ISO/DIS 23350

Hydrometry -- catching-type liquid precipitation measuring gauges

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DRAFT INTERNATIONAL STANDARD
ISO/DIS 23350
ISO/TC 113/SC 5 Secretariat: ANSI
Voting begins on: Voting terminates on:
2020-06-19 2020-09-11
Hydrometry — catching-type liquid precipitation
measuring gauges
ICS: 17.120.20
THIS DOCUMENT IS A DRAFT CIRCULATED
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ISO/DIS 23350:2020(E)
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PROVIDE SUPPORTING DOCUMENTATION. ISO 2020
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ISO/DIS 23350:2020(E)
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ii © ISO 2020 – All rights reserved
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ISO/DIS 23350:2020(E)
Contents Page

Introduction ................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Instrument specifications ........................................................................................................................................................................... 4

4.1 General ........................................................................................................................................................................................................... 4

4.2 General gauge specifications ....................................................................................................................................................... 4

4.3 Environment ............................................................................................................................................................................................. 4

4.3.1 General...................................................................................................................................................................................... 4

4.3.2 Temperature ........................................................................................................................................................................ 5

4.3.3 Relative humidity ............................................................................................................................................................ 5

5 Recording ..................................................................................................................................................................................................................... 5

5.1 Recording format .................................................................................................................................................................................. 5

5.2 Recording interval ................................................................................................................................................................................ 5

6 Environmental protection and housing........................................................................................................................................ 6

7 Installation ................................................................................................................................................................................................................. 6

8 Estimation of measurement uncertainty .................................................................................................................................... 6

8.1 General ........................................................................................................................................................................................................... 6

8.2 Factors of measurement uncertainty .................................................................................................................................. 7

8.3 Type-A estimation ................................................................................................................................................................................ 7

8.4 Type-B estimation ................................................................................................................................................................................ 7

8.5 Data uncertainty .................................................................................................................................................................................... 7

8.6 Combined uncertainty ...................................................................................................................................................................... 7

Annex A Catching-type liquid precipitation measuring gauges ............................................................................................. 8

Bibliography .............................................................................................................................................................................................................................16

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ISO/DIS 23350:2020(E)
Introduction

This Standard covers instrumentation that measures rainfall intensity (RI) and liquid precipitation by

collecting the volume of water that falls on a fixed area. The collected volume of water is divided by

the fixed area of the collecting device to give a value for volume per unit area, termed rainfall depth,

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and measured in mm⋅h or kg⋅m . Unlike many other meteorological instruments, there is no absolute

physical standard against which a raingauge (hereafter called catching-type liquid precipitation

measuring gauges) can be compared. Many different types, shapes, and sizes of catching-type liquid

precipitation measuring gauges are acceptable for the measurement of rainfall and rainfall depth, each

reflecting a specific requirement. Most consist of a circular collecting device, delineating the fixed area

of the sample, and a funnel leading into a storage reservoir and/or measuring system. Some types of

automatic gauges do not require a funnel. Since various sizes and shapes of orifice and gauge heights

are used in different countries, the measurements are not strictly comparable.

NOTE 1 This standard specifies only the functional requirements of catching-type liquid precipitation

measuring gauges, and does not include specification, design and installation conditions.

(REFERENCE: BS 7843-3:2012, Introduction)
(REFERENCE: WMO-No.:2012, CH 6.1.2 & CH 6.1.4.1)
(REFERENCE: BS EN 17277:2019)
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DRAFT INTERNATIONAL STANDARD ISO/DIS 23350:2020(E)
Hydrometry — catching-type liquid precipitation
measuring gauges
1 Scope

This International Standard specifies the typical requirements of instrumentation for measuring liquid

precipitation, primarily for the purpose of hydrological and meteorological observation. Its scope is

limited to both non-recording and recording catching-type precipitation gauges for the measurement

of liquid precipitation. The standard covers design criteria for the gauges and elements of uncertainty

that need to be considered in their construction.

