frozenthawed status of deeper soil. Surficial
a. 7.5 cm
freezing or thawing will not have the significant
impact on electromagnetic sensor system perfor-
mance that deeper penetration of the freezing or
thawing front will.
The effect of a sand inclusion on soil tempera-
ture is easily seen in Figure 9. The difference in
soil temperature, with and without an inclusion,
is plotted for both types of inclusions (sand and
sandy soil) and three depths. Above the inclusion
Day8(28 Oct is day120
(7.5 cm, Fig. 9a) the soil is generally cooler when a
sand inclusion is present, as indicated by a nega-
tive temperature difference. The material of the
inclusion makes a difference only in early winter
(days 53 to 60), when following a period of sus-
tained below-freezing temperatures, the soil sur-
face cycles between being frozen and unfrozen.
b. 22.5 cm.
During this period, soil above an inclusion of
sandy soil is sometimes warmer than it would be
in the absence of the inclusion, while soil above
an inclusion of sand is sometimes colder than it
would be without the inclusion. Subsequent tem-
perature differences for both types of inclusion
are consistent in sign and generally similar in
magnitude (less than 1C different). That the de-
pendence of the disruption in heat flow on the
Day (28 Oct is day11)0
material of the inclusion lessens during the win-
ter is a consequence of the freezing of the inclu-
sions. Unfrozen, the sand and sandy soil have
significantly different thermal conductivities,
with that of the sandy soil being 27% higher; fro-
zen, the two materials' conductivities are similar
(Table 1). While unfrozen, sand would less readi-
ly (than sandy soil) conduct heat from depth to
c. 37.5 cm
the overlying soil to counteract cooling events ini-
tiated at the soil surface.
Below the inclusion, the soil is generally
warmer (positive temperature difference). The
temperature difference at 37.5-cm depth (Fig. 9c)
is most dynamic in midwinter (days 75 to 100).
During this period, for the case of no inclusion,
the soil shows large fluctuations in temperature.
Soil below an inclusion does not experience tem-
perature changes of similar magnitude. Instead, it
is warmer (positive temperature difference) fol-
Day (28 Oct is day 1)
lowing a cooling episode and colder (negative
temperature difference) following a warming epi-
sode. This is a consequence of the temperature
Figure 9. Temperature differences (inclusion minus no
perturbations not propagating as readily through
inclusion) obtained from one-dimensional numerical
simulations of heat flow in a silty soil (17% moisture
sandy soil) to the soil beneath.
content) with no inclusion, with a sand inclusion
The temperature differences are largest when
present, or with a sandy soil inclusion present, under
the temperatures of the soil and the inclusion are
BC1 conditions. At the 22.5-cm depth, the temperature
compared. At a depth of 22.5 cm, which corre-
comparison is between sand or sandy soil and silty soil.