Hydrometry - On-site measurement of snow depth and depth of snowfall

This document defines the requirements for on-site measurements of snow depth and depth of snowfall. It provides guidance on manual and automatic measuring techniques, and information about sources of errors and measurement uncertainty.

Vor-Ort-Messung der Schneehöhe und der Schneefalltiefe

Mesurage sur site de la profondeur de neige et de la profondeur de la chute de neige

Hidrometrija - Merjenje globine snega in višine snežnih padavin na kraju samem

Ta dokument določa zahteve za meritve višine snežne odeje in višine novozapadlega snega na kraju samem. Določa usmeritve za tehnike ročnega in samodejnega merjenja in informacije o virih napak in merilni negotovosti.

General Information

Publication Date
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
Due Date
Completion Date

Buy Standard

Technical report
TP CEN/TR 17909:2023 - BARVE
English language
34 pages
sale 10% off
sale 10% off
e-Library read for
1 day

Standards Content (Sample)

SIST-TP CEN/TR 17909:2023
Hidrometrija - Merjenje globine snega in višine snežnih padavin na kraju samem
Hydrometry - On-site measurement of snow depth and depth of snowfall
Vor-Ort-Messung der Schneehöhe und der Schneefalltiefe
Mesurage sur site de la profondeur de neige et de la profondeur de la chute de neige
Ta slovenski standard je istoveten z: CEN/TR 17909:2023
07.060 Geologija. Meteorologija. Geology. Meteorology.
Hidrologija Hydrology
SIST-TP CEN/TR 17909:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST-TP CEN/TR 17909:2023

---------------------- Page: 2 ----------------------
SIST-TP CEN/TR 17909:2023

CEN/TR 17909


March 2023
ICS 07.060
English Version

Hydrometry - On-site measurement of snow depth and
depth of snowfall
Mesurage sur site de la profondeur de neige et de la Vor-Ort-Messung der Schneehöhe und der
profondeur de la chute de neige Schneefalltiefe

This Technical Report was approved by CEN on 6 February 2023. It has been drawn up by the Technical Committee CEN/TC 318.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.



CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 17909:2023 E
worldwide for CEN national Members.

---------------------- Page: 3 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Symbols . 10
5 Principles . 10
5.1 General . 10
5.2 Snow depth . 11
5.3 Depth of snowfall. 12
6 Measurement principles . 12
7 Siting and exposure . 12
7.1 General . 12
7.2 Terrain . 13
7.3 Wind . 13
7.4 Thermal radiation . 13
7.5 Obstacles . 13
7.6 Disturbance by humans and animals . 13
7.7 Maintenance of measurement site . 13
8 Measurement of snow depth . 14
8.1 General . 14
8.2 Calibration . 14
8.3 Manual measurements . 15
8.3.1 Measurement techniques . 15
8.3.2 Procedure. 15
8.4 Sources of error . 16
8.4.1 General . 16
8.4.2 Reading errors . 16
8.4.3 Misjudgement of the base level . 17
8.5 Automated measurements . 17
8.5.1 General . 17
8.5.2 Ultrasonic measurements . 18
8.5.3 Optical measurements . 20
8.5.4 Data quality control . 23
8.6 Sources of error . 23
8.6.1 General . 23
8.6.2 Optic measurements . 24
8.6.3 Ultrasonic measurements . 24
8.7 Choice of measuring method . 24
9 Measurement of depth of snowfall . 24
9.1 General . 24
9.2 Measurement . 25
9.2.1 Measurement techniques . 25

---------------------- Page: 4 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
9.2.2 Procedure . 25
9.3 Sources of error . 26
10 Quality assurance . 26
Annex A (informative) Snow stake . 27
Annex B (informative) Manual snow depth measuring devices . 28
Annex C (informative) Electronic probe . 29
Annex D (informative) Ultrasonic snow depth measuring station . 30
Annex E (informative) Laser snow depth measuring station . 31
Annex F (informative) Snow board . 32
Bibliography . 33


---------------------- Page: 5 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
European foreword
This document (CEN/TR 17909:2023) has been prepared by CEN/TC 318 “Hydrometry”, the secretariat
of which is held by BSI.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.