This International Standard is supplemented by an annex providing guidance on the types of catching-

type liquid precipitation measuring gauges currently available and the measurement uncertainty

associated with them (see Annex A).
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.
ISO 772:2011, Hydrometry — Vocabulary and symbols

ISO/IEC Guide 98-3:2008, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in

me a s ur ement (GUM: 1995)

JCGM 200:2012(E/F) International guide of metrology – Basic and general concepts and associated terms

(VIM) 3 Edition: 2008
3 Terms and definitions

For the purpose of this document, the terms and definitions given in ISO 772, BS 7843-3 and

ISO/IEC Guide 98-3 apply.
3.1
accuracy ( of measurement)
qualitative expression for the closeness of a measured value to the true value

Note 1 to entry: The quantitative expression of accuracy should be in terms of uncertainty. Good accuracy implies

small random and systematic errors.
[SOURCE: ISO 772:2011, CH 7.38]
3.2
calibration

process which establishes, under specified conditions, the relationship between the values indicated by

a catching-type liquid precipitation measuring gauge and the corresponding known values indicated by

a measurement standard with associated measurement uncertainties.
[SOURCE: BS 7843-3:2012, CH 3.1]
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ISO/DIS 23350:2020(E)
3.3
error of measurement
result of a measurement minus a true value of the measurand
Note 1 to entry: The term relates equally to
— the uncorrected result, and
— the corrected result.

Note 2 to entry: The known parts of the error of measurement may be compensated by applying the appropriate

correction. The error of the corrected result
[SOURCE: ISO 772:2011, CH 7.24]
3.4
precipitation (liquid and solid)

precipitation is defined as the liquid or solid products of the condensation of water vapour falling from

clouds or deposited from the air onto the ground. It includes rain, hail, snow, dew, rime, hoar frost, and

fog precipitation
[SOURCE: WMO No.8 :2012, CH 6.1.1]
3.5
rain measure

graduated measuring cylinder made of clear glass or plastic, used by the observer for measuring the

volume of collected liquid and melted solid precipitation
[SOURCE: BS 7843-3:2012, CH 3.10]
3.6
rainfall

total liquid component of precipitation, including condensation from the atmosphere, collected and

measured by a catching-type liquid precipitation measuring gauge
[SOURCE: BS 7843-3:2012, CH 3.7]
3.7
rainfall intensity
accumulated precipitation in unit time
[SOURCE: BS 7843-3:2012, CH 3.9]
3.8
raingauge
an instrument that measures rainfall
3.8.1
automatic raingauge
collecting raingauge that measures rainfall by automatic means
[SOURCE: BS 7843-3:2012, CH 3.11.1]
3.8.2
collecting raingauge

instrument that collects precipitation falling through an orifice of the known cross-sectional area for

the measurement of its water equivalent volume, mass or weight accumulated over a measured period

[SOURCE: BS 7843-3:2012, CH 3.11.2]
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ISO/DIS 23350:2020(E)
3.8.3
storage raingauge

collecting raingauge that accumulates rainfall and melted solid precipitation in a collecting vessel for

manual measurement of its volume
[SOURCE: BS 7843-3:2012, CH 3.11.3]
3.9
resolution

quantitative expression of the ability of an indication device to distinguish meaningfully between

closely adjacent values of the quantity indicated
[SOURCE: ISO 772:2011 CH 7.1]
3.10
uncertainty

estimate characterizing the range of values within which the true value of a measurand lies

[SOURCE: ISO 772:2011 CH 7.35]
3.10.1
combined uncertainty

standard uncertainty of the result of a measurement when that result is obtained from the values of

a number of other quantities, equal to the positive square root of a sum of terms, the terms being the

variances or covariances of these other quantities weighted according to how the measurement result

varies with changes in these quantities
[SOURCE: ISO 772:2011 CH 7.43]
3.10.2
expanded uncertainty

expanded uncertainty quantity defining an interval about the result of a measurement that may be

expected to encompass a large fraction of the values that could be attributed to the measurand

[SOURCE: ISO 772:2011 CH 7.42]
3.10.3
type A evaluation of uncertainty

evaluation of a component of measurement uncertainty by a statistical analysis of measured quantity

values obtained under defined measurement conditions
[SOURCE: ISO 772:2011 CH 7.40]
3.10.4
type B evaluation of uncertainty

evaluation of a component of measurement uncertainty determined by means other than a type A

evaluation of measurement uncertainty
[SOURCE: ISO 772:2011 CH 7.41]
3.10.5
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
[SOURCE: ISO 772:2011 CH 7.39]
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ISO/DIS 23350:2020(E)
4 Instrument specifications
4.1 General

Catching-type liquid precipitation measuring gauges are classified as non-recording and recording

types. The non-recording type has ordinary and storage gauges. The recording type has weighting,

tipping-bucket, and floating types. It usually has a resolution of 0.1 mm to 1 mm, and the measuring

rainfall intensities in the range 0.1 to 1,000 mm⋅h or higher. Measurement errors may occur according

to installation conditions, measurement environment, and solid precipitation.

