ECV T5: Snow cover
Assessment of the status of the
development of standards for the
Terrestrial Essential Climate Variables
PLEASE NOTE THIS REPORT IS STILL IN A PHASE OF WORK IN
PROGRESS
Contributors: Konrad Steffen, Richard Armstrong, Monica Monteduro, Reuben
Sessa add other contributors here
Draft version 4
1 September 2008
60
Global Terrestrial Observing System, Rome, 2008
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
Contents
Acronyms .................................................................................................................................. 3
1. Definition ............................................................................................................................. 4
2. Units of measure .............................................................................................................. 6
3. Methodology ....................................................................................................................... 6
3.1 In situ measurement ................................................................................................ 7
3.2 Snow depth .................................................................................................................. 7
4. Analysis products ........................................................................................................... 13
5. Reference .......................................................................................................................... 17
2
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
Acronyms
AMSR-E
CDIAC
CLPX
CRYSYS
CSCC
DMSP
EASE-Grid
ESDIM
GCM
GCOS
GSN
GTN-H
GTOS
GTS
HDF-EOS
HSDSD
HWR
IMS
MODIS
MSC
NASA
NDSI
NESDIS
NH
NISE
NOAA
NOHRSC
NSIDC
NWS
NWS/COOP
RSE
SMMR
SNOTEL
SR
SSM/I
SWE
UDG
WMO
Advanced Microwave Scanning Radiometer - Earth Observing
System
Carbon Dioxide Information and Analysis Center
Cold Land Processes Field Experiment
CRYosphere System in Canada
Campbell Scientific Canada
Defense Meteorological Satellite Program
Equal Area Scalable Earth Grid
Environmental Services Data and Information Management
Global Climate Model or General/Global Circulation Model
Global Climate Observing System
Ground Station Network
Global Terrestrial Network for Hydrology
Global Terrestrial Observing System
Global Telecommunications System
Hierarchical Data Format - Earth Observing System
Historical Soviet Daily Snow Depth
Hydrology and Water Resources
Ice Mapping System
Moderate Resolution Imaging Spectroradiometer
Meteorological Service of Canada
National Aeronautics and Space Administration
Normalized Difference Snow Index
National Environmental Satellite Data Information Service
Northern Hemisphere
Near Real-Time Ice and Snow Extent
National Oceanic and Atmospheric Administration
National Operational Hydrologic Remote Sensing Center
National Snow and Ice Data Center
National Weather Service
National Weather Service Cooperative Observer Program
random square error
Scanning Multifrequency Microwave Radiometer
Snowpack Telemetry
Sonic Ranger
Special Sensor Microwave Imager
Snow Water Equivalent
Ultrasonic Depth Gauge
World Meteorological Organization
3
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
Executive Summary
Executive summary needs to be added here (see guidelines -> bits below
extracted from the guidelines).
The executive summary will be the most important section of the report as it will be extracted
and compiled with the other executive summaries to form the actually submission report to
SBSTA. The individual ECV reports will also be provided as supporting documentation. The
executive summary will therefore have the widest audience including the policy makers.
Note that the Executive summary should be a maximum of two pages (font 12, times New
Roman) and should contain the sections listed below. Any Executive summary longer than the
two pages will be cut brutally (you are warned :o).
1. Small introduction on the ECV
2. Definition of the observations and the units
3. Indicate available methods, protocols, standards, validation procedures for the ECV and if
the meet the needed requirements.
4. Clearly out line under a subsection “Recommendations” what is required.
Additional information on the above points are also provided below.
8. Recommendations
Most important section with section 3.
Clear set of recommendations in a series of bullets should be provided in this section. This
should be in two subsections.
8.1 Standards and methods
Specific to methods, protocols, standards etc. recommendations including if certain methods or
protocols should undergo the process to become and internatinal standardization or if certain
validation process should be adopted.
8.2 other recommendations
Other recommendations related to the ECV.
4
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
1. Introduction
Short introduction on the importance of snow cover should be added here.
About one third of the Earth’s land surface may be covered seasonally by snow.
Up to 50% of the Northern Hemisphere land surface has snow cover during the
Northern Hemisphere winter. It has major effects on surface albedo and energy
balance and modifies the overlying atmospheric thickness and surface
temperatures. Snow cover has a number of important physical properties that
exert an influence on global and regional energy, water and carbon cycles. Snow
makes up a significant fraction of the water available for agriculture and water
supply in many semi-arid regions of the world where changes in snow cover
conditions can have serious economic and social impacts. Hence, regular
monitoring of snow cover (extent, depth and water equivalent) was identified as a
high priority activity for global climate monitoring
Snow Cover Area and Snow Depth
Snow depth is an important property of snow cover, influencing surface radiative
exchange and heat transfer and affecting frozen ground and permafrost
distribution and moisture recharge. It also has important operational and
ecological implications and observations of this variable are used for a multitude
of applications. Examples include roof snow load computations, assessment of
winter survival of crops, biological studies, calculation of forest fire indices,
validation of satellite algorithms and land surface process models and snow depth
analyses in support of numerical weather prediction.