---------------------- Page: 6 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
Snow depth, representative within a given area, is one of the most difficult weather parameters to be
measured in an accurate and consistent manner. Together with snow density it is the most important
factor in the estimation of snow water equivalent and thus of crucial importance for the assessment of
threatening hazards such as flooding, snow avalanches and building collapses. Preventive measures due
to the knowledge of snow amounts can save lives, properties and infrastructure. The data has a wide
variety of users, including national weather and hydrological services, waterpower industry, snow
avalanche forecasters, climate researchers, water resource managers, construction engineers, winter
resort managers, farmers, and many others.
In addition to weather forecasts, measurements of depth of snowfall (also called new snow height) are
essential in the preparedness of winter road plowing and airport snow removal. Resources can be
adapted to the current weather situation and serious traffic break downs can be reduced.
Much of the information in this document is based on the World Meteorological Organization (WMO)
Guide to Meteorological Instruments and Methods of Observation, Volume II – Measurement of
Cryospheric Variables, published in 2018.

---------------------- Page: 7 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
1 Scope
This document defines the requirements for on-site measurements of snow depth and depth of
snowfall. This document provides guidance on manual and automatic measuring techniques, and
information about sources of errors and measurement uncertainty.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
combined processes (such as sublimation, fusion or melting, evaporation and movement due to wind
and avalanches) that remove snow or ice from the surface of a glacier or from a snow field
[SOURCE: EN ISO 772:2022, 10.1]
blowing snow
snow being transported by wind high (approximately 2 m) above a snowpack (3.27) surface, where
visibility is noticeably reduced
Note 1 to entry: See also drifting snow (3.3).
[SOURCE: EN ISO 772:2022, 10.2]
drifting snow
snow being lifted from the snow surface and transported by wind just above the snow surface (3.23),
where visibility is not noticeably reduced
Note 1 to entry: See also blowing snow (3.2).
[SOURCE: EN ISO 772:2022, 10.6]
new snow
snow layer that is not transformed, densified or settled, from current or recent precipitation having
characteristic grain size range of 1 mm to 3 mm
Note 1 to entry: New snow height can be measured by use of a snow board (3.8).
[SOURCE: EN ISO 772:2022, 10.11]

---------------------- Page: 8 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
old snow
snow layers deposited from earlier precipitation, prior to fresh fallen snow, composed of
metamorphosed snow crystals
[SOURCE: EN ISO 772:2022, 10.12]
snow accumulation
all processes that add mass to the snowpack (3.27)
EXAMPLE Solid and liquid precipitation, ice deposition from atmospheric water vapor, snow deposited by
wind, avalanches, etc.
Note 1 to entry: Snow accumulation is the opposite of ablation (3.1).
[SOURCE: EN ISO 772:2022, 10.19]
snow avalanche
rapidly moving snow masses in volumes exceeding 100 m and with a minimum length of 50 m
Note 1 to entry: Large snow avalanches may contain rocks, soil, vegetation, and/or ice.
[SOURCE: EN ISO 772:2022, 10.20]
snow board
specially constructed board used to measure new snow (3.4) height manually
[SOURCE: EN ISO 772:2022, 10.21]
snow course
established line, or transect, of measurements of snow water equivalent (3.25) across a snow-covered
area in a representative terrain, where snow accumulation (3.6) is not homogeneously distributed in the
[SOURCE: EN ISO 772:2022, 10.23]
snow cover
accumulation of snow on the ground in its natural consistency
Note 1 to entry: See also snowpack (3.27).
[SOURCE: EN ISO 772:2022, 10.24]
snow cover extent
areal extent of snow-covered ground in relation to the total catchment
Note 1 to entry: It is usually expressed as per cent of total area in a given region.
[SOURCE: EN ISO 772:2022, 10.25]

