ASTM D4430-00(2006)
(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 E 177 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 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 ().
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.
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 for more specific safety precautionary information.)
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Designation:D4430–00 (Reapproved 2006)
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
1.1 Sensor systems used for making meteorological mea- 2.1 ASTM Standards:
surements may be tested for laboratory accuracy in environ- D1356 Terminology Relating to Sampling and Analysis of
mental chambers or wind tunnels, but natural exposure cannot Atmospheres
be fully simulated. Atmospheric quantities are continuously E177 Practice for Use of the Terms Precision and Bias in
variable in time and space; therefore, repeated measurements ASTM Test Methods
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-
ingtobeusedwithtwomeasuringsystemsindeterminingtheir D1356.
3.2 Definitions of Terms Specific to This Standard:
operational comparability (1,2).
1.2 The procedures provided produce measurement samples 3.2.1 difference (D)—the difference between the systematic
difference (d) of a set of samples and the true mean (µ) of the
that can be used for statistical analysis. Comparability is
defined in terms of specified statistical parameters. Other population:
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
1.4 Meteorologicaldeterminationsfrequentlyrequiresimul- i 5 1
taneous measurements to establish the spatial distribution of
3.2.3 operational comparability (C)—the root mean square
atmosphericquantitiesorperiodicallyrepeatedmeasurementto
(rms) of the difference between simultaneous readings from
determine the time distribution, or both. In some cases, a
two systems measuring the same quantity in the same environ-
number of identical systems may be used, but in others a
ment:
mixture of instrument systems may be employed. The proce-
N
dures described herein are used to determine the variability of
C56 ~X 2 X ! (3)
Π(
ai bi
N
i 5 1
like or unlike systems for making the same measurement.
1.5 This standard does not purport to address the safety
where:
concerns, if any, associated with its use. It is the responsibility
X = ith measurement made by one system,
ai
of the user of this standard to establish appropriate safety and
X = ith simultaneous measurement made by another
bi
health practices and determine the applicability of regulatory
system, and
limitations prior to use. (See 8.1 for more specific safety
N = number of samples used.
precautionary information.)
3.2.3.1 functional precision—the operational comparability
of identical systems.
This practice is under the jurisdiction ofASTM Committee D22 onAir Quality
and is the direct responsibility of Subcommittee D22.11 on Meteorology.
Current edition approved April 1, 2006. Published May 2006. Originally
´1 3
approved in 1984. Last previous edition approved in 2000 as D4430 - 00 . DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/D4430-00R06. 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 (2006)
3.2.4 estimated standard deviation of the difference (s)—a systems may be greater or smaller at high-wind speeds than at
measureofthedispersionofaseriesofdifferencesaroundtheir low-wind speeds). To test the data for such dependence, the
mean. range of measurements shall be divided into no less than three
class intervals and each class shall have a sufficient number of
2 2
s56 =C 2 d (4)
samples to represent the class. The change in rms difference
3.2.5 skewness (M)—the symmetry of the distribution (the
between classes indicates the dependence of the measurement
third moment about the mean).
difference on the magnitude of the measurement.
N
5. Significance and Use
~~X 2 X ! 2 d!
(
ai bi
i 5 1
M 5 (5)
5.1 This practice provides data needed for selection of
N
instrumentsystemstomeasuremeteorologicalquantitiesandto
M = 0 for normal distribution.
provide an estimate of the precision of measurements made by
3.2.6 kurtosis (K)—the peakedness of the distribution (the
such systems.
fourth moment about the mean), K = 3 for normal distribution.
5.2 This practice is based on the assumption that the
N
repeatedmeasurementofameteorologicalquantitybyasensor
~~X 2 X ! 2 d!
(
ai bi
system will vary randomly about the true value plus an
i 5 1
K 5 (6)
unknowable systematic difference. Given infinite resolution,
N
thesemeasurementswillhaveaGaussiandistributionaboutthe
3.2.7 response time (T)—the time required for the change in
systematic difference as defined by the Central LimitTheorem.
output of a measuring system to reach 63 % of a step function
If it is known or demonstrated that this assumption is invalid
change in the variable being measured.
for a particular quantity, conclusions based on the characteris-
3.2.8 identical systems—systems of the same make and
tics of a normal distribution must be avoided.
model produced by the same manufacturer.
3.2.9 resolution (r)—the smallest change in an atmospheric
6. Interferences
variable that is reported as a change in the measurement.
6.1 Exposure of the systems shall be such as to avoid
interference from sources, structures, or other conditions that
4. Summary of Practice
may produce a gradient in the measurement across the sample
4.1 The systems to be compared must make measurements
volume.
within a cylindrical volume of the ambient atmosphere not
6.2 A mutual interference by systems may produce a sys-
greater than 10 m in horizontal diameter.The vertical extent of
tematic difference (d) or bias that would not occur if one
the volume must be the lesser of1mor one-tenth H, where H
system were used by itself. That bias is not a part of the
is the height above the earth’s surface of the base of the
comparability and must be reported separately.
volume. The sample volume must be selected to ensure
6.3 A systematic difference greater than one increment of
homogeneous distribution of the variable being measured.
resolution must be investigated by interchanging the position
4.2 For some measurements (for example, visibility) the
of the sensors with an equal number of samples taken in each
horizontal distance or the height (for example, cloud height)
position. If the bias changes sign, it is due to the exposure and
may be the variable of interest. In the first case, one of the two
must be reported separately.
dimensions of horizontal distance is minimized and may not
7. Apparatus
exceed 10 m while all other criteria remain the same. In the
second case, all criteria for position and sampling described in
7.1 Theapparatususedisthecombinationofsensorsystems
4.1 remain unchanged and the measured height is treated as if
for which the op
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