Snow Water Equivalent (SWE)
Knowledge of the snow water equivalent (SWE), or amount of water in the
snowpack, is critical in the assessment of the energy and water cycle in the
climate system, in validating GCM1 snow cover simulations and for hydrology and
water resource planning.
2. Definition and units of measure
Several elements must be considered under the heading “snow cover”: snow
extent, snow depth, snow water equivalent, snow all and solid precipitation.
SNOW COVER: in general, the accumulation of snow on the ground
SNOW COVER EXTENT: the total land area covered by some amount of snow;
typically reported in square kilometers
1
Global Climate Model or General/Global Circulation Model.
5
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
SNOW COVER DEPTH: the combined total depth of both old and new snow on the
ground
SNOW WATER EQUIVALENT: the water content obtained from melting snow
(i.e.the thickness of the layer of water that would result from melting a given
snow depth) . This information is very important to weather forecast offices,
especially just before a thaw in order to assess river flood potential
SNOW COVER DURATION: does a definition need to be added here?
2. Units of measure:
SNOW COVER EXTENT:
Km2
SNOW COVER DEPTH:
Cm
SNOW WATER EQUIVALENT:
Liquid water equivalent (mm)
(Measurements of the spatial distribution of SWE ) Snow water equivalent can be
presented in units of kg/m2 or meters of depth of liquid water that would result
from melting the snow. SWE is the product of depth and density:
SWE = depth (m) x density (kg/m3) (units: kg/m2)
SWE = depth (m) x density (kg/m3) / density of water (kg/m3) (units: m)
3. Exisiting measurement methods, protocols
and standards
Overview
The WMO Guide to Hydrological Practices (WMO-No. 168) describes procedures for
collecting measurements of snow cover, snow depth, and water equivalent of
snow. Guidance for the location of gauges that are to be used to measure snow
depth and water equivalent of snow is provided and discussion of the design of
snow cover networks is given. Additional discussion of snow cover measurement is
given in the WMO Snow Cover Measurements and Areal Assessment of
Precipitation and Soil Moisture.
While for snow cover there is no specific global network, the parameters
connected to snow, are related to the GTN-Hydrology. GTN-H is the result of the
joint efforts of the WMO Hydrology and Water Resources (HWR) Department, the
Global Climate Observing System (GCOS) and the Global Terrestrial Observing
System (GTOS). GTN-H comprises existing networks, global databases and global
data product centres, and is based around a Coordination Group, see:
http://gtn-h.unh.edu/
Canadian National Plan for Cryospheric Monitoring
Canadian National Plan for Cryospheric Monitoring in Support of GCOS
6
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
Canada underwent an extensive exercise to determine a national monitoring
strategy for snow, as well as the rest of the cryosphere; the workshop summaries
and final report are online at:
www.ec.gc.ca/climate/CCAF-FACC/Science/nat2002/toc_e.htm
Snow Water Equivalent (SWE)
In support of improving the quality of snowfall, snow depth and water equivalent
observations, the National Weather Service (NWS) in the U.S. in conjunction with
Colorado State University, has rewritten guidelines for measurement of snowfall
and snow depth by official NWS cooperative weather observers. The new, more
concise guidelines, with funding provided by NOAA’s Environmental Services Data
and Information Management (ESDIM) Program, are presented. (reference?)
These guidelines are mostly important because they help to improve the quality of
snow observations coming from the meteorological and climatological U.S.
network. As no international network exists to provide standardized observations
or protocols these guidelines have also been considered as a reference because
they have already been adopted by a wide variety of private and government
snow measurement observers, which in turn allows for a more accurate collection,
comparison, and analysis of inter-network snow data.
3.1 In situ measurements
GCOS requirements are largely met by the operational snow cover product
prepared by the US National Environmental Satellite Data Information Service
(NESDIS), the NOAA Interactive Multisensor Snow and Ice Mapping System (IMS http://natice.noaa.gov/ims/index.htm). Canadian in situ observational records can
be used to infer additional information on regional snow cover extent, variability
and change.