---------------------- Page: 9 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
snow creep
internal deformation of the snowpack (3.27) due to gravity- and metamorphism-driven densification
[SOURCE: EN ISO 772:2022, 10.26]
snow density
mass per unit volume of snow
Note 1 to entry: Sometimes total and dry snow densities are measured separately. Total snow density
encompasses all constituents of snow (ice, liquid water, and air) while dry snow density refers to the ice matrix
and air only.
[SOURCE: EN ISO 772:2022, 10.27]
snow depth
total height of snowpack (3.27) measured vertically from the base to the snow surface (3.23)
Note 1 to entry: The slope-perpendicular equivalent of snow depth is the snowpack thickness (3.28).
[SOURCE: EN ISO 772:2022, 10.28]
snow distribution
spatial and temporal variability of snow cover (3.10) affected by snowfall, wind speed, elevation,
topography, vegetation and ablation (3.1)
[SOURCE: EN ISO 772:2022, 10.29]
snow glide
downhill movement of the snowpack (3.27) relative to the ground
[SOURCE: EN ISO 772:2022, 10.51]
snow height
vertical distance from a base to a specific level in the snow, or to the snow surface (3.23)
Note 1 to entry: Ground surface is usually taken as the base, but on firn fields and glaciers it refers to the level of
either the firn surface or glacier ice. The snow height is used to denote the location of layer boundaries but also
measurements such as snow temperatures relative to the base. Where only the upper part of the snowpack (3.27)
is of interest, the snow surface may be taken as the reference. This should be indicated by using negative
coordinate values. Snow depth (3.14) is the total height of the snowpack.
[SOURCE: EN ISO 772:2022, 10.32]
snow layering
stratification of the snowpack (3.27), where each layer is characterized by grain shape, grain size, layer
hardness, temperature, water content and density
[SOURCE: EN ISO 772:2022, 10.33]

---------------------- Page: 10 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
snow probe
instrument to manually measure large snow depths (3.14)
[SOURCE: EN ISO 772:2022, 10.40]
snow redistribution
distribution of previously deposited snow that was eroded and transported by the wind
Note 1 to entry: Redistribution features such as snowdrifts are usually formed from densely packed and friable
[SOURCE: EN ISO 772:2022, 10.17]
snow season
time period when the ground usually is covered by snow
[SOURCE: EN ISO 772:2022, 10.54]
snow stake
instrument for manual measurements of the snow depth (3.14)
[SOURCE: EN ISO 772:2022, 10.44]
snow surface
uppermost part of the snow cover (3.10), forming the interface to the atmosphere
[SOURCE: EN ISO 772:2022, 10.55]
snow survey
process of determining snow parameters, most often depth and density, at representative points,
usually along a snow course (3.9)
[SOURCE: EN ISO 772:2022, 10.45]
snow water equivalent (SWE)
height of the water layer, which would develop after the melting of the snowpack (3.27), if the melting
water remained without infiltration or evaporation on a given horizontal surface
Note 1 to entry: It can represent the snow cover (3.10) over a given region or a confined snow sample over the
corresponding area. The snow water equivalent is the product of the snow height (3.17) and the snow density
(3.13) divided by the density of water. It is typically expressed in millimetres of water equivalent, which is
equivalent to kilograms per square metre or litres of water per square metre.
[SOURCE: EN ISO 772:2022, 10.47]