The catching-type liquid precipitation measuring gauge shall be made of circular orifice and shall be

formed perpendicular to the outer slope and the inner surface with sharp edges. Edge diameters shall

be less than 0.2 percent of diameter in any direction. The surface of the funnel shall consist of a stable,

durable material such that the water drop is not maintained by surface tension, is freely moved towards

the orifice and is passed to the measuring mechanism.

NOTE Although this standard specifies the functional requirements of catching-type liquid precipitation

measuring gauges, consideration of the siting and exposure of gauges is important. More specifically, the installation

conditions, measurement environment, and solid precipitation are well documented in the references below.

(REFERENCE: BS 7843-3:2012, CH 7.2.3)
(REFERENCE: BS 7843-3:2012, CH 6.1.5)
(REFERENCE : WMO CIMO_Guide-7th_Edition-2008-WMO No 8, CH 6)
4.2 General gauge specifications

The gauge manufacturer should provide general specifications that may impact the measurement of

precipitation, these include but are not limited to:
a) Measurement range for precipitation intensity or total rainfall volume
b) Resolution
c) Accuracy
d) Size of orifice area
e) Standardized communication interfaces and protocols for data transmission
f) Power supply and consumption

g) Height of gauge (including rim height placement to avoid interference from deposited snow or other

materials near gauge)
4.3 Environment
4.3.1 General

Liquid precipitation measuring gauges shall operate within the ranges of temperature in 4.3.2 and the

ranges of relative humidity in 4.3.3.

NOTE 1 Wind should be taken into consideration in areas that are prone to inclement weather conditions

(REFERENCE : WMO Guide to Meteorological Instruments and Methods of Observation, PART 1 )

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ISO/DIS 23350:2020(E)
4.3.2 Temperature

Catching-type liquid precipitation measuring gauges shall operate within the following temperature

range:
a) Operating temperature
— Maximum temperature : +60 °C

— Minimum temperature (catching-type liquid precipitation measuring gauges, excluding heating or

weighing gauge without antifreeze) : 0 °C

— Minimum temperature (catching-type liquid precipitation measuring gauge, with heating or

weighing gauge with antifreeze) : –40 °C
b) Storage temperature
— Maximum temperature : +40 °C
— Minimum temperature : –20 °C
( REFERENCE : BS 7843-3:2012, CH 11.1~11.2)
4.3.3 Relative humidity

Catching-type liquid precipitation measuring gauges shall operate within the following relative

humidity range:
a) Operating relative humidity
— Maximum relative humidity : 100 % RH
— Minimum relative humidity : 0 % RH
b) Storage relative humidity
— Maximum relative humidity : 80% RH
— Minimum relative humidity : 0% RH
( REFERENCE : BS 7843-3:2012, CH 11.1~ 11.2)
5 Recording
5.1 Recording format

For recording and non-recording type liquid precipitation gauges, the length of each record to be stored

in a data storage gauge or manual recording shall be at least eight digits for the year, month and day,

eight digits for the hour, minute, second and millisecond (e.g. 2019/12/31 09:00:00:00). For rainfall

intensity (RI), there shall be at least five digits (e.g. 00.000 mm⋅h ), not including the decimal place, for

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the liquid precipitation amount which is measured in mm⋅h or kg⋅m .
5.2 Recording interval

The recording interval must be specified by the network operator to ensure regulatory compliance and

fit with regional and climatological constraints.

For recording type gauges, the measurement record of liquid precipitation should be transmitted to the

recording device instantaneously or at a specified time according to the gauge user.

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ISO/DIS 23350:2020(E)

Non-recording type liquid precipitation gauges should be read manually at a specified interval to

acquire the data.
Ordinary an
...