Identified GCOS requirements are for point measurements of daily snow depth at
GSN (ground station network) stations but these requirements are expanded by
wide ranging domestic needs for such data. As noted earlier, Canada has a
substantial database of daily snow depth measurements at synoptic stations,
extending back to the 1950s. In the early 1980s, the daily snow depth
measurement programme was extended to climatological stations, quadrupling
the number of observations in the national climate archive. For United States and
other station snow depth data, consult the date archive at the National Snow and
Ice Data Center (NSIDC) – http://nsidc.org. As a recent development, an
automatic snow depth sensor is now being deployed at an increasing number of
sites.
3.2 Snow depth direct measurements
Coverage and frequency
Snow depth is measured once daily at weather stations, but is not usually
reported over the Global Telecommunications System (GTS). There are about
7,000 land stations in the GTS reports. Global snow depth data are available from
the WMO-GTS Synoptic Reports for stations that do report that code group in real
7
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
time . Snowfall is not differentiated in 6-hourly/daily precipitation measurements
at GTS weather stations although type of precipitation is reported in the synoptic
weather code. Measurements of snow cover depth over extended areas together
with an established local correlation with density make it possible to approximate
the water content of the snow pack.
3
Point- and line-measurement methods of Snow depth
Manual determination of snow depths are made either by inserting a probe or by
observing snow height on fixed markers. Care should be taken when using fixed
markers to avoid errors because of local melt or snow drift around the marker.
Sighting along the snow surface a few metres from the marker can make this
error small. If snow depth is measured at fixed points, care should be taken to
disturb the snow close to the markers.
Automatic recording of snow depth can be made with ultrasonic techniques.
Several snow-depth sensors with low power consumption and low maintenance
requirements are now marketed. The distance from the sensor to the snow
surface is determined from the time required by an emitted signal to be reflected
and received by the sensor. Complementary air-temperature measurements are
required to compensate for temperature dependent variations in the speed of
sound in air. Anomalous results may occur during falling or blowing snow
conditions. The sensor can not distinguish low-density new fallen snow from air.
(Lundberg et al. 2001). The ultrasonic snow-depth technique seems well suited for
unattended, continuous and long-term measurements.
Snow ruler
Depth measurements of snow cover or snow accumulated on the ground are made
with a snow ruler or similar graduated rod which is pushed through the snow to
the ground surface. Representative depth measurements by this method may be
difficult to obtain in open areas since the snow cover undergoes drifting and
redistribution by the wind, and may have embedded ice layers that limit
penetration with a ruler. Care should be taken to ensure that the total depth is
measured, including the depth of any ice layers which may be present. In typical
examples, a number of measurements are made and averaged at each observing
station.
Measurement with graduated snow stakes
The most common method for determining the depth of snow cover, primarily in
regions of deep snow, is by means of calibrated stakes fixed at representative
sites that can be inspected easily from distant ground points or from aircraft by
means of binoculars or telescopes. The stakes should be painted white to minimize
the undue melting of snow immediately surrounding them. This procedure may be
acceptable if the representativeness of the site is proven and if the immediate
surroundings of the site (about 10 metres in radius) are protected against
trespassing. The readings are taken by sighting over the undisturbed snow surface.
The stakes should be painted white to minimize undue melting of snow
immediately surrounding them. The entire length of the stake should be
graduated in metres and centimetres. In inaccessible areas, stakes are provided
3
See: ftp://ftp.ncdc.noaa.gov/pub/data/globalsod.
8
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
with crossbars so that they can be read from a distance with the aid of field
glasses, telescopes, or from aircraft. In the case of measurements of snow depth
from aircraft, visual readings of snow stakes may be supplemented by large-scale
photographs of the snow stakes, which make the readings less subjective.
Ultrasonic ranging device
The development of an inexpensive ultrasonic ranging device to provide reliable
snow depth measurements at automatic stations has provided a feasible
alternative to the standard observation, both for snow depth and for fresh snow
fall (Goodison, et al., 1988). 4 The first sensor designed and manufactured by
Campbell Scientific Canada (CSCC) had the model designation CSMAL01. The
sensor subsequently had two major design changes, resulting in model
designation UDG01 (Ultrasonic Depth Gauge) and most recently the SR50 (Sonic
Ranger). The SR50 is a rugged, acoustic distance sensor, which measures the
elapsed time between emission and return of an ultrasonic pulse. This
measurement can be used to determine snow or water depth. An air temperature
measurement is required to correct for variations of the speed of sound in air. This
sensor can be utilized to quality control automatic recording gauge measurements
by providing additional details on the type (solid or liquid), amount, and timing of
precipitation. It measures in 0.6 seconds typical, its measurement range 1.6 to
32.8 ft (0.5 to 10 m). It is capable of an accuracy of ±0.4" (1 cm) or 0.4% of
distance to target which ever is greatest (Campbell Scientific 2007).