---------------------- Page: 11 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
change of the physical state of snowpack (3.27) from solid to liquid phase, mainly affected by various
meteorological factors (e.g. temperature, air humidity, radiation, wind, rain)
[SOURCE: EN ISO 772:2022, 10.36]
accumulation of snow on the ground at a given site and time
Note 1 to entry: It often consists of various layers with different physical and mechanical properties.
Note 2 to entry: See also snow cover (3.10).
[SOURCE: EN ISO 772:2022, 10.49]
snowpack thickness
total height of the snowpack (3.27) measured perpendicularly from the base to snow surface
Note 1 to entry: See also snow depth (3.14).
[SOURCE: EN ISO 772:2022, 10.53]
4 Symbols
Symbol Description Unit
φ Slope angle °
DS Snowpack thickness (slope-perpendicular measurement) cm
DN Thickness of new snow (slope-perpendicular measurement) cm
D Snow thickness (slope-perpendicular measurement) cm
L Snow layer thickness (slope-perpendicular measurement) cm
HS Snow depth, height of snowpack (vertical measurement) cm
HN Depth of snowfall, new snow height, (vertical measurement) cm
SOURCE: The International Classification for Seasonal Snow on the Ground, IACS-UNESCO 2009.
5 Principles
5.1 General
Snow depth and depth of snowfall are measured vertically from a base level up to the snow surface.
Snow depth measurements normally have the ground surface as the base, while depth of snowfall is
measured on a snow board placed on the old underlying snow surface. Depending on the type of
instrument, measurements can be obliged to be performed perpendicularly to the ground. The vertical
component, though, is calculated through the ground slope angle.

---------------------- Page: 12 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
5.2 Snow depth

Figure 1 — Relationship between snow depth (HS) and snowpack thickness (DS)
Snow depth, or height of snowpack, (HS) is the vertical distance from the base to the snow surface
(Figure 1). Unless otherwise specified, a snow depth measurement refers to a measurement at a single
location at a given time. The perpendicular distance from the base to the snow surface is defined as
snowpack thickness (DS), which is related to HS through the slope angle (φ) as follows:
DS HS⋅ cosϕ (1)
( )
The slope angle is the acute angle measured from the horizontal plane of the slope. Conversely, HS can
be derived from DS as follows:
HS DS⋅ cosϕ (2)
( )
The vertical distance to a certain coordinate inside a snowpack (Figure 2) is defined as snow height (H)
and the slope-perpendicular distance as snow thickness (D), both related to each other as described for
HS and DS in Formula 1. The measurement is used for location of snow layering boundaries or
measuring points inside the snow for, for example, snow temperature or liquid water content. Where
only the upper part of the snowpack is of interest, the snow surface may be taken as the reference. This
should be indicated by using negative coordinate values.

---------------------- Page: 13 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)

Figure 2 — Relationship between snow height (H) and snow thickness (D)
5.3 Depth of snowfall
Depth of snowfall, or new snow height, (HN) is the vertical depth of freshly fallen snow that has
accumulated on the base or on a snow board during a specific period, usually of 24 h. When reporting
depth of snowfall for observation periods other than for 24 h, the period is added in parentheses to the
symbol, for example, the symbol for an 8-h measurement becomes HN(8h). Thickness of new snow (DN)
is the perpendicular equivalent of HN. DN is related to HN via the slope angle (φ) as described for HS
and DS in Formula 1.
6 Measurement principles
Measurement of snow depth can be made manually by readings on fixed scales or by graduated devices
pushed through the snowpack. A fixed scale can also be read remotely by a camera mounted at the site
or send photos automatically by broadband or GSM for manual post-processing. The measurement can
also be recorded continually by use of automatic sensors mounted above the snow surface. A manual
measurement, though, is the reference for all types of automated snow depth measurement since
calibration and verification of the sensor’s reading shall be done manually at site.
The fact that the snowpack is compacting during the accumulation of new snow makes it difficult to find
automated methods useful for measurements of the depth of snowfall. Operative measurements are
made manually on snow boards, which are swept free from snow after measurement and placed on top
of the old snow surface.
7 Siting and exposure
7.1 General
The accumulation of snow is often extensively affected by redistribution during snowfall and by drifting
and melting between the snowfall events. To find a representative site for measurement of snow depth
there are a number of factors to take into account, of which some important are listed in 7.2 to 7.5.

