successful than the particle-based approaches,
AVAILABLE COMPUTER CODES
which in any case are somewhat artificial for most
In this section we provide information on spe-
applications to snow.
cific models and their sources. The entries are
While ice and snow are logically considered
listed by source and are grouped more or less by
together, one must distinguish the particular
area of application. For each model or package,
problems associated with each. Until recently,
information is given on applications, model fea-
few MMW sea-ice studies could be found with
tures and approach, and source contact. Com-
comparisons of simulations to data, exceptions
ments on each include information such as loca-
being the work of Lee and Mudaliar (1988) and
tion of reference discussion in the body of the
Mudaliar and Lee (1990). At present, one does
report, limitations and advantages, and status of
well to begin with the wealth of detail on sea-
code testing and facilitation. In some instances
ice phenomenology and sensing, measurement
considerations of code documentation, availabil-
and modeling, and theory and evaluation as
ity, ease of use, and support are subsumed in the
presented in the volume edited by Carsey (1992).
category "code usability."
A chapter by Winebrenner and others on theo-
Many notable models discussed in this report
retical modeling of sea-ice microwave/MMW
are not mentioned below because they failed in
behavior recounts the testing of various con-
some way to meet our general criteria for inclu-
trasting models on three reasonably well-char-
sion (e.g., insufficient information from origina-
acterized saline ice samples over a frequency
tors, complexity or resource requirements beyond
range that includes some of our span of inter-
the feasibility limits, unavailability of code, reli-
est. Any applicable model must somehow in-
ance on empirical quantities, lack of application/
clude the effects of elongated, oriented brine
testing against geophysical media, unlikely fu-
pockets or bubbles in the ice. Alternatively, it
ture support for the code, etc.). This should not be
can concentrate on the complementary shape of
interpreted as a negative judgment on the scien-
the individual crystals defining the boundaries
tific validity or research value of such models.
of those pockets. Models tested (and their origi-
nators) were designated to include independent
MPM
Rayleigh scattering layers (Drinkwater); dense
media RT (Tsang and West); dense-medium
Features
theory with integral equation method for rough
Computes complex refractivity profiles to-
surface (DMTIEM, by Fung and his co-work-
gether with power attenuation and propagation
ers); many-layer strong fluctuation theory (SFT
delay rates as functions of frequency, humidity,
by Stogryn/Grenfell); polarimetric SFT (Ngh-
or pressure for air, with possible inclusion of wa-
iem and the MIT team); and MRT (Lee and
ter vapor, haze, fog/cloud, and rain.
Mudaliar). The reader is referred to the above
reference for the details of these studies. Par-
Comments
ticularly in certain aspects and certain frequency
Refer to the discussion under Atmosphere, in
domains, successes are shown, although many
the Applications section.
questions remain. Among other things, models
Input factors may be frequency, barometric
based on rather different physical mechanisms
pressure, RH, temperature, haze type, sus-
sometimes still manage to provide more or less
pended water-droplet concentration, and rain
the same (correct) answers. This raises the ques-
rate. In different versions of the model, the user
tion of how much seemingly good results de-
inputs a range for one of the first three variables
rive from modeling technique and manipula-
and fixed values for some or all of the remaining
tion, as opposed to incorporation of mechanisms
ones. Rain treatment is very simple. The code is
that truly correspond to the dominant physical
easy to use, with plentiful comments and refer-
processes. Most of the work reported in Carsey's
ences embedded.
(1992) volume was part of a large ongoing ef-
fort, with some additional results reported else-
Source/contact
where. The reader is referred to IGARSS'94
Dr. Hans J. Liebe
(1994), with somewhat fewer sea-ice papers in
NTIA/ITS.S1
IGARSS'95 (1995) showing MMW content.
19
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