Measurement with snow tubes
The vertical depth of snow cover is also measured by direct observation with a
graduated snow tube, usually during the course of obtaining the water equivalent,
National Weather Service (NWS) guidelines for measurement of snowfall and
snow depth
The National Weather Service suggests to measure snowfall and snow depth in
locations where the effects of blowing and drifting are minimized. In open areas
where windblown snow cannot be avoided, several measurements may often be
necessary to obtain an average depth and they should not include the largest
drifts. If a daily schedule is possible it would be better to make snow observation
every 6 hours, this is the procedure followed by National Weather Service Forecast
Offices. More than four, six-hourly observations should not be summed to
determine 24-hour snowfall total.
Determine the total depth of snow, ice pellets, or ice on the ground. This
observation is taken once-a-day at the scheduled time of observation with a
measuring stick. It is taken by measuring the total depth of snow on exposed
ground at a permanently-mounted snow stake or by taking the average of several
4
In the early 1980's, the Atmospheric Environment Services of Environment Canada recognized the need for "a
reliable, low cost automatic snow depth sensor" and developed this sensor (Goodison et al. 1984, Goodison et
al.,1988). The ultra sonic wave reflection in air was used as the method for measuring snow depth, a technique
initially presented by Caillet et al.(1979), and Gubler (1981). The sensor determines the distance to a target by
sending out ultrasonic sound pulses and listening for the returning echoes from a target. The time from transmit to
the return of the echo is the basis for obtaining the distance measurement. Once the initial design and
verification were completed, a prototype sensor and technology was licensed to Campbell Scientific (Canada)
Corp. (CSCC) for
9
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
depth readings at or near the normal point of observation with a measuring stick.
When using a measuring stick, make sure the stick is pushed vertically into the
snow until the bottom of the stick rests on the ground. Do not mistake an ice layer
or crusted snow as "ground". The measurement should reflect the average depth
of snow, ice pellets, and glaze ice on the ground at a usual measurement site (not
disturbed by human activities). Measurements from rooftops, paved areas, and
the like should not be made. Report snow depth to the nearest whole inch (cm),
rounding up when one-half inch (cm) increments are reached (example 0.4 inches
gets reported as a trace (T), 3.5 inches gets reported as 4 inches). Note the same
procedure should be done with cm.
Barometric (experimental methodology only)
A method to measure snow depth along fixed profiles was presented by Kennett
(Kennett et al. 1996). The method is using a high precision barometer attached to
a PC to find the elevation along the profiles by measuring changes in barometric
pressure. Profiles are defined by fixed stakes. The elevation along profiles and
distance between stakes are surveyed when the ground is snow-free. The
barometric pressure is measured on the snowpack along the line. The barometer
is located on a sledge equipped with an odometer and pulled by a snowmobile at a
constant speed of 10±20 km/h, using a trigger to mark the stakes in the data file.
The snow depth at stakes and distance between stakes are used to calibrate the
barometer and odometer readings. The snow depth along the profile is calculated
as the difference between the surface (from the barometer) and the bare ground
(surveyed). The method has been tested both on snow-covered profiles and on
bare ground. The final testing was performed on bare ground along a roughly 1
km long profile. Tests were performed during both calm and windy conditions. The
method worked well during calm conditions when the average depth value was
reported to 0±4 cm with a random square error (RSE) of 11 cm. The method did
not perform so well during strong wind since a test during such conditions (on
bare ground) gave an average snow depth of 30±23 cm with RSE.48 cm.
Compaction of the snow pack from the weight of the snowmobile and the sledge
may be a problem when applied on low-density snow. The barometric method
seems to be a well suited method for measuring snow depths along a line but has
not been further tested or used for operational use.
3.3 Snow water equivalent (SWE)
Snow water equivalent is determined at snow courses (North America) or along
snow transects (Russia) at about 15-30 day or 10-day intervals, respectively.
Snow courses are considered to give the most precise information about SWE for
a whole catchment, but the high costs and the difficulties with access because of
bad weather can lead to loss of data (Lundberg et al. 2001). The data are in
agency archives and many are not digitized, European data are especially difficult
to access (cost and other restrictions).
