to determine the time distribution, or both. In some cases, a number of identical systems may be used, but in others a mixture of instrument systems may be employed. The procedures described herein are used to determine the variability of like or unlike systems for making the same measurement.
1.5 This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. (See 8.1 for more specific safety precautionary information.)
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Designation: D4430 − 00(Reapproved 2010)
Standard Practice for
Determining the Operational Comparability of
Meteorological Measurements
This standard is issued under the fixed designation D4430; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 Sensor systems used for making meteorological mea-
surements may be tested for laboratory accuracy in environ- D1356 Terminology Relating to Sampling and Analysis of
Atmospheres
mental chambers or wind tunnels, but natural exposure cannot
be fully simulated. Atmospheric quantities are continuously E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
variable in time and space; therefore, repeated measurements
of the same quantities as required by Practice E177 to
3. Terminology
determine precision are not possible. This practice provides
3.1 For additional definitions of terms, refer toTerminology
standard procedures for exposure, data sampling, and process-
D1356.
ingtobeusedwithtwomeasuringsystemsindeterminingtheir
operational comparability (1,2).
3.2 Definitions of Terms Specific to This Standard:
3.2.1 difference (D)—the difference between the systematic
1.2 The procedures provided produce measurement samples
difference (d) of a set of samples and the true mean (µ) of the
that can be used for statistical analysis. Comparability is
population:
defined in terms of specified statistical parameters. Other
statistical parameters may be computed by methods described
D 5 d 2 µ (1)
in other ASTM standards or statistics handbooks (3).
3.2.2 systematic difference (d)—the mean of the differences
1.3 Where the two measuring systems are identical, that is, in the measurement by the two systems:
same make, model, and manufacturer, the operational compa-
N
rability is called functional precision. d 5 X 2 X (2)
~ !
( ai bi
N
i51
1.4 Meteorologicaldeterminationsfrequentlyrequiresimul-
3.2.3 operational comparability (C)—the root mean square
taneous measurements to establish the spatial distribution of
(rms) of the difference between simultaneous readings from
atmosphericquantitiesorperiodicallyrepeatedmeasurementto
two systems measuring the same quantity in the same environ-
determine the time distribution, or both. In some cases, a
ment:
number of identical systems may be used, but in others a
N
mixture of instrument systems may be employed. The proce- 1
C56Π~X 2 X ! (3)
( ai bi
dures described herein are used to determine the variability of N
i51
like or unlike systems for making the same measurement.
where:
1.5 This standard does not purport to address the safety
X = ith measurement made by one system,
ai
concerns, if any, associated with its use. It is the responsibility
X = ith simultaneous measurement made by another
bi
of the user of this standard to establish appropriate safety and
system, and
health practices and determine the applicability of regulatory
N = number of samples used.
limitations prior to use. (See 8.1 for more specific safety
3.2.3.1 functional precision—the operational comparability
precautionary information.)
of identical systems.
3.2.4 estimated standard deviation of the difference (s)—a
measureofthedispersionofaseriesofdifferencesaroundtheir
This practice is under the jurisdiction ofASTM Committee D22 on Air Quality
mean.
and is the direct responsibility of Subcommittee D22.11 on Meteorology.
Current edition approved Oct. 1, 2010. Published March 2011. Originally
approved in 1984. Last previous edition approved in 2006 as D4430 - 00(2006). For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/D4430-00R10. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to the list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this practice. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4430 − 00 (2010)
2 2 low-wind speeds). To test the data for such dependence, the
s56=C 2 d (4)
range of measurements shall be divided into no less than three
3.2.5 skewness (M)—the symmetry of the distribution (the
class intervals and each class shall have a sufficient number of
third moment about the mean).
samples to represent the class. The change in rms difference
N
between classes indicates the dependence of the measurement
X 2 X 2 d
~~ ! !
( ai bi
difference on the magnitude of the measurement.
i51
M 5 (5)
N
5. Significance and Use
M = 0 for normal distribution.
5.1 This practice provides data needed for selection of
3.2.6 kurtosis (K)—the peakedness of the distribution (the
instrumentsystemstomeasuremeteorologicalquantitiesandto
fourth moment about the mean), K = 3 for normal distribution.
provide an estimate of the precision of measurements made by
N
such systems.
X 2 X 2 d
~~ ! !
( ai bi
i51
5.2 This practice is based on the assumption that the
K 5 (6)
N
repeated measurement of a meteorological quantity by a sensor
system will vary randomly about the true value plus an
3.2.7 response time (T)—the time required for the change in
unknowable systematic difference. Given infinite resolution,
output of a measuring system to reach 63 % of a step function
thesemeasurementswillhaveaGaussiandistributionaboutthe
change in the variable being measured.
systematic difference as defined by the Central LimitTheorem.
3.2.8 identical systems—systems of the same make and
If it is known or demonstrated that this assumption is invalid
model produced by the same manufacturer.
for a particular quantity, conclusions based on the characteris-
3.2.9 resolution (r)—the smallest change in an atmospheric
tics of a normal distribution must be avoided.
variable that is reported as a change in the measurement.
6. Interferences
4. Summary of Practice
6.1 Exposure of the systems shall be such as to avoid
4.1 The systems to be compared must make measurements
interference from sources, structures, or other conditions that
within a cylindrical volume of the ambient atmosphere not
may produce a gradient in the measurement across the sample
greater than 10 m in horizontal diameter. The vertical extent of
volume.
the volume must be the lesser of1mor one-tenth H, where H
6.2 A mutual interference by systems may produce a sys-
is the height above the earth’s surface of the base of the
tematic difference (d) or bias that would not occur if one
volume. The sample volume must be selected to ensure
system were used by itself. That bias is not a part of the
homogeneous distribution of the variable being measured.
comparability and must be reported separately.
4.2 For some measurements (for example, visibility) the
6.3 A systematic difference greater than one increment of
horizontal distance or the height (for example, cloud height)
resolution must be investigated by interchanging the position
may be the variable of interest. In the first case, one of the two
of the sensors with an equal number of samples taken in each
dimensions of horizontal distance is minimized and may not
position. If the bias changes sign, it is due to the exposure and
exceed 10 m while all other criteria remain the same. In the
must be reported separately.
second case, all criteria for position and sampling described in
4.1 remain unchanged and the measured height is treated as if 7. Apparatus
it were an atmospheric variable. The physical dimension of
7.1 Theapparatususedisthecombinationofsensorsystems
some measuring systems may exceed the spatial limits of 4.1
for which the operational
...
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