18.2 Contemporary Approaches
to Determine Water Content
in a Snow Cover
Traditional and most labor-consuming method
for snow water equivalent determination on the
explored area involves weighting of the snow
samples taken with snow-measuring cylinder at
the observation sites and linear snow courses,
both on forest and field lands.
In addition, there are methods to measure
snow cover characteristics by placing autonomous snow-measuring devices based on different
operation principles.
Snow pillow is an example of such devices,
targeted at weight measuring of the snow placed
above it. Pillow of the most used type looks like
a round container of the 3.7 m diameter, made of
some rubberized material and filled with no-frost
liquid. Hydrostatic pressure inside of the pillow
is a measure of the snow weight upon it. Water
equivalent measurements done with snow pillows can produce 5–10% difference compared
with traditional snow samples weighting.
Vertical radioactive snow gauges are another
type of autonomous devices. Their operation is
based on gamma-ray attenuation while passing
through some medium. Such attenuation depends
on the ray’s initial energy, stuff density and
thickness. High-energy gamma-rays source is
needed for this method. Cobalt-60 is often used
due to its high gamma energy and long half-life
period (5.25 years).
Lead protective container with the radiation
source is placed into the ground in such a way
that upper surface of the container is on the same
level with the ground surface, and gamma ray
beam is directed toward the radiation detector,
placed above the snow cover. Either GeigerMuller counter or scintiometer can be used as a
detector. Pulses from the counter are transferred
to the integrating and registering device.
Relatively expensive and complex equipment
is needed for such radioisotope devices. Also
there are special safety precautions, especially
when strong radiation source is used.
Gamma-radiation survey done from an aircraft
is useful to estimate snow water equivalent on
the area up to several thousands of square kilometers. Gamma-radiation survey uses the fact
that snow cover attenuates gamma rays radiated
by natural radioactive elements contained in the
soil upper layer. Water storage in a snow cover
can be calculated by using the gamma radiation
intensity measured over the surface of the snow
cover and the intensity measured in the same
route before the snowfall. Aircraft survey produces integral area estimation of the snow cover
water equivalent, as series of point measurements
are done along the fragments of a flight. This
method is recommended not only to map water
storage in the snow on lowlands, but also can be
used on hilled areas with heights difference up to
400 m.
Accuracy of the aircraft gamma survey of the
snow cover depends on the measuring equipment
quality, oscillations of the space radiation and the
ground air radioactivity, oscillations of the
humidity on upper 15 cm layer of the ground,
homogeneity of the snow deposit, absence of
long thaw periods, and so on. Supposed errors
are ± 10% with the low limit of approximately
10 mm of the water equivalent. Detailed experimental research has shown that standard deviation of the snow water equivalent measurements
done by an aircraft survey on a 10–20 km route
is about 8 mm and has random pattern.
The main disadvantage of listed at-ground
methods of the snow cover water equivalent
determination is the point nature of the carried
out measurements, which causes the necessity of
data interpolation to find out area characteristics,
and may cause substantial errors of the snow
water storage on large areas in case of nonhomogeneity of the snow cover forming conditions. From the other side, remote gamma survey
of the snow cover done from an aircraft does not
allow to make measurements at arbitrary weather
conditions.
Starting from 70th year of the last century,
remote sensing of the Earth surface is actively
used to carry on the express tests of the snow
236
A. A. Volchak et al.
to Determine Water Content
in a Snow Cover
Traditional and most labor-consuming method
for snow water equivalent determination on the
explored area involves weighting of the snow
samples taken with snow-measuring cylinder at
the observation sites and linear snow courses,
both on forest and field lands.
In addition, there are methods to measure
snow cover characteristics by placing autonomous snow-measuring devices based on different
operation principles.
Snow pillow is an example of such devices,
targeted at weight measuring of the snow placed
above it. Pillow of the most used type looks like
a round container of the 3.7 m diameter, made of
some rubberized material and filled with no-frost
liquid. Hydrostatic pressure inside of the pillow
is a measure of the snow weight upon it. Water
equivalent measurements done with snow pillows can produce 5–10% difference compared
with traditional snow samples weighting.
Vertical radioactive snow gauges are another
type of autonomous devices. Their operation is
based on gamma-ray attenuation while passing
through some medium. Such attenuation depends
on the ray’s initial energy, stuff density and
thickness. High-energy gamma-rays source is
needed for this method. Cobalt-60 is often used
due to its high gamma energy and long half-life
period (5.25 years).
Lead protective container with the radiation
source is placed into the ground in such a way
that upper surface of the container is on the same
level with the ground surface, and gamma ray
beam is directed toward the radiation detector,
placed above the snow cover. Either GeigerMuller counter or scintiometer can be used as a
detector. Pulses from the counter are transferred
to the integrating and registering device.
Relatively expensive and complex equipment
is needed for such radioisotope devices. Also
there are special safety precautions, especially
when strong radiation source is used.
Gamma-radiation survey done from an aircraft
is useful to estimate snow water equivalent on
the area up to several thousands of square kilometers. Gamma-radiation survey uses the fact
that snow cover attenuates gamma rays radiated
by natural radioactive elements contained in the
soil upper layer. Water storage in a snow cover
can be calculated by using the gamma radiation
intensity measured over the surface of the snow
cover and the intensity measured in the same
route before the snowfall. Aircraft survey produces integral area estimation of the snow cover
water equivalent, as series of point measurements
are done along the fragments of a flight. This
method is recommended not only to map water
storage in the snow on lowlands, but also can be
used on hilled areas with heights difference up to
400 m.
Accuracy of the aircraft gamma survey of the
snow cover depends on the measuring equipment
quality, oscillations of the space radiation and the
ground air radioactivity, oscillations of the
humidity on upper 15 cm layer of the ground,
homogeneity of the snow deposit, absence of
long thaw periods, and so on. Supposed errors
are ± 10% with the low limit of approximately
10 mm of the water equivalent. Detailed experimental research has shown that standard deviation of the snow water equivalent measurements
done by an aircraft survey on a 10–20 km route
is about 8 mm and has random pattern.
The main disadvantage of listed at-ground
methods of the snow cover water equivalent
determination is the point nature of the carried
out measurements, which causes the necessity of
data interpolation to find out area characteristics,
and may cause substantial errors of the snow
water storage on large areas in case of nonhomogeneity of the snow cover forming conditions. From the other side, remote gamma survey
of the snow cover done from an aircraft does not
allow to make measurements at arbitrary weather
conditions.
Starting from 70th year of the last century,
remote sensing of the Earth surface is actively
used to carry on the express tests of the snow
236
A. A. Volchak et al.