Snow water equivalent is one of the hydrological variables relevant to climate
change that is part of the new GCOS/WMO-sponsored GTN-H (Global Terrestrial
Network for Hydrology) which was implemented in 2001 to improve accessibility
of already existing data. The WMO guide to hydrological practices (WMO 1994)
gives criteria for ideal locations of snow-course measurements in mountainous
areas. In addition to the requirements already given for precipitation gauges,
snow course should be undertaken at sites sufficiently accessible to ensure
10
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
continuity of surveys and, if total seasonal accumulation should be measured, at
elevations and exposures where there is little or no melting prior to peak
accumulation. The ground surface should be cleared of rocks, stumps and bushes
for two metres in all directions from each sampling point. In order to avoid any
systematic error because of snow drift it may be necessary to perform an
extensive survey, with long traverses and a large number of sampling points, prior
to finally determining location, length and sampling distance for a snow course.
Once the prevailing length and direction of the snowdrifts have been ascertained it
should be possible to reduce the number of sampling points (WMO, 1994).
(Lundberg et al. 2001)
3.4 Satellite Measurements
Identified GCOS requirements relating to snow cover area are for information on
global snow cover extent at 25 km resolution. Equally, operational snow water
equivalent monitoring undertaken by the Meteorological Service of Canada (MSC),
using all-weather passive microwave data, provides detailed weekly information
on snow cover extent over the Canadian prairies that is useful for monitoring and
model validation. Stated GCOS requirements for SWE include a requirement for
daily global satellite coverage at 25 km resolution. Meeting this requirement,
however, necessitates satellite algorithm development and validation over all
representative vegetation and terrain types. As a further requirement, bi-weekly
snow course measurements, representative of terrain and land-cover, are needed
11
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
in the vicinity of GCOS Surface Network (GSN) stations and this requires the
assembly of an archive of snow course data.
MSC coordinated a national hard-copy compilation of snow course observations
from 1955 to 1985 (Taken by MSC, provincial water resource agencies and
hydroelectric companies). At peak levels, in the early 1980s, there were over
1700 snow course observations contributed by various agencies but this number
declined to around 800 in the early 1990s. A number of agencies continued to
send snow course data, in digital format, to MSC after 1985 and in 1995 a
CRYSYS data rescue project was initiated to digitize all the available snow course
data and place it on CD-ROM. MSC also carry out near real-time monitoring of
SWE over the Canadian prairies from passive microwave satellite data and this
approach has recently been extended to the adjacent boreal forest region. Work is
currently in progress to apply these methods to the entire period of passive
microwave data coverage (1978 onwards) to generate consistent gridded SWE
datasets for model validation and other applications. MSC is planning to establish
a national snow course monitoring network and database in collaboration with the
various provincial agencies and utilities that maintain snow course networks.
Snow cover is mapped routinely by satellites. NOAA-NESDIS provides operational
hemispheric products; NASA develops hemispheric research products. See details
below.
A snow-melt data set for Arctic sea ice from 1979-1998 prepared by S. Drobot
and M. Anderson is available from NSIDC: http://nsidc.org/data/nsidc-0105.html
3.5 Summary of requirements and gaps
In this section you need to highlight if there is any methodological gaps, (e.g. the community
needs to adopt a common methodology, standard or validation or inter comparison needs to
occur). This includes issues of lack of adoption of standards by countries, issues of equipment,
etc.
Issues of related to data quality, management, access (i.e. data is relevant and can be used by
broad stakeholder community) should be included here.
Also you can include if the ECV is meeting current and new requirements of stakeholders and
if a revision is required (can be done by cross checking the IGOS reports and other recent
documents).
4. Contributing networks and agencies
A list of institutions and agencies undertaking the measurements and collaborating in
developing the different products should be highlighted here.
12
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
5. Available data and products
Available Point data
Snow depth is reported in the WMO synoptic code. Snow water equivalent data
are largely based on snow surveys conducted by countries at higher latitudes.
Available Gridded data
Daily operational products of areal extent of snow cover in the Northern
Hemisphere are generated by the NOAA National Environmental Satellite Data and
Information Service (NESDIS). Regionally, operational snow water equivalent
products are prepared daily for the western portion of the USA by the
NOAA/National Operational Hydrology Remote Sensing Center using ground based
and airborne survey data as well as satellite data. Products for the eastern USA
are made as needed based on snow cover analysis.
Snow cover extent:
(i) daily NH-extent map since May 1999, and gridded data (1024 by 1024 box grid,
ca. 25 km), monthly statistics (frequency, anomaly) for NH, N-America and Asia.
[Weekly data for 1966-1999]. Interactive Multisensor Snow and Ice Mapping
System (IMS) Daily Northern Hemisphere Snow & Ice Analysis:
http://orbit-net.nesdis.noaa.gov/crad/sat/surf/snow/HTML/snow.htm.