---------------------- Page: 14 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
7.2 Terrain
The measurement site should be as horizontal and flat as possible within a range of at least 100 m
radius, sheltered by vegetation from the influence of strong winds and safe from snow glide and snow
creep. Steep slopes, troughs, terrain edges or large rocks in the immediate vicinity of the measuring site
should be avoided as well as hollows and gullies, ridges and humps, where snow accumulation or snow
redistribution due to wind effects often occur. Inconsistencies of the ground within the measurement
site should be minimized by preparation with sand or gravel. At automatic measuring sites, constructed
plates sometimes could be preferred. It is important though that the constructions have thermal
properties which do not differ too much from the ground.
7.3 Wind
To ensure representative values it is essential to perform the measurements in locations where the
effects of blowing and drifting snow are minimized. In open areas where windblown snow cannot be
avoided, the mean value at the site should be estimated from several measurements, enough to give a
representative value.
7.4 Thermal radiation
Measuring sites should not be situated in urban areas where thermal effects could influence the snow
cover, nor at locations with unrepresentative sun exposure or shadow. To avoid ablation due to
absorption of solar radiation, stationary snow measurement equipment should be painted with, or
constructed by material in, light colour.
7.5 Obstacles
Structures and obstructions that could affect the wind patterns close to the measuring site should be
avoided. Recommended locations of measurement sites are at places sufficiently distant from larger
trees or rock outcrops and buildings, which could disturb natural snow accumulation and melting. The
minimum recommended distance between the sampling point and the nearest obstacle is roughly equal
to the height of the obstacle. In heavily forested locations, it is important to use clearings to avoid the
interception of snow by the tree canopy. Dense grass can cause a layer of air between the ground and
the bottom layer of the snow, particularly early in the winter season. This space between the ground
and the snow should not be included in the snow depth. Though, it may be very difficult to estimate if
this layer is present or not.
7.6 Disturbance by humans and animals
To prevent disturbance of the snow surface, measurement sites are preferably situated where people or
animals are not passing by frequently. It is recommended to use marker bands and reflectors to make
the equipment more visible even during night-time. If necessary, the installation should be surrounded
by a fence. It is important, though, that the fence does not disturb the general snow accumulation at the
7.7 Maintenance of measurement site
After the growing season ground vegetation should be cut at the target area and any objects that could
disturb the measurements must be removed. If necessary, holes in the ground should be filled up,
stones and grass tufts removed, and the measuring site prepared with filling material in order to level
the ground. Adequate preparation of the target area increases the measurement accuracy.
Trees and bushes might be removed or trimmed before they have grown too high or too dense. Fences,
marks, reflexes, and signs should be looked over and the stability of the installations should be checked
to withstand soil frost or storms.

---------------------- Page: 15 ----------------------
SIST-TP CEN/TR 17909:2023
CEN/TR 17909:2023 (E)
8 Measurement of snow depth
8.1 General
Snow depth can vary significantly within short distances. For a correct estimation it might be necessary
to perform measurements at several points. Before establishment of a new measuring site the
accumulation of snow should be studied.
If a snow depth measurement is carried out together with measurement of snow density the snow
water equivalent (SWE) at the site can be calculated. For assessment of SWE in whole catchments it is
important to take into account the variability of snow depth within the landscape, which normally is
significantly bigger than snow density. This can be made by snow surveys along carefully selected
transects (snow courses) in the study area. The number of samples and the length of snow courses
should be determined by the snow variability. Snow courses should be selected to represent the terrain
characteristics of the catchment, considering parameters such as elevation, slope, inclination,
coordinate, aspect, curvature, and the proportion of forest and open field. Snow courses can be short
with manual readings on 5 to 10 snow stakes installed 5 to 10 m apart or up to severa

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.