ASTM D4430-00
(Practice)Standard Practice for Determining the Operational Comparability of Meteorological Measurements
Standard Practice for Determining the Operational Comparability of Meteorological Measurements
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 all of 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: D 4430 – 00 An American National Standard
Standard Practice for
Determining the Operational Comparability of
Meteorological Measurements
This standard is issued under the fixed designation D 4430; 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 (e) 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- D 1356 Terminology Relating to Sampling and Analysis of
mental chambers or wind tunnels, but natural exposure cannot Atmospheres
be fully simulated. Atmospheric quantities are continuously E 177 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 E 177 to
3. Terminology
determine precision are not possible. This practice provides
3.1 For additional definitions of terms, refer to Terminology
standard procedures for exposure, data sampling, and process-
ing to be used with two measuring systems in determining their D 1356.
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 Meteorological determinations frequently require simul- i 5 1
taneous measurements to establish the spatial distribution of
3.2.3 operational comparability (C)—the root mean square
atmospheric quantities or periodically repeated measurement to
(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)
˛ (
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.
3.2.4 estimated standard deviation of the difference (s)—a
measure of the dispersion of a series of differences around their
This practice is under the jurisdiction of ASTM Committee D22 on Sampling
mean.
and Analysis of Atmospheres and is the direct responsibility of Subcommittee
2 2
D22.11on Meteorology.
s56 =C 5 d (4)
Current edition approved Sept. 10, 2000. Published November 2000. Originally
published as D 4430 – 84. Last previous edition D 4430 – 96.
2 3
The boldface numbers in parentheses refer to the list of references at the end of Annual Book of ASTM Standards, Vol 11.03.
this practice. Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 4430
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
5.1 This practice provides data needed for selection of
M 5 (5)
N
instrument systems to measure meteorological quantities and to
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
repeated measurement of a meteorological quantity by a sensor
N
~~X 2 X ! 2 d!
( system will vary randomly about the true value plus an
ai bi
i 5 1
K 5 (6)
unknowable systematic difference. Given infinite resolution,
N
these measurements will have a Gaussian distribution about the
3.2.7 response time (T)—the time required for the change in
systematic difference as defined by the Central Limit Theorem.
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.
6. Interferences
3.2.9 resolution (r)—the smallest change in an atmospheric
6.1 Exposure of the systems shall be such as to avoid
variable that is reported as a change in the measurement.
interference from sources, structures, or other conditions that
4. Summary of Practice may produce a gradient in the measurement across the sample
volume.
4.1 The systems to be compared must make measurements
6.2 A mutual interference by systems may produce a sys-
within a cylindrical volume of the ambient atmosphere not
tematic difference (d) or bias that would not occur if one
greater than 10 m in horizontal diameter. The vertical extent of
system were used by itself. That bias is not a part of the
the volume must be the lesser of1mor one-tenth H, where H
comparability and must be reported separately.
is the height above the earth’s surface of the base of the
6.3 A systematic difference greater than one increment of
volume. The sample volume must be selected to ensure
resolution must be investigated by interchanging the position
homogeneous distribution of the variable being measured.
of the sensors with an equal number of samples taken in each
4.2 For some measurements (for example, visibility) the
position. If the bias changes sign, it is due to the exposure and
horizontal distance or the height (for example, cloud height)
must be reported separately.
may be the variable of interest. In the first case, one of the two
dimensions of horizontal distance is minimized and may not
7. Apparatus
exceed 10 m while all other criteria remain the same. In the
7.1 The apparatus used is the combination of sensor systems
second case, all criteria for position and sampling described in
for which the operational comparability or functional precision
4.1 remain unchanged and the measured height is treated as if
is to be determined plus the data-processing equipment re-
it were an atmospheric variable. The physical dimension of
quired to extract the data and calculate the statistical param-
some measuring systems may exceed the spatial limits of 4.1
eters.
(for example, a rotating beam ceilometer with a 200-m
baseline). In those cases the systems must be instal
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