(ii) The Northern Hemisphere Equal Area Scalable Earth Grid (EASE-Grid) Weekly
Snow Cover and Sea Ice Extent product combines snow cover and sea ice extent
at weekly intervals for October 1978 through June 2008, and snow cover alone for
October 1966 through October 1978 (sea ice data were not available prior to
October 23, 1978). The data set is the first representation of combined snow and
sea ice measurements derived from satellite observations for the period of record.
Data are provided in a 25 km equal area grid (NSIDC EASE- Grid):
http://nsidc.org/data/nsidc-0046.html.
(iii) The Near Real-Time SSM/I EASE-Grid Daily Global Ice Concentration and
Snow Extent product (Near Real-Time Ice and Snow Extent, NISE) provides daily,
global near real-time maps of sea ice concentrations and snow extent. The
National Snow and Ice Data Center (NSIDC) creates the NISE product using
passive microwave data from the Defense Meteorological Satellite Program (DMSP)
F13 Special Sensor Microwave/Imager (SSM/I). These data are not suitable for
time series, anomalies, or trends analyses. They are meant to provide a best
estimate of current ice and snow conditions based on information and algorithms
available at the time the data are acquired. See http://nsidc.org/data/nise1.html .
(iv) Moderate Resolution Imaging Spectroradiometer (MODIS) products include
level 2 swath data (MOD10_L2) at 500 m resolution, level 3 gridded daily and 8day composites (MOD10A1 and MOD10A2, respectively) at 500 m resolution, and
level 3 daily and 8-day global maps on a climate modeller’s grid (MOD10C1 and
MOD10C2, respectively) at 0.05 degree resolution. MODIS snow cover data are
based on a snow mapping algorithm that employs a Normalized Difference Snow
Index (NDSI) and other criteria tests. Data also contain local and global metadata
(see http://modis-snow-ice.gsfc.nasa.gov/intro.html).
Users' Guide:
13
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
http://modis-snow-ice.gsfc.nasa.gov/sugkc.html.
Order data from: http://nsidc.org/data/modis
Snow depth: operational global daily snow depth analysis by the Canadian
Meteorological Centre http://weatheroffice.ec.gc.ca/analysis/index_e.html.
National products include:
(a) the Historical Soviet Daily Snow Depth Version 2 (HSDSD) product on CD-ROM,
based on observations from 1881 to 1995 at 284 World Meteorological
Organization (WMO) stations throughout Russia and the former Soviet Union. The
area covered is 35° to 75° N latitude and 20° to 180° E longitude. The State
Hydrometeorological Service in Obninsk, Russia, provided the data through the
US-Russia Agreement on Co-operation in the Field of Protection of the
Environment, Working Group VIII data exchange program. (Armstrong, R. 2001.
Historical Soviet Daily Snow Depth Version 2 (HSDSD). Boulder, CO, USA:
National Snow and Ice Data Center. CD-ROM: http://nsidc.org/data/g01092.html.
b) NOAA Experimental Daily NWS/COOP Snow Depth and Snowfall Graphics and
Data - Daily snow depth (most recent day) and snowfall graphics (most recent 1,
2, 3 and 7 days) and data for the contiguous United States. (c) Daily snow depth
data for 1062 observing stations across the contiguous US covering the period
1871-1997 are available from the Carbon Dioxide Information and Analysis Center
(CDIAC) http://cdiac.ornl.gov/
(Easterling et al., 1999). (d) Daily snow depth
data for Canada at several 1,000 stations covering the entire period of record up
to 1999 are published on CD-ROM and are freely available for research use
(Meteorological Service of Canada, 2000: Canadian Snow Data CD-ROM): CRYSYS
Project, Climate Processes and Earth Observation Division, Meteorological Service
of Canada, Downsview, Ontario].
Snow depth and water equivalent are also observed by other national, state,
provincial and private networks in many countries on a 10 day - monthly basis.
The Advanced Microwave Scanning Radiometer - Earth Observing System (AMSRE) instrument on the NASA EOS Aqua satellite provides global passive microwave
measurements of terrestrial, oceanic, and atmospheric variables for the
investigation of water and energy cycles.
The Level-3 snow water equivalent (SWE) data sets contain SWE data and quality
assurance flags mapped to Northern and Southern Hemisphere 25 km Equal-Area
Scalable Earth Grids (EASE-Grids). Data are stored in Hierarchical Data Format Earth Observing System (HDF-EOS) format, and are available via FTP, CD-ROM,
8-mm tape, DLT, or DVD-ROM. See NSIDC's HDF-EOS Web page for more
information about this format http://nsidc.org/data/hdfeos/index.html Files
contain core metadata, product-specific attributes, and 721 x 721 pixel data grids
in 1-byte unsigned integer format.
These AMSR-E data are used to estimate daily, five day and monthly global snow
water equivalent (SWE). The standard daily SWE product has evolved from a
static semi-empirical algorithm to a more dynamic algorithm that incorporates
estimates of snow properties in the retrieval process.
Order data from: http://nsidc.org/data/amsre
14
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
NSIDC has produced the Global EASE-Grid Monthly Snow Water Equivalent
Climatology Product. This data set comprises monthly satellite-derived snow water
equivalent (SWE) climatologies from November 1978 through December 2007,
updated routinely, gridded to the Northern and Southern 25 km EASE-Grids. This
data set is the first available global product to merge snow water equivalent
derived from SMMR and SSM/I passive microwave sensors with snow extent
derived from weekly NOAA (optical sensor) snow maps. It currently is the only
historical product to include Southern Hemisphere passive microwave-derived
snow water equivalent. http://nsidc.org/data/nsidc-0271.html
The Former Soviet Union Hydrological Snow Surveys are based on observations at
1,345 sites throughout the Former Soviet Union between 1966 and 1990, and at
91 of those sites between 1991 and 1996. These observations include snow
depths at World Meteorological Organization (WMO) stations and snow depth and
snow water equivalent measured over a nearby snow course transect. The station
snow depth measurements are a ten-day average of individual snow depth
measurements. The transect snow depth data are the spatial average of 100 to
200 individual measuring points. The transect snow water equivalent is the spatial
average of twenty individual measuring points
(http://nsidc.org/data/g01170.html).
Weekly maps of SWE from SSM/I over the Canadian prairies are available from:
http://www.msc.ec.gc.ca/ccrp/SNOW/snow_swe.html.
The National Operational Hydrologic Remote Sensing Center provides
comprehensive snow observations, analyses, data sets and map products for the
Nation. NOAA’s Source for Snow Information
http://www.nohrsc.noaa.gov/nsa/
 National Snow Observation Database
 Airborne Snow Surveys
 Satellite Snow Cover Mapping
 Snow Modeling and Data Assimilation
 Analyses, Maps, and Interactive Visualization Tools
 Integrated Snow Datasets for Geospatial Applications
 Applied Snow Research
NOHRSC products and services support a wide variety of government and privatesector applications in water resource management, disaster emergency
preparedness, weather and flood forecasting, agriculture, transportation and
commerce.
Airborne Snow Survey Program http://www.nohrsc.noaa.gov/snowsurvey/
The NOHRSC measures snow water equivalent and soil moisture using gamma
radiation remote sensing. This unique observing system includes two low-flying
aircraft to conduct surveys in 31 states, including Alaska, as well as in 8 Canadian
provinces. Four NOAA Corps officers pilot the aircraft and operate the remote
sensing systems. The data are incorporated into the National Snow Analyses.
You'll find survey data, schedules, flight line locations, aerial photos, and
information http://www.nohrsc.noaa.gov/nh_snowcover/
Northern Hemisphere Snow Cover http://www.nohrsc.noaa.gov/nh_snowcover/
15
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
The areal extent of snow cover is mapped daily using polar-orbiting and
geostationary satellite imagery. Maps are provided for the U.S. and the northern
hemisphere.
Weekly snow extent and water equivalent for the western United States include
anomalies and elevational extent map
http://www.nohrsc.nws.gov/html/opps/opps.htm
SNOTEL network database for the western United States compiled by Serreze et al.
(1999). The data are primarily from pressure pillows that weigh the snow pack.
Canadian snow course observations (~2000 sites, mostly in the period. 19501995) are published on the Snow CD (MSC, 2000)
The NASA Cold Land Processes Field Experiment (CLPX) conducted during the
period 2001-2004 was a multi-sensor, multi-scale field program of nested study
areas in Colorado and Wyoming, USA, designed to extend the current local-scale
understanding of water fluxes, storage, and transformations to regional and global
scales. Using ground, airborne, and spaceborne observations, the experiment
emphasizes the development of a strong synergism between process-oriented
understanding, land surface models, and microwave remote sensing. Data were
collected during two seasons: mid-winter, when conditions are generally frozen
and dry, and early spring, a transitional period when both frozen and thawed, dry
and wet conditions are widespread. For more information on CLPX, see
http://nsidc.org/data/clpx/intro.html
6. Other issues
Other issues of concern can be raised in this section, for example issues of lack of funding,
problems of data access, lack of government support (e.g. research sites not becoming part of
the networks or data not being realised), continuity of technologies, etc.
This section should not be big too big just high light the major issues of concern.
7. Conclusions
A general summary of the finding of the report in regards to available standards, methods,
validation, etc. and their adoption should be placed here.
8. Recommendations
Most important section with section 3.
Clear set of recommendations in a series of bullets should be provided in this section. This
should be in two subsections.
8.1 Standards and methods
Specific to methods, protocols, standards etc. recommendations including if certain methods or
protocols should undergo the process to become and internatinal standardization or if certain
validation process should be adopted.
8.2 other recommendations
16
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
Other recommendations related to the ECV.
Reference
Allison, I., Barry, R.G. and Goodison, B.E. (eds.; 2001): Climate and Cryosphere
Project Science and Co-ordination Plan Version 1. WCRP-114, WMO/TD No. 1053,
Geneva: 45, 53-54).
Armstrong, R.L., and M.J. Brodzik. (2001). Recent Northern Hemisphere snow
extent: a comparison of data derived from visible and microwave sensors.
Geophysical Research Letters 28(19): 3673-3676.
Barry, R.G. (1995): Observing systems and data sets related to the cryosphere in
Canada: a contribution to planning for the Global Climate Observing System.
Atmosphere - Ocean 33 (4): 771-807
Campbell Scientific Companies. 2007. SR50 Sonic Ranging Sensor. Instruction
Manual. Utah
Doesken, Nolan J., A. Judson, 1996: The Snow Booklet: A Guide to the Science,
Climatology, and Measurement of Snow in the United States. Colorado State
University.
Easterling, D.R., Karl, T.R., Lawrimore, J.H. and Del Greco, S.A. (1999): United
States Historical Climatology Network Daily Temperature, Precipitation, and Snow
Data for 1871-1997. ORNL/CDIAC-118, NDP-070. Carbon Dioxide Information
Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee. 84 pp.
Frei, A., and D.A. Robinson. (1999). Northern Hemisphere snow extent: regional
variability 1972-1994. International Journal of Climatology 19: 1535-1560.
Goodison, D.E., Brown, R.D. and Crane, R.G. (lead authors; 1999): Cryospheric
systems.
Eos
Science
Plan,
NASA
pp.
261-307.
http://eospso.gsfc.nasa.gov/ftp_docs/Ch6.pdf
Goodison, B. E., et al., 1988: The Canadian automatic snow depth sensor: a
performance update. Proceedings of
the Fifth-sixth Annual Western Snow
Conference, Atmospheric Environment Service, Canada, pp. 178–181.
Groisman, P., T.R. Karl, and R.W. Knight. (1994). Observed impact of snow cover
on the heat balance and the rise of continental spring temperatures. Science 263:
198-200.
Lundberg, A., and Halldin, S., (2001). Snow measurement techniques for landsurface-atmosphere exchange studies in boreal landscapes. Theoretical and
Applied Climatology 70, 215-230
17
T5
ECV T05: Assessment of Standards for the Snow Cover Essential Climate Variable
Kennett M, Laumann T, Elvehùy H (1996) Snow-pro-et barometer-basert utstyr
for profilmaÈlning av snùdyp. Norges Vassdrags- og Energiverk NVE rapport 14,
10 pp
Robinson. D.A. (1993). Recent Trends in Northern Hemisphere Snow Cover.
Fourth Symposium on Global Change Studies. American Meteorological Society.
Anaheim, CA.
Serreze, M.C., Clark, M.P., Armstrong, R.L., McGinnis, D.A. and Pulwarty, R.S.
(1999): Characteristics of the western United States snowpack from snowpack
telemetry (SNOTEL) data. Water Resources Research 7: 2145-2160
GCOS (2003): Status Report on the Key Climate Variables Technical Supplement
to the Second Report on the Adequacy of the Global Observing Systems for
Climate . Draft Version 2.7 10th September 2003
U.S. Department of Commerce, (1997): Snow Measurement Guidelines for
National Weather Service Cooperative Observers. Silver Spring, MD.
Vorosmarty, C. J and 15 others (The Ad Hoc Group on Global Water Data). (2001)
Global water data: An endangered species. EOS 82(3), 54,56,58.
World Meteorological Organization, 1992: Snow Cover Measurements and Areal
Assessment of Precipitation and Soil Moisture (B. Sevruk). Operational Hydrology
Report No. 35, WMO–No. 749, Geneva.
WMO 1994, Guide to hydrological practices, data acquisition and processing,
analysing forecasting and other applications, fifth edition, WMO report No 168,
WMO, Geneva, 286 pp .
Web Sites
List useful websites here
18
T5